text: /*
  ** 2007 October 14
  **
  ** The author disclaims copyright to this source code.  In place of
  ** a legal notice, here is a blessing:
  **
  **    May you do good and not evil.
  **    May you find forgiveness for yourself and forgive others.
  **    May you share freely, never taking more than you give.
  **
  *************************************************************************
  ** This file contains the C functions that implement a memory
  ** allocation subsystem for use by SQLite. 
  **
  ** This version of the memory allocation subsystem omits all
  ** use of malloc(). The SQLite user supplies a block of memory
  ** before calling sqlite3_initialize() from which allocations
  ** are made and returned by the xMalloc() and xRealloc() 
  ** implementations. Once sqlite3_initialize() has been called,
  ** the amount of memory available to SQLite is fixed and cannot
  ** be changed.
  **
  ** This version of the memory allocation subsystem is included
  ** in the build only if SQLITE_ENABLE_MEMSYS3 is defined.
  */
  #include "sqliteInt.h"
  
  /*
  ** This version of the memory allocator is only built into the library
  ** SQLITE_ENABLE_MEMSYS3 is defined. Defining this symbol does not
  ** mean that the library will use a memory-pool by default, just that
  ** it is available. The mempool allocator is activated by calling
  ** sqlite3_config().
  */
  #ifdef SQLITE_ENABLE_MEMSYS3
  
  /*
  ** Maximum size (in Mem3Blocks) of a "small" chunk.
  */
  #define MX_SMALL 10
  
  
  /*
  ** Number of freelist hash slots
  */
  #define N_HASH  61
  
  /*
  ** A memory allocation (also called a "chunk") consists of two or 
  ** more blocks where each block is 8 bytes.  The first 8 bytes are 
  ** a header that is not returned to the user.
  **
  ** A chunk is two or more blocks that is either checked out or
  ** free.  The first block has format u.hdr.  u.hdr.size4x is 4 times the
  ** size of the allocation in blocks if the allocation is free.
  ** The u.hdr.size4x&1 bit is true if the chunk is checked out and
  ** false if the chunk is on the freelist.  The u.hdr.size4x&2 bit
  ** is true if the previous chunk is checked out and false if the
  ** previous chunk is free.  The u.hdr.prevSize field is the size of
  ** the previous chunk in blocks if the previous chunk is on the
  ** freelist. If the previous chunk is checked out, then
  ** u.hdr.prevSize can be part of the data for that chunk and should
  ** not be read or written.
  **
  ** We often identify a chunk by its index in mem3.aPool[].  When
  ** this is done, the chunk index refers to the second block of
  ** the chunk.  In this way, the first chunk has an index of 1.
  ** A chunk index of 0 means "no such chunk" and is the equivalent
  ** of a NULL pointer.
  **
  ** The second block of free chunks is of the form u.list.  The
  ** two fields form a double-linked list of chunks of related sizes.
  ** Pointers to the head of the list are stored in mem3.aiSmall[] 
  ** for smaller chunks and mem3.aiHash[] for larger chunks.
  **
  ** The second block of a chunk is user data if the chunk is checked 
  ** out.  If a chunk is checked out, the user data may extend into
  ** the u.hdr.prevSize value of the following chunk.
  */
  typedef struct Mem3Block Mem3Block;
  struct Mem3Block {
    union {
      struct {
        u32 prevSize;   /* Size of previous chunk in Mem3Block elements */
        u32 size4x;     /* 4x the size of current chunk in Mem3Block elements */
      } hdr;
      struct {
        u32 next;       /* Index in mem3.aPool[] of next free chunk */
        u32 prev;       /* Index in mem3.aPool[] of previous free chunk */
      } list;
    } u;
  };
  
  /*
  ** All of the static variables used by this module are collected
  ** into a single structure named "mem3".  This is to keep the
  ** static variables organized and to reduce namespace pollution
  ** when this module is combined with other in the amalgamation.
  */
  SQLITE_WSD struct Mem3Global {
    /*
    ** Memory available for allocation. nPool is the size of the array
    ** (in Mem3Blocks) pointed to by aPool less 2.
    */
    u32 nPool;
    Mem3Block *aPool;
  
    /*
    ** True if we are evaluating an out-of-memory callback.
    */
    int alarmBusy;
    
    /*
    ** Mutex to control access to the memory allocation subsystem.
    */
    sqlite3_mutex *mutex;
    
    /*
    ** The minimum amount of free space that we have seen.
    */
    u32 mnMaster;
  
