Question

I am trying to establish a communication pipe between a C executable and python script.
Below is the Python script, and the weird thing about this is the following. If I run
the python script as below, then the C executable NEVER sees any data on the socket.

However, if I uncomment the Reader class (ie., only writting to the socket is enabled)
then the C executeable ALWAYS receives the data on the socket. Has anyone an explanation why this is not working when the Reader and Writer thread are running simultaneously?

class Reader(Thread):
    def __init__(self):
        Thread.__init__(self)
        self.daemon = True
    def run(self):
        while True:
            s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
            s.connect("/tmp/demo_socket")               
            nonce = s.recv(4)
            s.close

            if len(nonce) == 4:
                print("Result received \n")

class Writer(Thread):
    def __init__(self):
        Thread.__init__(self)
    def run(self):
        while True:
            payload = "Hello World"
            s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
            s.connect("/tmp/demo_socket")           
            s.send(payload)
            s.close()

reader = Reader()
writer = Writer()

reader.start()
writer.start()


try:
    while True:
        sleep(10000)
except KeyboardInterrupt:
    print("Terminated")

EDIT:

As suggested I am trying to open the connection globally as below but that gives me two additional problems:

1) After sending data, only 4 bytes should be received on the Python end but it seems I am receiving an endless stream of data…

2) Where can I close this globally opened stream?

s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
s.connect("/tmp/demo_socket")  

class Reader(Thread):
    def __init__(self):
        Thread.__init__(self)
        self.daemon = True
    def run(self):
        while True:        
            nonce = s.recv(4)

            if len(nonce) == 4:
                print("Result received \n")

class Writer(Thread):
    def __init__(self):
        Thread.__init__(self)
    def run(self):
        while True:
            payload = "Hello World"         
            s.send(payload)

reader = Reader()
writer = Writer()

reader.start()
writer.start()


try:
    while True:
        sleep(10000)
except KeyboardInterrupt:
    print("Terminated")

Answer 1

1) After sending data, only 4 bytes should be received on the Python end but it seems I am receiving an endless stream of data…

Your sender keeps on sending, and if the data you receive are replies to that, the server keeps on answering.

2) Where can I close this globally opened stream?

After you don’t need it any longer… Do you have a stop condition or something like that?