text: /*
   * sgen-pinning.c: The pin queue.
   *
   * Copyright 2001-2003 Ximian, Inc
   * Copyright 2003-2010 Novell, Inc.
   * Copyright (C) 2012 Xamarin Inc
   *
   * This library is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Library General Public
   * License 2.0 as published by the Free Software Foundation;
   *
   * This library is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Library General Public License for more details.
   *
   * You should have received a copy of the GNU Library General Public
   * License 2.0 along with this library; if not, write to the Free
   * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
   */
  
  #include "config.h"
  #ifdef HAVE_SGEN_GC
  
  #include "metadata/sgen-gc.h"
  #include "metadata/sgen-pinning.h"
  #include "metadata/sgen-protocol.h"
  #include "metadata/sgen-pointer-queue.h"
  
  static SgenPointerQueue pin_queue;
  static size_t last_num_pinned = 0;
  
  #define PIN_HASH_SIZE 1024
  static void *pin_hash_filter [PIN_HASH_SIZE];
  
  void
  sgen_init_pinning (void)
  {
  	memset (pin_hash_filter, 0, sizeof (pin_hash_filter));
  	pin_queue.mem_type = INTERNAL_MEM_PIN_QUEUE;
  }
  
  void
  sgen_finish_pinning (void)
  {
  	last_num_pinned = pin_queue.next_slot;
  	sgen_pointer_queue_clear (&pin_queue);
  }
  
  void
  sgen_pin_stage_ptr (void *ptr)
  {
  	/*very simple multiplicative hash function, tons better than simple and'ng */ 
  	int hash_idx = ((mword)ptr * 1737350767) & (PIN_HASH_SIZE - 1);
  	if (pin_hash_filter [hash_idx] == ptr)
  		return;
  
  	pin_hash_filter [hash_idx] = ptr;
  
  	sgen_pointer_queue_add (&pin_queue, ptr);
  }
  
  gboolean
  sgen_find_optimized_pin_queue_area (void *start, void *end, size_t *first_out, size_t *last_out)
  {
  	size_t first = sgen_pointer_queue_search (&pin_queue, start);
  	size_t last = sgen_pointer_queue_search (&pin_queue, end);
  	SGEN_ASSERT (0, last == pin_queue.next_slot || pin_queue.data [last] >= end, "Pin queue search gone awry");
  	*first_out = first;
  	*last_out = last;
  	return first != last;
  }
  
  void**
  sgen_pinning_get_entry (size_t index)
  {
  	SGEN_ASSERT (0, index <= pin_queue.next_slot, "Pin queue entry out of range");
  	return &pin_queue.data [index];
  }
  
  void
  sgen_find_section_pin_queue_start_end (GCMemSection *section)
  {
  	SGEN_LOG (6, "Pinning from section %p (%p-%p)", section, section->data, section->end_data);
  
  	sgen_find_optimized_pin_queue_area (section->data, section->end_data,
  			&section->pin_queue_first_entry, &section->pin_queue_last_entry);
  
  	SGEN_LOG (6, "Found %zd pinning addresses in section %p",
  			section->pin_queue_last_entry - section->pin_queue_first_entry, section);
  }
  
  /*This will setup the given section for the while pin queue. */
  void
  sgen_pinning_setup_section (GCMemSection *section)
  {
  	section->pin_queue_first_entry = 0;
  	section->pin_queue_last_entry = pin_queue.next_slot;
  }
  
  void
  sgen_pinning_trim_queue_to_section (GCMemSection *section)
  {
  	SGEN_ASSERT (0, section->pin_queue_first_entry == 0, "Pin queue trimming assumes the whole pin queue is used by the nursery");
  	pin_queue.next_slot = section->pin_queue_last_entry;
  }
  
