text: /*
  Copyright (C) 2001-2012, Parrot Foundation.
  
  =head1 NAME
  
  src/gc/gc_gms.c - Generational M&S
  
  =head1 DESCRIPTION
  
  Generational, non-compacting, mark and sweep GC.
  
  Objects are stored in N (up to 8) different lists; one for each generation.
  Collection with lower number is younger.  PObj_GC_generation_0_FLAG,
  PObj_GC_generation_1_FLAG, PObj_GC_generation_2_FLAG determine which
  generation an object is in.  PObj_GC_on_dirty_list_FLAG is set by Write
  Barrier.
  
  "Dirty" objects are moved into "dirty_list" out of C<generation> list.
  
  Invariant: new reference from old-to-new generation can be introduced either:
      - from objects already in "dirty_list"
      - or with moving referent object into "dirty_list"
  
  Corollary: objects in "dirty_list" either:
      - not referenced at all
      - referenced from same or younger generation
      - their referents are on "dirty_list" too
  
  (Proof is very simple and left as exercise for reader)
  
  Notation
  1. "*A1:B2" is a live object A in generation 1 referenced by an object B in generation 2.
  2. "B0" is a non-live object B in generation 0 not referenced by anything.
  3. gn: generation n.
  4. R: root set.
  5. D: dirty list.
  
  GC algorithm is:
  
  0. Pre-requirements:
      a) Invariant described above to maintain dirty_list.
      b) Maintain invariant by
          i) "sealing" all objects in old generations with Write Barriers.
          ii) Write Barrier will:
              - Unseal object
              - Set "on_dirty_list" flag
              - Move object into "dirty_list"
      c) gc_gms_mark_pmc_header ignores:
          i) objects from generation older than C<self->gen_to_collect>.
          ii) objects with on_dirty_list flag set.
          iii) move objects to "work_list" for fully mark objects without recursion.
  
  1. Trigger GC (based on phase of the Moon for simplicity. We can tune Moon later).
  
  2. Choose K - how many collections we want to collect. Collections [0..K] will
  be collected. Remember K in C<self->gen_to_collect>.
  
  3. Move all objects from dirty_list which has all direct children in
  generations not younger than object back to original lists. Reason for this is
  "corollary of invariant". We can either collect such objects or they will be
  marked by referents from "dirty_list". To perform calculation of youngest
  child's generation we temporary override .mark_pmc_header with
  C<gc_gms_get_youngest_generation> which iterate over direct children only.
  
  4. Trace root objects. According to "0. Pre-requirements" we will ignore all
  "old" objects. All relevant objects are moved into "work_list".
  
  5. Iterate over "dirty_set" calling VTABLE_mark on it. It will move all
  children into "work_list".
  
  6. Iterate over "work_list" calling VTABLE_mark on it.
  
  7. Soil nursery root PMCs from C-stack.
  
  Main reason for it:
  
       PMC *res = Parrot_pmc_new(interp);
       <do something to fill a lot of guts. E.g. Hash.clone>
       return *res;
  
  C<Hash.clone> can trigger GC. C<res> _will_ not be sealed by any automatic
  methods (e.g. pmc2c vtable overrides).
  
  8. Sweep generations starting from K:
      - Destroy all dead objects
      - Move live objects into generation max(K+1, N)
      - Paint them white.
  
  9. ...
  
  10. Profit!
  
  We are not cleaning "dirty_list" after this process to rescan it again on next
  iteration. It allows us to keep track of old-to-new inter-generations
  references between iterations. Objects from "dirty_list" which is ready to be
  collected handled by "Step 3".
  
  
  Pictures of GC steps.
  TBD
  
  =cut
  
  */
  
  #include "parrot/parrot.h"
  #include "parrot/gc_api.h"
  #include "parrot/pointer_array.h"
  #include "gc_private.h"
  #include "fixed_allocator.h"
  
  #define PANIC_OUT_OF_MEM(size) failed_allocation(__LINE__, (size))
  
  #ifdef THREAD_DEBUG
  #  define PARROT_GC_ASSERT_INTERP(pmc, interp) \
      PARROT_ASSERT((pmc) == NULL || (pmc)->orig_interp == (interp))
  #else
  #  define PARROT_GC_ASSERT_INTERP(pmc, interp)
  #endif
  
  /*
   * Maximum number of collections
   * NB:
   *  1. Maximum number is 8 due limit number of bits in PMC.flags.
   *  2. Don't forget to update gc_gms_select_generation_to_collect after changing it!
   */
  #define MAX_GENERATIONS     4
  
  /* We allocate additional space in front of PObj* to store additional pointer */
  typedef struct pmc_alloc_struct {
      void *ptr;
      PMC   pmc;   /* NB: Value! */
  } pmc_alloc_struct;
  
  typedef struct string_alloc_struct {
      void    *ptr;
      STRING   str;   /* NB: Value! */
  } string_alloc_struct;
  
  #define PMC2PAC(p) ((pmc_alloc_struct *)((char*)(p) - sizeof (void *)))
  #define STR2PAC(p) ((string_alloc_struct *)((char*)(p) - sizeof (void *)))
  
  
  /* Get generation from PObj->flags */
  #define POBJ2GEN(pobj)                                                  \
          ((size_t)(((pobj)->flags & PObj_GC_generation_0_FLAG) ? 1 : 0)  \
           + (((pobj)->flags & PObj_GC_generation_1_FLAG) ? 2 : 0)        \
           + (((pobj)->flags & PObj_GC_generation_2_FLAG) ? 4 : 0))
  
  /* Get flags for generation number */
  #define GEN2FLAGS(gen)                                  \
          (((gen) & 1 ? PObj_GC_generation_0_FLAG : 0)    \
           | ((gen) & 2 ? PObj_GC_generation_1_FLAG : 0)  \
           | ((gen) & 4 ? PObj_GC_generation_2_FLAG : 0))
  
  #define SET_GEN_FLAGS(pmc, gen) PObj_flags_SETTO((pmc), \
          ((pmc)->flags & ~PObj_GC_all_generation_FLAGS) | GEN2FLAGS(gen))
  
  /* Private information */
  typedef struct MarkSweep_GC {
      /* Allocator for PMC headers */
      struct Pool_Allocator  *pmc_allocator;
  
      /* During M&S gather new live objects in this list */
      struct Parrot_Pointer_Array     *work_list;
  
      /* During M&S gather new live objects in this list */
      struct Parrot_Pointer_Array     *dirty_list;
  
      /*
       * During checking of dirty_list it will be set to generation of youngest
       * child
       */
      size_t    youngest_child;
  
      /* Currently allocate objects. */
      struct Parrot_Pointer_Array     *objects[MAX_GENERATIONS];
  
      /* Allocator for strings */
      struct Pool_Allocator           *string_allocator;
  
      /* MAX_GENERATIONS generations of strings */
      struct Parrot_Pointer_Array     *strings[MAX_GENERATIONS];
  
      /* Fixed-size allocator */
      struct Fixed_Allocator *fixed_size_allocator;
  
      /* String GC */
      struct String_GC        string_gc;
  
      /* Amount of allocated memory before trigger gc */
      size_t                  gc_threshold;
  
      /* During GC phase - which generation we are collecting */
      size_t                  gen_to_collect;
  
      /* GC blocking */
      UINTVAL gc_mark_block_level;  /* How many outstanding GC block
                                       requests are there? */
      UINTVAL gc_mark_block_level_locked;  /* How many outstanding GC block
                                       requests are there from other threads? */
      UINTVAL gc_sweep_block_level; /* How many outstanding GC block
                                       requests are there? */
  
      UINTVAL num_early_gc_PMCs;    /* how many PMCs want immediate destruction */
  
      UINTVAL locked;               /* is the GC lock already taken? */
  
  } MarkSweep_GC;
  
  /* Callback to destroy PMC or free string storage */
  typedef void (*sweep_cb)(PARROT_INTERP, PObj *obj);
  
  /* HEADERIZER HFILE: src/gc/gc_private.h */
  
  /* HEADERIZER BEGIN: static */
  /* Don't modify between HEADERIZER BEGIN / HEADERIZER END.  Your changes will be lost. */
  
  PARROT_DOES_NOT_RETURN
  static void failed_allocation(unsigned int line, size_t size);
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static Parrot_Buffer* gc_gms_allocate_buffer_header(PARROT_INTERP,
      size_t size)
          __attribute__nonnull__(1);
  
  static void gc_gms_allocate_buffer_storage(PARROT_INTERP,
      ARGIN(Parrot_Buffer *str),
      size_t size)
          __attribute__nonnull__(1)
          __attribute__nonnull__(2);
  
  PARROT_CAN_RETURN_NULL
  static void* gc_gms_allocate_fixed_size_storage(PARROT_INTERP, size_t size)
          __attribute__nonnull__(1);
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static void * gc_gms_allocate_memory_chunk(PARROT_INTERP, size_t size);
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static void * gc_gms_allocate_memory_chunk_zeroed(PARROT_INTERP,
      size_t size);
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static void* gc_gms_allocate_pmc_attributes(PARROT_INTERP, ARGMOD(PMC *pmc))
          __attribute__nonnull__(1)
          __attribute__nonnull__(2)
          FUNC_MODIFIES(*pmc);
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static PMC* gc_gms_allocate_pmc_header(PARROT_INTERP, UINTVAL flags)
          __attribute__nonnull__(1);
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static STRING* gc_gms_allocate_string_header(PARROT_INTERP, UINTVAL flags)
          __attribute__nonnull__(1);
  
  static void gc_gms_allocate_string_storage(PARROT_INTERP,
      ARGIN(STRING *str),
      size_t size)
          __attribute__nonnull__(1)
          __attribute__nonnull__(2);
  
  static void gc_gms_block_GC_mark(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  static void gc_gms_block_GC_mark_locked(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  static void gc_gms_block_GC_sweep(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  static void gc_gms_check_sanity(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  static void gc_gms_cleanup_dirty_list(PARROT_INTERP,
      ARGIN(MarkSweep_GC *self),
      ARGIN(Parrot_Pointer_Array *dirty_list))
          __attribute__nonnull__(1)
          __attribute__nonnull__(2)
          __attribute__nonnull__(3);
  
  static void gc_gms_compact_memory_pool(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  static size_t gc_gms_count_used_pmc_memory(PARROT_INTERP,
      ARGIN(Parrot_Pointer_Array *list))
          __attribute__nonnull__(1)
          __attribute__nonnull__(2);
  
  static size_t gc_gms_count_used_string_memory(PARROT_INTERP,
      ARGIN(Parrot_Pointer_Array *list))
          __attribute__nonnull__(1)
          __attribute__nonnull__(2);
  
  static void gc_gms_finalize(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  static void gc_gms_free_buffer_header(PARROT_INTERP,
      ARGFREE(Parrot_Buffer *s),
      size_t size)
          __attribute__nonnull__(1);
  
  static void gc_gms_free_fixed_size_storage(PARROT_INTERP,
      size_t size,
      ARGMOD(void *data))
          __attribute__nonnull__(1)
          __attribute__nonnull__(3)
          FUNC_MODIFIES(*data);
  
  static void gc_gms_free_memory_chunk(PARROT_INTERP, ARGFREE(void *data));
  static void gc_gms_free_pmc_attributes(PARROT_INTERP, ARGMOD(PMC *pmc))
          __attribute__nonnull__(1)
          __attribute__nonnull__(2)
          FUNC_MODIFIES(*pmc);
  
  static void gc_gms_free_pmc_attributes_locked(PARROT_INTERP,
      ARGMOD(PMC *pmc))
          __attribute__nonnull__(1)
          __attribute__nonnull__(2)
          FUNC_MODIFIES(*pmc);
  
  static void gc_gms_free_pmc_header(PARROT_INTERP, ARGFREE(PMC *pmc))
          __attribute__nonnull__(1);
  
  static void gc_gms_free_string_header(PARROT_INTERP, ARGFREE(STRING *s))
          __attribute__nonnull__(1);
  
  static size_t gc_gms_get_gc_info(PARROT_INTERP, Interpinfo_enum which)
          __attribute__nonnull__(1);
  