    /*
    ** iMaster is the index of the master chunk.  Most new allocations
    ** occur off of this chunk.  szMaster is the size (in Mem3Blocks)
    ** of the current master.  iMaster is 0 if there is not master chunk.
    ** The master chunk is not in either the aiHash[] or aiSmall[].
    */
    u32 iMaster;
    u32 szMaster;
  
    /*
    ** Array of lists of free blocks according to the block size 
    ** for smaller chunks, or a hash on the block size for larger
    ** chunks.
    */
    u32 aiSmall[MX_SMALL-1];   /* For sizes 2 through MX_SMALL, inclusive */
    u32 aiHash[N_HASH];        /* For sizes MX_SMALL+1 and larger */
  } mem3 = { 97535575 };
  
  #define mem3 GLOBAL(struct Mem3Global, mem3)
  
  /*
  ** Unlink the chunk at mem3.aPool[i] from list it is currently
  ** on.  *pRoot is the list that i is a member of.
  */
  void memsys3UnlinkFromList(u32 i, u32 *pRoot){
    u32 next = mem3.aPool[i].u.list.next;
    u32 prev = mem3.aPool[i].u.list.prev;
    assert( sqlite3_mutex_held(mem3.mutex) );
    if( prev==0 ){
      *pRoot = next;
    }else{
      mem3.aPool[prev].u.list.next = next;
    }
    if( next ){
      mem3.aPool[next].u.list.prev = prev;
    }
    mem3.aPool[i].u.list.next = 0;
    mem3.aPool[i].u.list.prev = 0;
  }
  
  /*
  ** Unlink the chunk at index i from 
  ** whatever list is currently a member of.
  */
  void memsys3Unlink(u32 i){
    u32 size, hash;
    assert( sqlite3_mutex_held(mem3.mutex) );
    assert( (mem3.aPool[i-1].u.hdr.size4x & 1)==0 );
    assert( i>=1 );
    size = mem3.aPool[i-1].u.hdr.size4x/4;
    assert( size==mem3.aPool[i+size-1].u.hdr.prevSize );
    assert( size>=2 );
    if( size <= MX_SMALL ){
      memsys3UnlinkFromList(i, &mem3.aiSmall[size-2]);
    }else{
      hash = size % N_HASH;
      memsys3UnlinkFromList(i, &mem3.aiHash[hash]);
    }
  }
  
  /*
  ** Link the chunk at mem3.aPool[i] so that is on the list rooted
  ** at *pRoot.
  */
  void memsys3LinkIntoList(u32 i, u32 *pRoot){
    assert( sqlite3_mutex_held(mem3.mutex) );
    mem3.aPool[i].u.list.next = *pRoot;
    mem3.aPool[i].u.list.prev = 0;
    if( *pRoot ){
      mem3.aPool[*pRoot].u.list.prev = i;
    }
    *pRoot = i;
  }
  
  /*
  ** Link the chunk at index i into either the appropriate
  ** small chunk list, or into the large chunk hash table.
  */
  void memsys3Link(u32 i){
    u32 size, hash;
    assert( sqlite3_mutex_held(mem3.mutex) );
    assert( i>=1 );
    assert( (mem3.aPool[i-1].u.hdr.size4x & 1)==0 );
    size = mem3.aPool[i-1].u.hdr.size4x/4;
    assert( size==mem3.aPool[i+size-1].u.hdr.prevSize );
    assert( size>=2 );
    if( size <= MX_SMALL ){
      memsys3LinkIntoList(i, &mem3.aiSmall[size-2]);
    }else{
      hash = size % N_HASH;
      memsys3LinkIntoList(i, &mem3.aiHash[hash]);
    }
  }
  
  /*
  ** If the STATIC_MEM mutex is not already held, obtain it now. The mutex
  ** will already be held (obtained by code in malloc.c) if
  ** sqlite3GlobalConfig.bMemStat is true.
  */
  void memsys3Enter(void){
    if( sqlite3GlobalConfig.bMemstat==0 && mem3.mutex==0 ){
      mem3.mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MEM);
    }
    sqlite3_mutex_enter(mem3.mutex);
  }
  void memsys3Leave(void){
    sqlite3_mutex_leave(mem3.mutex);
  }
  
