[cros] Add RecursiveLock for CrOS implementation.

[cros] Add RecursiveLock for CrOS implementation.


BUG=157348
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=166186

[Dmitry Vyukov, 2012-11-02 09:52:20]

You usually implement recursive mutex as follows. It's much cheaper and faster.

class RecursiveLock {
public:
	RecursiveLock()
		: owner_()
		, recursion_() {
	}

	~RecursiveLock() {
	}

	void Acquire() {
		Atomic32 me = PlatformThread::CurrentId();
		if (me != NoBarrier_Load(&owner_) {
			mtx_.Lock();
			assert(recursion_ == 0);
			assert(owner_ == 0);
			NoBarrier_Store(&owner_, me);
		}
		recursion_++;
	}

	void Release() {
		assert(&owner_ == PlatformThread::CurrentId());
		assert(recursion_ > 0);
		if (!--recursion_) {
			NoBarrier_Store(&owner_, 0);
			mtx_.Unlock();
		}
	}

private:
	Lock mtx_;
	Atomic32 owner_;
	int recursion_;
};


You code looks correct as well. You do not need volatile for lock_count_, it's
confusing.

[Ivan Korotkov, 2012-11-02 11:00:49]

Thanks! I like your implementation more, updated.

Adding Roger for OWNERS approval.

[Dmitry Vyukov, 2012-11-02 11:51:12]

LGTM

[Roger Tawa OOO till Jul 10th, 2012-11-02 20:21:22]

lgtm

[commit-bot: I haz the power, 2012-11-03 13:21:05]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ivankr@chromium.org/11361057/6002

[commit-bot: I haz the power, 2012-11-03 16:41:17]

Retried try job too often for step(s) content_browsertests

[commit-bot: I haz the power, 2012-11-06 08:29:57]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ivankr@chromium.org/11361057/7006

[commit-bot: I haz the power, 2012-11-06 10:39:03]

Change committed as 166186