fixes to address Pierre's comments from May 2 review

Author: dgrove-oss

src/event/workqueue.c

@@ -215,7 +215,8 @@ _dispatch_workq_monitor_pools(void *context DISPATCH_UNUSED)
 
 // temporary until we switch over to QoS based interface.
 static dispatch_queue_t
-get_root_queue_from_legacy_priority(int priority) {
+get_root_queue_from_legacy_priority(int priority)
+{
 	switch (priority) {
 	case WORKQ_HIGH_PRIOQUEUE:
 		return &_dispatch_root_queues[DISPATCH_ROOT_QUEUE_IDX_USER_INITIATED_QOS];
@@ -252,6 +253,7 @@ _dispatch_workq_init_once(void *context DISPATCH_UNUSED)
 	dispatch_source_set_timer(ds, dispatch_time(DISPATCH_TIME_NOW, 0),
 			NSEC_PER_SEC, 0);
 	dispatch_source_set_event_handler_f(ds, _dispatch_workq_monitor_pools);
+	dispatch_set_context(ds, ds); // avoid appearing as leaked
 	dispatch_activate(ds);
 }
 

src/queue.c

@@ -151,7 +151,7 @@ static struct dispatch_pthread_root_queue_context_s
 struct dispatch_root_queue_context_s {
 	union {
 		struct {
-			unsigned int volatile dgq_pending;
+			int volatile dgq_pending;
 #if HAVE_PTHREAD_WORKQUEUES
 			qos_class_t dgq_qos;
 			int dgq_wq_priority, dgq_wq_options;
@@ -669,6 +669,10 @@ _dispatch_root_queues_init_workq(int *wq_supported)
 			}
 #endif // DISPATCH_USE_LEGACY_WORKQUEUE_FALLBACK
 			qc->dgq_kworkqueue = pwq ? pwq : (void*)(~0ul);
+			// because the fastpath of _dispatch_global_queue_poke didn't
+			// know yet that we're using the internal pool implementation
+			// we have to undo its setting of dgq_pending
+			qc->dgq_pending = 0;
 		}
 #if DISPATCH_USE_LEGACY_WORKQUEUE_FALLBACK
 		if (!disable_wq) {
@@ -694,13 +698,6 @@ _dispatch_root_queue_init_pthread_pool(dispatch_root_queue_context_t qc,
 		thread_pool_size = pool_size;
 	}
 	qc->dgq_thread_pool_size = thread_pool_size;
-	if (qc->dgq_kworkqueue == (void*)(~0ul)) {
-		// when _dispatch_root_queues_init is invoked from
-		// _dispatch_global_queue_poke_slow we need to clear
-		// dgq_pending here because qc->dgq_kworkqueue wasn't
-		// initialized to (~0ul) when we went through _dispatch_global_queue_poke
-		qc->dgq_pending = 0;
-	}
 #if HAVE_PTHREAD_WORKQUEUES
 	if (qc->dgq_qos) {
 		(void)dispatch_assume_zero(pthread_attr_init(&pqc->dpq_thread_attr));
@@ -1991,9 +1988,8 @@ _dispatch_pthread_root_queue_create(const char *label, unsigned long flags,
 	dispatch_pthread_root_queue_context_t pqc;
 	dispatch_queue_flags_t dqf = 0;
 	size_t dqs;
-	uint8_t pool_size_u = flags & _DISPATCH_PTHREAD_ROOT_QUEUE_FLAG_POOL_SIZE ?
+	int32_t pool_size = flags & _DISPATCH_PTHREAD_ROOT_QUEUE_FLAG_POOL_SIZE ?
 			(int8_t)(flags & ~_DISPATCH_PTHREAD_ROOT_QUEUE_FLAG_POOL_SIZE) : 0;
-	int32_t pool_size = (int32_t)pool_size_u;
 
 	dqs = sizeof(struct dispatch_queue_s) - DISPATCH_QUEUE_CACHELINE_PAD;
 	dqs = roundup(dqs, _Alignof(struct dispatch_root_queue_context_s));
@@ -5445,7 +5441,7 @@ _dispatch_worker_thread4(void *context)
 	dispatch_root_queue_context_t qc = dq->do_ctxt;
 
 	_dispatch_introspection_thread_add();
-	int pending = (int)os_atomic_dec2o(qc, dgq_pending, relaxed);
+	int pending = os_atomic_dec2o(qc, dgq_pending, relaxed);
 	dispatch_assert(pending >= 0);
 	_dispatch_root_queue_drain(dq, _dispatch_get_priority());
 	_dispatch_voucher_debug("root queue clear", NULL);
@@ -5491,8 +5487,10 @@ _dispatch_worker_thread(void *context)
 	dispatch_root_queue_context_t qc = dq->do_ctxt;
 	dispatch_pthread_root_queue_context_t pqc = qc->dgq_ctxt;
 
-	int pending = (int)os_atomic_dec2o(qc, dgq_pending, relaxed);
-	dispatch_assert(pending >= 0);
+	int pending = os_atomic_dec2o(qc, dgq_pending, relaxed);
+	if (unlikely(pending < 0)) {
+		DISPATCH_INTERNAL_CRASH(pending, "Pending thread request underflow");
+	}
 
 	if (pqc->dpq_observer_hooks.queue_will_execute) {
 		_dispatch_set_pthread_root_queue_observer_hooks(