如何同时运行两个函数

Question

I am running test but I want to run 2 functions at the same time. I have a camera and I am telling it to move via suds, I am then logging into the camera via SSH to check the speed the camera is set to. When I check the speed the camera has stopped so no speed is available. Is there a way I can get these functions to run at the same time to test the speed of the camera. Sample code is below:

class VerifyPan(TestAbsoluteMove):

    def runTest(self):

        self.dest.PanTilt._x=350

        # Runs soap move command
        threading.Thread(target = SudsMove).start()

        self.command = './ptzpanposition -c 0 -u degx10'

        # Logs into camera and checks speed
        TestAbsoluteMove.Ssh(self)

        # Position of the camera verified through Ssh (No decimal point added to the Ssh value)
        self.assertEqual(self.Value, '3500')

I have now tried the threading module as mentioned below. The thread does not run in sync with the function TestAbsoluteMove.Ssh(). Is there any other code I need to make this work.

I have looked at putting arguments into the thread statement that state the thread runs when the Ssh() function. Does anyone know what to enter in this statement?

Sorry if I haven't explained correctly. The 'SudsMove' function moves the camera and the 'Ssh' function logs into the camera and checks the speed the camera is currently moving at. The problem is that by the time the 'Ssh' function logs in the camera has stopped. I need both functions to run in parallel so I can check the camera speed while it is still moving.

Thanks

Answer 1

Import the threading module and run SudsMove() like so:

threading.Thread(target = SudsMove).start()

That will create and start a background thread which does the movement.

ANSWER TO EDITED QUESTION:

As far as I understand this, TestAbsoluteMove.Ssh(self) polls the speed once and stores the result in self.Value ?! And you're testing the expected end tilt/rotation/position with self.assertEqual(self.Value, '3500') ?!

If that's correct, you should wait for the camera to start its movement. You could probably poll the speed in a certain interval:

# Move camera in background thread
threading.Thread(target = SudsMove).start()

# What does this do?
self.command = './ptzpanposition -c 0 -u degx10'

# Poll the current speed in an interval of 250 ms
import time
measuredSpeedsList = []

for i in xrange(20):
    # Assuming that this call will put the result in self.Value
    TestAbsoluteMove.Ssh(self)
    measuredSpeedsList.append(self.Value)
    time.sleep(0.25)

print "Measured movement speeds: ", measuredSpeedsList

The movement speed will be the biggest value in measuredSpeedsList (ie max(measuredSpeedsList) ). Hope that makes sense...

Answer 2

If you want to use the common Python implementation (CPython), you can certainly use the multiprocessing module, which does wonders (you can pass non-pickleable arguments to subprocesses, kill tasks,…), offers an interface similar to that of threads, and does not suffer from the Global Interpreter Lock.

The downside is that subprocesses are spawned, which takes more time than creating threads; this should only be a problem if you have many, many short tasks. Also, since data is passed (via serialization) between processes, large data both takes a long time to pass around and ends up having a large memory footprint (as it is duplicated between each process). In situations where each task takes a "long" time and the data in and out of each task is not too large, the multiprocessing module should be great.

Answer 3

There can only be one thread running at the same time. This has been answered extensively here . One solution will be to use two separate processes. The above answer provides some tips.

Answer 4

If you can get your code to run under Jython or IronPython, then you can run several threads simultaneously; they don't have that goofy "Global Interpreter Lock" thing of CPython.