Multithread select() bug

From: Andre Ben Hamou
Date: Mon May 10 2004 - 16:29:50 EST

Here's the scenario...

- parent thread P creates a connected socket pair S[0, 1]
- P spawns a child thread C and passes it S
- C selects on S[0]
- P closes S[0]

As I understand the semantics of the select call, C should now return immediately in response to the closure (and it does on Mac OS X). However, the following test code behaves otherwise for the two test cases I've tried (2.4.21 and 2.6.5). Compilation command used: 'gcc foobar.c -lpthread'.


Andre Ben Hamou
Imperial College London

--- BEGIN TEST CODE (foobar.c)---

#include <assert.h> // assert
#include <pthread.h> // pthread_create
#include <sys/select.h> // select
#include <sys/types.h> // socketpair
#include <sys/socket.h> // socketpair
#include <unistd.h> // sleep
#include <stdio.h> // printf

void *threadFuntion (void *sockets) {
int socket = ((int *)sockets)[0];
struct timeval timeout = {tv_sec: 5, tv_usec: 0};

// Allocate a file descriptor set with the passed socket
fd_set fds;
FD_ZERO (&fds);
FD_SET (socket, &fds);

// Select to read / register exceptions on the FD set
select (socket + 1, &fds, NULL, &fds, &timeout);

return NULL;

int main (void) {
int sockets[2];
pthread_t thread;

// Create a connected pair of sockets
assert (socketpair (PF_UNIX, SOCK_STREAM, 0, sockets) != -1);
printf ("sockets: {%i, %i}\n", sockets[0], sockets[1]);

// Create a POSIX thread
// - use the default configuration
// - invoke 'threadFunction' as the root function of the thread
// - pass the socket array to 'threadFunction'
assert (pthread_create (&thread,
sockets) == 0);

// Wait for a second and then close the socket being selected on
sleep (1);
assert (close (sockets[0]) == 0);
printf ("Socket closed\n");

// Wait for the thread to exit - SHOULD BE ~ INSTANTANEOUS
assert (pthread_join (thread, NULL) == 0);
printf ("Thread joined\n");

assert (close (sockets[1]) == 0);
return 0;



...and, on the seventh day, God switched off his Mac.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at