  PARROT_CAN_RETURN_NULL
  static void * gc_gms_get_high_pmc_ptr(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  PARROT_CAN_RETURN_NULL
  static void * gc_gms_get_high_str_ptr(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  PARROT_CAN_RETURN_NULL
  static void * gc_gms_get_low_pmc_ptr(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  PARROT_CAN_RETURN_NULL
  static void * gc_gms_get_low_str_ptr(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  static unsigned int gc_gms_is_blocked_GC_mark(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  static unsigned int gc_gms_is_blocked_GC_sweep(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  static int gc_gms_is_pmc_ptr(PARROT_INTERP, ARGIN_NULLOK(void *ptr))
          __attribute__nonnull__(1);
  
  static int gc_gms_is_string_ptr(PARROT_INTERP, ARGIN_NULLOK(void *ptr))
          __attribute__nonnull__(1);
  
  static void gc_gms_iterate_live_strings(PARROT_INTERP,
      string_iterator_callback callback,
      ARGIN_NULLOK(void *data))
          __attribute__nonnull__(1);
  
  static void gc_gms_mark_and_sweep(PARROT_INTERP, UINTVAL flags)
          __attribute__nonnull__(1);
  
  static void gc_gms_mark_pmc_header(PARROT_INTERP, ARGMOD(PMC *pmc))
          __attribute__nonnull__(1)
          __attribute__nonnull__(2)
          FUNC_MODIFIES(*pmc);
  
  static void gc_gms_mark_str_header(PARROT_INTERP, ARGMOD(STRING *str))
          __attribute__nonnull__(2)
          FUNC_MODIFIES(*str);
  
  static void gc_gms_pmc_get_youngest_generation(PARROT_INTERP,
      ARGIN(PMC *pmc))
          __attribute__nonnull__(1)
          __attribute__nonnull__(2);
  
  static void gc_gms_pmc_needs_early_collection(PARROT_INTERP, PMC *pmc)
          __attribute__nonnull__(1);
  
  static void gc_gms_print_stats(PARROT_INTERP, ARGIN(const char* header))
          __attribute__nonnull__(1)
          __attribute__nonnull__(2);
  
  static void gc_gms_process_dirty_list(PARROT_INTERP,
      ARGIN(MarkSweep_GC *self),
      ARGIN(Parrot_Pointer_Array *dirty_list))
          __attribute__nonnull__(1)
          __attribute__nonnull__(2)
          __attribute__nonnull__(3);
  
  static void gc_gms_process_work_list(PARROT_INTERP,
      ARGIN(MarkSweep_GC *self),
      ARGIN(Parrot_Pointer_Array *work_list))
          __attribute__nonnull__(1)
          __attribute__nonnull__(2)
          __attribute__nonnull__(3);
  
  static void gc_gms_reallocate_buffer_storage(PARROT_INTERP,
      ARGIN(Parrot_Buffer *str),
      size_t size)
          __attribute__nonnull__(1)
          __attribute__nonnull__(2);
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static void * gc_gms_reallocate_memory_chunk(PARROT_INTERP,
      ARGFREE(void *from),
      size_t size);
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static void * gc_gms_reallocate_memory_chunk_zeroed(PARROT_INTERP,
      ARGFREE(void *data),
      size_t newsize,
      size_t oldsize);
  
  static void gc_gms_reallocate_string_storage(PARROT_INTERP,
      ARGIN(STRING *str),
      size_t size)
          __attribute__nonnull__(1)
          __attribute__nonnull__(2);
  
  static void gc_gms_seal_object(PARROT_INTERP, ARGIN(PMC *pmc))
          __attribute__nonnull__(2);
  
  static size_t gc_gms_select_generation_to_collect(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  static void gc_gms_str_get_youngest_generation(PARROT_INTERP,
      ARGIN(STRING *str))
          __attribute__nonnull__(1)
          __attribute__nonnull__(2);
  
  static void gc_gms_sweep_pools(PARROT_INTERP, ARGMOD(MarkSweep_GC *self))
          __attribute__nonnull__(1)
          __attribute__nonnull__(2)
          FUNC_MODIFIES(*self);
  
  static void gc_gms_unblock_GC_mark(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  static void gc_gms_unblock_GC_mark_locked(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  static void gc_gms_unblock_GC_sweep(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  static void gc_gms_unseal_object(PARROT_INTERP, ARGIN(PMC *pmc))
          __attribute__nonnull__(2);
  
  static void gc_gms_validate_objects(PARROT_INTERP)
          __attribute__nonnull__(1);
  
  static void gc_gms_validate_pmc(PARROT_INTERP, ARGIN(PMC *pmc))
          __attribute__nonnull__(1)
          __attribute__nonnull__(2);
  
  static void gc_gms_validate_str(PARROT_INTERP, ARGIN(STRING *str))
          __attribute__nonnull__(2);
  
  static void gc_gms_write_barrier(PARROT_INTERP, ARGMOD(PMC *pmc))
          __attribute__nonnull__(1)
          __attribute__nonnull__(2)
          FUNC_MODIFIES(*pmc);
  
  static int gen2flags(int gen);
  #define ASSERT_ARGS_failed_allocation __attribute__unused__ int _ASSERT_ARGS_CHECK = (0)
  #define ASSERT_ARGS_gc_gms_allocate_buffer_header __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_allocate_buffer_storage \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(str))
  #define ASSERT_ARGS_gc_gms_allocate_fixed_size_storage \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_allocate_memory_chunk __attribute__unused__ int _ASSERT_ARGS_CHECK = (0)
  #define ASSERT_ARGS_gc_gms_allocate_memory_chunk_zeroed \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (0)
  #define ASSERT_ARGS_gc_gms_allocate_pmc_attributes \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(pmc))
  #define ASSERT_ARGS_gc_gms_allocate_pmc_header __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_allocate_string_header __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_allocate_string_storage \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(str))
  #define ASSERT_ARGS_gc_gms_block_GC_mark __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_block_GC_mark_locked __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_block_GC_sweep __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_check_sanity __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_cleanup_dirty_list __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(self) \
      , PARROT_ASSERT_ARG(dirty_list))
  #define ASSERT_ARGS_gc_gms_compact_memory_pool __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_count_used_pmc_memory __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(list))
  #define ASSERT_ARGS_gc_gms_count_used_string_memory \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(list))
  #define ASSERT_ARGS_gc_gms_finalize __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_free_buffer_header __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_free_fixed_size_storage \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(data))
  #define ASSERT_ARGS_gc_gms_free_memory_chunk __attribute__unused__ int _ASSERT_ARGS_CHECK = (0)
  #define ASSERT_ARGS_gc_gms_free_pmc_attributes __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(pmc))
  #define ASSERT_ARGS_gc_gms_free_pmc_attributes_locked \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(pmc))
  #define ASSERT_ARGS_gc_gms_free_pmc_header __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_free_string_header __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_get_gc_info __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_get_high_pmc_ptr __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_get_high_str_ptr __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_get_low_pmc_ptr __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_get_low_str_ptr __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_is_blocked_GC_mark __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_is_blocked_GC_sweep __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_is_pmc_ptr __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_is_string_ptr __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_iterate_live_strings __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_mark_and_sweep __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_mark_pmc_header __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(pmc))
  #define ASSERT_ARGS_gc_gms_mark_str_header __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(str))
  #define ASSERT_ARGS_gc_gms_pmc_get_youngest_generation \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(pmc))
  #define ASSERT_ARGS_gc_gms_pmc_needs_early_collection \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_print_stats __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(header))
  #define ASSERT_ARGS_gc_gms_process_dirty_list __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(self) \
      , PARROT_ASSERT_ARG(dirty_list))
  #define ASSERT_ARGS_gc_gms_process_work_list __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(self) \
      , PARROT_ASSERT_ARG(work_list))
  #define ASSERT_ARGS_gc_gms_reallocate_buffer_storage \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(str))
  #define ASSERT_ARGS_gc_gms_reallocate_memory_chunk \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (0)
  #define ASSERT_ARGS_gc_gms_reallocate_memory_chunk_zeroed \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (0)
  #define ASSERT_ARGS_gc_gms_reallocate_string_storage \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(str))
  #define ASSERT_ARGS_gc_gms_seal_object __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(pmc))
  #define ASSERT_ARGS_gc_gms_select_generation_to_collect \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_str_get_youngest_generation \
       __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(str))
  #define ASSERT_ARGS_gc_gms_sweep_pools __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(self))
  #define ASSERT_ARGS_gc_gms_unblock_GC_mark __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_unblock_GC_mark_locked __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_unblock_GC_sweep __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_unseal_object __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(pmc))
  #define ASSERT_ARGS_gc_gms_validate_objects __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp))
  #define ASSERT_ARGS_gc_gms_validate_pmc __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(pmc))
  #define ASSERT_ARGS_gc_gms_validate_str __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(str))
  #define ASSERT_ARGS_gc_gms_write_barrier __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
         PARROT_ASSERT_ARG(interp) \
      , PARROT_ASSERT_ARG(pmc))
  #define ASSERT_ARGS_gen2flags __attribute__unused__ int _ASSERT_ARGS_CHECK = (0)
  /* Don't modify between HEADERIZER BEGIN / HEADERIZER END.  Your changes will be lost. */
  /* HEADERIZER END: static */
  
  /*
  
  =head1 Functions
  
  =over 4
  
  =item C<static void gc_gms_mark_and_sweep(PARROT_INTERP, UINTVAL flags)>
  
  This function is called from the GC API function C<Parrot_gc_mark_and_sweep>.
  
  Flags can be a combination of these values:
  
    GC_finish_FLAG
    GC_lazy_FLAG
    GC_trace_stack_FLAG
  
  =cut
  
  */
  
  
  /*
  
  =item C<void Parrot_gc_gms_init(PARROT_INTERP, Parrot_GC_Init_Args *args)>
  
  Initializes the generational collector
  
  =cut
  
  */
  
  void
  Parrot_gc_gms_init(PARROT_INTERP, ARGIN(Parrot_GC_Init_Args *args))
  {
      ASSERT_ARGS(Parrot_gc_gms_init)
      struct MarkSweep_GC *self;
      const Parrot_Float4 nursery_size = (args->nursery_size > 0)
                          ? args->nursery_size
                          : GC_DEFAULT_NURSERY_SIZE;
  
      /* We have to transfer ownership of memory to parent interp in threaded parrot */
      interp->gc_sys->finalize_gc_system = NULL; /* gc_gms_finalize; */
  
      interp->gc_sys->do_gc_mark                  = gc_gms_mark_and_sweep;
      interp->gc_sys->compact_string_pool         = gc_gms_compact_memory_pool;
  
      /*
      interp->gc_sys->mark_special                = gc_gms_mark_special;
      */
      interp->gc_sys->pmc_needs_early_collection  = gc_gms_pmc_needs_early_collection;
  
      interp->gc_sys->allocate_pmc_header         = gc_gms_allocate_pmc_header;
      interp->gc_sys->free_pmc_header             = gc_gms_free_pmc_header;
  
      interp->gc_sys->allocate_string_header      = gc_gms_allocate_string_header;
      interp->gc_sys->free_string_header          = gc_gms_free_string_header;
  
      interp->gc_sys->allocate_bufferlike_header  = gc_gms_allocate_buffer_header;
      interp->gc_sys->free_bufferlike_header      = gc_gms_free_buffer_header;
  
      interp->gc_sys->allocate_pmc_attributes     = gc_gms_allocate_pmc_attributes;
      interp->gc_sys->free_pmc_attributes         = gc_gms_free_pmc_attributes_locked;
  
      interp->gc_sys->is_pmc_ptr                  = gc_gms_is_pmc_ptr;
      interp->gc_sys->is_string_ptr               = gc_gms_is_string_ptr;
      interp->gc_sys->mark_pmc_header             = gc_gms_mark_pmc_header;
      interp->gc_sys->mark_str_header             = gc_gms_mark_str_header;
  
      interp->gc_sys->block_mark                  = gc_gms_block_GC_mark;
      interp->gc_sys->block_mark_locked           = gc_gms_block_GC_mark_locked;
      interp->gc_sys->unblock_mark                = gc_gms_unblock_GC_mark;
      interp->gc_sys->unblock_mark_locked         = gc_gms_unblock_GC_mark_locked;
      interp->gc_sys->is_blocked_mark             = gc_gms_is_blocked_GC_mark;
  
      interp->gc_sys->block_sweep                 = gc_gms_block_GC_sweep;
      interp->gc_sys->unblock_sweep               = gc_gms_unblock_GC_sweep;
      interp->gc_sys->is_blocked_sweep            = gc_gms_is_blocked_GC_sweep;
  
      interp->gc_sys->allocate_string_storage     = gc_gms_allocate_string_storage;
      interp->gc_sys->reallocate_string_storage   = gc_gms_reallocate_string_storage;
  
      interp->gc_sys->allocate_buffer_storage     = gc_gms_allocate_buffer_storage;
      interp->gc_sys->reallocate_buffer_storage   = gc_gms_reallocate_buffer_storage;
  
      interp->gc_sys->allocate_fixed_size_storage = gc_gms_allocate_fixed_size_storage;
      interp->gc_sys->free_fixed_size_storage     = gc_gms_free_fixed_size_storage;
  
      /* We don't distinguish between chunk and chunk_with_pointers */
      interp->gc_sys->allocate_memory_chunk       = gc_gms_allocate_memory_chunk;
      interp->gc_sys->reallocate_memory_chunk     = gc_gms_reallocate_memory_chunk;
      interp->gc_sys->allocate_memory_chunk_with_interior_pointers
                  = gc_gms_allocate_memory_chunk_zeroed;
      interp->gc_sys->reallocate_memory_chunk_with_interior_pointers
                  = gc_gms_reallocate_memory_chunk_zeroed;
      interp->gc_sys->free_memory_chunk           = gc_gms_free_memory_chunk;
  
      interp->gc_sys->get_low_str_ptr             = gc_gms_get_low_str_ptr;
      interp->gc_sys->get_high_str_ptr            = gc_gms_get_high_str_ptr;
      interp->gc_sys->get_low_pmc_ptr             = gc_gms_get_low_pmc_ptr;
      interp->gc_sys->get_high_pmc_ptr            = gc_gms_get_high_pmc_ptr;
  
      interp->gc_sys->iterate_live_strings        = gc_gms_iterate_live_strings;
      interp->gc_sys->write_barrier               = gc_gms_write_barrier;
  
      interp->gc_sys->get_gc_info                 = gc_gms_get_gc_info;
  
      {
          size_t i;
  
          self = mem_internal_allocate_zeroed_typed(MarkSweep_GC);
  
          self->pmc_allocator = Parrot_gc_pool_new(interp,
              sizeof (pmc_alloc_struct));
  
          self->string_allocator = Parrot_gc_pool_new(interp,
              sizeof (string_alloc_struct));
  
          /* Allocate list for gray objects */
          self->work_list  = NULL;
          self->dirty_list = Parrot_pa_new(interp);
  
          for (i = 0; i < MAX_GENERATIONS; i++) {
              self->objects[i] = Parrot_pa_new(interp);
              self->strings[i] = Parrot_pa_new(interp);
          }
  
          self->fixed_size_allocator = Parrot_gc_fixed_allocator_new(interp);
  
          /*
           * Collect every nursery_size/100 of system memory.
           *
           * Configured by runtime parameter (default 2%).
           */
          self->gc_threshold = Parrot_sysmem_amount(interp) * nursery_size / 100;
  
          Parrot_gc_str_initialize(interp, &self->string_gc);
      }
  
      interp->gc_sys->gc_private = self;
  
  }
  
  static void
  gc_gms_mark_and_sweep(PARROT_INTERP, UINTVAL flags)
  {
      ASSERT_ARGS(gc_gms_mark_and_sweep)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      int gen = -1;
  
      if (interp->thread_data)
          LOCK(interp->thread_data->interp_lock);
  
      /* GC is blocked */
      if (self->gc_mark_block_level || self->gc_mark_block_level_locked)
          goto DONE;
  
      /* Ignore it. Will cleanup in gc_gms_finalize */
      if (flags & GC_finish_FLAG)
          goto DONE;
  
      /* Ignore calls from String GC. We know better when to trigger GC */
      if (flags & GC_strings_cb_FLAG)
          goto DONE;
  
      /* Block further GC calls */
      ++self->gc_mark_block_level;
      self->work_list = Parrot_pa_new(interp);
  
      interp->gc_sys->stats.gc_mark_runs++;
  
      gc_gms_print_stats(interp, "Before");
  
      gc_gms_check_sanity(interp);
      /*
      2. Choose K - how many collections we want to collect. Collections [0..K]
      will be collected. Remember K in C<self->gen_to_collect>.
      */
      self->gen_to_collect = gen = gc_gms_select_generation_to_collect(interp);
  
      /*
      3. Move all objects from collections younger K from dirty_list
      back to original lists. Reason for this is "corollary of invariant". We can
      either collect such objects or they will be marked by referents from
      "dirty_list".
      */
      gc_gms_cleanup_dirty_list(interp, self, self->dirty_list);
      gc_gms_print_stats(interp, "After cleanup");
  
      /*
      4. Trace root objects. According to "0. Pre-requirements" we will ignore all
      "old" objects. All relevant objects are moved into "work_list".
      */
      if (! Interp_flags_TEST(interp, PARROT_IS_THREAD))
          gc_gms_mark_pmc_header(interp, PMCNULL);
      Parrot_gc_trace_root(interp, NULL, GC_TRACE_FULL);
  
      if (interp->pdb && interp->pdb->debugger)
          Parrot_gc_trace_root(interp->pdb->debugger, NULL, GC_TRACE_FULL);
  
      gc_gms_print_stats(interp, "After trace_roots");
      gc_gms_check_sanity(interp);
  
      /*
      5. Iterate over "dirty_set" calling VTABLE_mark on it. It will move all
      children into "work_list".
      */
      gc_gms_process_dirty_list(interp, self, self->dirty_list);
      gc_gms_print_stats(interp, "After dirty_list");
      gc_gms_check_sanity(interp);
  
      /*
      6. Iterate over "work_list" calling VTABLE_mark on it.
      */
      gc_gms_process_work_list(interp, self, self->work_list);
      gc_gms_print_stats(interp, "After work_list");
      gc_gms_check_sanity(interp);
  
      /*
      7. Sweep generations starting from K:
          - Destroy all dead objects
          - Move live objects into generation max(K+1, N)
          - Paint them white.
      */
      gc_gms_sweep_pools(interp, self);
      gc_gms_check_sanity(interp);
  
      /* Update some stats */
      interp->gc_sys->stats.header_allocs_since_last_collect  = 0;
      interp->gc_sys->stats.mem_used_last_collect             = 0;
  
      self->gc_mark_block_level--;
  
      /* We swept all dead objects */
      self->num_early_gc_PMCs                      = 0;
  
      /* Don't compact after nursery collection */
      if (gen)
          gc_gms_compact_memory_pool(interp);
  
      gc_gms_check_sanity(interp);
  
      gc_gms_print_stats(interp, "After");
  
      Parrot_pa_destroy(interp, self->work_list);
      self->work_list = NULL;
  
      gc_gms_validate_objects(interp);
  
  DONE:
      if (interp->thread_data)
          UNLOCK(interp->thread_data->interp_lock);
  }
  
  /*
  
  =item C<static size_t gc_gms_select_generation_to_collect(PARROT_INTERP)>
  
  Select how many generations we do want to collect.
  
