SQLite

** Turn a relative pathname into a full pathname.  Return a pointer
** to the full pathname stored in space obtained from sqliteMalloc().
** The calling function is responsible for freeing this space once it
** is no longer needed.
*/
char *sqlite3UnixFullPathname(const char *zRelative){
  char *zFull = 0;
  int i, j;
  if( zRelative[0]=='/' ){
    sqlite3SetString(&zFull, zRelative, (char*)0);
  }else{
    char *zBuf = sqliteMalloc(5000);
    if( zBuf==0 ){
      return 0;
    }
    zBuf[0] = 0;
    sqlite3SetString(&zFull, getcwd(zBuf, 5000), "/", zRelative,
                    (char*)0);
    sqliteFree(zBuf);
  }
  /*
  ** Remove "/./" path elements and convert "/A/./" path elements
  ** to just "/".
  */
  if( zFull ){
    for(i=j=0; zFull[i]; i++){
      if( zFull[i]=='/' ){
        if( zFull[i+1]=='/' ) continue;
        if( zFull[i+1]=='.' && zFull[i+2]=='/' ){
          i += 1;
          continue;
        }
        if( zFull[i+1]=='.' && zFull[i+2]=='.' && zFull[i+3]=='/' ){
          while( j>0 && zFull[j-1]!='/' ){ j--; }
          i += 3;
          continue;
        }
      }
      zFull[j++] = zFull[i];
    }
    zFull[j] = 0;
  }
  return zFull;
}

/*
** Change the value of the fullsync flag in the given file descriptor.
*/
static void unixSetFullSync(OsFile *id, int v){

**     write-op queue.   So async.queueMutex is held for the duration
**     of these operations to prevent other threads from changing the
**     queue in mid operation.
**    
**
**         asyncLock, asyncUnlock, asyncLockState, asyncCheckReservedLock
**    
**     These primitives implement in-process locking using a hash table
**     on the file name.  Files are locked correctly for connections coming
**     from the same process.  But other processes cannot see these locks
**     and will therefore not honor them.
**
**
**         asyncFileHandle.
**    
**     The sqlite3OsFileHandle() function is currently only used when 
**     debugging the pager module. Unless sqlite3OsClose() is called on the
**     file (shouldn't be possible for other reasons), the underlying 

/*
** State information is held in the static variable "async" defined
** as follows:
*/
static struct TestAsyncStaticData {
  pthread_mutex_t queueMutex;  /* Mutex for access to write operation queue */
  pthread_mutex_t writerMutex; /* Prevents multiple writer threads */
  pthread_mutex_t lockMutex;   /* For access to aLock hash table */
  pthread_cond_t queueSignal;  /* For waking up sleeping writer thread */
  pthread_cond_t emptySignal;  /* Notify when the write queue is empty */
  AsyncWrite *pQueueFirst;     /* Next write operation to be processed */
  AsyncWrite *pQueueLast;      /* Last write operation on the list */
  Hash aLock;                  /* Files locked */
  volatile int ioDelay;             /* Extra delay between write operations */
  volatile int writerHaltWhenIdle;  /* Writer thread halts when queue empty */
  volatile int writerHaltNow;       /* Writer thread halts after next op */
} async = {
  PTHREAD_MUTEX_INITIALIZER,
  PTHREAD_MUTEX_INITIALIZER,
  PTHREAD_MUTEX_INITIALIZER,
  PTHREAD_COND_INITIALIZER,
  PTHREAD_COND_INITIALIZER,
};

/* Possible values of AsyncWrite.op */
#define ASYNC_NOOP          0
#define ASYNC_WRITE         1
#define ASYNC_SYNC          2
#define ASYNC_TRUNCATE      3
#define ASYNC_CLOSE         4
#define ASYNC_OPENDIRECTORY 5
#define ASYNC_SETFULLSYNC   6

#define ASYNC_DELETE        7
#define ASYNC_OPENEXCLUSIVE 8
#define ASYNC_SYNCDIRECTORY 9

/* Names of opcodes.  Used for debugging only.
** Make sure these stay in sync with the macros above!
*/
static const char *azOpcodeName[] = {
  "NOOP", "WRITE", "SYNC", "TRUNCATE", "CLOSE",
  "OPENDIR", "SETFULLSYNC", "DELETE", "OPENEX", "SYNCDIR",
};

/*
** Entries on the write-op queue are instances of the AsyncWrite
** structure, defined here.
**
** The interpretation of the iOffset and nByte variables varies depending 

