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#pragma once

//	Semaphore class for asynchronous I/O resourcelocking

class Semaphore {
	
	private:
	
	//	The semaphore is a single element OS queue.  If the element is
	//	in the queue, the resource is unlocked, otherwise it is locked.
	
		QHdr		mQueue;
		QElem		mElement;
		
	public:
	
	//	Locks the semaphore atomically so that no one else can
	//	use the resource
	//		Returns 0 if successful, 1 if in use
	
	inline	int		Lock		(void)	{return ::Dequeue (&mElement, &mQueue);};
	
	//	Unlocks the semaphore atomically, so that others can 
	//	use the resource

	inline	void	Unlock		(void)	{if (!mQueue.qHead) ::Enqueue (&mElement, &mQueue);};
	
	//	Constructs an unlocked semaphore
	
	inline			Semaphore	(void)	{mQueue.qHead = mQueue.qTail = nil; Unlock ();};
	};