Class: Mutex

Inherits:

Object

• Object
• Mutex

Defined in:

thread.c,
thread.c

Overview

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

Example:

require 'thread'
semaphore = Mutex.new

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

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

Instance Method Summary

• #new ⇒ Object constructor

  Creates a new Mutex.

• #lock ⇒ self

  Attempts to grab the lock and waits if it isn’t available.

• #locked? ⇒ Boolean

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

• #owned? ⇒ Boolean

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

• #sleep(timeout = nil) ⇒ Numeric

  Releases the lock and sleeps timeout seconds if it is given and non-nil or forever.

• #synchronize { ... } ⇒ Object

  Obtains a lock, runs the block, and releases the lock when the block completes.

• #try_lock ⇒ Boolean

  Attempts to obtain the lock and returns immediately.

• #unlock ⇒ self

  Releases the lock.

Constructor Details

#new ⇒ Object

Creates a new Mutex

# File 'thread.c', line 4173

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

Instance Method Details

#lock ⇒ self

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

Returns:

• (self)

# File 'thread.c', line 4301

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

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

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

	while (mutex->th != th) {
	    int interrupted;
	    enum rb_thread_status prev_status = th->status;
	    volatile int timeout_ms = 0;
	    struct rb_unblock_callback oldubf;

	    set_unblock_function(th, lock_interrupt, mutex, &oldubf, FALSE);
	    th->status = THREAD_STOPPED_FOREVER;
	    th->locking_mutex = self;

	    native_mutex_lock(&mutex->lock);
	    th->vm->sleeper++;
	    /*
	     * Carefully! while some contended threads are in lock_func(),
	     * vm->sleepr 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_ms = 100;
		patrol_thread = th;
	    }

	    GVL_UNLOCK_BEGIN();
	    interrupted = lock_func(th, mutex, (int)timeout_ms);
	    native_mutex_unlock(&mutex->lock);
	    GVL_UNLOCK_END();

	    if (patrol_thread == th)
		patrol_thread = NULL;

	    reset_unblock_function(th, &oldubf);

	    th->locking_mutex = Qfalse;
	    if (mutex->th && interrupted == 2) {
		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);

	    if (interrupted) {
		RUBY_VM_CHECK_INTS_BLOCKING(th);
	    }
	}
    }
    return self;
}

#locked? ⇒ Boolean

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

Returns:

• (Boolean)

Returns:

• (Boolean)

# File 'thread.c', line 4191

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

#owned? ⇒ Boolean

Returns true if this lock is currently held by current thread. This API is experimental, and subject to change.

Returns:

• (Boolean)

Returns:

• (Boolean)

# File 'thread.c', line 4377

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) ⇒ Numeric

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.

Returns:

• (Numeric)

# File 'thread.c', line 4530

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 { ... } ⇒ Object

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

Yields:

# File 'thread.c', line 4561

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 ⇒ Boolean

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

Returns:

• (Boolean)

# File 'thread.c', line 4218

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

    native_mutex_lock(&mutex->lock);
    if (mutex->th == 0) {
	mutex->th = GET_THREAD();
	locked = Qtrue;

	mutex_locked(GET_THREAD(), self);
    }
    native_mutex_unlock(&mutex->lock);

    return locked;
}

#unlock ⇒ self

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

Returns:

• (self)

# File 'thread.c', line 4432

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;
}