CODEWITHSUNDEEP
pythonunixsubprocessdaemon
Ivan Kolesnikov
Ivan Kolesnikov

Reputation: 1811

Reading and writing data via named pipe with demonization

I have two scripts:
The first one ('Reader') is reading data from named pipe and the second ('Writer') is writing data to named pipe. I am run 'Writer' from daemon (daemon was created with double fork mechanism). If 'Writer' crash I want to print a message about it in 'Reader'. Please see following Python code('Reader'):

pipe = open(pipe_path, 'r')
while True:
    data = pipe.readline()
    if not data:
        print('Alarm')
        break

But when 'Writer' is crashing then 'Reader' is stuck on following line:

data = pipe.readline()

But if I run 'Writer' from terminal everything works fine (Alarm message is printing when not data in pipe). And everything works fine if I open pipe with:

os.open(pipe_path, os.O_RDONLY | os.O_NONBLOCK)

But this method not suitable for me because I need to wait a time on start when 'Writer' start write data into pipe

In order not to create a zombie I do next in daemon:

def childHandler(signum, frame):
    os.wait3(os.WNOHANG)
signal.signal(signal.SIGCHLD, zombieKiller)

How to prevent the 'Reader' stuck and correctly handle the signal from the child process ?

Upvotes: 1

Views: 399

Answers (1)

user7725701
user7725701

Reputation:

Try to use this in the daemon: 

fdPipe = os.open(pipe_path, os.O_WRONLY | os.O_NONBLOCK)

Upvotes: 1

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