Hello,

As the documentation explains, when poll() is interrupted by a signal, it should return -1/EINTR.
However, I'm getting a return indicating that all of the polling descriptors are ready, but when I check their flags out, none of them are
ready. (Note that the same code behaves as expected on Linux)

This is on the Generic 4.7 release kernel.

Here's a snippet of code that I wrote to deal smoothly this behavior: (specifically, the last line)


   pollfd wait_fd[2];
   wait_fd[0].fd = sock_fd;
   wait_fd[0].events = POLLOUT;
   wait_fd[1].fd = abort_fd;
   wait_fd[1].events = POLLIN;
   int rfds;
   do
      rfds = poll(wait_fd, 2, NULL);
   while((rfds < 0 && errno == EINTR) || (rfds > 0 && !wait_fd[0].revents && !wait_fd[1].revents));


The thing is, I have no idea if this this is a feature or bug, or what. :-P

Thanks for any input,

Yarin

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What does that NULL do ?

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This is not valid - poll takes an int argument here. NULL is interpreted
as 0 (return immediately) on most platforms, which means you're
busy-waiting. And that poll() will usually return 0 ("timeout reached").
This matches your observations, as far as I can tell.

I *think* you meant:

  while ((rfds = poll(wait_fd, 2, INFTIM)) == -1 && errno == EINTR);
  if (rfds == -1)
  	err(1, "Poll failed");

Note that poll cannot return 0 here.

		Joachim

-- 
TFMotD: poll (2) - synchronous I/O multiplexing
http://www.joachimschipper.nl/

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