Optimize speed of switching to a handler thread.

src/factory/WFTaskFactory.cc

@@ -52,6 +52,24 @@ public:
 	}
 };
 
+class __WFCanceledTimerTask : public __WFTimerTask
+{
+protected:
+	virtual void dispatch()
+	{
+		if (this->scheduler->sleep(this) >= 0)
+			this->cancel();
+		else
+			this->handle(WFT_STATE_SYS_ERROR, errno);
+	}
+
+public:
+	__WFCanceledTimerTask(CommScheduler *scheduler, timer_callback_t&& cb) :
+		__WFTimerTask(-1, 0, scheduler, std::move(cb))
+	{
+	}
+};
+
 WFTimerTask *WFTaskFactory::create_timer_task(time_t seconds, long nanoseconds,
 											  timer_callback_t callback)
 {
@@ -59,6 +77,12 @@ WFTimerTask *WFTaskFactory::create_timer_task(time_t seconds, long nanoseconds,
 							 std::move(callback));
 }
 
+WFTimerTask *WFTaskFactory::create_timer_task(timer_callback_t callback)
+{
+	return new __WFCanceledTimerTask(WFGlobal::get_scheduler(),
+									 std::move(callback));
+}
+
 /* Deprecated. */
 WFTimerTask *WFTaskFactory::create_timer_task(unsigned int microseconds,
 											  timer_callback_t callback)
@@ -1096,7 +1120,7 @@ int WFTaskFactory::release_guard_safe(const std::string& name, void *msg)
 	if (!node)
 		return 0;
 
-	timer = WFTaskFactory::create_timer_task(0, 0, [node](WFTimerTask *timer) {
+	timer = WFTaskFactory::create_timer_task([node](WFTimerTask *timer) {
 		node->guard->WFConditional::signal(timer->user_data);
 	});
 	timer->user_data = msg;

src/factory/WFTaskFactory.h

@@ -219,21 +219,24 @@ public:
 	static WFTimerTask *create_timer_task(time_t seconds, long nanoseconds,
 										  timer_callback_t callback);
 
-	/* create a named timer. */
+	/* Create a named timer. */
 	static WFTimerTask *create_timer_task(const std::string& timer_name,
 										  time_t seconds, long nanoseconds,
 										  timer_callback_t callback);
 
-	/* cancel all timers under the name. */
+	/* Cancel all timers under the name. */
 	static int cancel_by_name(const std::string& timer_name)
 	{
 		return WFTaskFactory::cancel_by_name(timer_name, (size_t)-1);
 	}
 
-	/* cancel at most 'max' timers under the name. */
+	/* Cancel at most 'max' timers under the name. */
 	static int cancel_by_name(const std::string& timer_name, size_t max);
 
-	/* timer in microseconds (deprecated) */
+	/* Timer to be canceled immediately after started. */
+	static WFTimerTask *create_timer_task(timer_callback_t callback);
+
+	/* Timer in microseconds. (deprecated) */
 	static WFTimerTask *create_timer_task(unsigned int microseconds,
 										  timer_callback_t callback);
 

src/factory/WFTaskFactory.inl

@@ -491,9 +491,7 @@ SubTask *WFComplexClientTask<REQ, RESP, CTX>::done()
 		auto&& cb = std::bind(&WFComplexClientTask::switch_callback,
 							  this,
 							  std::placeholders::_1);
-		WFTimerTask *timer;
-
-		timer = WFTaskFactory::create_timer_task(0, 0, std::move(cb));
+		WFTimerTask *timer = WFTaskFactory::create_timer_task(std::move(cb));
 		series->push_front(timer);
 	}
 	else