  =cut
  
  */
  static size_t
  gc_gms_select_generation_to_collect(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_select_generation_to_collect)
      /* TODO Use less naive approach. E.g. count amount of allocated memory in
       * older generations */
      size_t runs = interp->gc_sys->stats.gc_mark_runs;
  /*
      if (runs % 100000000 == 0)
          return 8;
      if (runs % 10000000 == 0)
          return 7;
      if (runs % 1000000 == 0)
          return 6;
      if (runs % 100000 == 0)
          return 5;
      if (runs % 10000 == 0)
          return 4;
  */
      if (runs % 1000 == 0)
          return 3;
      if (runs % 100 == 0)
          return 2;
      if (runs % 10 == 0)
          return 1;
      return 0;
  }
  
  /*
  
  =item C<static void gc_gms_cleanup_dirty_list(PARROT_INTERP, MarkSweep_GC *self,
  Parrot_Pointer_Array *dirty_list)>
  
  Move all objects from collections younger K from dirty_list
  back to original lists. Reason for this is "corollary of invariant". We can
  either collect such objects or they will be marked by referents from
  "dirty_list".
  
  =cut
  
  */
  static void
  gc_gms_cleanup_dirty_list(PARROT_INTERP,
          ARGIN(MarkSweep_GC *self),
          ARGIN(Parrot_Pointer_Array *dirty_list))
  {
      ASSERT_ARGS(gc_gms_cleanup_dirty_list)
  
      /* Override with special version of mark */
      interp->gc_sys->mark_pmc_header = gc_gms_pmc_get_youngest_generation;
      interp->gc_sys->mark_str_header = gc_gms_str_get_youngest_generation;
  
      POINTER_ARRAY_ITER(dirty_list,
          pmc_alloc_struct *item = (pmc_alloc_struct *)ptr;
          PMC              *pmc  = &(item->pmc);
          size_t            gen  = POBJ2GEN(pmc);
  
          self->youngest_child = gen;
          PARROT_GC_ASSERT_INTERP(pmc, interp);
  
          if (PObj_custom_mark_TEST(pmc))
              VTABLE_mark(interp, pmc);
  
          if (PMC_metadata(pmc) && self->youngest_child > POBJ2GEN(PMC_metadata(pmc)))
              self->youngest_child = POBJ2GEN(PMC_metadata(pmc));
  
          /* All children aren't younger than us - get rid of it */
          if (self->youngest_child >= gen) {
              PObj_live_CLEAR(pmc);
              PObj_GC_on_dirty_list_CLEAR(pmc);
              Parrot_pa_remove(interp, dirty_list, item->ptr);
              item->ptr = Parrot_pa_insert(self->objects[gen], item);
              gc_gms_seal_object(interp, pmc);
          }
          else {
              /* Survival */
              /* This check used to be
               * if ((gen <= self->gen_to_collect) && (gen < MAX_GENERATIONS - 1))
               * Unfortunatelly it's wrong.
               * Consider this:
               * A1* -> B1* -> C0. (Object in generation notation. Star denotes "dirt
               * During gen0 collecting will "sink" A object, but not B. This picture
               * A2 -> B1* -> C1
               * After collecting gen1 we'll sink all of them:
               * A3 -> B2 -> C2.
               * And after collecting of gen2 we'll collect B and C incorrectly.
               * Because A(3) will be in older generation than B and C.
               */
              if (gen < MAX_GENERATIONS - 1) {
                  SET_GEN_FLAGS(pmc, gen + 1);
              }
          };);
  
      interp->gc_sys->mark_pmc_header = gc_gms_mark_pmc_header;
      interp->gc_sys->mark_str_header = gc_gms_mark_str_header;
  }
  
  /*
  
  =item C<static void gc_gms_process_dirty_list(PARROT_INTERP, MarkSweep_GC *self,
  Parrot_Pointer_Array *dirty_list)>
  
  Iterate over "dirty_set" calling VTABLE_mark on it. It will move all
  children into "work_list".
  
  =cut
  
  */
  static void
  gc_gms_process_dirty_list(PARROT_INTERP,
          ARGIN(MarkSweep_GC *self),
          ARGIN(Parrot_Pointer_Array *dirty_list))
  {
      ASSERT_ARGS(gc_gms_process_dirty_list)
  
      POINTER_ARRAY_ITER(dirty_list,
          PMC * const pmc = &((pmc_alloc_struct *)ptr)->pmc;
          PARROT_GC_ASSERT_INTERP(pmc, interp);
  
          if (PObj_custom_mark_TEST(pmc))
              VTABLE_mark(interp, pmc);
  
          if (PMC_metadata(pmc))
              Parrot_gc_mark_PMC_alive(interp, PMC_metadata(pmc)););
  }
  
  /*
  
  =item C<static void gc_gms_process_work_list(PARROT_INTERP, MarkSweep_GC *self,
  Parrot_Pointer_Array *work_list)>
  
  Process work list moving objects back to own generation
  
  =cut
  
  */
  static void
  gc_gms_process_work_list(PARROT_INTERP,
          ARGIN(MarkSweep_GC *self),
          ARGIN(Parrot_Pointer_Array *work_list))
  {
      ASSERT_ARGS(gc_gms_process_work_list)
  
      POINTER_ARRAY_ITER(work_list,
          PMC * const pmc = &((pmc_alloc_struct *)ptr)->pmc;
          PARROT_GC_ASSERT_INTERP(pmc, interp);
  
          if (PObj_custom_mark_TEST(pmc))
              VTABLE_mark(interp, pmc);
  
          if (PMC_metadata(pmc))
              Parrot_gc_mark_PMC_alive(interp, PMC_metadata(pmc)););
  
      gc_gms_print_stats(interp, "Before cleaning work_list");
  
      /* Move processed objects back to own generation */
      POINTER_ARRAY_ITER(work_list,
          pmc_alloc_struct * const item = (pmc_alloc_struct *)ptr;
          PMC              * const pmc  = &(item->pmc);
          const size_t             gen  = POBJ2GEN(pmc);
  
          PARROT_ASSERT(!PObj_GC_on_dirty_list_TEST(pmc));
          PARROT_GC_ASSERT_INTERP(pmc, interp);
  
          Parrot_pa_remove(interp, work_list, item->ptr);
          item->ptr = Parrot_pa_insert(self->objects[gen], item););
  
  }
  
  /*
  
  =item C<static void gc_gms_sweep_pools(PARROT_INTERP, MarkSweep_GC *self)>
  
  Sweep generations starting from K:
      - Destroy all dead objects
      - Move live objects into generation max(K+1, N)
      - Paint them white.
  
  =cut
  
  */
  static void
  gc_gms_sweep_pools(PARROT_INTERP, ARGMOD(MarkSweep_GC *self))
  {
      ASSERT_ARGS(gc_gms_sweep_pools)
  
      INTVAL i;
  
      for (i = self->gen_to_collect; i >= 0; i--) {
          /* Don't move to generation beyond last */
          const int move_to_old = (i + 1) != MAX_GENERATIONS;
  
          POINTER_ARRAY_ITER(self->objects[i],
              pmc_alloc_struct * const item = (pmc_alloc_struct *)ptr;
              PMC              * const pmc  = &(item->pmc);
  
              PARROT_ASSERT(PObj_constant_TEST(pmc) || (int)POBJ2GEN(pmc) == i);
              PARROT_GC_ASSERT_INTERP(pmc, interp);
  
              /* Paint live objects white */
              if (PObj_live_TEST(pmc) || PObj_constant_TEST(pmc)) {
                  PObj_live_CLEAR(pmc);
  
                  if (move_to_old) {
                      SET_GEN_FLAGS(pmc, i + 1);
  
                      Parrot_pa_remove(interp, self->objects[i], item->ptr);
                      /* If this was freshly allocated object in C stack - move it to dirty list */
                      if (PObj_GC_soil_root_TEST(pmc)) {
                          item->ptr = Parrot_pa_insert(self->dirty_list, item);
                          PObj_GC_soil_root_CLEAR(pmc);
                          PObj_GC_on_dirty_list_SET(pmc);
                      }
                      else {
                          item->ptr = Parrot_pa_insert(self->objects[i + 1], item);
                          gc_gms_seal_object(interp, pmc);
                      }
                  }
              }
              else {
                  Parrot_pa_remove(interp, self->objects[i], item->ptr);
  
                  interp->gc_sys->stats.memory_used -= sizeof (PMC);
  
                  /* this is manual inlining of Parrot_pmc_destroy() */
                  if (PObj_custom_destroy_TEST(pmc))
                      VTABLE_destroy(interp, pmc);
  
                  if (pmc->vtable->attr_size && PMC_data(pmc))
                      gc_gms_free_pmc_attributes(interp, pmc);
                  PMC_data(pmc) = NULL;
  
                  PObj_on_free_list_SET(pmc);
                  PObj_gc_CLEAR(pmc);
  
                  Parrot_gc_pool_free(interp, self->pmc_allocator, ptr);
              });
  
          POINTER_ARRAY_ITER(self->strings[i],
              string_alloc_struct * const item = (string_alloc_struct *)ptr;
              STRING * const str = &(item->str);
  
              PARROT_ASSERT(!PObj_on_free_list_TEST(str));
  
              /* Paint live objects white */
              if (PObj_live_TEST(str) || PObj_constant_TEST(str)) {
                  PObj_live_CLEAR(str);
                  if (move_to_old) {
                      Parrot_pa_remove(interp, self->strings[i], item->ptr);
                      item->ptr = Parrot_pa_insert(self->strings[i + 1], item);
                      SET_GEN_FLAGS(str, i + 1);
                  }
              }
  
              else {
                  Parrot_pa_remove(interp, self->strings[i], item->ptr);
                  if (Buffer_bufstart(str) && !PObj_external_TEST(str))
                      Parrot_gc_str_free_buffer_storage(
                          interp, &self->string_gc, (Parrot_Buffer*)str);
  
                  interp->gc_sys->stats.memory_used -= sizeof (STRING);
  
                  PObj_on_free_list_SET(str);
  
                  Parrot_gc_pool_free(interp, self->string_allocator, ptr);
              });
      }
  
  }
  
  
  /*
  
  =item C<static void gc_gms_mark_pmc_header(PARROT_INTERP, PMC *pmc)>
  
  mark as grey
  
  =cut
  
  */
  
  static void
  gc_gms_mark_pmc_header(PARROT_INTERP, ARGMOD(PMC *pmc))
  {
      ASSERT_ARGS(gc_gms_mark_pmc_header)
      MarkSweep_GC      * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      pmc_alloc_struct  * const item = PMC2PAC(pmc);
      const size_t gen  = POBJ2GEN(pmc);
  
      PARROT_ASSERT(!PObj_on_free_list_TEST(pmc)
          || !"Resurrecting of dead objects is not supported");
  
      PARROT_GC_ASSERT_INTERP(pmc, interp);
  
      /* Object was already marked as grey. Or live. Or dead. Skip it */
      if (PObj_live_TEST(pmc))
          return;
  
      /* If object too old - skip it */
      if (gen > self->gen_to_collect)
          return;
  
      /* Object is on dirty_list. */
      if (PObj_GC_on_dirty_list_TEST(pmc))
          return;
  
      /* mark it live. */
      PObj_live_SET(pmc);
  
      PARROT_ASSERT(self->work_list);
      Parrot_pa_remove(interp, self->objects[gen], item->ptr);
      item->ptr = Parrot_pa_insert(self->work_list, item);
  }
  
  /*
  
  =item C<static void gc_gms_mark_str_header(PARROT_INTERP, STRING *str)>
  
  Mark String
  
  =cut
  
  */
  
  static void
  gc_gms_mark_str_header(SHIM_INTERP, ARGMOD(STRING *str))
  {
      ASSERT_ARGS(gc_gms_mark_str_header)
  
      PObj_live_SET(str);
  }
  
  
  /*
  
  =item C<static void gc_gms_compact_memory_pool(PARROT_INTERP)>
  
  Stub for compacting memory pools.
  
