SQLite

/*
** 2008 July 24
**
** 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 an alternative memory allocation system for SQLite.
** This system is implemented as a wrapper around the default memory
** allocation system (usually the one found in mem1.c - system malloc).
**
** This system differentiates between requests for "small" allocations 
** (by default those of 128 bytes or less) and "large" allocations (all
** others). The 256 byte threshhold is configurable at runtime.
**
** All requests for large allocations are passed through to the
** default memory allocation system.
**
** Requests for small allocations are met by allocating space within
** one or more larger "chunks" of memory obtained from the default
** memory allocation system. Chunks of memory are usually 64KB or 
** larger. The algorithm used to manage space within each chunk is
** the same as that used by mem5.c. 
**
** This strategy is designed to prevent the default memory allocation
** system (usually the system malloc) from suffering from heap 
** fragmentation. On some systems, heap fragmentation can cause a 
** significant real-time slowdown.
**
** $Id: mem6.c,v 1.3 2008/07/25 08:49:00 danielk1977 Exp $
*/

#ifdef SQLITE_ENABLE_MEMSYS6

#include "sqliteInt.h"

/*

    assert((iOffset+nAlloc)>pChunk->nBlock);
  }

  return pChunk;
}

struct Mem6Global {
  sqlite3_mem_methods parent;     /* Used to allocate chunks */
  int nMinAlloc;                  /* Minimum allowed allocation size */
  int nThreshold;                 /* Allocs larger than this go to parent */
  sqlite3_mutex *mutex;
  Mem6Chunk *pChunk;              /* Singly linked list of all memory chunks */
} mem6;


static void mem6Enter(void){
  sqlite3_mutex_enter(mem6.mutex);
}

static void mem6Leave(void){
  sqlite3_mutex_leave(mem6.mutex);
}

/*
** Based on the number and size of the currently allocated chunks, return
** the size of the next chunk to allocate, in bytes.
*/
static int nextChunkSize(void){
  int iTotal = 0;
  Mem6Chunk *p;
  for(p=mem6.pChunk; p; p=p->pNext){
    iTotal += mem6.parent.xSize((void *)p);
  }
  if( iTotal==0 ){
    iTotal = MIN_CHUNKSIZE;
  }
  return iTotal;
}

/*
** The argument is a pointer that may or may not have been allocated from
** one of the Mem6Chunk objects managed within mem6. If it is, return

  return 0;
}

static void freeChunk(Mem6Chunk *pChunk){
  Mem6Chunk **pp = &mem6.pChunk;
  for( pp=&mem6.pChunk; *pp!=pChunk; pp = &(*pp)->pNext );
  *pp = (*pp)->pNext;
  mem6.parent.xFree(pChunk);
}

static void *memsys6Malloc(int nByte){
  Mem6Chunk *pChunk;
  void *p = 0;


  mem6Enter();
  if( nByte>mem6.nThreshold ){
    p = mem6.parent.xMalloc(nByte);
  }else{
    for(pChunk=mem6.pChunk; !p && pChunk; pChunk=pChunk->pNext){
      p = chunkMalloc(pChunk, nByte);
    }
  
    if( !p ){
      int iSize = nextChunkSize();
      p = mem6.parent.xMalloc(iSize);
      if( p ){
        pChunk = chunkInit((u8 *)p, iSize, mem6.nMinAlloc);
        pChunk->pNext = mem6.pChunk;
        mem6.pChunk = pChunk;
        p = chunkMalloc(pChunk, nByte);
        assert(p);
      }
    }
  }
  mem6Leave();


  return p;
}

static int memsys6Size(void *p){
  Mem6Chunk *pChunk;
  int iSize;
  mem6Enter();
  pChunk = findChunk(p);
  iSize = (pChunk ? chunkSize(pChunk, p) : mem6.parent.xSize(p));
  mem6Leave();
  return iSize;
}

static void memsys6Free(void *p){
  Mem6Chunk *pChunk;


  mem6Enter();
  pChunk = findChunk(p);
  if( pChunk ){
    chunkFree(pChunk, p);
    if( chunkIsEmpty(pChunk) ){
      freeChunk(pChunk);
    }
  }else{
    mem6.parent.xFree(p);
  }
  mem6Leave();
}

static void *memsys6Realloc(void *p, int nByte){
  void *p2;

  int iFullSz;
  for(iFullSz=mem6.nMinAlloc; iFullSz<n; iFullSz *= 2);
  return iFullSz;
}

static int memsys6Init(void *pCtx){
  u8 bMemstat = sqlite3Config.bMemstat;
  mem6.parent = *sqlite3MemGetDefault();
  mem6.nMinAlloc = 16;
  mem6.pChunk = 0;
  mem6.nThreshold = sqlite3Config.nSmall;
  if( mem6.nThreshold<=0 ){
    mem6.nThreshold = SMALL_MALLOC_DEFAULT_THRESHOLD;
  }
  if( !bMemstat ){
    mem6.mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MEM);
  }

  /* Initialize the parent allocator. */
#ifdef SQLITE_MEMDEBUG
  sqlite3Config.bMemstat = 1;
#endif
  mem6.parent.xInit(mem6.parent.pAppData);
#ifdef SQLITE_MEMDEBUG
  sqlite3Config.bMemstat = bMemstat;
#endif

  return SQLITE_OK;
}

static void memsys6Shutdown(void *pCtx){
  if( mem6.parent.xShutdown ){
    mem6.parent.xShutdown(mem6.parent.pAppData);
  }
  memset(&mem6, 0, sizeof(mem6));
}

/*
** This routine is the only routine in this file with external 
** linkage. It returns a pointer to a static sqlite3_mem_methods
** struct populated with the memsys6 methods.