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Using Mutex Objects

You can use a mutex object to protect a shared resource from simultaneous access by multiple threads or processes. Each thread must wait for ownership of the mutex before it can execute the code that accesses the shared resource. For example, if several threads share access to a database, the threads can use a mutex object to permit only one thread at a time to write to the database.

In the following example, a process uses the CreateMutex function to create a named mutex object or open a handle to an existing mutex object.

HANDLE hMutex;
// Create a mutex with no initial owner.
hMutex = CreateMutex(
NULL,                       // no security attributes
FALSE,                      // initially not owned
"MutexToProtectDatabase");  // name of mutex
if (hMutex == NULL)
{
// Check for error.
}

When a thread of this process writes to the database, as in the next example, it first requests ownership of the mutex. If it gets ownership, the thread writes to the database and then releases its ownership.

The example uses structured exception-handling syntax to ensure that the thread properly releases the mutex object. The __finally block of code is executed no matter how the __try block terminates (unless the __try block includes a call to the TerminateThread function). This prevents the mutex object from being abandoned inadvertently.

BOOL FunctionToWriteToDatabase(HANDLE hMutex)
{
DWORD dwWaitResult;
// Request ownership of mutex.
dwWaitResult = WaitForSingleObject(
hMutex,   // handle to mutex
5000L);   // five-second time-out interval
switch (dwWaitResult)
{
// The thread got mutex ownership.
case WAIT_OBJECT_0:
__try {
// Write to the database.
}
__finally {
// Release ownership of the mutex object.
if (! ReleaseMutex(hMutex)) {
// Deal with error.
}
break;
}
// Cannot get mutex ownership due to time-out.
case WAIT_TIMEOUT:
return FALSE;
// Got ownership of the abandoned mutex object.
case WAIT_ABANDONED:
return FALSE;
}
return TRUE;
}
posted on 2007-08-17 16:13 jinfeng_wang 阅读(564) 评论(2)  编辑  收藏 所属分类: cppZZ

评论

# re: Using Mutex Objects (zz) 2007-11-15 18:24 ZHANG/WEI
都是英文,有些看不清楚哦
能不能换成中文啊,这样好像好点,对吗?  回复  更多评论
  

# re: Using Mutex Objects (zz) 2008-01-19 16:45 情深深鲜花礼品网
英文的才原版。  回复  更多评论
  


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