  /*
  ** Called when we are unable to satisfy an allocation of nBytes.
  */
  void memsys3OutOfMemory(int nByte){
    if( !mem3.alarmBusy ){
      mem3.alarmBusy = 1;
      assert( sqlite3_mutex_held(mem3.mutex) );
      sqlite3_mutex_leave(mem3.mutex);
      sqlite3_release_memory(nByte);
      sqlite3_mutex_enter(mem3.mutex);
      mem3.alarmBusy = 0;
    }
  }
  
  
  /*
  ** Chunk i is a free chunk that has been unlinked.  Adjust its 
  ** size parameters for check-out and return a pointer to the 
  ** user portion of the chunk.
  */
  void *memsys3Checkout(u32 i, u32 nBlock){
    u32 x;
    assert( sqlite3_mutex_held(mem3.mutex) );
    assert( i>=1 );
    assert( mem3.aPool[i-1].u.hdr.size4x/4==nBlock );
    assert( mem3.aPool[i+nBlock-1].u.hdr.prevSize==nBlock );
    x = mem3.aPool[i-1].u.hdr.size4x;
    mem3.aPool[i-1].u.hdr.size4x = nBlock*4 | 1 | (x&2);
    mem3.aPool[i+nBlock-1].u.hdr.prevSize = nBlock;
    mem3.aPool[i+nBlock-1].u.hdr.size4x |= 2;
    return &mem3.aPool[i];
  }
  
  /*
  ** Carve a piece off of the end of the mem3.iMaster free chunk.
  ** Return a pointer to the new allocation.  Or, if the master chunk
  ** is not large enough, return 0.
  */
  void *memsys3FromMaster(u32 nBlock){
    assert( sqlite3_mutex_held(mem3.mutex) );
    assert( mem3.szMaster>=nBlock );
    if( nBlock>=mem3.szMaster-1 ){
      /* Use the entire master */
      void *p = memsys3Checkout(mem3.iMaster, mem3.szMaster);
      mem3.iMaster = 0;
      mem3.szMaster = 0;
      mem3.mnMaster = 0;
      return p;
    }else{
      /* Split the master block.  Return the tail. */
      u32 newi, x;
      newi = mem3.iMaster + mem3.szMaster - nBlock;
      assert( newi > mem3.iMaster+1 );
      mem3.aPool[mem3.iMaster+mem3.szMaster-1].u.hdr.prevSize = nBlock;
      mem3.aPool[mem3.iMaster+mem3.szMaster-1].u.hdr.size4x |= 2;
      mem3.aPool[newi-1].u.hdr.size4x = nBlock*4 + 1;
      mem3.szMaster -= nBlock;
      mem3.aPool[newi-1].u.hdr.prevSize = mem3.szMaster;
      x = mem3.aPool[mem3.iMaster-1].u.hdr.size4x & 2;
      mem3.aPool[mem3.iMaster-1].u.hdr.size4x = mem3.szMaster*4 | x;
      if( mem3.szMaster < mem3.mnMaster ){
        mem3.mnMaster = mem3.szMaster;
      }
      return (void*)&mem3.aPool[newi];
    }
  }
  
  /*
  ** *pRoot is the head of a list of free chunks of the same size
  ** or same size hash.  In other words, *pRoot is an entry in either
  ** mem3.aiSmall[] or mem3.aiHash[].  
  **
  ** This routine examines all entries on the given list and tries
  ** to coalesce each entries with adjacent free chunks.  
  **
  ** If it sees a chunk that is larger than mem3.iMaster, it replaces 
  ** the current mem3.iMaster with the new larger chunk.  In order for
  ** this mem3.iMaster replacement to work, the master chunk must be
  ** linked into the hash tables.  That is not the normal state of
  ** affairs, of course.  The calling routine must link the master
  ** chunk before invoking this routine, then must unlink the (possibly
  ** changed) master chunk once this routine has finished.
  */
  void memsys3Merge(u32 *pRoot){
    u32 iNext, prev, size, i, x;
  
    assert( sqlite3_mutex_held(mem3.mutex) );
    for(i=*pRoot; i>0; i=iNext){
      iNext = mem3.aPool[i].u.list.next;
      size = mem3.aPool[i-1].u.hdr.size4x;
      assert( (size&1)==0 );
      if( (size&2)==0 ){
        memsys3UnlinkFromList(i, pRoot);
        assert( i > mem3.aPool[i-1].u.hdr.prevSize );
        prev = i - mem3.aPool[i-1].u.hdr.prevSize;
        if( prev==iNext ){
          iNext = mem3.aPool[prev].u.list.next;
        }
        memsys3Unlink(prev);
        size = i + size/4 - prev;
        x = mem3.aPool[prev-1].u.hdr.size4x & 2;
        mem3.aPool[prev-1].u.hdr.size4x = size*4 | x;
        mem3.aPool[prev+size-1].u.hdr.prevSize = size;
        memsys3Link(prev);
        i = prev;
      }else{
        size /= 4;
      }
      if( size>mem3.szMaster ){
        mem3.iMaster = i;
        mem3.szMaster = size;
      }
    }
  }
  
