SQLite

#define MAX(x,y) ((x)>(y)?(x):(y))

/* Forward references */
typedef struct AsyncWrite AsyncWrite;
typedef struct AsyncFile AsyncFile;

/* Enable for debugging */
static int sqlite3async_trace = 0;
# define TRACE(X) if( sqlite3async_trace ) asyncTrace X
static void asyncTrace(const char *zFormat, ...){
  char *z;
  va_list ap;
  va_start(ap, zFormat);
  z = sqlite3_vmprintf(zFormat, ap);
  va_end(ap);
  fprintf(stderr, "[%d] %s", (int)pthread_self(), z);
  free(z);
}




/*
** THREAD SAFETY NOTES
**
** Basic rules:
**
**     * Both read and write access to the global write-op queue must be 

#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 
** on the value of AsyncWrite.op:
**

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

  /* 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);

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

    /* 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,

    ** so that the AsyncWrite structure can be safely removed from the 
    ** global write-op queue.
    */
    if( !holdingMutex ){
      pthread_mutex_lock(&async.queueMutex);
      holdingMutex = 1;
    }
    /* TRACE(("UNLINK %p\n", p)); */
    if( p==async.pQueueLast ){
      async.pQueueLast = 0;
    }
    async.pQueueFirst = p->pNext;
    sqlite3OsFree(p);
    assert( holdingMutex );

  Tcl_Obj *CONST objv[]
){
  if( async.writerHaltNow==0 && async.writerHaltWhenIdle==0 ){
    Tcl_AppendResult(interp, "would block forever", (char*)0);
    return TCL_ERROR;
  }
  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);
  return TCL_OK;
}


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

/*
** This routine registers the custom TCL commands defined in this
** module.  This should be the only procedure visible from outside
** of this module.
*/
int Sqlitetestasync_Init(Tcl_Interp *interp){
#if OS_UNIX && THREADSAFE && defined(SQLITE_ENABLE_REDEF_IO)
  Tcl_CreateObjCommand(interp,"sqlite3async_enable",testAsyncEnable,0,0);
  Tcl_CreateObjCommand(interp,"sqlite3async_halt",testAsyncHalt,0,0);
  Tcl_CreateObjCommand(interp,"sqlite3async_delay",testAsyncDelay,0,0);
  Tcl_CreateObjCommand(interp,"sqlite3async_start",testAsyncStart,0,0);
  Tcl_CreateObjCommand(interp,"sqlite3async_wait",testAsyncWait,0,0);
  Tcl_LinkVar(interp, "sqlite3async_trace",
      (char*)&sqlite3async_trace, TCL_LINK_INT);
#endif  /* OS_UNIX and THREADSAFE and defined(SQLITE_ENABLE_REDEF_IO) */
  return TCL_OK;
}