/*
** This procedure runs in a separate thread, reading messages off of the
** write queue and processing them one by one.
**
** If async.writerHaltNow is true, then this procedure exits
** after processing a single message.
**
** If async.writerHaltWhenIdle is true, then this procedure exits when
** the write queue is empty.
**
** If both of the above variables are false, this procedure runs
** indefinately, waiting for operations to be added to the write queue
** and processing them in the order in which they arrive.
**
** An artifical delay of async.ioDelay milliseconds is inserted before
** each write operation in order to simulate the effect of a slow disk.
**
** Only one instance of this procedure may be running at a time.
*/
static void *asyncWriterThread(void *NotUsed){
AsyncWrite *p = 0;
int rc = SQLITE_OK;
int holdingMutex = 0;
if( pthread_mutex_trylock(&async.writerMutex) ){
return 0;
}
while( async.writerHaltNow==0 ){
OsFile *pBase = 0;
if( !holdingMutex ){
pthread_mutex_lock(&async.queueMutex);
}
while( (p = async.pQueueFirst)==0 ){
pthread_cond_broadcast(&async.emptySignal);
if( async.writerHaltWhenIdle ){
pthread_mutex_unlock(&async.queueMutex);
break;
}else{
ASYNC_TRACE(("IDLE\n"));
pthread_cond_wait(&async.queueSignal, &async.queueMutex);
ASYNC_TRACE(("WAKEUP\n"));
}
}
if( p==0 ) break;
holdingMutex = 1;
/* 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,
** perform the IO, and then re-request the mutex before removing 'p' from
** the head of the write-op queue. The idea is to increase concurrency with
** sqlite threads.
**
** * An ASYNC_CLOSE operation.
** * An ASYNC_OPENEXCLUSIVE operation. For this one, we relinquish
** the mutex, call the underlying xOpenExclusive() function, then
** re-aquire the mutex before seting the AsyncFile.pBaseRead
** variable.
** * ASYNC_SYNC and ASYNC_WRITE operations, if
** SQLITE_ASYNC_TWO_FILEHANDLES was set at compile time and two
** file-handles are open for the particular file being "synced".
*/
if( async.ioError!=SQLITE_OK && p->op!=ASYNC_CLOSE ){
p->op = ASYNC_NOOP;
}
if( p->pFile ){
pBase = p->pFile->pBaseWrite;
if(
p->op==ASYNC_CLOSE ||
p->op==ASYNC_OPENEXCLUSIVE ||
(pBase && (p->op==ASYNC_SYNC || p->op==ASYNC_WRITE) )
){
pthread_mutex_unlock(&async.queueMutex);
holdingMutex = 0;
}
if( !pBase ){
pBase = p->pFile->pBaseRead;
}
}
switch( p->op ){
case ASYNC_NOOP:
break;
case ASYNC_WRITE:
assert( pBase );
ASYNC_TRACE(("WRITE %s %d bytes at %d\n",
p->pFile->zName, p->nByte, p->iOffset));
rc = sqlite3OsSeek(pBase, p->iOffset);
if( rc==SQLITE_OK ){
rc = sqlite3OsWrite(pBase, (const void *)(p->zBuf), p->nByte);
}
break;
case ASYNC_SYNC:
assert( pBase );
ASYNC_TRACE(("SYNC %s\n", p->pFile->zName));
rc = sqlite3OsSync(pBase, p->nByte);
break;
case ASYNC_TRUNCATE:
assert( pBase );
ASYNC_TRACE(("TRUNCATE %s to %d bytes\n", p->pFile->zName, p->iOffset));
rc = sqlite3OsTruncate(pBase, p->iOffset);
break;
case ASYNC_CLOSE:
ASYNC_TRACE(("CLOSE %s\n", p->pFile->zName));
sqlite3OsClose(&p->pFile->pBaseWrite);
sqlite3OsClose(&p->pFile->pBaseRead);
sqlite3OsFree(p->pFile);
break;
case ASYNC_OPENDIRECTORY:
assert( pBase );
ASYNC_TRACE(("OPENDIR %s\n", p->zBuf));
sqlite3OsOpenDirectory(pBase, p->zBuf);
