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graph.h  view on Meta::CPAN

    int          notify_fd;
    int          backing_fd;
} GraphHandle;

/* ================================================================
 * Mutex (same pattern as Heap)
 * ================================================================ */

static const struct timespec graph_lock_timeout = { 2, 0 };

static inline int graph_pid_alive(uint32_t pid) {
    if (pid == 0) return 1;
    return !(kill((pid_t)pid, 0) == -1 && errno == ESRCH);
}

static inline void graph_mutex_lock(GraphHeader *hdr) {
    uint32_t mypid = GRAPH_MUTEX_BIT | ((uint32_t)getpid() & GRAPH_MUTEX_PID);
    for (int spin = 0; ; spin++) {
        uint32_t expected = 0;
        if (__atomic_compare_exchange_n(&hdr->mutex, &expected, mypid,
                1, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED))

graph.h  view on Meta::CPAN

#endif
            continue;
        }
        __atomic_add_fetch(&hdr->mutex_waiters, 1, __ATOMIC_RELAXED);
        uint32_t cur = __atomic_load_n(&hdr->mutex, __ATOMIC_RELAXED);
        if (cur != 0) {
            long rc = syscall(SYS_futex, &hdr->mutex, FUTEX_WAIT, cur,
                              &graph_lock_timeout, NULL, 0);
            if (rc == -1 && errno == ETIMEDOUT && cur >= GRAPH_MUTEX_BIT) {
                uint32_t pid = cur & GRAPH_MUTEX_PID;
                if (!graph_pid_alive(pid) &&
                    __atomic_compare_exchange_n(&hdr->mutex, &cur, 0,
                            0, __ATOMIC_ACQ_REL, __ATOMIC_RELAXED)) {
                    /* Recovered — wake one waiter so it can proceed. */
                    syscall(SYS_futex, &hdr->mutex, FUTEX_WAKE, 1, NULL, NULL, 0);
                }
            }
        }
        __atomic_sub_fetch(&hdr->mutex_waiters, 1, __ATOMIC_RELAXED);
        spin = 0;
    }