  /*
   * This is called when we've run out of memory during a major collection.
   *
   * After collecting potential pin entries and sorting the array, this is what it looks like:
   *
   * +--------------------+---------------------------------------------+--------------------+
   * | major heap entries |               nursery entries               | major heap entries |
   * +--------------------+---------------------------------------------+--------------------+
   *
   * Of course there might not be major heap entries before and/or after the nursery entries,
   * depending on where the major heap sections are in the address space, and whether there
   * were any potential pointers there.
   *
   * When we pin nursery objects, we compact the nursery part of the pin array, which leaves
   * discarded entries after the ones that actually pointed to nursery objects:
   *
   * +--------------------+-----------------+---------------------------+--------------------+
   * | major heap entries | nursery entries | discarded nursery entries | major heap entries |
   * +--------------------+-----------------+---------------------------+--------------------+
   *
   * When, due to being out of memory, we late pin more objects, the pin array looks like
   * this:
   *
   * +--------------------+-----------------+---------------------------+--------------------+--------------+
   * | major heap entries | nursery entries | discarded nursery entries | major heap entries | late entries |
   * +--------------------+-----------------+---------------------------+--------------------+--------------+
   *
   * This function gets rid of the discarded nursery entries by nulling them out.  Note that
   * we can late pin objects not only in the nursery but also in the major heap, which happens
   * when evacuation fails.
   */
  void
  sgen_pin_queue_clear_discarded_entries (GCMemSection *section, size_t max_pin_slot)
  {
  	void **start = sgen_pinning_get_entry (section->pin_queue_last_entry);
  	void **end = sgen_pinning_get_entry (max_pin_slot);
  	void *addr;
  
  	for (; start < end; ++start) {
  		addr = *start;
  		if ((char*)addr < section->data || (char*)addr > section->end_data)
  			break;
  		*start = NULL;
  	}
  }
  
  /* reduce the info in the pin queue, removing duplicate pointers and sorting them */
  void
  sgen_optimize_pin_queue (void)
  {
  	sgen_pointer_queue_sort_uniq (&pin_queue);
  }
  
  size_t
  sgen_get_pinned_count (void)
  {
  	return pin_queue.next_slot;
  }
  
  void
  sgen_dump_pin_queue (void)
  {
  	int i;
  
  	for (i = 0; i < last_num_pinned; ++i) {
  		void *ptr = pin_queue.data [i];
  		SGEN_LOG (3, "Bastard pinning obj %p (%s), size: %zd", ptr, sgen_safe_name (ptr), sgen_safe_object_get_size (ptr));
  	}
  }
  
  typedef struct _CementHashEntry CementHashEntry;
  struct _CementHashEntry {
  	char *obj;
  	unsigned int count;
  };
  
  static CementHashEntry cement_hash [SGEN_CEMENT_HASH_SIZE];
  static CementHashEntry cement_hash_concurrent [SGEN_CEMENT_HASH_SIZE];
  
  static gboolean cement_enabled = TRUE;
  static gboolean cement_concurrent = FALSE;
  
  void
  sgen_cement_init (gboolean enabled)
  {
  	cement_enabled = enabled;
  }
  
  void
  sgen_cement_reset (void)
  {
  	SGEN_ASSERT (1, !cement_concurrent, "Concurrent cementing cannot simply be reset");
  
  	memset (cement_hash, 0, sizeof (cement_hash));
  	binary_protocol_cement_reset ();
  }
  
  /*
   * The reason we cannot simply reset cementing at the start of a
   * concurrent collection is that the nursery collections running
   * concurrently must keep pinning the cemented objects, because we
   * don't have the global remsets that point to them anymore - if the
   * nursery collector moved the cemented objects, we'd have invalid
   * pointers in the major heap.
   *
   * What we do instead is to reset cementing at the start of concurrent
   * collections in such a way that nursery collections happening during
   * the major collection still pin the formerly cemented objects.  We
   * have a shadow cementing table for that purpose.  The nursery
   * collections still work with the old cementing table, while the
   * major collector builds up a new cementing table, adding global
   * remsets whenever needed like usual.  When the major collector
   * finishes, the old cementing table is replaced by the new one.
   */
  
  void
  sgen_cement_concurrent_start (void)
  {
  	SGEN_ASSERT (1, !cement_concurrent, "Concurrent cementing has already been started");
  	cement_concurrent = TRUE;
  
  	memset (cement_hash_concurrent, 0, sizeof (cement_hash));
  }
  
  void
  sgen_cement_concurrent_finish (void)
  {
  	SGEN_ASSERT (1, cement_concurrent, "Concurrent cementing hasn't been started");
  	cement_concurrent = FALSE;
  
  	memcpy (cement_hash, cement_hash_concurrent, sizeof (cement_hash));
  }
  
  gboolean
  sgen_cement_lookup (char *obj)
  {
  	guint hv = mono_aligned_addr_hash (obj);
  	int i = SGEN_CEMENT_HASH (hv);
  