break;
case ASYNC_SETFULLSYNC:
assert( pBase );
ASYNC_TRACE(("SETFULLSYNC %s %d\n", p->pFile->zName, p->nByte));
sqlite3OsSetFullSync(pBase, p->nByte);
break;
case ASYNC_DELETE:
ASYNC_TRACE(("DELETE %s\n", p->zBuf));
rc = xOrigDelete(p->zBuf);
break;
case ASYNC_SYNCDIRECTORY:
ASYNC_TRACE(("SYNCDIR %s\n", p->zBuf));
rc = xOrigSyncDirectory(p->zBuf);
break;
case ASYNC_OPENEXCLUSIVE: {
AsyncFile *pFile = p->pFile;
int delFlag = ((p->iOffset)?1:0);
OsFile *pBase = 0;
ASYNC_TRACE(("OPEN %s delFlag=%d\n", p->zBuf, delFlag));
assert(pFile->pBaseRead==0 && pFile->pBaseWrite==0);
rc = xOrigOpenExclusive(p->zBuf, &pBase, delFlag);
assert( holdingMutex==0 );
pthread_mutex_lock(&async.queueMutex);
holdingMutex = 1;
if( rc==SQLITE_OK ){
pFile->pBaseRead = pBase;
}
break;
}
default: assert(!"Illegal value for AsyncWrite.op");
}
/* If we didn't hang on to the mutex during the IO op, obtain it now
** so that the AsyncWrite structure can be safely removed from the
** global write-op queue.
*/
if( !holdingMutex ){
pthread_mutex_lock(&async.queueMutex);
holdingMutex = 1;
}
/* ASYNC_TRACE(("UNLINK %p\n", p)); */
if( p==async.pQueueLast ){
async.pQueueLast = 0;
}
async.pQueueFirst = p->pNext;
sqlite3OsFree(p);
assert( holdingMutex );
/* An IO error has occured. We cannot report the error back to the
** connection that requested the I/O since the error happened
** asynchronously. The connection has already moved on. There
** really is nobody to report the error to.
**
** The file for which the error occured may have been a database or
** journal file. Regardless, none of the currently queued operations
** associated with the same database should now be performed. Nor should
** any subsequently requested IO on either a database or journal file
** handle for the same database be accepted until the main database
** file handle has been closed and reopened.
**
** Furthermore, no further IO should be queued or performed on any file
** handle associated with a database that may have been part of a
** multi-file transaction that included the database associated with
** the IO error (i.e. a database ATTACHed to the same handle at some
** point in time).
*/
if( rc!=SQLITE_OK ){
async.ioError = rc;
}
/* Drop the queue mutex before continuing to the next write operation
** in order to give other threads a chance to work with the write queue.
*/
if( !async.pQueueFirst || !async.ioError ){
sqlite3ApiExit(0, 0);
pthread_mutex_unlock(&async.queueMutex);
holdingMutex = 0;
if( async.ioDelay>0 ){
sqlite3OsSleep(async.ioDelay);
}else{
sched_yield();
}
}
}
pthread_mutex_unlock(&async.writerMutex);
return 0;
}
static int jtSleep(sqlite3_vfs *pVfs, int nMicro){
return sqlite3OsSleep(g.pVfs, nMicro);
}
/*
** Sleep for nMicro microseconds. Return the number of microseconds
** actually slept.
*/
static int tvfsSleep(sqlite3_vfs *pVfs, int nMicro){
return sqlite3OsSleep(PARENTVFS(pVfs), nMicro);
}
/*
** Sleep for a little while. Return the amount of time slept.
*/
int sqlite3_sleep(int ms){
return sqlite3OsSleep(ms);
}
/*
** Sleep for a little while. Return the amount of time slept.
*/
SQLITE_EXPORT int sqlite3_sleep(int ms){
return sqlite3OsSleep(ms);
}