  /*
  ** Return a block of memory of at least nBytes in size.
  ** Return NULL if unable.
  **
  ** This function assumes that the necessary mutexes, if any, are
  ** already held by the caller. Hence "Unsafe".
  */
  void *memsys3MallocUnsafe(int nByte){
    u32 i;
    u32 nBlock;
    u32 toFree;
  
    assert( sqlite3_mutex_held(mem3.mutex) );
    assert( sizeof(Mem3Block)==8 );
    if( nByte<=12 ){
      nBlock = 2;
    }else{
      nBlock = (nByte + 11)/8;
    }
    assert( nBlock>=2 );
  
    /* STEP 1:
    ** Look for an entry of the correct size in either the small
    ** chunk table or in the large chunk hash table.  This is
    ** successful most of the time (about 9 times out of 10).
    */
    if( nBlock <= MX_SMALL ){
      i = mem3.aiSmall[nBlock-2];
      if( i>0 ){
        memsys3UnlinkFromList(i, &mem3.aiSmall[nBlock-2]);
        return memsys3Checkout(i, nBlock);
      }
    }else{
      int hash = nBlock % N_HASH;
      for(i=mem3.aiHash[hash]; i>0; i=mem3.aPool[i].u.list.next){
        if( mem3.aPool[i-1].u.hdr.size4x/4==nBlock ){
          memsys3UnlinkFromList(i, &mem3.aiHash[hash]);
          return memsys3Checkout(i, nBlock);
        }
      }
    }
  
    /* STEP 2:
    ** Try to satisfy the allocation by carving a piece off of the end
    ** of the master chunk.  This step usually works if step 1 fails.
    */
    if( mem3.szMaster>=nBlock ){
      return memsys3FromMaster(nBlock);
    }
  
  
    /* STEP 3:  
    ** Loop through the entire memory pool.  Coalesce adjacent free
    ** chunks.  Recompute the master chunk as the largest free chunk.
    ** Then try again to satisfy the allocation by carving a piece off
    ** of the end of the master chunk.  This step happens very
    ** rarely (we hope!)
    */
    for(toFree=nBlock*16; toFree<(mem3.nPool*16); toFree *= 2){
      memsys3OutOfMemory(toFree);
      if( mem3.iMaster ){
        memsys3Link(mem3.iMaster);
        mem3.iMaster = 0;
        mem3.szMaster = 0;
      }
      for(i=0; i<N_HASH; i++){
        memsys3Merge(&mem3.aiHash[i]);
      }
      for(i=0; i<MX_SMALL-1; i++){
        memsys3Merge(&mem3.aiSmall[i]);
      }
      if( mem3.szMaster ){
        memsys3Unlink(mem3.iMaster);
        if( mem3.szMaster>=nBlock ){
          return memsys3FromMaster(nBlock);
        }
      }
    }
  
    /* If none of the above worked, then we fail. */
    return 0;
  }
  
  /*
  ** Free an outstanding memory allocation.
  **
  ** This function assumes that the necessary mutexes, if any, are
  ** already held by the caller. Hence "Unsafe".
  */
  void memsys3FreeUnsafe(void *pOld){
    Mem3Block *p = (Mem3Block*)pOld;
    int i;
    u32 size, x;
    assert( sqlite3_mutex_held(mem3.mutex) );
    assert( p>mem3.aPool && p<&mem3.aPool[mem3.nPool] );
    i = p - mem3.aPool;
    assert( (mem3.aPool[i-1].u.hdr.size4x&1)==1 );
    size = mem3.aPool[i-1].u.hdr.size4x/4;
    assert( i+size<=mem3.nPool+1 );
    mem3.aPool[i-1].u.hdr.size4x &= ~1;
    mem3.aPool[i+size-1].u.hdr.prevSize = size;
    mem3.aPool[i+size-1].u.hdr.size4x &= ~2;
    memsys3Link(i);
  
