Attachment 11382 Details for Bug 23861 – test program that exposes rdlock stall

test program that exposes rdlock stall

wrloop.cc (text/x-c++src), 2.23 KB, created by Rik Prohaska on 2018-11-05 15:25:30 UTC

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Creator: Rik Prohaska

Created: 2018-11-05 15:25:30 UTC

Size: 2.23 KB

patch

obsolete

>// this program sometimes causes a thread to stall indefinately inside rdlock even
>// when the reader writer lock is not locked.  in addition, a thread may spin rather
>// wait on the futex.  both of these occur because the RWAITING bit is not set in the
>// expected value in the futex_wait system call.  these failures only occur when
>// using the PREFER_WRITER_NONRECURSIVE attribute.
>// this program works fine when using a PREFER_READER or PREFER_WRITER attribute.
>
>#include <stdlib.h>
>#include <unistd.h>
>#include <assert.h>
>#include <cstring>
>#include <atomic>
>#include <thread>
>#include <pthread.h>
>
>std::atomic_int do_exit = 0;
>pthread_rwlockattr_t mylock_attr;
>pthread_rwlock_t mylock;
>
>void wrloop(void) {
>    int r;
>    while (!do_exit) {
>        if (random() & 1) {
>            r = pthread_rwlock_wrlock(&mylock);
>            assert(r == 0);
>            r = pthread_rwlock_unlock(&mylock);
>            assert(r == 0);
>        } else {
>            r = pthread_rwlock_rdlock(&mylock);
>            assert(r == 0);
>            r = pthread_rwlock_unlock(&mylock);
>            assert(r == 0);
>        }
>    }
>}
>
>int main(int argc, char *argv[]) {
>    int r;
>
>    r = pthread_rwlockattr_init(&mylock_attr);
>    assert(r == 0);
>    if (argc > 1) {
>        if (strcmp(argv[1], "--prefer-reader") == 0) {
>            r = pthread_rwlockattr_setkind_np(&mylock_attr, PTHREAD_RWLOCK_PREFER_READER_NP);
>            assert(r == 0);
>        } else if (strcmp(argv[1], "--prefer-writer") == 0) {
>            r = pthread_rwlockattr_setkind_np(&mylock_attr, PTHREAD_RWLOCK_PREFER_WRITER_NP);
>            assert(r == 0);
>        } else if (strcmp(argv[1], "--prefer-writer-nonrecursive") == 0) {
>            r = pthread_rwlockattr_setkind_np(&mylock_attr, PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP);
>            assert(r == 0);
>        } else
>            abort();
>    }
>    r = pthread_rwlock_init(&mylock, &mylock_attr);
>    assert(r == 0);
>
>    const int N = 3;
>    std::thread tids[N];
>    for (int i=0; i<N; i++) 
>        tids[i] = std::thread(wrloop);
>    sleep(60);
>    do_exit = 1;
>    for (int i=0; i<N; i++)
>        tids[i].join();
>    r = pthread_rwlock_destroy(&mylock);
>    assert(r == 0);
>    r = pthread_rwlockattr_destroy(&mylock_attr);
>    assert(r == 0);
>    return 0;
>}

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Attachments on bug 23861: 11382