The Microsoft. Win32. API provides 4 functions for dealing with
waitable timer objects, providing very high resolution (100 nSec.) timer
capabilities for applications.

The CWaitableTimer is a wrapper class for the Microsoft. Win32.
API waitable timer objects. The class is intended to be extended and
accessed by derivative classes.

The class constructor establishes the timer and default properties.
There are numerous methods for setting and accessing the timer’s
properties and 2 methods used for starting and stopping the timer.

This class does not directly implement the callback function features.
If it is desired, this functionality should be added in the derivative
class. The base class sets a waitable timer event and waits for the
event to be reset via a wait complete or reset of the timer.

The CWaitableTimer class can be extended
(sub-classed) to provide access to specific structures and values, and to
enhace its capabilities. Refer to the Microsoft Platform
SDK: DLLs, Processes, and Threads
documentation from the MSDN

CWaitableTimer contains the following methods,
more completely documented in the download file:

  • CWaitableTimer(CString p_TimerName, bool p_Periodic, LONG p_Period);

    p_TimerName is a string specifying the name of the timer object.
    The name is limited to MAX_PATH characters, and is case sensitive.
    If the string specified in p_TimerName matches the name of
    an existing named timer object, an OpenWaitableTimer operation
    is performed to connect the new CWaitableTimer object to the existing
    timer object. If p_TimerName is not specified, or no match
    to an existing timer object is found, a CreateWaitableTimer
    operation is performed to create a new timer object.

    p_Periodic is set to true to create a
    periodic timer, set to false to create a
    manual reset timer.

    p_Period is the timer period in mSec.

    CWaitableTimer establishes the timer object and default
    properties. The timer HANDLE is allocated but the timer is not
    started (refer to Start).

  • bool Start(void);

    Start activates the waitable timer using the current values.
    When the due time arrives, the timer is signaled.

  • bool Stop(void);

    The timer is stopped. The timer handle and settings remain in tact.

  • void Period(LONG p_Period);

    p_Period – the period (timeout value) of the counter, in mSec.

    Specifies the period of the timer, in milliseconds. If p_Period
    is zero, the timer is signaled once. If p_Period is greater
    than zero, the timer is periodic (automatically reactivates
    each time the period elapses, until the timer is canceled).

  • void Expires(__int64 p_Expires);
    void Expires(__int64 p_Expires, bool p_Relative, int p_BaseTime);

    p_Expires is the timer expiration count. Specifies when
    the state of the timer is to be set to signaled, in 100 nanosecond
    intervals. The format is the FILETIME structure,
    a 64-bit value representing the number of 100-nanosecond
    intervals since January 1, 1601.

    Set p_Relative true to indicate a count relative to the
    current system time, false to indicates an absolute (UTC)

    For relative timers, p_BaseTime specifies the format of
    the value in p_Expires.


    Set the timer expiration count. Form 1 sets the timer expiration count
    in 100 nSec increments (64-bits). Form 2 allows specification of a base
    time to apply to the value in p_Expires, signifying (100)
    nanoseconds, microseconds, milliseconds,
    seconds, minutes or hours.

  • HANDLE TimerHandle(void);

    Returns a handle to the timer.

  • bool Valid(void);

    Returns the setting of the global flag g_valid. g_valid
    is true if the timer has been initialized. It is false if the timer
    has not been initialized, or a fatal error has occurred.

  • DWORD Error(void);

    Returns the value of the last error recorded.

  • int Result(void);

    Return the value in the result field. This field
    contains a value indicating the result of the
    last operation.

Installing and Using the Class

To use this class,

  1. Copy CWaitableTimer.cpp and CWaitableTimer.h
    to the same directory as your project or class libraries;
  2. Include CWaitableTimer.cpp and CWaitableTimer.h in your project;
  3. Add CWaitableTimer.h to any modules which make reference
    to CWaitableTimer
    or one of its’ methods or variables.
    This will normally take the form of

      #include "CWaitableTimer.h"

    in the header files in which the
    CWaitableTimer object
    is declared;

  4. Create and initialize a timer object;
  5. Start the timer;
  6. Process timer events and wait for the timer to expire.
    Waitable timers can be used with any of the
    four types of wait functions: single-object,
    multiple-object, alertable or registered; and
  7. Stop the timer and release the timer object.

Creating a Single Event, Manual Reset Timer

This example shows one way to create a single shot (manual reset) 5
second timer object. This example will use the
WaitForSingleObject function to synchronize with the timer:

int l_TimeValue = 5 * 1000;  // 5000 mSec = 5 sec
CWaitableTimer * g_pTimer;

//		Attempt to get a timer object
g_pTimer = new CWaitableTimer("MyTimer",    // Timer name
false,        // true = periodic
l_TimeValue); // 5 seconds
if (! g_pTimer->Valid())
//    Unable to get a timer handle.
//    Handle error and delete the timer object
delete g_pTimer;

//         Start timer, if possible
if (! g_pTimer->Start())
//        Unable to start Timer
//        Handle error and delete the timer object
delete g_pTimer;

//    Wait for timer interrupt(s)
while (true)
if (WaitForSingleObject(g_pTimer->TimerHandle(),
2 * l_TimeValue) != WAIT_OBJECT_0)
//    Timer didn't respond in the required time
//    Handle error and delete the timer object
//    Process timer interrupt
//    For a single shot (Manual reset)
//    timer, exit the loop

//        Stop timer, if possible

delete g_pTimer;

Sample Application

A VisualC++ 6 workspace containing a sample project is included
with the CWaitableTimer download:


    A Windows console program which demonstrates single and
    multiple event timers.


Download CWaitableTimer class – 39 Kb

Download demo projects – 91 Kb

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