Fix TaskScheduler.waitAndProcess to not block if any tasks were resumed.

In situations where no events were involved in an multi-task scenario, the old behavior could lead to the process to starve or hang until an event arrived.

source/vibe/core/core.d

@@ -1131,7 +1131,7 @@ package(vibe) void performIdleProcessing()
 			again = s_idleHandler();
 		else again = false;
 
-		again = (s_scheduler.schedule() || again) && !getExitFlag();
+		again = (s_scheduler.schedule() == ScheduleStatus.busy || again) && !getExitFlag();
 
 		if (again) {
 			auto er = eventDriver.core.processEvents(0.seconds);

source/vibe/core/task.d

@@ -57,7 +57,6 @@ struct Task {
 		if (!fiber) return Task.init;
 		auto tfiber = cast(TaskFiber)fiber;
 		assert(tfiber !is null, "Invalid or null fiber used to construct Task handle.");
-		if (!tfiber.m_running) return Task.init;
 		return () @trusted { return Task(tfiber, tfiber.m_taskCounter); } ();
 	}
 
@@ -104,6 +103,7 @@ struct Task {
 		md.put(nativeToLittleEndian(() @trusted { return cast(size_t)cast(void*)m_fiber; } ()));
 		md.put(nativeToLittleEndian(m_taskCounter));
 		Base64.encode(md.finish()[0 .. 3], dst);
+		if (!this.running) dst.put("-fin");
 	}
 
 	bool opEquals(in ref Task other) const @safe nothrow { return m_fiber is other.m_fiber && m_taskCounter == other.m_taskCounter; }
@@ -458,8 +458,10 @@ final package class TaskFiber : Fiber {
 
 	package void handleInterrupt()
 	@safe {
-		if (m_interrupt)
+		if (m_interrupt) {
+			m_interrupt = false;
 			throw new InterruptException;
+		}
 	}
 }
 
@@ -551,7 +553,7 @@ package struct TaskScheduler {
 		bool any_events = false;
 		while (true) {
 			// process pending tasks
-			schedule();
+			bool any_tasks_processed = schedule() != ScheduleStatus.idle;
 
 			logTrace("Processing pending events...");
 			ExitReason er = eventDriver.core.processEvents(0.seconds);
@@ -565,7 +567,7 @@ package struct TaskScheduler {
 					break;
 				case ExitReason.timeout:
 					if (!scheduledTaskCount)
-						return any_events ? ExitReason.idle : ExitReason.timeout;
+						return any_events || any_tasks_processed ? ExitReason.idle : ExitReason.timeout;
 					break;
 				case ExitReason.idle:
 					any_events = true;
@@ -686,8 +688,12 @@ package struct TaskScheduler {
 		Returns:
 			Returns `true` $(I iff) there are more tasks left to process.
 	*/
-	bool schedule()
+	ScheduleStatus schedule()
 	{
+		if (m_taskQueue.empty)
+			return ScheduleStatus.idle;
+
+
 		if (!m_markerTask) m_markerTask = new TaskFiber; // TODO: avoid allocating an actual task here!
 
 		assert(Task.getThis() == Task.init, "TaskScheduler.schedule() may not be called from a task!");
@@ -703,13 +709,13 @@ package struct TaskScheduler {
 			resumeTask(t.task);
 
 			assert(!m_taskQueue.empty, "Marker task got removed from tasks queue!?");
-			if (m_taskQueue.empty) return false; // handle gracefully in release mode
+			if (m_taskQueue.empty) return ScheduleStatus.idle; // handle gracefully in release mode
 		}
 
 		// remove marker task
 		m_taskQueue.popFront();
 
-		return !m_taskQueue.empty;
+		return m_taskQueue.empty ? ScheduleStatus.allProcessed : ScheduleStatus.busy;
 	}
 
 	/// Resumes execution of a yielded task.
@@ -740,6 +746,12 @@ package struct TaskScheduler {
 	}
 }
 
+package enum ScheduleStatus {
+	idle,
+	allProcessed,
+	busy
+}
+
 private struct TaskFiberQueue {
 	@safe nothrow: