Make function server_base::start_listen() and server_base::stop_listen thread safe.

Fix race condition during call acceptor::async_accept concurrently.

examples/echo_server/echo_server.cpp

@@ -182,7 +182,7 @@ public:
 	normal_server(service_pump& service_pump_) : server_base(service_pump_) {}
 
 protected:
-	virtual int async_accept_num() {return 1;} //this make on_accept to be called in single thread, because stop_listen() is not thread safe
+	virtual int async_accept_num() {return 1;}
 	virtual bool on_accept(object_ctype& socket_ptr) {stop_listen(); return true;}
 };
 

include/ascs/config.h

@@ -664,8 +664,10 @@
  *
  * HIGHLIGHT:
  * Support changing the send buffer and recv buffer at runtime.
+ * Make function server_base::start_listen() and server_base::stop_listen thread safe.
  *
  * FIX:
+ * Fix race condition during call acceptor::async_accept concurrently.
  *
  * ENHANCEMENTS:
  * Try parsing messages even errors occurred.

include/ascs/tcp/server.h

@@ -49,6 +49,10 @@ public:
 
 	bool start_listen()
 	{
+		std::lock_guard<std::mutex> lock(mutex);
+		if (is_listening())
+			return false;
+
 		asio::error_code ec;
 		if (!acceptor.is_open()) {acceptor.open(server_addr.protocol(), ec); assert(!ec);} //user maybe has opened this acceptor (to set options for example)
 #ifndef ASCS_NOT_REUSE_ADDRESS
@@ -88,7 +92,7 @@ public:
 		return true;
 	}
 	bool is_listening() const {return acceptor.is_open();}
-	void stop_listen() {asio::error_code ec; acceptor.cancel(ec); acceptor.close(ec);}
+	void stop_listen() {std::lock_guard<std::mutex> lock(mutex); asio::error_code ec; acceptor.cancel(ec); acceptor.close(ec);}
 
 	asio::ip::tcp::acceptor& next_layer() {return acceptor;}
 	const asio::ip::tcp::acceptor& next_layer() const {return acceptor;}
@@ -158,7 +162,7 @@ protected:
 	virtual void uninit() {this->stop(); stop_listen(); force_shutdown();} //if you wanna graceful shutdown, call graceful_shutdown before service_pump::stop_service invocation.
 
 	virtual bool on_accept(typename Pool::object_ctype& socket_ptr) {return true;}
-	virtual void start_next_accept() {do_async_accept(create_object());}
+	virtual void start_next_accept() {std::lock_guard<std::mutex> lock(mutex); do_async_accept(create_object());}
 
 	//if you want to ignore this error and continue to accept new connections immediately, return true in this virtual function;
 	//if you want to ignore this error and continue to accept new connections after a specific delay, start a timer immediately and return false (don't call stop_listen()),
@@ -216,6 +220,7 @@ private:
 private:
 	asio::ip::tcp::endpoint server_addr;
 	asio::ip::tcp::acceptor acceptor;
+	std::mutex mutex;
 };
 
 }} //namespace