/*
* ProcWakeup -- wake up a process by releasing its private___ semaphore.
*
* Also remove the process from the wait queue and set its links invalid.
* RETURN: the next process in the wait queue.
*
* The appropriate lock partition lock must be held by caller.
*
* XXX: presently, this code is only used for the "success" case, and only
* works correctly for that case. To clean up in failure case, would need
* to twiddle the lock's request counts too --- see RemoveFromWaitQueue.
* Hence, in practice the waitStatus parameter must be STATUS_OK.
*/
PGPROC *
ProcWakeup(PGPROC *proc, int waitStatus)
{
PGPROC *retProc;
/* Proc should be sleeping ... */
if (proc->links.prev == NULL ||
proc->links.next == NULL)
return NULL;
Assert(proc->waitStatus == STATUS_WAITING);
/* Save next process before we zap the list link */
retProc = (PGPROC *) proc->links.next;
/* Remove process from wait queue */
SHMQueueDelete(&(proc->links));
(proc->waitLock->waitProcs.size)--;
/* Clean up process' state and pass it the ok/fail signal */
proc->waitLock = NULL;
proc->waitProcLock = NULL;
proc->waitStatus = waitStatus;
/* And awaken it */
SetLatch(&proc->procLatch);
return retProc;
}
/*
* Acquire SyncRepLock and cancel any wait currently in progress.
*/
static void
SyncRepCancelWait(void)
{
LWLockAcquire(SyncRepLock, LW_EXCLUSIVE);
if (!SHMQueueIsDetached(&(MyProc->syncRepLinks)))
SHMQueueDelete(&(MyProc->syncRepLinks));
MyProc->syncRepState = SYNC_REP_NOT_WAITING;
LWLockRelease(SyncRepLock);
}
void
SyncRepCleanupAtProcExit(void)
{
if (!SHMQueueIsDetached(&(MyProc->syncRepLinks)))
{
LWLockAcquire(SyncRepLock, LW_EXCLUSIVE);
SHMQueueDelete(&(MyProc->syncRepLinks));
LWLockRelease(SyncRepLock);
}
}
void
SyncRepCleanupAtProcExit(int code, Datum arg)
{
if (!SHMQueueIsDetached(&(MyProc->syncRepLinks)))
{
LWLockAcquire(SyncRepLock, LW_EXCLUSIVE);
SHMQueueDelete(&(MyProc->syncRepLinks));
LWLockRelease(SyncRepLock);
}
DisownLatch(&MyProc->waitLatch);
}
/*
* ProcKill() -- Destroy the per-proc data structure for
* this process. Release any of its held spin locks.
*/
static void
ProcKill(int exitStatus, int pid)
{
PROC *proc;
SHMEM_OFFSET location;
/* --------------------
* If this is a FATAL exit the postmaster will have to kill all the
* existing backends and reinitialize shared memory. So all we don't
* need to do anything here.
* --------------------
*/
if (exitStatus != 0)
return;
if (! pid)
{
pid = getpid();
}
ShmemPIDLookup(pid,&location);
if (location == INVALID_OFFSET)
return;
proc = (PROC *) MAKE_PTR(location);
if (proc != MyProc) {
Assert( pid != getpid() );
} else
MyProc = NULL;
/* ---------------
* Assume one lock table.
* ---------------
*/
ProcReleaseSpins(proc);
LockReleaseAll(1,&proc->lockQueue);
/* ----------------
* get off the wait queue
* ----------------
*/
LockLockTable();
if (proc->links.next != INVALID_OFFSET) {
Assert(proc->waitLock->waitProcs.size > 0);
SHMQueueDelete(&(proc->links));
--proc->waitLock->waitProcs.size;
}
SHMQueueElemInit(&(proc->links));
UnlockLockTable();
return;
}
/*
* ProcWakeup -- wake up a process by releasing its private semaphore.
*
* remove the process from the wait queue and set its links invalid.
* RETURN: the next process in the wait queue.
*/
PROC *
ProcWakeup(PROC *proc, int errType)
{
PROC *retProc;
/* assume that spinlock has been acquired */
if (proc->links.prev == INVALID_OFFSET ||
proc->links.next == INVALID_OFFSET)
return((PROC *) NULL);
retProc = (PROC *) MAKE_PTR(proc->links.prev);
/* you have to update waitLock->waitProcs.size yourself */
SHMQueueDelete(&(proc->links));
SHMQueueElemInit(&(proc->links));
proc->errType = errType;
IpcSemaphoreUnlock(proc->sem.semId, proc->sem.semNum, IpcExclusiveLock);
return retProc;
}
/* --------------------
* We only get to this routine if we got SIGALRM after DEADLOCK_TIMEOUT
* while waiting for a lock to be released by some other process. After
* the one minute deadline we assume we have a deadlock and must abort
* this transaction. We must also indicate that I'm no longer waiting
* on a lock so that other processes don't try to wake me up and screw
* up my semaphore.
* --------------------
*/
void
HandleDeadLock(int sig)
{
LOCK *lock;
int size;
LockLockTable();
/* ---------------------
* Check to see if we've been awoken by anyone in the interim.
*
* If we have we can return and resume our transaction -- happy day.
* Before we are awoken the process releasing the lock grants it to
* us so we know that we don't have to wait anymore.
*
* Damn these names are LONG! -mer
* ---------------------
*/
if (IpcSemaphoreGetCount(MyProc->sem.semId, MyProc->sem.semNum) ==
IpcSemaphoreDefaultStartValue) {
UnlockLockTable();
return;
}
/*
* you would think this would be unnecessary, but...
*
* this also means we've been removed already. in some ports
* (e.g., sparc and aix) the semop(2) implementation is such that
* we can actually end up in this handler after someone has removed
* us from the queue and bopped the semaphore *but the test above
* fails to detect the semaphore update* (presumably something weird
* having to do with the order in which the semaphore wakeup signal
* and SIGALRM get handled).
*/
if (MyProc->links.prev == INVALID_OFFSET ||
MyProc->links.next == INVALID_OFFSET) {
UnlockLockTable();
return;
}
lock = MyProc->waitLock;
size = lock->waitProcs.size; /* so we can look at this in the core */
/* ------------------------
* Get this process off the lock's wait queue
* ------------------------
*/
Assert(lock->waitProcs.size > 0);
--lock->waitProcs.size;
SHMQueueDelete(&(MyProc->links));
SHMQueueElemInit(&(MyProc->links));
/* ------------------
* Unlock my semaphore so that the count is right for next time.
* I was awoken by a signal, not by someone unlocking my semaphore.
* ------------------
*/
IpcSemaphoreUnlock(MyProc->sem.semId, MyProc->sem.semNum, IpcExclusiveLock);
/* -------------
* Set MyProc->errType to STATUS_ERROR so that we abort after
* returning from this handler.
* -------------
*/
MyProc->errType = STATUS_ERROR;
/*
* if this doesn't follow the IpcSemaphoreUnlock then we get lock
* table corruption ("LockReplace: xid table corrupted") due to
* race conditions. i don't claim to understand this...
*/
UnlockLockTable();
elog(NOTICE, "Timeout -- possible deadlock");
return;
}
