读写锁 SRWLOCK

读写锁在对资源进行保护的同时，还能区分想要读取资源值的线程（读取者线程）和想要更新资源的线程（写入者线程）。

对于读取者线程，读写锁会允许他们并发的执行。当有写入者线程在占有资源时，读写锁会让其它写入者线程和读取者线程等待。

用读写锁来解决读者写者问题会使代码非常清晰和简洁。

typedef RTL_SRWLOCK SRWLOCK, *PSRWLOCK;
typedef struct _RTL_SRWLOCK {                            
    PVOID Ptr;                                       
} RTL_SRWLOCK, *PRTL_SRWLOCK; 
 
// 初始化读写锁
WINBASEAPI
VOID
WINAPI
InitializeSRWLock (
     __out PSRWLOCK SRWLock
 );
 
// 独占式访问
WINBASEAPI
VOID
WINAPI
AcquireSRWLockExclusive (
     __inout PSRWLOCK SRWLock
 );
 
// 共享式访问
WINBASEAPI
VOID
WINAPI
AcquireSRWLockShared (
     __inout PSRWLOCK SRWLock
 );
 
// 独占式释放
WINBASEAPI
VOID
WINAPI
ReleaseSRWLockExclusive (
     __inout PSRWLOCK SRWLock
 );
 
// 共享式释放
WINBASEAPI
VOID
WINAPI
ReleaseSRWLockShared (
     __inout PSRWLOCK SRWLock
 );

// SRWLock.cpp : 定义控制台应用程序的入口点。
//
 
#include "stdafx.h"
#include <iostream>  
#include <windows.h>  
#include <process.h>  
 
using namespace std;
unsigned int __stdcall ReadThread(PVOID ParameterData);
unsigned int __stdcall WriteThread(PVOID ParameterData);
 
const int NUM = 30, READER_SIZE = 10;
HANDLE ThreadRead[NUM],  ThreadWrite[NUM];
SRWLOCK __SRWLock;
 
int main() 
{
    InitializeSRWLock(&__SRWLock);
 
    int i = 0;
    for (; i<NUM; i++) {
        ThreadRead[i] = (HANDLE)_beginthreadex(NULL, 0, ReadThread, NULL, 0, NULL);
        ThreadWrite[i] = (HANDLE)_beginthreadex(NULL, 0, WriteThread, NULL, 0, NULL);
    }
 
    WaitForMultipleObjects(NUM, ThreadRead, TRUE, INFINITE);
    WaitForMultipleObjects(NUM, ThreadWrite, TRUE, INFINITE);
 
    cout << "运行完毕" << endl;
    getchar();
    return 0;
}
 
unsigned int __stdcall ReadThread(PVOID ParameterData) {
    AcquireSRWLockShared(&__SRWLock);
 
    cout << "ID" << GetCurrentThreadId() << "   Read Thread Begin!" << endl;
    Sleep(100);
    cout << "ID" << GetCurrentThreadId() << "   Read Thread Terminate!" << endl;
 
    ReleaseSRWLockShared(&__SRWLock);
    return 0;
}
 
unsigned int __stdcall WriteThread(PVOID ParameterData) {
    AcquireSRWLockExclusive(&__SRWLock);
    cout << "ID" << GetCurrentThreadId() << "       WRITE Thread Begin~~~~~~~~~~" << endl;
    Sleep(200);
    cout << "ID" << GetCurrentThreadId() << "     WRITE Thread Terminate~~~~~~" << endl;
    ReleaseSRWLockExclusive(&__SRWLock);
    return 0;
}