Using Named Objects
The following examples illustrate the use of object names by creating and
opening named objects.
Mutex
The first process uses the
CreateMutex function to create the mutex object. Note that the function succeeds even if
there is an existing object with the same name.
// One process creates the mutex object.
HANDLE hMutex;
DWORD dwErr;
hMutex = CreateMutex(
NULL, // no security descriptor
FALSE, // mutex not owned
"NameOfMutexObject"); // object name
if (hMutex == NULL)
printf("CreateMutex error: %d\n", GetLastError() );
else
if ( GetLastError() == ERROR_ALREADY_EXISTS )
printf("CreateMutex opened existing mutex\n");
else
printf("CreateMutex created new mutex\n");
The second process uses the
OpenMutex function to open a handle of the existing mutex. This function fails if a
mutex object with the specified name does not exist. The access parameter requests
full access to the mutex object, which is necessary for the handle to be used
in any of the wait functions.
// Another process opens a handle of the existing mutex.
HANDLE hMutex;
hMutex = OpenMutex(
MUTEX_ALL_ACCESS, // request full access
FALSE, // handle not inheritable
"NameOfMutexObject"); // object name
if (hMutex == NULL)
printf("OpenMutex error: %d\n", GetLastError() );
Semaphore
The following example uses the
CreateSemaphore function to illustrate a named-object creation operation that fails if the
object already exists.
HANDLE CreateNewSemaphore(LPSECURITY_ATTRIBUTES lpsa,
LONG cInitial, LONG cMax, LPTSTR lpszName)
{
HANDLE hSem;
// Create or open a named semaphore.
hSem = CreateSemaphore(
lpsa, // security attributes
cInitial, // initial count
cMax, // maximum count
lpszName); // semaphore name
// Close handle, and return NULL if existing semaphore opened.
if (hSem != NULL && GetLastError() == ERROR_ALREADY_EXISTS)
{
CloseHandle(hSem);
return NULL;
}
// If new semaphore was created, return the handle.
return hSem;
}
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