  =cut
  
  */
  static void
  gc_gms_compact_memory_pool(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_compact_memory_pool)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
  
      Parrot_gc_str_compact_pool(interp, &self->string_gc);
  }
  
  /*
  
  =item C<static PMC* gc_gms_allocate_pmc_header(PARROT_INTERP, UINTVAL flags)>
  
  =item C<static void gc_gms_free_pmc_header(PARROT_INTERP, PMC *pmc)>
  
  =item C<static STRING* gc_gms_allocate_string_header(PARROT_INTERP, UINTVAL
  flags)>
  
  =item C<static void gc_gms_free_string_header(PARROT_INTERP, STRING *s)>
  
  =item C<static void* gc_gms_allocate_pmc_attributes(PARROT_INTERP, PMC *pmc)>
  
  =item C<static void gc_gms_free_pmc_attributes_locked(PARROT_INTERP, PMC *pmc)>
  
  =item C<static void gc_gms_free_pmc_attributes(PARROT_INTERP, PMC *pmc)>
  
  =item C<static void gc_gms_allocate_string_storage(PARROT_INTERP, STRING *str,
  size_t size)>
  
  =item C<static void gc_gms_reallocate_string_storage(PARROT_INTERP, STRING *str,
  size_t size)>
  
  =item C<static void gc_gms_allocate_buffer_storage(PARROT_INTERP, Parrot_Buffer
  *str, size_t size)>
  
  =item C<static void gc_gms_reallocate_buffer_storage(PARROT_INTERP,
  Parrot_Buffer *str, size_t size)>
  
  =item C<static void* gc_gms_allocate_fixed_size_storage(PARROT_INTERP, size_t
  size)>
  
  =item C<static void gc_gms_free_fixed_size_storage(PARROT_INTERP, size_t size,
  void *data)>
  
  Functions for allocating/deallocating various objects.
  
  */
  
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static void*
  gc_gms_allocate_pmc_attributes(PARROT_INTERP, ARGMOD(PMC *pmc))
  {
      ASSERT_ARGS(gc_gms_allocate_pmc_attributes)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      const size_t  attr_size = pmc->vtable->attr_size;
  
      if (interp->thread_data)
          LOCK(interp->thread_data->interp_lock);
  
      PMC_data(pmc) = Parrot_gc_fixed_allocator_allocate(interp,
                          self->fixed_size_allocator, attr_size);
      memset(PMC_data(pmc), 0, attr_size);
  
      interp->gc_sys->stats.memory_used           += attr_size;
      interp->gc_sys->stats.mem_used_last_collect += attr_size;
  
      if (interp->thread_data)
          UNLOCK(interp->thread_data->interp_lock);
  
      return PMC_data(pmc);
  }
  
  static void
  gc_gms_free_pmc_attributes_locked(PARROT_INTERP, ARGMOD(PMC *pmc))
  {
      ASSERT_ARGS(gc_gms_free_pmc_attributes_locked)
      if (PMC_data(pmc)) {
          MarkSweep_GC * const self   = (MarkSweep_GC *)interp->gc_sys->gc_private;
  
          if (interp->thread_data && ! self->locked)
              LOCK(interp->thread_data->interp_lock);
  
          gc_gms_free_pmc_attributes(interp, pmc);
  
          if (interp->thread_data && ! self->locked)
              UNLOCK(interp->thread_data->interp_lock);
      }
  }
  
  static void
  gc_gms_free_pmc_attributes(PARROT_INTERP, ARGMOD(PMC *pmc))
  {
      ASSERT_ARGS(gc_gms_free_pmc_attributes)
      if (PMC_data(pmc)) {
          GC_Subsystem * const gc_sys = interp->gc_sys;
          MarkSweep_GC * const self   = (MarkSweep_GC *)gc_sys->gc_private;
          const UINTVAL        size   = pmc->vtable->attr_size;
  
          Parrot_gc_fixed_allocator_free(interp, self->fixed_size_allocator, PMC_data(pmc), size);
  
          gc_sys->stats.memory_used           -= size;
          gc_sys->stats.mem_used_last_collect -= size;
      }
  }
  
  PARROT_CAN_RETURN_NULL
  static void*
  gc_gms_allocate_fixed_size_storage(PARROT_INTERP, size_t size)
  {
      ASSERT_ARGS(gc_gms_allocate_fixed_size_storage)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      void *storage;
  
      if (interp->thread_data)
          LOCK(interp->thread_data->interp_lock);
  
      interp->gc_sys->stats.memory_used           += size;
      interp->gc_sys->stats.mem_used_last_collect += size;
  
      storage = Parrot_gc_fixed_allocator_allocate(interp, self->fixed_size_allocator, size);
  
      if (interp->thread_data)
          UNLOCK(interp->thread_data->interp_lock);
  
      return storage;
  }
  
  static void
  gc_gms_free_fixed_size_storage(PARROT_INTERP, size_t size, ARGMOD(void *data))
  {
      ASSERT_ARGS(gc_gms_free_fixed_size_storage)
      if (data) {
          const MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
  
          interp->gc_sys->stats.memory_used           -= size;
          interp->gc_sys->stats.mem_used_last_collect -= size;
  
          Parrot_gc_fixed_allocator_free(interp, self->fixed_size_allocator, data, size);
      }
  }
  
  /*
  
  =item C<static size_t gc_gms_get_gc_info(PARROT_INTERP, Interpinfo_enum which)>
  
  GC introspection function.
  gets stats based on enum which
  
  =cut
  
  */
  static size_t
  gc_gms_get_gc_info(PARROT_INTERP, Interpinfo_enum which)
  {
      ASSERT_ARGS(gc_gms_get_gc_info)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
  
      if (which == IMPATIENT_PMCS)
          return self->num_early_gc_PMCs;
      if (which == TOTAL_PMCS) {
          /* It's higher than actual number of allocated PMCs */
          size_t ret = 0;
          size_t i;
          for (i = 0; i < MAX_GENERATIONS; i++) {
              ret += Parrot_pa_count_allocated(interp, self->objects[i]);
          }
          return ret;
      }
      if (which == ACTIVE_PMCS) {
          /* It's higher than actual number of allocated PMCs */
          size_t ret = 0;
          size_t i;
          for (i = 0; i < MAX_GENERATIONS; i++) {
              ret += Parrot_pa_count_used(interp, self->objects[i]);
          }
          return ret;
      }
  
      return Parrot_gc_get_info(interp, which, &interp->gc_sys->stats);
  }
  
  
  
  /*
  =item C<static void gc_gms_finalize(PARROT_INTERP)>
  
  Finalize GC subsystem.
  
  =cut
  */
  static void
  gc_gms_finalize(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_finalize)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      size_t        i;
  
      Parrot_gc_str_finalize(interp, &self->string_gc);
  
      for (i = 0; i < MAX_GENERATIONS; i++) {
          Parrot_pa_destroy(interp, self->objects[i]);
          Parrot_pa_destroy(interp, self->strings[i]);
      }
  
      Parrot_gc_pool_destroy(interp, self->pmc_allocator);
      Parrot_gc_pool_destroy(interp, self->string_allocator);
      Parrot_gc_fixed_allocator_destroy(interp, self->fixed_size_allocator);
  }
  
  /*
  
  =item C<gc_gms_maybe_mark_and_sweep(PARROT_INTERP)>
  
  Maybe M&S. Depends on total allocated memory, memory allocated since last alloc
  and phase of the Moon.
  
  =cut
  
  */
  
  #define gc_gms_maybe_mark_and_sweep(i) \
      do { \
          MarkSweep_GC * const self = (MarkSweep_GC *)(i)->gc_sys->gc_private; \
      \
          /* Collect every gc_threshold. */ \
          if (!self->gc_mark_block_level \
          &&  (i)->gc_sys->stats.mem_used_last_collect > self->gc_threshold) \
              gc_gms_mark_and_sweep(interp, 0); \
      } while (0)
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static PMC*
  gc_gms_allocate_pmc_header(PARROT_INTERP, SHIM(UINTVAL flags))
  {
      ASSERT_ARGS(gc_gms_allocate_pmc_header)
      MarkSweep_GC     * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      Pool_Allocator   * const pool = self->pmc_allocator;
      pmc_alloc_struct *item;
  
      gc_gms_maybe_mark_and_sweep(interp);
  
      if (interp->thread_data)
          LOCK(interp->thread_data->interp_lock);
  
      /* Increase used memory. Not precisely accurate due Pool_Allocator paging */
      ++interp->gc_sys->stats.header_allocs_since_last_collect;
  
      interp->gc_sys->stats.memory_used           += sizeof (PMC);
      interp->gc_sys->stats.mem_used_last_collect += sizeof (PMC);
  
      item         = (pmc_alloc_struct *)Parrot_gc_pool_allocate(interp, pool);
      item->ptr    = Parrot_pa_insert(self->objects[0], item);
  
      if (interp->thread_data)
          UNLOCK(interp->thread_data->interp_lock);
  
      return &(item->pmc);
  }
  
  static void
  gc_gms_free_pmc_header(PARROT_INTERP, ARGFREE(PMC *pmc))
  {
      ASSERT_ARGS(gc_gms_free_pmc_header)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
  
      if (pmc) {
          const size_t gen = POBJ2GEN(pmc);
  
          PARROT_GC_ASSERT_INTERP(pmc, interp);
  
