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C++多线程同步之Semaphore(信号量)
原文: https://www.cnblogs.com/lenmom/p/7998969.html
相关函数和头文件//头文件
#include <windows.h>
//创建信号量API
HANDLE WINAPI CreateSemaphore(
_In_opt_ LPSECURITY_ATTRIBUTES lpSemaphoreAttributes,//指向SECURITY_ATTRIBUTES的指针;
_In_ LONG lInitialCount, //信号量对象的初始值;
_In_ LONG lMaximumCount, //信号量对象的最大值,这个值必须大于0;
_In_opt_ LPCTSTR lpName //信号量对象的名称;
);
//等待信号量API
DWORD WINAPI WaitForSingleObject(
_In_ HANDLE hHandle, //信号量对象句柄
_In_ DWORD dwMilliseconds //等待信号量时间,INFINET代表永久等待;
);
返回值:
WAIT_ABANDONED(0x00000080L) 表示拥有信号量的线程再终止前未释放该信号量;
WAIT_OBJECT_0(0x00000000L) 表示等到了信号量;
WAIT_TIMEOUT(0x00000102L) 表示等待超时;
WAIT_FAILED((DWORD)0xFFFFFFFF) 表示该函数执行失败,用GetLastError()得到错误码;
//释放信号量句柄
BOOL WINAPI ReleaseSemaphore(
_In_ HANDLE hSemaphore, //信号量对象句柄;
_In_ LONG lReleaseCount, //信号量释放的值,必须大于0;
_Out_opt_ LPLONG lpPreviousCount //前一次信号量值的指针,不需要可置为空;
);
返回值:成功返回非0;
Win32平台下源码
#include <iostream>
#include <windows.h>
using namespace std;
HANDLE g_hSemaphore = NULL; //声明信号量变量
unsigned long WINAPI Fun(LPVOID lpParamter)
{
int iRunTime = 0;
//执行100次跳出
while(++iRunTime<100)
{
WaitForSingleObject(g_hSemaphore, INFINITE); //信号量值-1
cout << "Fun() is running!"<<endl;
ReleaseSemaphore(g_hSemaphore, 1, NULL); //信号量值+1
Sleep(10);
}
ExitThread(-1);
}
int main()
{
//创建信号量对象
g_hSemaphore = CreateSemaphore(NULL //信号量的安全特性
, 1 //设置信号量的初始计数。可设置零到最大值之间的一个值
, 1 //设置信号量的最大计数
, NULL //指定信号量对象的名称
);
if(NULL == g_hSemaphore)
{
cout << "create hSemaphore failed! error_code:"<<GetLastError()<<endl;
return 0;
}
int iRunTime = 0;
unsigned long ulThreadId = 0;
//创建一个子线程
HANDLE hThread = CreateThread(NULL, 0, Fun, NULL, 0, &ulThreadId);
//执行100次跳出
while(++iRunTime<100)
{
WaitForSingleObject(g_hSemaphore, INFINITE); //信号量值-1
cout << "main() is running, Thread id is " << ulThreadId <<endl;
ReleaseSemaphore(g_hSemaphore, 1, NULL); //信号量值+1
Sleep(10);
}
system("pause");
return 0;
}
执行结果:
可见未对屏幕资源产生“争夺”的情况,达到线程同步的目的。
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