  	SGEN_ASSERT (5, sgen_ptr_in_nursery (obj), "Looking up cementing for non-nursery objects makes no sense");
  
  	if (!cement_enabled)
  		return FALSE;
  
  	if (!cement_hash [i].obj)
  		return FALSE;
  	if (cement_hash [i].obj != obj)
  		return FALSE;
  
  	return cement_hash [i].count >= SGEN_CEMENT_THRESHOLD;
  }
  
  gboolean
  sgen_cement_lookup_or_register (char *obj)
  {
  	guint hv;
  	int i;
  	CementHashEntry *hash;
  	gboolean concurrent_cementing = sgen_concurrent_collection_in_progress ();
  
  	if (!cement_enabled)
  		return FALSE;
  
  	if (concurrent_cementing)
  		SGEN_ASSERT (5, cement_concurrent, "Cementing wasn't inited with concurrent flag");
  
  	if (concurrent_cementing)
  		hash = cement_hash_concurrent;
  	else
  		hash = cement_hash;
  
  	hv = mono_aligned_addr_hash (obj);
  	i = SGEN_CEMENT_HASH (hv);
  
  	SGEN_ASSERT (5, sgen_ptr_in_nursery (obj), "Can only cement pointers to nursery objects");
  
  	if (!hash [i].obj) {
  		SGEN_ASSERT (5, !hash [i].count, "Cementing hash inconsistent");
  		hash [i].obj = obj;
  	} else if (hash [i].obj != obj) {
  		return FALSE;
  	}
  
  	if (hash [i].count >= SGEN_CEMENT_THRESHOLD)
  		return TRUE;
  
  	++hash [i].count;
  	if (hash [i].count == SGEN_CEMENT_THRESHOLD) {
  		if (G_UNLIKELY (MONO_GC_OBJ_CEMENTED_ENABLED())) {
  			MonoVTable *vt G_GNUC_UNUSED = (MonoVTable*)SGEN_LOAD_VTABLE (obj);
  			MONO_GC_OBJ_CEMENTED ((mword)obj, sgen_safe_object_get_size ((MonoObject*)obj),
  					vt->klass->name_space, vt->klass->name);
  		}
  		binary_protocol_cement (obj, (gpointer)SGEN_LOAD_VTABLE (obj),
  				(int)sgen_safe_object_get_size ((MonoObject*)obj));
  	}
  
  	return FALSE;
  }
  
  static void
  pin_from_hash (CementHashEntry *hash, gboolean has_been_reset)
  {
  	int i;
  	for (i = 0; i < SGEN_CEMENT_HASH_SIZE; ++i) {
  		if (!hash [i].count)
  			continue;
  
  		if (has_been_reset)
  			SGEN_ASSERT (5, hash [i].count >= SGEN_CEMENT_THRESHOLD, "Cementing hash inconsistent");
  
  		sgen_pin_stage_ptr (hash [i].obj);
  		/* FIXME: do pin stats if enabled */
  	}
  }
  
  void
  sgen_pin_cemented_objects (void)
  {
  	pin_from_hash (cement_hash, TRUE);
  	if (cement_concurrent)
  		pin_from_hash (cement_hash_concurrent, FALSE);
  }
  
  void
  sgen_cement_clear_below_threshold (void)
  {
  	int i;
  	for (i = 0; i < SGEN_CEMENT_HASH_SIZE; ++i) {
  		if (cement_hash [i].count < SGEN_CEMENT_THRESHOLD) {
  			cement_hash [i].obj = NULL;
  			cement_hash [i].count = 0;
  		}
  	}
  }
  
  #endif /* HAVE_SGEN_GC */
  