Threads in other processes can open a handle to an existing timer by specifying its name in a call to the OpenWaitableTimer function. The creating thread can specify a name for the timer object. The creating thread specifies whether the timer is a manual-reset timer or a synchronization timer. A timer of either type can also be a periodic timer.Ī thread uses the CreateWaitableTimer or CreateWaitableTimerEx function to create a timer object. There are two types of waitable timers that can be created: manual-reset and synchronization. Waitable Timer ObjectsĪ waitable timer object is a synchronization object whose state is set to signaled when the specified due time arrives. #Work timer windows code#04 seconds (2000 counts) elapsed while the code executed. If the application calls QueryPerformanceCounter immediately before and immediately after the section of code to be timed, the counter values might be 1500 counts and 3500 counts, respectively. For example, suppose that QueryPerformanceFrequency indicates that the frequency of the high-resolution performance counter is 50,000 counts per second. By calling this function at the beginning and end of a section of code, an application essentially uses the counter as a high-resolution timer. The QueryPerformanceCounter function retrieves the current value of the high-resolution performance counter. On some processors, for example, the count might be the cycle rate of the processor clock. The value of the count is processor dependent. If a high-resolution performance counter exists on the system, you can use the QueryPerformanceFrequency function to express the frequency, in counts per second. Some systems include a high-resolution performance counter that provides high-resolution elapsed times. High-Resolution TimerĪ counter is a general term used in programming to refer to an incrementing variable. For more information, see Waitable Timer Objects. If you need to be notified when a timer elapses, use a waitable timer. Therefore, you need to dispatch messages in the calling thread, even when you use TimerProc instead of processing WM_TIMER. If you specify a TimerProc callback function, the default window procedure calls the callback function when it processes WM_TIMER. If no window handle is specified in the call to SetTimer, the application that created the timer must monitor its message queue for WM_TIMER messages and dispatch them to the appropriate window. Whenever the time-out value for the timer elapses, the system posts a WM_TIMER message to the window associated with the timer. If you specify a window handle in the call to SetTimer, the application associates the timer with that window. The first parameter of a WM_TIMER message contains the identifier of the timer that posted the message. When creating a timer, an application can either specify an identifier or have the system create a unique value. To use system resources efficiently, applications should destroy timers that are no longer necessary.Įach timer has a unique identifier. An application can change a timer's time-out value by using SetTimer and can destroy a timer by using the KillTimer function. A new timer starts timing the interval as soon as it is created. This topic includes the following sections.Īpplications create timers by using the SetTimer function. Because a timer's accuracy depends on the system clock rate and how often the application retrieves messages from the message queue, the time-out value is only approximate. Each time the specified interval (or time-out value) for a timer elapses, the system notifies the window associated with the timer. An application uses a timer to schedule an event for a window after a specified time has elapsed. #Work timer windows how to#This topic describes how to create, identify, set, and delete timers.
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