pthread_cond_signal deadlocks

问题

What could be the cause if a call to pthread_cond_signal deadlocks?

From what I understand (man page), it is implemented internally with a mutex, but what could cause this internal mutex lock operation to deadlock?

EDIT: I am debugging an application which seem to deadlock on some occasions. A few of the stacktraces look like this:

Thread 1 (Thread 0xf6dff6c0 (LWP 32001)):
#0  0xffffe410 in __kernel_vsyscall ()
#1  0x00af15de in __lll_mutex_lock_wait () from /lib/tls/libpthread.so.0
#2  0x00aef3eb in pthread_cond_signal@@GLIBC_2.3.2 () from /lib/tls/libpthread.so.0
#3  0xf4cc8d83 in xxx

回答1:

Well, one thing to look for might be this caveat from the man page, which sounds particularly applicable:

The condition functions are not async-signal safe, and should not be called from a signal handler. In particular, calling pthread_cond_signal or pthread_cond_broadcast from a signal handler may deadlock the calling thread.

Apart from that, you could also see this if the internal mutex within the pthread_cond_t has been overwritten by a stray write beyond the bounds of some other variable.

来源：https://stackoverflow.com/questions/4345315/pthread-cond-signal-deadlocks