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Win32 Synchronization

Win32 Synchronization. CS470 -- Spring 2002. Overview. Kernel Synchronization - Spinlocks Executive Synchronization - Dispatcher Objects Wait Operations Dispatcher Objects - Events, Semaphores, Mutex objects, Waitable Timers. Kernel Synchronization.

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Win32 Synchronization

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  1. Win32 Synchronization CS470 -- Spring 2002

  2. Overview • Kernel Synchronization - Spinlocks • Executive Synchronization - Dispatcher Objects • Wait Operations • Dispatcher Objects - Events, Semaphores, Mutex objects, Waitable Timers

  3. Kernel Synchronization • Manipulating IRQL selectively disables interrupts -- controls context switching • IRQL only works on a single processor • Spinlocks, based e.g. on test & set instructions, work for multiprocessors • Busy-wait wastes cycles - so holder is never preempted, is not allowed to cause page faults, do system calls, cause interrupts or exceptions, etc.

  4. Executive Synchronization • Executive also uses spinlocks • Also uses dispatcher objects • Dispatcher objects also available to user programs - Win32 calls include WaitForSingleObject and WaitForMultipleObjects applicable to processes, threads, events, semaphores, mutex objects, waitable timers, file objects, etc.

  5. Thread Dispatcher States Create Destroy Reinitialize Initialized-0 Ready to run All Set Ready-1 Terminated-4 Waiting-5 Get resource Need Resource Wait for Object Transition-6 Done Select Preempt Running-2 Preempt Standby-3 Context-Switch

  6. Dispatcher Database Dispatchers Thread 1 KWAIT_BLOCKS Process 5 Thread 2 Timer 0 Thread 3 Thread 4

  7. Wait Operations (1 of 2) • DWORD WaitForSingleObjectEx( HANDLE hHandle, DWORD dwMilliseconds BOOL bAlertable); • Returns WAIT_OBJECT_0 (zero), WAIT_TIMEOUT, WAIT_FAILED, or WAIT_IO_COMPLETION • If object non-signaled, block thread. When signaled, one or more threads are readied - can change state of object.

  8. Wait Operations (2 of 2) • DWORD WaitForMultipleObjectsEx( DWORD nCount, CONST HANDLE *lpHandles BOOL fWaitAll, DWORD dwMilliseconds, BOOL bAlertable); • WAIT_OBJECT_0 to WAIT_OBJECT_n-1 to specify first signaled handle (if fWaitAll if false).

  9. Events (1 of 2) • HANDLE CreateEvent ( LPSECURITY_ATTRIBUTES lpSA, BOOL bManualReset, BOOL bInitialState, LPCTSTR lpName); • HANDLE OpenEvent ( DWORD dwDesiredAccess, BOOL bInheritHandle, LPCTSTR lpName);

  10. Events (2 of 2) • BOOL SetEvent ( HANDLE hEvent ); • BOOL ResetEvent ( HANDLE hEvent ); • BOOL PulseEvent ( HANDLE hEvent ); • manual-reset versus auto-reset events • setting versus pulsing • CloseHandle used to close events

  11. Mutual Exclusion (Events) • Initialization: hEvent = CreateEvent( NULL, FALSE, TRUE, NULL); • Critical Section Entry: WaitForSingleObjectEx( hEvent, INFINITE, FALSE); • Critical Section Exit: SetEvent(hEvent);

  12. Semaphores (1 of 2) • HANDLE CreateSemaphore ( LPSECURITY_ATTRIBUTES lpSA, LONG lInitialCount, LONG lMaximumCount, LPCTSTR lpName ); • HANDLE OpenSemaphore ( DWORD dwDesiredAccess, BOOL bInheritHandle, LPCTSTR lpName );

  13. Semaphores (2 of 2) • BOOL ReleaseSemaphore ( HANDLE hSemaphore, LONG lReleaseCount, LPLONG lpPreviousCount ); • lReleaseCount is 1 to release semaphore or larger in order to set an initial value. • CloseHandle to close semaphore handle

  14. Mutual Exclusion (Semaphore) • Initialization: hSemaphore = CreateSemaphore( NULL, 1, 1, NULL); • Critical Section Entry: WaitForSingleObjectEx( hSemaphore, INFINITE, FALSE); • Critical Section Exit: ReleaseSemaphore( hSemaphore, 1, &previous);

  15. Mutex Objects (1 of 2) • HANDLE CreateMutex ( LPSECURITY_ATTRIBUTES lpSA, BOOL bInitialOwner, LPCTSTR lpName ); • HANDLE OpenMutex ( DWORD dwDesiredAccess, BOOL bInheritHandle, LPCTSTR lpName );

  16. Mutex Objects (2 of 2) • BOOL ReleaseMutex ( HANDLE hMutex ); • Owner can make additional calls Wait calls without blocking, but must call ReleaseMutex the same number of times. • Use CloseHandle to close mutex handles.

  17. Mutual Exclusion (Mutex) • Initialization: hMutex = CreateMutex( NULL, FALSE, NULL); • Critical Section Entry: WaitForSingleObject( hMutex, INFINITE, FALSE); • Critical Section Exit: ReleaseMutex(hMutex);

  18. Waitable Timers (1 of 2) • HANDLE CreateWaitableTimer ( LPSECURITY_ATTRIBUTES lpSA, BOOL bManualReset, LPCTSTR lpTimerName ); • HANDLE OpenWaitableTimer ( DWORD dwDesiredAccess, BOOL bInheritHandle, LPCTSTR lpTimerName );

  19. Waitable Timers (2 of 2) • BOOL SetWaitableTimer ( HANDLE hTimer, const LARGE_INTEGER *pDueTime, LONG lPeriod, PTIMERAPCROUTINE pfnCompletionRoutine, LPVOID lpArgToCompletionRoutine, BOOL fResume ); BOOL CancelWaitableTimer (HANDLE);

  20. Mutual Exclusion (Timer) 1 of 2 • Initialization: LARGE_INTEGER dueTime = {-1, -1}; hTimer = (HANDLE) CreateWaitableTimer( NULL, FALSE, NULL); SetWaitableTimer( hTimer, &dueTime, 0, NULL, NULL, FALSE);

  21. Mutual Exclusion (Timer) 2 of 2 • Critical Section Entry: WaitForSingleObjectEx(hTimer, INFINITE, FALSE); • Critical Section Exit: LARGE_INTEGER dueTime = {-1, -1}; SetWaitableTimer(hTimer, &dueTime, 0, NULL, NULL, FALSE);

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