Mutex

Mutex implements a simple semaphore that can be used to coordinate access to shared data from multiple concurrent threads.

Example:

semaphore = Mutex.new

a = Thread.new {
  semaphore.synchronize {
    # access shared resource
  }
}

b = Thread.new {
  semaphore.synchronize {
    # access shared resource
  }
}

Public Class Methods

new → mutex click to toggle source

Creates a new Mutex

 
               static VALUE
mutex_initialize(VALUE self)
{
    return self;
}

Public Instance Methods

lock → self click to toggle source

Attempts to grab the lock and waits if it isn't available. Raises ThreadError if mutex was locked by the current thread.

 
               VALUE
rb_mutex_lock(VALUE self)
{
    rb_thread_t *th = GET_THREAD();
    rb_mutex_t *mutex;
    GetMutexPtr(self, mutex);

    /* When running trap handler */
    if (!FL_TEST_RAW(self, MUTEX_ALLOW_TRAP) &&
        th->ec->interrupt_mask & TRAP_INTERRUPT_MASK) {
        rb_raise(rb_eThreadError, "can't be called from trap context");
    }

    if (rb_mutex_trylock(self) == Qfalse) {
        struct sync_waiter w;

        if (mutex->th == th) {
            rb_raise(rb_eThreadError, "deadlock; recursive locking");
        }

        w.th = th;

        while (mutex->th != th) {
            enum rb_thread_status prev_status = th->status;
            struct timeval *timeout = 0;
            struct timeval tv = { 0, 100000 }; /* 100ms */

            th->status = THREAD_STOPPED_FOREVER;
            th->locking_mutex = self;
            th->vm->sleeper++;
            /*
             * Carefully! while some contended threads are in native_sleep(),
             * vm->sleeper is unstable value. we have to avoid both deadlock
             * and busy loop.
             */
            if ((vm_living_thread_num(th->vm) == th->vm->sleeper) &&
                !patrol_thread) {
                timeout = &tv;
                patrol_thread = th;
            }

            list_add_tail(&mutex->waitq, &w.node);
            native_sleep(th, timeout); /* release GVL */
            list_del(&w.node);
            if (!mutex->th) {
                mutex->th = th;
            }

            if (patrol_thread == th)
                patrol_thread = NULL;

            th->locking_mutex = Qfalse;
            if (mutex->th && timeout && !RUBY_VM_INTERRUPTED(th->ec)) {
                rb_check_deadlock(th->vm);
            }
            if (th->status == THREAD_STOPPED_FOREVER) {
                th->status = prev_status;
            }
            th->vm->sleeper--;

            if (mutex->th == th) mutex_locked(th, self);

            RUBY_VM_CHECK_INTS_BLOCKING(th->ec);
        }
    }
    return self;
}

locked? → true or false click to toggle source

Returns true if this lock is currently held by some thread.

 
               VALUE
rb_mutex_locked_p(VALUE self)
{
    rb_mutex_t *mutex;
    GetMutexPtr(self, mutex);
    return mutex->th ? Qtrue : Qfalse;
}

owned? → true or false click to toggle source

Returns true if this lock is currently held by current thread.

 
               VALUE
rb_mutex_owned_p(VALUE self)
{
    VALUE owned = Qfalse;
    rb_thread_t *th = GET_THREAD();
    rb_mutex_t *mutex;

    GetMutexPtr(self, mutex);

    if (mutex->th == th)
        owned = Qtrue;

    return owned;
}

sleep(timeout = nil) → number click to toggle source

Releases the lock and sleeps timeout seconds if it is given and non-nil or forever. Raises ThreadError if mutex wasn't locked by the current thread.

When the thread is next woken up, it will attempt to reacquire the lock.

Note that this method can wakeup without explicit Thread#wakeup call. For example, receiving signal and so on.

 
               static VALUE
mutex_sleep(int argc, VALUE *argv, VALUE self)
{
    VALUE timeout;

    rb_scan_args(argc, argv, "01", &timeout);
    return rb_mutex_sleep(self, timeout);
}

synchronize { ... } → result of the block click to toggle source

Obtains a lock, runs the block, and releases the lock when the block completes. See the example under Mutex.

 
               static VALUE
rb_mutex_synchronize_m(VALUE self, VALUE args)
{
    if (!rb_block_given_p()) {
        rb_raise(rb_eThreadError, "must be called with a block");
    }

    return rb_mutex_synchronize(self, rb_yield, Qundef);
}

try_lock → true or false click to toggle source

Attempts to obtain the lock and returns immediately. Returns true if the lock was granted.

 
               VALUE
rb_mutex_trylock(VALUE self)
{
    rb_mutex_t *mutex;
    VALUE locked = Qfalse;
    GetMutexPtr(self, mutex);

    if (mutex->th == 0) {
        rb_thread_t *th = GET_THREAD();
        mutex->th = th;
        locked = Qtrue;

        mutex_locked(th, self);
    }

    return locked;
}

unlock → self click to toggle source

Releases the lock. Raises ThreadError if mutex wasn't locked by the current thread.

 
               VALUE
rb_mutex_unlock(VALUE self)
{
    const char *err;
    rb_mutex_t *mutex;
    GetMutexPtr(self, mutex);

    err = rb_mutex_unlock_th(mutex, GET_THREAD());
    if (err) rb_raise(rb_eThreadError, "%s", err);

    return self;
}