CODEWITHSUNDEEP
pythonmultithreading
Harry Cho
Harry Cho

Reputation: 2529

How to have one thread listen for data while main thread is doing some operation

I am trying to create a one thread to listen for incoming data from COM serial port while main thread is doing some operation.

Here is my code (some codes are omitted for brevity) :

def readMsg( serial ):
    msgArray = []
    while ( True ):
        char = "0x" + serial.read().encode('hex')
        if char == '0xfd':
            msgArray = []
            msgArray.append(char)
        elif char == '0xfc':
            msgArray.append(char)
            print debugPrefix, "ComPort:", (serial.port + 1), msgArray
        elif char == '0x':
            pass
        else:
            msgArray.append(char)


# Find available ports                  
initializeComPorts() 

# Print port infos
printComPorts() 

# Opens serial and returns opened serial
serialPort = openPort(1);

print "thread started"
readMsgThread = threading.Thread( target=readMsg(serialPort) )
readMsgThread.setDaemon( True )
readMsgThread.start()

print "sending some data"
serialPort.send('h')

When I execute the code readMsgThread listens fine, but the line print "sending some data" is never executed. Can someone please explain what am I missing? I've been stuck at this for a while.

Thanks you very much.

Upvotes: 3

Views: 690

Answers (1)

Tim Peters
Tim Peters

Reputation: 70715

I can't test this for you, but think carefully about this line:

readMsgThread = threading.Thread( target=readMsg(serialPort) )

That calls readMsg(serialPort) at the time the assignment is excecuted, and passes the result as target. I'm guessing you almost certainly want to do:

readMsgThread = threading.Thread( target=readMsg, args=(serialPort,) )

instead.

To clarify a little more, because you're calling readMsg on that line, no further lines will be executed until readMsg returns. But that function never returns. That's why "sending some data" is never seen. In fact, you never get to the

readMsgThread.setDaemon( True )

statement either.

Upvotes: 8

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