SQLite

/*
** This function is called during initialization (sqlite3_initialize()) to
** install the default pluggable cache module, assuming the user has not
** already provided an alternative.
*/
void sqlite3PCacheSetDefault(void){
  static const sqlite3_pcache_methods2 defaultMethods = {
    1,                       /* iVersion */
    0,                       /* pArg */
    pcache1Init,             /* xInit */
    pcache1Shutdown,         /* xShutdown */
    pcache1Create,           /* xCreate */
    pcache1Cachesize,        /* xCachesize */
    pcache1Pagecount,        /* xPagecount */
    pcache1Fetch,            /* xFetch */

**
** The sqlite3_pcache type is opaque.  It is implemented by
** the pluggable module.  The SQLite core has no knowledge of
** its size or internal structure and never deals with the
** sqlite3_pcache object except by holding and passing pointers
** to the object.
**
** See [sqlite3_pcache_methods2] for additional information.
*/
typedef struct sqlite3_pcache sqlite3_pcache;

/*
** CAPI3REF: Custom Page Cache Object
**
** The sqlite3_pcache_page object represents a single page in the
** page cache.  The page cache will allocate instances of this
** object.  Various methods of the page cache use pointers to instances
** of this object as parameters or as their return value.
**
** See [sqlite3_pcache_methods2] for additional information.
*/
typedef struct sqlite3_pcache_page sqlite3_pcache_page;
struct sqlite3_pcache_page {
  void *pBuf;        /* The content of the page */
  void *pExtra;      /* Extra information associated with the page */
};

/*
** CAPI3REF: Application Defined Page Cache.
** KEYWORDS: {page cache}
**
** ^(The [sqlite3_config]([SQLITE_CONFIG_PCACHE2], ...) interface can
** register an alternative page cache implementation by passing in an 

** ^The xDestroy() method is used to delete a cache allocated by xCreate().
** All resources associated with the specified cache should be freed. ^After
** calling the xDestroy() method, SQLite considers the [sqlite3_pcache*]
** handle invalid, and will not use it with any other sqlite3_pcache_methods
** functions.
*/
typedef struct sqlite3_pcache_methods2 sqlite3_pcache_methods2;





struct sqlite3_pcache_methods2 {
  int iVersion;
  void *pArg;
  int (*xInit)(void*);
  void (*xShutdown)(void*);
  sqlite3_pcache *(*xCreate)(int szPage, int szExtra, int bPurgeable);
  void (*xCachesize)(sqlite3_pcache*, int nCachesize);
  int (*xPagecount)(sqlite3_pcache*);
  sqlite3_pcache_page *(*xFetch)(sqlite3_pcache*, unsigned key, int createFlag);

static void installInitWrappers(void){
  sqlite3_mutex_methods mutexmethods = {
    wrMutexInit,  wrMutexEnd,   wrMutexAlloc,
    wrMutexFree,  wrMutexEnter, wrMutexTry,
    wrMutexLeave, wrMutexHeld,  wrMutexNotheld
  };
  sqlite3_pcache_methods2 pcachemethods = {
    1, 0,
    wrPCacheInit,      wrPCacheShutdown,  wrPCacheCreate, 
    wrPCacheCachesize, wrPCachePagecount, wrPCacheFetch,
    wrPCacheUnpin,     wrPCacheRekey,     wrPCacheTruncate,  
    wrPCacheDestroy
  };
  sqlite3_mem_methods memmethods = {
    wrMemMalloc,   wrMemFree,    wrMemRealloc,

void installTestPCache(
  int installFlag,            /* True to install.  False to uninstall. */
  unsigned discardChance,     /* 0-100.  Chance to discard on unpin */
  unsigned prngSeed,          /* Seed for the PRNG */
  unsigned highStress         /* Call xStress agressively */
){
  static const sqlite3_pcache_methods2 testPcache = {
    1,
    (void*)&testpcacheGlobal,
    testpcacheInit,
    testpcacheShutdown,
    testpcacheCreate,
    testpcacheCachesize,
    testpcachePagecount,
    testpcacheFetch,