fixed race condition during queue shutdown

Problems could happen if the queue worker needed to be cancelled
and this cancellation happened inside queue-code (including
wtp, wti). We have now solved this by disabling cancellation while
in this code and only enabling it when working inside the user consumer.
This exactly matches the use case for which cancellation may be needed.

1 files changed, 9 insertions, 4 deletions

diff --git a/runtime/wti.c b/runtime/wti.c
index e5237885..aade156e 100644
--- a/runtime/wti.c
+++ b/runtime/wti.c
@@ -184,12 +184,11 @@ finalize_it:
 
 
 /* cancellation cleanup handler for queueWorker ()
- * Updates admin structure and frees ressources.
+ * Most importantly, it must bring back the batch into a consistent state.
  * Keep in mind that cancellation is disabled if we run into
  * the cancel cleanup handler (and have been cancelled).
  * rgerhards, 2008-01-16
  */
-// TODO: REMOVE THIS FUNCTION, CURRENTLY ONLY PRESENT TO PROVIDE DEBUG OUTPUT -- rgerhards, 2009-10-14
 static void
 wtiWorkerCancelCleanup(void *arg)
 {
@@ -224,7 +223,6 @@ doIdleProcessing(wti_t *pThis, wtp_t *pWtp, int *pbInactivityTOOccured)
 
 	if(pThis->bAlwaysRunning) {
 		/* never shut down any started worker */
-dbgprintf("YYY/ZZZ: wti Idle wait cond busy, mutex %p\n", pWtp->pmutUsr);
 		d_pthread_cond_wait(pWtp->pcondBusy, pWtp->pmutUsr);
 	} else {
 		timeoutComp(&t, pWtp->toWrkShutdown);/* get absolute timeout */
@@ -238,7 +236,11 @@ dbgprintf("YYY/ZZZ: wti Idle wait cond busy, mutex %p\n", pWtp->pmutUsr);
 }
 
 
-/* generic worker thread framework
+/* generic worker thread framework. Note that we prohibit cancellation
+ * during almost all times, because it can have very undesired side effects.
+ * However, we may need to cancel a thread if the consumer blocks for too
+ * long (during shutdown). So what we do is block cancellation, and every
+ * consumer must enable it during the periods where it is safe.
  */
 #pragma GCC diagnostic ignored "-Wempty-body"
 rsRetVal
@@ -248,6 +250,7 @@ wtiWorker(wti_t *pThis)
 	int bInactivityTOOccured = 0;
 	rsRetVal localRet;
 	rsRetVal terminateRet;
+	int iCancelStateSave;
 	DEFiRet;
 
 	ISOBJ_TYPE_assert(pThis, wti);
@@ -256,6 +259,7 @@ wtiWorker(wti_t *pThis)
 
 	dbgSetThrdName(pThis->pszDbgHdr);
 	pthread_cleanup_push(wtiWorkerCancelCleanup, pThis);
+	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &iCancelStateSave);
 
 	/* now we have our identity, on to real processing */
 	while(1) { /* loop will be broken below - need to do mutex locks */
@@ -300,6 +304,7 @@ RUNLOG_VAR("%d", terminateRet);
 
 	/* indicate termination */
 	pthread_cleanup_pop(0); /* remove cleanup handler */
+	pthread_setcancelstate(iCancelStateSave, NULL);
 
 	RETiRet;
 }