    /* Try to expand the master using the newly freed chunk */
    if( mem3.iMaster ){
      while( (mem3.aPool[mem3.iMaster-1].u.hdr.size4x&2)==0 ){
        size = mem3.aPool[mem3.iMaster-1].u.hdr.prevSize;
        mem3.iMaster -= size;
        mem3.szMaster += size;
        memsys3Unlink(mem3.iMaster);
        x = mem3.aPool[mem3.iMaster-1].u.hdr.size4x & 2;
        mem3.aPool[mem3.iMaster-1].u.hdr.size4x = mem3.szMaster*4 | x;
        mem3.aPool[mem3.iMaster+mem3.szMaster-1].u.hdr.prevSize = mem3.szMaster;
      }
      x = mem3.aPool[mem3.iMaster-1].u.hdr.size4x & 2;
      while( (mem3.aPool[mem3.iMaster+mem3.szMaster-1].u.hdr.size4x&1)==0 ){
        memsys3Unlink(mem3.iMaster+mem3.szMaster);
        mem3.szMaster += mem3.aPool[mem3.iMaster+mem3.szMaster-1].u.hdr.size4x/4;
        mem3.aPool[mem3.iMaster-1].u.hdr.size4x = mem3.szMaster*4 | x;
        mem3.aPool[mem3.iMaster+mem3.szMaster-1].u.hdr.prevSize = mem3.szMaster;
      }
    }
  }
  
  /*
  ** Return the size of an outstanding allocation, in bytes.  The
  ** size returned omits the 8-byte header overhead.  This only
  ** works for chunks that are currently checked out.
  */
  int memsys3Size(void *p){
    Mem3Block *pBlock;
    assert( p!=0 );
    pBlock = (Mem3Block*)p;
    assert( (pBlock[-1].u.hdr.size4x&1)!=0 );
    return (pBlock[-1].u.hdr.size4x&~3)*2 - 4;
  }
  
  /*
  ** Round up a request size to the next valid allocation size.
  */
  int memsys3Roundup(int n){
    if( n<=12 ){
      return 12;
    }else{
      return ((n+11)&~7) - 4;
    }
  }
  
  /*
  ** Allocate nBytes of memory.
  */
  void *memsys3Malloc(int nBytes){
    sqlite3_int64 *p;
    assert( nBytes>0 );          /* malloc.c filters out 0 byte requests */
    memsys3Enter();
    p = memsys3MallocUnsafe(nBytes);
    memsys3Leave();
    return (void*)p; 
  }
  
  /*
  ** Free memory.
  */
  void memsys3Free(void *pPrior){
    assert( pPrior );
    memsys3Enter();
    memsys3FreeUnsafe(pPrior);
    memsys3Leave();
  }
  
  /*
  ** Change the size of an existing memory allocation
  */
  void *memsys3Realloc(void *pPrior, int nBytes){
    int nOld;
    void *p;
    if( pPrior==0 ){
      return sqlite3_malloc(nBytes);
    }
    if( nBytes<=0 ){
      sqlite3_free(pPrior);
      return 0;
    }
    nOld = memsys3Size(pPrior);
    if( nBytes<=nOld && nBytes>=nOld-128 ){
      return pPrior;
    }
    memsys3Enter();
    p = memsys3MallocUnsafe(nBytes);
    if( p ){
      if( nOld<nBytes ){
        memcpy(p, pPrior, nOld);
      }else{
        memcpy(p, pPrior, nBytes);
      }
      memsys3FreeUnsafe(pPrior);
    }
    memsys3Leave();
    return p;
  }
  
  /*
  ** Initialize this module.
  */
  int memsys3Init(void *NotUsed){
    UNUSED_PARAMETER(NotUsed);
    if( !sqlite3GlobalConfig.pHeap ){
      return SQLITE_ERROR;
    }
  
    /* Store a pointer to the memory block in global structure mem3. */
    assert( sizeof(Mem3Block)==8 );
    mem3.aPool = (Mem3Block *)sqlite3GlobalConfig.pHeap;
    mem3.nPool = (sqlite3GlobalConfig.nHeap / sizeof(Mem3Block)) - 2;
  