** ASYNC_DELETE:
**     iOffset -> Unused.
**     nByte   -> Number of bytes of zBuf points to (file name).
**
** ASYNC_OPENEXCLUSIVE:
**     iOffset -> Value of "delflag".
**     nByte   -> Number of bytes of zBuf points to (file name).
**
**
** For an ASYNC_WRITE operation, zBuf points to the data to write to the file. 
** This space is sqliteMalloc()d along with the AsyncWrite structure in a
** single blob, so is deleted when sqliteFree() is called on the parent 
** structure.
*/
struct AsyncWrite {

/* 
** The AsyncFile structure is a subclass of OsFile used for asynchronous IO.
*/
struct AsyncFile {
  IoMethod *pMethod;   /* Must be first */
  int ioError;         /* Value of any asychronous error we have seen */
  i64 iOffset;         /* Current seek() offset in file */
  char *zName;         /* Underlying OS filename - used for debugging */
  int nName;           /* Number of characters in zName */
  OsFile *pBaseRead;   /* Read handle to the underlying Os file */
  OsFile *pBaseWrite;  /* Write handle to the underlying Os file */
};

/*
** Add an entry to the end of the global write-op list. pWrite should point 
** to an AsyncWrite structure allocated using sqlite3OsMalloc().  The writer

  if( async.pQueueLast ){
    assert( async.pQueueFirst );
    async.pQueueLast->pNext = pWrite;
  }else{
    async.pQueueFirst = pWrite;
  }
  async.pQueueLast = pWrite;
  TRACE(("PUSH %p (%s %s)\n", pWrite, azOpcodeName[pWrite->op],
         pWrite->pFile ? pWrite->pFile->zName : "-"));

  /* Drop the queue mutex */
  pthread_mutex_unlock(&async.queueMutex);

  /* The writer thread might have been idle because there was nothing
  ** on the write-op queue for it to do.  So wake it up. */
  pthread_cond_signal(&async.queueSignal);

** at the moment anyway.
*/
static int asyncFileHandle(OsFile *id){
  return sqlite3OsFileHandle(((AsyncFile *)id)->pBaseRead);
}

/*
** No disk locking is performed.  We keep track of locks locally in
** the async.aLock hash table.  Locking should appear to work the same
** as with standard (unmodified) SQLite as long as all connections 
** come from this one process.  Connections from external processes
** cannot see our internal hash table (obviously) and will thus not
** honor our locks.
*/
static int asyncLock(OsFile *id, int lockType){
  AsyncFile *pFile = (AsyncFile*)id;
  TRACE(("LOCK %d (%s)\n", lockType, pFile->zName));
  pthread_mutex_lock(&async.lockMutex);
  sqlite3HashInsert(&async.aLock, pFile->zName, pFile->nName, (void*)lockType);
  pthread_mutex_unlock(&async.lockMutex);
  return SQLITE_OK;
}
static int asyncUnlock(OsFile *id, int lockType){
  return asyncLock(id, lockType);
}

/*
** This function is called when the pager layer first opens a database file
** and is checking for a hot-journal.
*/
static int asyncCheckReservedLock(OsFile *id){
  AsyncFile *pFile = (AsyncFile*)id;
  int rc;
  pthread_mutex_lock(&async.lockMutex);
  rc = (int)sqlite3HashFind(&async.aLock, pFile->zName, pFile->nName);
  pthread_mutex_unlock(&async.lockMutex);
  TRACE(("CHECK-LOCK %d (%s)\n", rc, pFile->zName));
  return rc;
}

/* 
** This is broken. But sqlite3OsLockState() is only used for testing anyway.
*/
static int asyncLockState(OsFile *id){
  return SQLITE_OK;

*/
static int asyncOpenFile(
  const char *zName,     /* The name of the file to be opened */
  OsFile **pFile,        /* Put the OsFile structure here */
  OsFile *pBaseRead,     /* The real OsFile from the real I/O routine */
  int openForWriting     /* Open a second file handle for writing if true */
){
  int rc, i, n;
  AsyncFile *p;
  OsFile *pBaseWrite = 0;

  static IoMethod iomethod = {
    asyncClose,
    asyncOpenDirectory,
    asyncRead,

    int dummy;
    rc = xOrigOpenReadWrite(zName, &pBaseWrite, &dummy);
    if( rc!=SQLITE_OK ){
      goto error_out;
    }
  }

  n = strlen(zName);
  for(i=n-1; i>=0 && zName[i]!='/'; i--){}
  p = (AsyncFile *)sqlite3OsMalloc(sizeof(AsyncFile) + n - i);
  if( !p ){
    rc = SQLITE_NOMEM;
    goto error_out;
  }
  memset(p, 0, sizeof(AsyncFile));
  p->zName = (char*)&p[1];
  strcpy(p->zName, &zName[i+1]);
  p->nName = n - i;
  p->pMethod = &iomethod;
  p->pBaseRead = pBaseRead;
  p->pBaseWrite = pBaseWrite;
  p->ioError = SQLITE_OK;
  
