CppCMS/atomic_counter.h

#ifndef CPPCMS_ATOMIC_COUNT_H
#define CPPCMS_ATOMIC_COUNT_H

#include "defs.h"
#if !defined(CPPCMS_WIN32)
#	include <pthread.h>
#endif


namespace cppcms {

	///
	/// \brief Atomic counter is a class that allows perform counting in thread safe way.
	///
	/// It is mainly used for reference counting. Under Windows it uses Interlocked API, under
	/// other platforms it used built-in atomic operations or fails back to pthreads locking implementation.
	///
	/// Notes: 
	///
	/// -  This counter is not safe for use in process shared memory, when pthreads fall-back is used
	/// -  Under POSIX platform pthread_mutex_t is always present in order to make sure that we can implement
	///    or remove pthread fall-back at any point not affecting ABI
	///

	class CPPCMS_API atomic_counter {
	public:
		///
		/// Create a counter with initial value v
		///
    		explicit atomic_counter( long v );
		~atomic_counter();

		///
		/// Increment and return the result after increment atomically
		///
    		long operator++()
		{
			return inc();
		}
		///
		/// Decrement and return the result after decrement atomically
		///
    		long operator--()
		{
			return dec();
		}
		///
		/// Return current value - atomically
		///
		operator long() const 
		{
			return get();
		}
	private:
		long inc();
		long dec();
		long get() const;

		atomic_counter(atomic_counter const &);
		atomic_counter & operator=(atomic_counter const &);

		mutable long value_;
		#if !defined(CPPCMS_WIN32)
		// Is actually used for platforms without lock
		// it would not be used when atomic operations
		// available
		mutable pthread_mutex_t mutex_;
		#endif
	};

} // cppcms

#endif