运行多个线程

您可以运行应用程序逻辑处理线程，也可以使用其他线程处理其他后台进程。例如，您可以创建一个线程为调试提供 HTTP 流量，或创建一个线程以监控推理结果并将数据发送到 AWS。

要运行多个线程，可以使用 Python 标准库中的线程模块为每个进程创建一个线程。以下示例显示了调试服务器示例应用程序的主循环，该循环创建了一个应用程序对象并使用它来运行三个线程。

例 packages/123456789012-DEBUG_SERVER-1.0/application.py - 主循环

def main():
    panorama = panoramasdk.node()
    while True:
        try:
            # Instantiate application
            logger.info('INITIALIZING APPLICATION')
            app = Application(panorama)
            # Create threads for stream processing, debugger, and client
            app.run_thread = threading.Thread(target=app.run_cv)
            app.server_thread = threading.Thread(target=app.run_debugger)
            app.client_thread = threading.Thread(target=app.run_client)
            # Start threads
            logger.info('RUNNING APPLICATION')
            app.run_thread.start()
            logger.info('RUNNING SERVER')
            app.server_thread.start()
            logger.info('RUNNING CLIENT')
            app.client_thread.start()
            # Wait for threads to exit
            app.run_thread.join()
            app.server_thread.join()
            app.client_thread.join()
            logger.info('RESTARTING APPLICATION')
        except:
            logger.exception('Exception during processing loop.')

当所有线程都退出时，应用程序会自行重新启动。run_cv 循环处理来自摄像机视频流的图像。如果它收到停止信号，就会关闭调试程序进程，而调试程序进程在 HTTP 服务器上运行，无法自行关闭。每个线程必须处理各自的错误。如果未捕获并记录错误，则线程将以静默方式退出。

例 packages/123456789012-DEBUG_SERVER-1.0/application.py - 处理循环

    # Processing loop
    def run_cv(self):
        """Run computer vision workflow in a loop."""
        logger.info("PROCESSING STREAMS")
        while not self.terminate:
            try:
                self.process_streams()
                # turn off debug logging after 15 loops
                if logger.getEffectiveLevel() == logging.DEBUG and self.frame_num == 15:
                    logger.setLevel(logging.INFO)
            except:
                logger.exception('Exception on processing thread.')
        # Stop signal received
        logger.info("SHUTTING DOWN SERVER")
        self.server.shutdown()
        self.server.server_close()
        logger.info("EXITING RUN THREAD")

线程通过应用程序的 self 对象进行通信。要重新启动应用程序处理循环，调试程序线程会调用 stop 方法。此方法设置了一个 terminate 属性，向其他线程发出关闭信号。

例 packages/123456789012-DEBUG_SERVER-1.0/application.py - 停止方法

    # Interrupt processing loop
    def stop(self):
        """Signal application to stop processing."""
        logger.info("STOPPING APPLICATION")
        # Signal processes to stop
        self.terminate = True
    # HTTP debug server
    def run_debugger(self):
        """Process debug commands from local network."""
        class ServerHandler(SimpleHTTPRequestHandler):
            # Store reference to application
            application = self
            # Get status
            def do_GET(self):
                """Process GET requests."""
                logger.info('Get request to {}'.format(self.path))
                if self.path == "/status":
                    self.send_200('OK')
                else:
                    self.send_error(400)
            # Restart application
            def do_POST(self):
                """Process POST requests."""
                logger.info('Post request to {}'.format(self.path))
                if self.path == '/restart':
                    self.send_200('OK')
                    ServerHandler.application.stop()
                else:
                    self.send_error(400)