  *pFile = (OsFile *)p;
  return SQLITE_OK;

    if( p->op==ASYNC_DELETE && 0==strcmp(p->zBuf, z) ){
      ret = 0;
    }else if( p->op==ASYNC_OPENEXCLUSIVE && 0==strcmp(p->zBuf, z) ){
      ret = 1;
    }
  }

  TRACE(("EXISTS: %s = %d\n", z, ret));
  pthread_mutex_unlock(&async.queueMutex);
  return ret;
}

/*
** Call this routine to enable or disable the
** asynchronous IO features implemented in this file. 
**
** This routine is not even remotely threadsafe.  Do not call
** this routine while any SQLite database connections are open.
*/
static void asyncEnable(int enable){
  if( enable && xOrigOpenReadWrite==0 ){
    sqlite3HashInit(&async.aLock, SQLITE_HASH_BINARY, 1);
    
    xOrigOpenReadWrite = sqlite3Os.xOpenReadWrite;
    xOrigOpenReadOnly = sqlite3Os.xOpenReadOnly;
    xOrigOpenExclusive = sqlite3Os.xOpenExclusive;
    xOrigDelete = sqlite3Os.xDelete;
    xOrigFileExists = sqlite3Os.xFileExists;
    xOrigSyncDirectory = sqlite3Os.xSyncDirectory;

    sqlite3Os.xOpenReadWrite = asyncOpenReadWrite;
    sqlite3Os.xOpenReadOnly = asyncOpenReadOnly;
    sqlite3Os.xOpenExclusive = asyncOpenExclusive;
    sqlite3Os.xDelete = asyncDelete;
    sqlite3Os.xFileExists = asyncFileExists;
    sqlite3Os.xSyncDirectory = asyncSyncDirectory;
  }
  if( !enable && xOrigOpenReadWrite!=0 ){
    sqlite3HashClear(&async.aLock);

    sqlite3Os.xOpenReadWrite = xOrigOpenReadWrite;
    sqlite3Os.xOpenReadOnly = xOrigOpenReadOnly;
    sqlite3Os.xOpenExclusive = xOrigOpenExclusive;
    sqlite3Os.xDelete = xOrigDelete;
    sqlite3Os.xFileExists = xOrigFileExists;
    sqlite3Os.xSyncDirectory = xOrigSyncDirectory;

      }else{
        TRACE(("IDLE\n"));
        pthread_cond_wait(&async.queueSignal, &async.queueMutex);
        TRACE(("WAKEUP\n"));
      }
    }
    if( p==0 ) break;
    TRACE(("PROCESSING %p (%s %s)\n", p, azOpcodeName[p->op],
            p->pFile ? p->pFile->zName : "-"));

    /* Right now this thread is holding the mutex on the write-op queue.
    ** Variable 'p' points to the first entry in the write-op queue. In
    ** the general case, we hold on to the mutex for the entire body of
    ** the loop. 
    **
    ** However in the cases enumerated below, we relinquish the mutex,

*/
static int testAsyncWait(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  int cnt = 10;
  if( async.writerHaltNow==0 && async.writerHaltWhenIdle==0 ){
    Tcl_AppendResult(interp, "would block forever", (char*)0);
    return TCL_ERROR;
  }
  while( cnt-- && !pthread_mutex_trylock(&async.writerMutex) ){
    pthread_mutex_unlock(&async.writerMutex);
    sched_yield();
  }
  if( cnt>=0 ){
    TRACE(("WAIT\n"));
    pthread_mutex_lock(&async.queueMutex);
    pthread_cond_broadcast(&async.queueSignal);
    pthread_mutex_unlock(&async.queueMutex);
    pthread_mutex_lock(&async.writerMutex);
    pthread_mutex_unlock(&async.writerMutex);
  }else{
    TRACE(("NOTHING TO WAIT ON\n"));
  }
  return TCL_OK;
}


#endif  /* OS_UNIX and THREADSAFE and defined(SQLITE_ENABLE_REDEF_IO) */

/*