          /* We should never free objects from dirty list directly! */
          PARROT_ASSERT(!PObj_GC_on_dirty_list_TEST(pmc));
  
          if (PObj_on_free_list_TEST(pmc))
              return;
  
          if (interp->thread_data)
              LOCK(interp->thread_data->interp_lock);
  
          self->locked = 1;
  
          Parrot_pa_remove(interp, self->objects[gen], PMC2PAC(pmc)->ptr);
          PObj_on_free_list_SET(pmc);
  
          Parrot_pmc_destroy(interp, pmc);
  
          Parrot_gc_pool_free(interp, self->pmc_allocator, PMC2PAC(pmc));
  
          --interp->gc_sys->stats.header_allocs_since_last_collect;
          interp->gc_sys->stats.memory_used           -= sizeof (PMC);
          interp->gc_sys->stats.mem_used_last_collect -= sizeof (PMC);
  
          self->locked = 0;
  
          if (interp->thread_data)
              UNLOCK(interp->thread_data->interp_lock);
      }
  }
  
  /*
  
  =item C<static int gc_gms_is_pmc_ptr(PARROT_INTERP, void *ptr)>
  
  establish if *ptr is.owned
  
  =cut
  
  */
  
  static int
  gc_gms_is_pmc_ptr(PARROT_INTERP, ARGIN_NULLOK(void *ptr))
  {
      ASSERT_ARGS(gc_gms_is_pmc_ptr)
      MarkSweep_GC     * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      PObj             * const obj  = (PObj *)ptr;
      pmc_alloc_struct * const item = PMC2PAC(ptr);
  
      /* Not aligned pointers aren't pointers */
      if (!obj || !item || ((size_t)obj & 3) || ((size_t)item & 3))
          return 0;
  
      if (!Parrot_gc_pool_is_owned(interp, self->pmc_allocator, item))
          return 0;
  
      PARROT_GC_ASSERT_INTERP((PMC*)ptr, interp);
  
      /* black or white objects marked already. */
      if (PObj_is_live_or_free_TESTALL(obj))
          return 0;
  
      /* If object too old - skip it */
      if (POBJ2GEN(obj) > self->gen_to_collect)
          return 0;
  
      /* Object is on dirty_list. */
      if (PObj_GC_on_dirty_list_TEST(obj))
          return 0;
  
      /* Pool.is_owned isn't precise enough (yet) */
      if (Parrot_pa_is_owned(self->objects[POBJ2GEN(obj)], item, item->ptr)) {
          if (POBJ2GEN(obj) == 0)
              PObj_GC_soil_root_SET(obj);
          return 1;
      }
  
      return 0;
  }
  
  /*
  
  =item C<gc_gms_allocate_string_header(PARROT_INTERP, STRING *str)>
  
  =item C<gc_gms_free_string_header(PARROT_INTERP, STRING *s)>
  
  =item C<static Parrot_Buffer* gc_gms_allocate_buffer_header(PARROT_INTERP,
  size_t size)>
  
  =item C<static void gc_gms_free_buffer_header(PARROT_INTERP, Parrot_Buffer *s,
  size_t size)>
  
  Allocate/free string/buffer headers.
  
  */
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static STRING*
  gc_gms_allocate_string_header(PARROT_INTERP, SHIM(UINTVAL flags))
  {
      ASSERT_ARGS(gc_gms_allocate_string_header)
      MarkSweep_GC     * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      Pool_Allocator   * const pool = self->string_allocator;
      string_alloc_struct *item;
      STRING              *ret;
  
      gc_gms_maybe_mark_and_sweep(interp);
  
      if (interp->thread_data)
          LOCK(interp->thread_data->interp_lock);
  
      /* Increase used memory.
       * Not precisely accurate due to Pool_Allocator paging.  */
      ++interp->gc_sys->stats.header_allocs_since_last_collect;
      interp->gc_sys->stats.memory_used           += sizeof (STRING);
      interp->gc_sys->stats.mem_used_last_collect += sizeof (STRING);
  
      item = (string_alloc_struct *)Parrot_gc_pool_allocate(interp, pool);
      item->ptr = Parrot_pa_insert(self->strings[0], item);
  
      if (interp->thread_data)
          UNLOCK(interp->thread_data->interp_lock);
  
      ret = &(item->str);
      memset(ret, 0, sizeof (STRING));
      return ret;
  }
  
  static void
  gc_gms_free_string_header(PARROT_INTERP, ARGFREE(STRING *s))
  {
      ASSERT_ARGS(gc_gms_free_string_header)
  
      if (s && !PObj_on_free_list_TEST(s)) {
          MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
          const size_t         gen = POBJ2GEN(s);
  
          Parrot_pa_remove(interp, self->strings[gen], STR2PAC(s)->ptr);
  
          if (Buffer_bufstart(s) && !PObj_external_TEST(s))
              Parrot_gc_str_free_buffer_storage(interp,
                  &self->string_gc, (Parrot_Buffer *)s);
  
          PObj_on_free_list_SET(s);
  
          Parrot_gc_pool_free(interp, self->string_allocator, STR2PAC(s));
  
          --interp->gc_sys->stats.header_allocs_since_last_collect;
          interp->gc_sys->stats.memory_used           -= sizeof (STRING);
          interp->gc_sys->stats.mem_used_last_collect -= sizeof (STRING);
      }
  }
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static Parrot_Buffer*
  gc_gms_allocate_buffer_header(PARROT_INTERP, SHIM(size_t size))
  {
      ASSERT_ARGS(gc_gms_allocate_buffer_header)
      return (Parrot_Buffer*)gc_gms_allocate_string_header(interp, 0);
  }
  
  static void
  gc_gms_free_buffer_header(PARROT_INTERP, ARGFREE(Parrot_Buffer *s), SHIM(size_t size))
  {
      ASSERT_ARGS(gc_gms_free_buffer_header)
      gc_gms_free_string_header(interp, (STRING*)s);
  }
  
  /*
  
  =item C<static int gc_gms_is_string_ptr(PARROT_INTERP, void *ptr)>
  
  establish if string *ptr is owned
  
  =cut
  
  */
  
  static int
  gc_gms_is_string_ptr(PARROT_INTERP, ARGIN_NULLOK(void *ptr))
  {
      ASSERT_ARGS(gc_gms_is_string_ptr)
      MarkSweep_GC     * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      PObj             * const obj  = (PObj *)ptr;
      string_alloc_struct * const item = STR2PAC(ptr);
  
      /* Not aligned pointers aren't pointers */
      if (!obj || !item || ((size_t)obj & 3) || ((size_t)item & 3))
          return 0;
  
      if (!Parrot_gc_pool_is_owned(interp, self->string_allocator, item))
          return 0;
  
      /* black or white objects marked already. */
      if (PObj_is_live_or_free_TESTALL(obj))
          return 0;
  
      /* If object too old - skip it */
      if (POBJ2GEN(&item->str) > self->gen_to_collect)
          return 0;
  
      if (Parrot_pa_is_owned(self->strings[POBJ2GEN(obj)], item, item->ptr))
          return 1;
  
      return 0;
  }
  
  /*
  
  item C<void gc_gms_allocate_string_storage(PARROT_INTERP, STRING *str, size_t
  size)>
  
  =item C<void gc_gms_reallocate_string_storage(PARROT_INTERP, STRING *str, size_t
  size)>
  
  =item C<void gc_gms_allocate_buffer_storage(PARROT_INTERP, Parrot_Buffer *str, size_t
  size)>
  
  =item C<void gc_gms_reallocate_buffer_storage(PARROT_INTERP, Parrot_Buffer *str, size_t
  size)>
  
  Functions for allocating strings/buffers storage.
  
  =cut
  */
  
  static void
  gc_gms_allocate_string_storage(PARROT_INTERP, ARGIN(STRING *str), size_t size)
  {
      ASSERT_ARGS(gc_gms_allocate_string_storage)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      Parrot_gc_str_allocate_string_storage(interp, &self->string_gc, str, size);
      interp->gc_sys->stats.memory_used           += size;
      interp->gc_sys->stats.mem_used_last_collect += size;
  }
  
  static void
  gc_gms_reallocate_string_storage(PARROT_INTERP, ARGIN(STRING *str), size_t size)
  {
      ASSERT_ARGS(gc_gms_reallocate_string_storage)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      Parrot_gc_str_reallocate_string_storage(interp, &self->string_gc, str, size);
      interp->gc_sys->stats.memory_used           += size;
      interp->gc_sys->stats.mem_used_last_collect += size;
  }
  
  static void
  gc_gms_allocate_buffer_storage(PARROT_INTERP, ARGIN(Parrot_Buffer *str), size_t size)
  {
      ASSERT_ARGS(gc_gms_allocate_buffer_storage)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      Parrot_gc_str_allocate_buffer_storage(interp, &self->string_gc, str, size);
      interp->gc_sys->stats.memory_used           += size;
      interp->gc_sys->stats.mem_used_last_collect += size;
  }
  
  static void
  gc_gms_reallocate_buffer_storage(PARROT_INTERP, ARGIN(Parrot_Buffer *str), size_t size)
  {
      ASSERT_ARGS(gc_gms_reallocate_buffer_storage)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      Parrot_gc_str_reallocate_buffer_storage(interp, &self->string_gc, str, size);
      interp->gc_sys->stats.memory_used           += size;
      interp->gc_sys->stats.mem_used_last_collect += size;
  }
  
  /*
  
  =item C<static void gc_gms_iterate_live_strings(PARROT_INTERP,
  string_iterator_callback callback, void *data)>
  
  Iterate over live string invoking callback for each of them. Used during
  compacting of string pool.
  
  =cut
  */
  static void
  gc_gms_iterate_live_strings(PARROT_INTERP,
          string_iterator_callback callback,
          ARGIN_NULLOK(void *data))
  {
      ASSERT_ARGS(gc_gms_iterate_live_strings)
  
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      size_t             i;
      for (i = 0; i < MAX_GENERATIONS; i++) {
          POINTER_ARRAY_ITER(self->strings[i],
              STRING *s = &((string_alloc_struct *)ptr)->str;
              callback(interp, (Parrot_Buffer *)s, data););
      }
  }
  
  
  
  
  /*
  
  =item C<static void gc_gms_block_GC_mark(PARROT_INTERP)>
  
  Blocks the GC from performing its mark phase.
  
  =item C<static void gc_gms_unblock_GC_mark(PARROT_INTERP)>
  
  Unblocks the GC mark.
  
  =item C<static void gc_gms_block_GC_mark_locked(PARROT_INTERP)>
  
  Blocks the GC from performing its mark phase.
  To be used from threads other than PARROT_INTERP.
  
  =item C<static void gc_gms_unblock_GC_mark_locked(PARROT_INTERP)>
  
  Unblocks the GC mark.
  To be used from threads other than PARROT_INTERP.
  
