用std::atomic實現簡單的讀寫鎖

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/hpp file#include <atomic>#ifndef ns_mutex_header_#define ns_mutex_header_namespace ns{	struct mutex	{		mutex();			void req(int is_read)volatile;		void unreq(int is_read)volatile;		inline void req_read(){req(1);}		inline void req_write(){req(0);}		inline void unreq_read(){unreq(1);}		inline void unreq_write(){unreq(0);}		struct enter		{		   enter(mutex* ths_,int is_read_=1):ths(ths_),is_read(is_read_){ths->req(is_read);}		   ~enter(){ths->unreq(is_read);}		 private:			mutex* ths;			int is_read;		};	private:		std::atomic<uint32_t> read_flags,write_flags;	};};#endif//ns_mutex_header_#include "ns_mutex.h"#include <unistd.h>namespace ns{	mutex::mutex()	{		write_flags=read_flags=0;	}	void mutex::req(int is_read)volatile	{		if(is_read)		{		again_read:					while(write_flags!=0)usleep(100);						++read_flags;			if(write_flags!=0)			{				--read_flags;				goto again_read;			}		}		else		{			uint32_t e(0);			while(!write_flags.compare_exchange_strong(0,1,e,1))e=0,usleep(100);			while(read_flags!=0)usleep(100);					}	}	void mutex::unreq(int is_read)volatile	{		if(is_read)--read_flags;		else --write_flags;	}};