Solution to the problem that python methods cannot be used in threads

In python, defining a method can be called directly, but creating a thread to call it may cause failure. This phenomenon often occurs when using COM objects for system operations, and is called in the form of threads.

The exception prompt is as follows:

syntax error。WMI returned a syntax error: you're probably running inside a thread without first calling pythoncom.CoInitialize[Ex] (no underlying exception)

If you observe carefully, the solution has been given in the exception prompt. When running a thread, you need to call the pythoncom.CoInitialize() method. I used the WMI module in my program to try to obtain some system information.

The cause of the exception (presumed) is a COM mechanism problem. Since the COM mechanism allows any two components to communicate with each other without having to care about what kind of computer and operating system it is running on, nor what language the component is compiled in, this makes COM technology powerful. vitality. The purpose of initializing the COM environment is to make the API calling COM work properly, that is, to call CoInitialize or CoInitializeEX before the COM operation. Therefore, in the thread function, if you use the com object, you must call CoInitialize or CoInitializeEX, and use CoUninitialize to release the object when exiting. .
Case:

c === send = 0.0 t += float(t.BytesReceivedPersec) / 1024 / 1024+= float(t.BytesSentPersec) / 1024 / 1024 rec, send

This code is to obtain the upstream and downstream traffic (i.e. sending traffic and receiving traffic) based on the computer’s network card ), it can be run directly. However, when used in the get or post method of tornado's RequestHandler, an exception syntax error and related prompts will be thrown. In RequestHandler, the post or get request is considered a background thread method, so com needs to be instantiated before instantiating the WMI com component.

Why is the post or get request in RequestHandler considered a background thread method? This problem can be seen from the code using tornado. The code is as follows:

if __name__ == '__main__':
    app = tornado.web.Application(
        handlers=[(r"/test/(\w+)", testHandler),
                  (r'/', MainHandler)]
    )
    server = tornado.httpserver.HTTPServer(app)
    server = server.listen(8848)
    tornado.ioloop.IOLoop.instance().start();

After configuring the routing rules for tornado, we started the httpserver service, and finally created a process to run tornado. Each post or get request calls the corresponding Handler through routing, which is executed in the thread. Therefore, in the case, if the system traffic is obtained through the com component WMI and placed in the get method, an error will be reported. The modification is as follows:

    def get(self):
        res = {}        pythoncom.CoInitialize()
        c = wmi.WMI()
        interfaces = c.Win32_PerfRawData_Tcpip_NetworkInterface()        print len(interfaces)
        rec = send = 0.0        for t in interfaces:            print t.Name
            rec += float(t.BytesReceivedPersec) / 1024 / 1024
            send += float(t.BytesSentPersec) / 1024 / 1024        print rec, send
        res["receive"] = "%.2f" % rec
        res["send"] = "%.2f" % send       
        self._write_json(res)

There are many types in the module (types also have many attributes), and it is very painful to query them during specific use. The statistical traffic in the case uses Win32_PerfRawData_Tcpip_NetworkInterface, and there are also solutions that use Win32_PerfRawData_Tcpip_TCPv4. The two statistics are very different. Please choose according to the actual situation.

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