#ifndef _PREAD_WRITE_LOCK_H_
#define _PREAD_WRITE_LOCK_H_  

#include "usg_common.h"
#include "psem.h"
class PReadWriteLock {
private:
	unsigned int readCount = 0;
  sem_t countMutex;
  sem_t writeMutex;


public:
	PReadWriteLock() {
		if (sem_init(&countMutex, 1, 1) == -1)
    	err_exit(errno, "PReadWriteLock sem_init");

   	if (sem_init(&writeMutex, 1, 1) == -1)
    	err_exit(errno, "PReadWriteLock sem_init");
	}

	void lockRead() {
		//readCount是共享变量，所以需要实现一个锁来控制读写  
 //synchronized(PReadWriteLock.class){}  
	  psem_wait(&countMutex);
    //只有是第一个读者，才将写锁加锁。其他的读者都是进行下一步  
    if(readCount == 0){ 
    	psem_wait(&writeMutex); 
       
    }  
    ++readCount;  
    psem_post(&countMutex);  
	}


	void unlockRead(){  
       
    psem_wait(&countMutex);  
    readCount--;  
    //只有当读者都读完了，才会进行写操作  
    if(readCount == 0){  
      psem_post(&writeMutex);   
    }
    psem_post(&countMutex);  
  } 


  void lockWrite(){
  	psem_wait(&writeMutex);    
  }  

  void unlockWrite(){
  	psem_post(&writeMutex);    
  }   
};

#endif