    /* Initialize the master block. */
    mem3.szMaster = mem3.nPool;
    mem3.mnMaster = mem3.szMaster;
    mem3.iMaster = 1;
    mem3.aPool[0].u.hdr.size4x = (mem3.szMaster<<2) + 2;
    mem3.aPool[mem3.nPool].u.hdr.prevSize = mem3.nPool;
    mem3.aPool[mem3.nPool].u.hdr.size4x = 1;
  
    return SQLITE_OK;
  }
  
  /*
  ** Deinitialize this module.
  */
  void memsys3Shutdown(void *NotUsed){
    UNUSED_PARAMETER(NotUsed);
    mem3.mutex = 0;
    return;
  }
  
  
  
  /*
  ** Open the file indicated and write a log of all unfreed memory 
  ** allocations into that log.
  */
  void sqlite3Memsys3Dump(const char *zFilename){
  #ifdef SQLITE_DEBUG
    FILE *out;
    u32 i, j;
    u32 size;
    if( zFilename==0 || zFilename[0]==0 ){
      out = stdout;
    }else{
      out = fopen(zFilename, "w");
      if( out==0 ){
        fprintf(stderr, "** Unable to output memory debug output log: %s **\n",
                        zFilename);
        return;
      }
    }
    memsys3Enter();
    fprintf(out, "CHUNKS:\n");
    for(i=1; i<=mem3.nPool; i+=size/4){
      size = mem3.aPool[i-1].u.hdr.size4x;
      if( size/4<=1 ){
        fprintf(out, "%p size error\n", &mem3.aPool[i]);
        assert( 0 );
        break;
      }
      if( (size&1)==0 && mem3.aPool[i+size/4-1].u.hdr.prevSize!=size/4 ){
        fprintf(out, "%p tail size does not match\n", &mem3.aPool[i]);
        assert( 0 );
        break;
      }
      if( ((mem3.aPool[i+size/4-1].u.hdr.size4x&2)>>1)!=(size&1) ){
        fprintf(out, "%p tail checkout bit is incorrect\n", &mem3.aPool[i]);
        assert( 0 );
        break;
      }
      if( size&1 ){
        fprintf(out, "%p %6d bytes checked out\n", &mem3.aPool[i], (size/4)*8-8);
      }else{
        fprintf(out, "%p %6d bytes free%s\n", &mem3.aPool[i], (size/4)*8-8,
                    i==mem3.iMaster ? " **master**" : "");
      }
    }
    for(i=0; i<MX_SMALL-1; i++){
      if( mem3.aiSmall[i]==0 ) continue;
      fprintf(out, "small(%2d):", i);
      for(j = mem3.aiSmall[i]; j>0; j=mem3.aPool[j].u.list.next){
        fprintf(out, " %p(%d)", &mem3.aPool[j],
                (mem3.aPool[j-1].u.hdr.size4x/4)*8-8);
      }
      fprintf(out, "\n"); 
    }
    for(i=0; i<N_HASH; i++){
      if( mem3.aiHash[i]==0 ) continue;
      fprintf(out, "hash(%2d):", i);
      for(j = mem3.aiHash[i]; j>0; j=mem3.aPool[j].u.list.next){
        fprintf(out, " %p(%d)", &mem3.aPool[j],
                (mem3.aPool[j-1].u.hdr.size4x/4)*8-8);
      }
      fprintf(out, "\n"); 
    }
    fprintf(out, "master=%d\n", mem3.iMaster);
    fprintf(out, "nowUsed=%d\n", mem3.nPool*8 - mem3.szMaster*8);
    fprintf(out, "mxUsed=%d\n", mem3.nPool*8 - mem3.mnMaster*8);
    sqlite3_mutex_leave(mem3.mutex);
    if( out==stdout ){
      fflush(stdout);
    }else{
      fclose(out);
    }
  #else
    UNUSED_PARAMETER(zFilename);
  #endif
  }
  
  /*
  ** This routine is the only routine in this file with external 
  ** linkage.
  **
  ** Populate the low-level memory allocation function pointers in
  ** sqlite3GlobalConfig.m with pointers to the routines in this file. The
  ** arguments specify the block of memory to manage.
  **
  ** This routine is only called by sqlite3_config(), and therefore
  ** is not required to be threadsafe (it is not).
  */
  const sqlite3_mem_methods *sqlite3MemGetMemsys3(void){
    static const sqlite3_mem_methods mempoolMethods = {
       memsys3Malloc,
       memsys3Free,
       memsys3Realloc,
       memsys3Size,
       memsys3Roundup,
       memsys3Init,
       memsys3Shutdown,
       0
    };
    return &mempoolMethods;
  }
  
  #endif /* SQLITE_ENABLE_MEMSYS3 */
  