Problems with poll()/write() on non-blocking sockets
Problems with poll()/write() on non-blocking sockets
- Subject: Problems with poll()/write() on non-blocking sockets
- From: Jakub Bednar <email@hidden>
- Date: Wed, 26 May 2010 15:09:41 +0200
Hello everyone,
during stress testing of my network application I have found some strange behavior of Mac OS X sockets.
I have a communication thread, that calls a poll() checking whether data can be written to a non-blocking
socket. Upon exit from this function I check for POLLERR or POLLHUP and then perform a write() to the socket.
If the write returns -1 and errno is set to EINTR or EAGAIN, I go back to poll. Otherwise I close the socket as there
was an error.
This works great most of the time, but during stress testing I found out a strange behavior (e.g. after 8 hours of
video streaming). The poll() unblocks the socket and call to write() returns -1 with errno EAGAIN immediately.
I go back to poll() and the same happens again leading to busy loop.
I found one post telling that it is correct for poll() to unblock a socket and that the socket can become non-writable
before I manage to call write(), but this is happing all the time for my socket and never recovers. Should I
consider EAGAIN to be an error and close the connection? Wouldn't this cause another problems? I can't see
another way out of this issue and I don't even understand why this is happening. I'm not asking for nor handling
OUT-OF-BAND data flags in poll() but I don't think it could cause the problem.
Another thing is, that Shark's System Trace keeps telling me that the syscall write returned 0x0 and not -1.
Maybe a bug in C library?
Can anyone please help me out of this or explain why is this happening?
Thanks a lot,
Jakub _______________________________________________
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