  =item C<static void gc_gms_block_GC_sweep(PARROT_INTERP)>
  
  Blocks the GC from performing its sweep phase.
  
  =item C<static void gc_gms_unblock_GC_sweep(PARROT_INTERP)>
  
  Unblocks GC sweep.
  
  =item C<static unsigned int gc_gms_is_blocked_GC_mark(PARROT_INTERP)>
  
  Determines if the GC mark is currently blocked.
  
  =item C<static unsigned int gc_gms_is_blocked_GC_sweep(PARROT_INTERP)>
  
  Determines if the GC sweep is currently blocked.
  
  =cut
  
  */
  
  static void
  gc_gms_block_GC_mark(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_block_GC_mark)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      ++self->gc_mark_block_level;
  }
  
  static void
  gc_gms_unblock_GC_mark(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_unblock_GC_mark)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      if (self->gc_mark_block_level)
          --self->gc_mark_block_level;
  }
  
  static void
  gc_gms_block_GC_mark_locked(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_block_GC_mark_locked)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      LOCK(interp->thread_data->interp_lock);
      ++self->gc_mark_block_level_locked;
      UNLOCK(interp->thread_data->interp_lock);
  }
  
  static void
  gc_gms_unblock_GC_mark_locked(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_unblock_GC_mark_locked)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      LOCK(interp->thread_data->interp_lock);
      if (self->gc_mark_block_level_locked)
          --self->gc_mark_block_level_locked;
      UNLOCK(interp->thread_data->interp_lock);
  }
  
  static void
  gc_gms_block_GC_sweep(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_block_GC_sweep)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      ++self->gc_sweep_block_level;
  }
  
  static void
  gc_gms_unblock_GC_sweep(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_unblock_GC_sweep)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      if (self->gc_sweep_block_level)
          --self->gc_sweep_block_level;
  }
  
  static unsigned int
  gc_gms_is_blocked_GC_mark(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_is_blocked_GC_mark)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      return self->gc_mark_block_level;
  }
  
  static unsigned int
  gc_gms_is_blocked_GC_sweep(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_is_blocked_GC_sweep)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      return self->gc_sweep_block_level;
  }
  
  
  
  /*
  
  =item C<static void * gc_gms_allocate_memory_chunk(PARROT_INTERP, size_t size)>
  
  =item C<static void * gc_gms_reallocate_memory_chunk(PARROT_INTERP, void *from,
  size_t size)>
  
  =item C<static void * gc_gms_allocate_memory_chunk_zeroed(PARROT_INTERP, size_t
  size)>
  
  =item C<static void * gc_gms_reallocate_memory_chunk_zeroed(PARROT_INTERP, void
  *data, size_t newsize, size_t oldsize)>
  
  =item C<static void gc_gms_free_memory_chunk(PARROT_INTERP, void *data)>
  
  =item C<static void failed_allocation(unsigned int line, size_t size)>
  
  TODO Write docu.
  
  */
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static void *
  gc_gms_allocate_memory_chunk(SHIM_INTERP, size_t size)
  {
      ASSERT_ARGS(gc_gms_allocate_memory_chunk)
      void * const ptr = malloc(size);
  #if defined(DETAIL_MEMORY_DEBUG)
      fprintf(stderr, "Allocated %i at %p\n", size, ptr);
  #endif
      if (!ptr && size)
          PANIC_OUT_OF_MEM(size);
      return ptr;
  }
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static void *
  gc_gms_reallocate_memory_chunk(SHIM_INTERP, ARGFREE(void *from), size_t size)
  {
      ASSERT_ARGS(gc_gms_reallocate_memory_chunk)
      void *ptr;
  #if defined(DETAIL_MEMORY_DEBUG)
      fprintf(stderr, "Freed %p (realloc -- %i bytes)\n", from, size);
  #endif
      if (from)
          ptr = realloc(from, size);
      else
          ptr = calloc(1, size);
  #if defined(DETAIL_MEMORY_DEBUG)
      fprintf(stderr, "Allocated %i at %p\n", size, ptr);
  #endif
      if (!ptr && size)
          PANIC_OUT_OF_MEM(size);
      return ptr;
  }
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static void *
  gc_gms_allocate_memory_chunk_zeroed(SHIM_INTERP, size_t size)
  {
      ASSERT_ARGS(gc_gms_allocate_memory_chunk_zeroed)
      void * const ptr = calloc(1, size);
  #if defined(DETAIL_MEMORY_DEBUG)
      fprintf(stderr, "Allocated %i at %p\n", size, ptr);
  #endif
      if (!ptr && size)
          PANIC_OUT_OF_MEM(size);
      return ptr;
  }
  
  PARROT_MALLOC
  PARROT_CAN_RETURN_NULL
  static void *
  gc_gms_reallocate_memory_chunk_zeroed(SHIM_INTERP, ARGFREE(void *data),
          size_t newsize, size_t oldsize)
  {
      ASSERT_ARGS(gc_gms_reallocate_memory_chunk_zeroed)
      void * const ptr = realloc(data, newsize);
      if (newsize > oldsize)
          memset((char*)ptr + oldsize, 0, newsize - oldsize);
      return ptr;
  }
  
  static void
  gc_gms_free_memory_chunk(SHIM_INTERP, ARGFREE(void *data))
  {
      ASSERT_ARGS(gc_gms_free_memory_chunk)
  #if defined(DETAIL_MEMORY_DEBUG)
      fprintf(stderr, "Freed %p\n", data);
  #endif
      if (data)
          free(data);
  }
  
  PARROT_DOES_NOT_RETURN
  static void
  failed_allocation(unsigned int line, size_t size)
  {
      ASSERT_ARGS(failed_allocation)
      fprintf(stderr, "Failed allocation of %lu bytes\n", (unsigned long)size);
      Parrot_x_panic_and_exit(NULL, "Out of mem", __FILE__, line);
  }
  
  
  /*
  
  =item C<static void gc_gms_pmc_needs_early_collection(PARROT_INTERP, PMC *pmc)>
  
  Mark a PMC as needing timely destruction.
  
  The C<pmc> argument is currently unused.
  
  =cut
  
  */
  
  static void
  gc_gms_pmc_needs_early_collection(PARROT_INTERP, SHIM(PMC *pmc))
  {
      ASSERT_ARGS(gc_gms_pmc_needs_early_collection)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      ++self->num_early_gc_PMCs;
  }
  
  /*
  =item C<static void gc_gms_write_barrier(PARROT_INTERP, PMC *pmc)>
  
  WriteBarrier for PMC. Add to root_objects list for mandatory next collecting.
  This is automatically added by pmc2c to all VTABLE function which are marked
  with C<:write> in src/vtable.tbl.
  
  =cut
  */
  static void
  gc_gms_write_barrier(PARROT_INTERP, ARGMOD(PMC *pmc))
  {
      ASSERT_ARGS(gc_gms_write_barrier)
  
      if (PObj_is_shared_TEST(pmc) && Interp_flags_TEST(interp, PARROT_IS_THREAD)) {
          gc_gms_write_barrier(interp->thread_data->main_interp, pmc);
          return;
      }
  
      if (interp->thread_data)
          LOCK(interp->thread_data->interp_lock);
  
      {
          MarkSweep_GC     * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
          const size_t             gen  = POBJ2GEN(pmc);
          pmc_alloc_struct * const item = PMC2PAC(pmc);
  
          if (pmc->flags & PObj_GC_on_dirty_list_FLAG)
              goto DONE;
  
          if (!gen)
              goto DONE;
  
          PARROT_GC_ASSERT_INTERP(pmc, interp);
  
          Parrot_pa_remove(interp, self->objects[gen], item->ptr);
          item->ptr = Parrot_pa_insert(self->dirty_list, item);
  
          pmc->flags |= PObj_GC_on_dirty_list_FLAG;
  
          /* We don't need it anymore */
          gc_gms_unseal_object(interp, pmc);
      }
  
  DONE:
      if (interp->thread_data)
          UNLOCK(interp->thread_data->interp_lock);
  }
  
  /*
  
  =item C<static void * gc_gms_get_low_str_ptr(PARROT_INTERP)>
  
  =item C<static void * gc_gms_get_high_str_ptr(PARROT_INTERP)>
  
  =item C<static void * gc_gms_get_low_pmc_ptr(PARROT_INTERP)>
  
  =item C<static void * gc_gms_get_high_pmc_ptr(PARROT_INTERP)>
  
  Get memory boudaries.
  
  */
  
  PARROT_CAN_RETURN_NULL
  static void *
  gc_gms_get_low_str_ptr(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_get_low_str_ptr)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      return Parrot_gc_pool_low_ptr(interp, self->string_allocator);
  }
  
  PARROT_CAN_RETURN_NULL
  static void *
  gc_gms_get_high_str_ptr(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_get_high_str_ptr)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      return Parrot_gc_pool_high_ptr(interp, self->string_allocator);
  }
  
  PARROT_CAN_RETURN_NULL
  static void *
  gc_gms_get_low_pmc_ptr(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_get_low_pmc_ptr)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      return Parrot_gc_pool_low_ptr(interp, self->pmc_allocator);
  }
  
  PARROT_CAN_RETURN_NULL
  static void *
  gc_gms_get_high_pmc_ptr(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_get_high_pmc_ptr)
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      return Parrot_gc_pool_high_ptr(interp, self->pmc_allocator);
  }
  
  
  /*
  
  =item C<static size_t gc_gms_count_used_string_memory(PARROT_INTERP,
  Parrot_Pointer_Array *list)>
  
  find amount of used string memory
  
  Currently disabled, returns always C<0>.
  
  =cut
  
  */
  
  static size_t
  gc_gms_count_used_string_memory(PARROT_INTERP, ARGIN(Parrot_Pointer_Array *list))
  {
      ASSERT_ARGS(gc_gms_count_used_string_memory)
  
      size_t total_amount = 0;
  #if 0
      List_Item_Header *tmp = list->first;
      while (tmp) {
          List_Item_Header *next = tmp->next;
          PObj             *obj  = LLH2Obj_typed(tmp, PObj);
          STRING           *str  = (STRING*)obj;
  
          /* Header size */
          total_amount += sizeof (List_Item_Header)
                          + sizeof (STRING*);
          total_amount += str->bufused;
  
          tmp = next;
      }
  #endif
      return total_amount;
  }
  
  /*
  
  =item C<static size_t gc_gms_count_used_pmc_memory(PARROT_INTERP,
  Parrot_Pointer_Array *list)>
  
  find amount of used pmc memory
  
  Currently disabled, returns always C<0>.
  
