Potential Unsound Issue in `SharedMutex`

[CXWorks]

Hi, thanks for your time to read this issue.

Our static analyzer find a potential unsound issue in SharedMutex, where the drop fuction needs to check if the pthread_mutex is unlocked and destroying a locked pthread_mutex is considered as undefined behaviors in doc.

process-sync-rs/src/mutex.rs

Lines 123 to 128 in f1a207a

	fn drop(&mut self) {
	if getpid() == self.owner_pid {
	check_libc_err(unsafe { pthread_mutex_destroy(self.mutex.get_mut()) })
	.expect("cannot destroy mutex");
	}
	}

A potentail PoC code is like:

#[deny(unsafe_code)]
use process_sync::SharedMutex;

fn main() {
    if let Ok(mut s) = SharedMutex::new(){
        if let Ok(_) = s.lock(){
            drop(s);
        }
    }
}

FYI, a good way to handle is like std library:

https://github.com/rust-lang/rust/blob/414482f6a0d4e7290f614300581a0b55442552a3/library/std/src/sys/sync/mutex/pthread.rs#L55-L64

Thanks again for your time.