Hi, According to the manpage select() on a nonblocking socket returns "readable" when a receive/read operation on the socket won't block. I've noticed that select occasionally returns a socket as "readable", but a following read() call will return EAGAIN. I understand that this doesn't conflict with what the manpage says, but I'm wondering why the socket is returned as readable at all, when clearly there is nothing there to read yet? Below is an strace of what's happening. I cannot tell from that whether the read call got interrupted by SIGALRM, or whether the alarm occured after read was done, but shouldn't read() return EINTR if it was interrupted by a signal? The program is single-threaded, so there are no other threads reading the data before us. select(9, [0 3 4 5 6 7 8], [], NULL, NULL) = 1 (in [7]) read(7, "m", 300) = 1 select(9, [0 3 4 5 6 7 8], [], NULL, NULL) = 1 (in [7]) read(7, "e", 299) = 1 select(9, [0 3 4 5 6 7 8], [], NULL, NULL) = 1 (in [7]) read(7, "d", 298) = 1 select(9, [0 3 4 5 6 7 8], [], NULL, NULL) = 1 (in [7]) read(7, 0x242827, 297) = -1 EAGAIN (Resource temporarily unavailable) --- SIGALRM (Alarm clock) --- sigreturn() = ? (mask now []) select(9, [0 3 4 5 6 7 8], [6], NULL, NULL) = 2 (in [7], out [6]) read(7, "i", 297) = 1 select(9, [0 3 4 5 6 7 8], [], NULL, NULL) = 1 (in [7]) read(7, "t", 296) = 1 select(9, [0 3 4 5 6 7 8], [], NULL, NULL) = ? ERESTARTNOHAND (To be restarted) --- SIGALRM (Alarm clock) --- sigreturn() = ? (mask now []) Can someone enlighten me? -Udo. - : send the line "unsubscribe linux-net" in the body of a message to majordomo@vger.kernel.org