  =cut
  
  */
  
  static size_t
  gc_gms_count_used_pmc_memory(PARROT_INTERP, ARGIN(Parrot_Pointer_Array *list))
  {
      ASSERT_ARGS(gc_gms_count_used_pmc_memory)
  
      size_t total_amount = 0;
  #if 0
      List_Item_Header *tmp = list->first;
      while (tmp) {
          List_Item_Header *next = tmp->next;
          PMC              *obj  = LLH2Obj_typed(tmp, PMC);
  
          /* Header size */
          total_amount += sizeof (List_Item_Header)
                          + sizeof (PMC*);
          total_amount += obj->vtable->attr_size;
  
          tmp = next;
      }
  #endif
      return total_amount;
  }
  
  /*
  =item C<static void gc_gms_seal_object(PARROT_INTERP, PMC *pmc)>
  
  =item C<static void gc_gms_unseal_object(PARROT_INTERP, PMC *pmc)>
  
  Seal/unseal object with write barrier.
  
  =cut
  */
  static void
  gc_gms_seal_object(SHIM_INTERP, ARGIN(PMC *pmc))
  {
      ASSERT_ARGS(gc_gms_seal_object)
      /* "Seal" object with write barrier */
      PObj_GC_need_write_barrier_SET(pmc);
  }
  
  static void
  gc_gms_unseal_object(SHIM_INTERP, ARGIN(PMC *pmc))
  {
      ASSERT_ARGS(gc_gms_unseal_object)
      /* "Unseal" object with write barrier */
      PObj_GC_need_write_barrier_CLEAR(pmc);
  }
  
  /*
  
  =item C<static void gc_gms_check_sanity(PARROT_INTERP)>
  
  sanity check
  
  Only enabled with C<-DMEMORY_DEBUG> in C<ccflags>.
  
  =cut
  
  */
  
  static void
  gc_gms_check_sanity(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_check_sanity)
  #ifdef MEMORY_DEBUG
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      size_t            i;
  
      for (i = 0; i < MAX_GENERATIONS; i++) {
          POINTER_ARRAY_ITER(self->objects[i],
              PMC *pmc = &(((pmc_alloc_struct*)ptr)->pmc);
              PARROT_GC_ASSERT_INTERP(pmc, interp);
              PARROT_ASSERT((POBJ2GEN(pmc) == i)
                  || !"Object from wrong generation");
  
              if (i)
                  PARROT_ASSERT(PObj_GC_need_write_barrier_TEST(pmc)
                      || !"Unsealed object in old generation"););
  
          POINTER_ARRAY_ITER(self->strings[i],
              STRING *str = &(((string_alloc_struct*)ptr)->str);
              PARROT_ASSERT((POBJ2GEN(str) == i)
                  || !"String from wrong generation"););
      }
  
      POINTER_ARRAY_ITER(self->dirty_list,
          PMC *pmc = &(((pmc_alloc_struct*)ptr)->pmc);
          PARROT_GC_ASSERT_INTERP(pmc, interp);
          PARROT_ASSERT(PObj_GC_on_dirty_list_TEST(pmc)
              || !"Object in dirty_list without dirty_flag"););
  
      POINTER_ARRAY_ITER(self->work_list,
          PMC *pmc = &(((pmc_alloc_struct*)ptr)->pmc);
          PARROT_GC_ASSERT_INTERP(pmc, interp);
          PARROT_ASSERT(!PObj_GC_on_dirty_list_TEST(pmc)
              || !"Dirty object in work_list"););
  #else
      UNUSED(interp);
  #endif
  }
  
  /*
  
  =item C<void gc_gms_print_stats_always(PARROT_INTERP, const char* header)>
  
  =item C<static void gc_gms_print_stats(PARROT_INTERP, const char* header)>
  
  debug functions
  
  Only enabled with C<-DMEMORY_DEBUG> in C<ccflags>.
  
  =cut
  
  */
  
  void
  gc_gms_print_stats_always(PARROT_INTERP, ARGIN(const char* header))
  {
      ASSERT_ARGS(gc_gms_print_stats_always)
  
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      size_t            i;
  
      fprintf(stderr, "%s\ntotal: %lu, gen: %lu, ", header,
              (unsigned long)interp->gc_sys->stats.gc_mark_runs,
              (unsigned long)self->gen_to_collect);
  
      fprintf(stderr, "dirty: %lu, work: %lu\n",
              (unsigned long)Parrot_pa_count_used(interp, self->dirty_list),
              self->work_list
                ? (unsigned long)Parrot_pa_count_used(interp, self->work_list)
                : 0);
  
      for (i = 0; i < MAX_GENERATIONS; i++)
          fprintf(stderr, "GEN %lu: %lu objects, %lu strings\n",
                  (unsigned long)i,
                  (unsigned long)Parrot_pa_count_used(interp, self->objects[i]),
                  (unsigned long)Parrot_pa_count_used(interp, self->strings[i]));
  
  #if 1
      fprintf(stderr, "parent: 0x%x, tid: %d\n", interp->parent_interpreter,
              interp->thread_data ? interp->thread_data->tid : -1);
  
      fprintf(stderr, "PMC: %lu\n",
              Parrot_gc_pool_allocated_size(interp, self->pmc_allocator));
      fprintf(stderr, "STRING: %lu\n",
              Parrot_gc_pool_allocated_size(interp, self->string_allocator));
      fprintf(stderr, "buffers: %lu\n",
              self->string_gc.memory_pool->total_allocated);
      fprintf(stderr, "const buffers: %lu\n",
              self->string_gc.constant_string_pool->total_allocated);
      fprintf(stderr, "attrs: %lu\n",
              Parrot_gc_fixed_allocator_allocated_memory(interp,
                self->fixed_size_allocator));
  #endif
      fprintf(stderr, "\n");
  
  }
  
  static void
  gc_gms_print_stats(PARROT_INTERP, ARGIN(const char* header))
  {
      ASSERT_ARGS(gc_gms_print_stats)
  
  #ifdef MEMORY_DEBUG
      gc_gms_print_stats_always(interp, header);
  #else
      UNUSED(interp);
      UNUSED(header);
  #endif
  
  }
  
  /*
  
  =item C<static void gc_gms_validate_pmc(PARROT_INTERP, PMC *pmc)>
  
  =item C<static void gc_gms_validate_str(PARROT_INTERP, STRING *str)>
  
  =item C<static void gc_gms_validate_objects(PARROT_INTERP)>
  
  Validation routines
  
  =cut
  
  */
  static void
  gc_gms_validate_pmc(PARROT_INTERP, ARGIN(PMC *pmc))
  {
      ASSERT_ARGS(gc_gms_validate_pmc)
  
      if (PObj_on_free_list_TEST(pmc))
          Parrot_confess("Dead object found!", __FILE__, __LINE__);
  
      if (PObj_live_TEST(pmc))
          return;
  
      PObj_live_SET(pmc);
  
      if (PObj_custom_mark_TEST(pmc))
          VTABLE_mark(interp, pmc);
  
  }
  
  static void
  gc_gms_validate_str(SHIM_INTERP, ARGIN(STRING *str))
  {
      ASSERT_ARGS(gc_gms_validate_str)
  
  #ifdef PARROT_ASSERTS_ON
      PARROT_ASSERT(!PObj_on_free_list_TEST(str));
  #else
      UNUSED(str);
  #endif
  }
  
  static void
  gc_gms_validate_objects(PARROT_INTERP)
  {
      ASSERT_ARGS(gc_gms_validate_objects)
  
  /* GH #880 validate is not thread-safe, problematic only on darwin */
  #if defined(THREAD_DEBUG) && !defined(__APPLE__)
      INTVAL i;
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
  
  #  ifdef MEMORY_DEBUG
      fprintf(stderr, "GMS Validate\n");
  #  endif
      interp->gc_sys->mark_pmc_header = gc_gms_validate_pmc;
      interp->gc_sys->mark_str_header = gc_gms_validate_str;
      Parrot_gc_trace_root(interp, NULL, GC_TRACE_FULL);
      interp->gc_sys->mark_pmc_header = gc_gms_mark_pmc_header;
      interp->gc_sys->mark_str_header = gc_gms_mark_str_header;
  
  #  ifdef MEMORY_DEBUG
      fprintf(stderr, "GMS Clear Generations\n");
  #  endif
      for (i = 0; i < MAX_GENERATIONS; i++) {
          POINTER_ARRAY_ITER(self->objects[i],
              PMC * const pmc = &((pmc_alloc_struct *)ptr)->pmc;
              PARROT_GC_ASSERT_INTERP(pmc, interp);
              PObj_live_CLEAR(pmc););
      }
  #  ifdef MEMORY_DEBUG
      fprintf(stderr, "\n");
  #  endif
  #else
      UNUSED(interp);
  #endif
  }
  
  /*
  
  =item C<static void gc_gms_pmc_get_youngest_generation(PARROT_INTERP, PMC *pmc)>
  
  =item C<static void gc_gms_str_get_youngest_generation(PARROT_INTERP, STRING
  *str)>
  
  Calculate youngest generation of PMC children. Used to remove items from
  dirty_list.
  
  =cut
  
  */
  static void
  gc_gms_pmc_get_youngest_generation(PARROT_INTERP, ARGIN(PMC *pmc))
  {
      ASSERT_ARGS(gc_gms_pmc_get_youngest_generation)
  
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      const size_t         gen  = POBJ2GEN(pmc);
  
      if (gen < self->youngest_child)
          self->youngest_child = gen;
  }
  
  static void
  gc_gms_str_get_youngest_generation(PARROT_INTERP, ARGIN(STRING *str))
  {
      ASSERT_ARGS(gc_gms_str_get_youngest_generation)
  
      MarkSweep_GC * const self = (MarkSweep_GC *)interp->gc_sys->gc_private;
      const size_t         gen  = POBJ2GEN(str);
  
      if (gen < self->youngest_child)
          self->youngest_child = gen;
  }
  
  /*
  
  =item C<int pobj2gen(PObj *pmc)>
  
  =item C<static int gen2flags(int gen)>
  
  helper functions to check and use macro
  
  =cut
  
  */
  
  int
  pobj2gen(ARGIN(PObj *pmc))
  {
      ASSERT_ARGS(pobj2gen)
  
      return POBJ2GEN(pmc);
  }
  
  static int
  gen2flags(int gen)
  {
      ASSERT_ARGS(gen2flags)
  
      return GEN2FLAGS(gen);
  }
  
  /*
  
  =back
  
  =cut
  
  */
  
  /*
   * Local variables:
   *   c-file-style: "parrot"
   * End:
   * vim: expandtab shiftwidth=4 cinoptions='\:2=2' :
   */
  