Messages in this thread | | | From | "David Schwartz" <> | Subject | RE: recv() hangs until SIGCHLD ? | Date | Fri, 10 Oct 2008 21:48:45 -0700 |
| |
Nicolas Cannasse wrote:
> In some rare cases, one (or several) threads are hanging in recv(). > Both lsof and ls /proc/<pid>/fd show that the socket used is in > ESTABLISHED mode but when checking on the host on which it's connected > (a mysql DB) we can't find the corresponding client socket (as it's > been closed already on the other side).
Blocking sockets will block until data is received. If no other thread is sending data, this can block forever.
> We are using the Boehm GC which uses the signals SIGXCPU and SIGPWR to > pause+restart the threads when running a GC cycle. We are correctly > handling EINTR in send() and recv() by restarting the call in case > they get interrupted this way. > > However, when attaching GDB to our locked thread it seems that even > when the GC runs, recv() does not exit (the breakpoint after it is not > reached). If we send SIGCHLD to the hanging thread with GDB, recv() > does exit and the thread is correctly unlocked. If we don't, it will > hang forever.
Why shouldn't it hang forever? What was supposed to wake it that's not?
> Any idea how we can stop this from happening or what additional things > we can check to get more informations on what's occurring ?
You say a thread is hanging in receive and not returning. But you've yet to explain why it should return. Was it interrupted by a signal? Was data received? Is the socket non-blocking? Why isn't this expected behavior? Blocking sockets block, full stop.
DS
| |