More reliable taskq fini; avoids deadlock during shutdown.

1 files changed, 43 insertions, 4 deletions

diff --git a/src/core/taskq.c b/src/core/taskq.c
index 33116ec9..5fbcdb33 100644
--- a/src/core/taskq.c
+++ b/src/core/taskq.c
@@ -57,14 +57,13 @@ nni_taskq_thread(void *self)
 			continue;
 		}
 
-		if (tq->tq_close) {
-			break;
-		}
 		if (tq->tq_waiting) {
 			tq->tq_waiting = 0;
 			nni_cv_wake(&tq->tq_cv);
 		}
-
+		if (tq->tq_close) {
+			break;
+		}
 		nni_cv_wait(&tq->tq_cv);
 	}
 	nni_mtx_unlock(&tq->tq_mtx);
@@ -122,12 +121,52 @@ fail:
 	return (rv);
 }
 
+static void
+nni_taskq_drain_locked(nni_taskq *tq)
+{
+	// We need to first let the taskq completely drain.
+	for (;;) {
+		int busy = 0;
+		if (!nni_list_empty(&tq->tq_tasks)) {
+			busy = 1;
+		} else {
+			int i;
+			for (i = 0; i < tq->tq_nthreads; i++) {
+				if (tq->tq_threads[i].tqt_running != 0) {
+					busy = 1;
+					break;
+				}
+			}
+		}
+		if (!busy) {
+			break;
+		}
+		tq->tq_waiting++;
+		nni_cv_wait(&tq->tq_cv);
+	}
+}
+
+void
+nni_taskq_drain(nni_taskq *tq)
+{
+	nni_mtx_lock(&tq->tq_mtx);
+	nni_taskq_drain_locked(tq);
+	nni_mtx_unlock(&tq->tq_mtx);
+}
+
 void
 nni_taskq_fini(nni_taskq *tq)
 {
 	int i;
+	int busy;
+
+	// First drain the taskq completely.  This is necessary since some
+	// tasks that are presently running may need to schedule additional
+	// tasks, and we don't want those to block.
 
 	nni_mtx_lock(&tq->tq_mtx);
+	nni_taskq_drain_locked(tq);
+
 	tq->tq_close = 1;
 	nni_cv_wake(&tq->tq_cv);
 	nni_mtx_unlock(&tq->tq_mtx);