Hi everbody,

I am developing a multithreaded app. Think that one of my threads is connected to a device via tcp/ip and blocked at recv() call. Since i am using blocking socket.Another thread pings the destination of first thread to check whether connection is alive. If the connection is not alive, i am sending signal with pthread_kill. Although signal is handled, the blocked thread doesn't return from recv() call.

I also tried closing the socket instead of sending signal. Again nothing happened. Lastly I tried "select" giving timeout.Again unsuccessfull.

As a result, here is the question :

Using nptl, if one of thread is blocked at a function call, how can we unblock that ?

TIA

Interesting, pthread_kill with SIGIO should unblock the recv call on that thread assuming you pass the correct thread ID. A close call in a different thread on the same handle should also work. Additionally, a select loop with something like the code below should also work. I have tried select code like this with a socket set to O_NONBLOCK on RH9 and RHEL4 U2 with no problems. What distribution/version are you using? What happens if you use the select code with O_NONBLOCK?

while (!gQuitReceiving) {

/* Copy global read set */
ReadSet = gReadSet;

/* Default timeout for select call is one second
This must be reset each loop */
Timeout.tv_sec = 1;
Timeout.tv_usec = 0;

/* Block on read set (this returns -1 on error but
just check individual FileDescriptors for error) */
if ((SelectCount = select(gMaxSocket, &ReadSet, NULL, NULL,
&Timeout)) == -1) {
perror("Error select");
continue;
}
/* Check if something is available */
if (!SelectCount) {
continue;
}
/* Loop through file descriptors, start from 0 to
ignore values not set */
for (FileDescriptor = 0;
FileDescriptor < gMaxSocket;
FileDescriptor++) {
/* Something came in on one of the
descriptors we are checking out */
if (FD_ISSET(FileDescriptor, &ReadSet)) {
/* call recv here */

Hi Denes,

I tried 3 different approach. Two of them is still unsuccesful:

1) Sending SIGIO with pthread_kill. (I checked thread ID.It is right.Does socket needs special flags ? Can be related to pthread library ?)
2) Closing socket from another thread.

Third one,using select, was also unsuccesful with my implementation. But when I looked at your sample code, I noticed that you initalize readset in every loop. I was not doing that. With that initialization in each loop, at last it worked. Magic is "ReadSet = gReadSet" line.

I am using Suse with 2.6.4-52-default kernel. NPTL version is 0.61 (getconf GNU_LIBPTHREAD_VERSION).

Thanks