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Example: Using a Waitable Timer
Program 14-3 shows how to use a waitable timer to signal the user periodically.
Program 14-3. TimeBeep.c: A Periodic Signal
/* Chapter 14. TimeBeep.c. Periodic alarm.
/* Usage: TimeBeep period (in milliseconds). */
#include "EvryThng.h"
static BOOL WINAPI Handler (DWORD CntrlEvent);
static VOID APIENTRY Beeper (LPVOID, DWORD, DWORD);
volatile static BOOL Exit = FALSE;
HANDLE hTimer;
int _tmain (int argc, LPTSTR argv [])
{
DWORD Count = 0, Period;
LARGE_INTEGER DueTime;
/* Catch Ctrl-c to terminate operation. See Chapter 4. */
SetConsoleCtrlHandler (Handler, TRUE);
Period = _ttoi (argv [1]) * 1000;
DueTime.QuadPart = -(LONGLONG)Period * 10000;
/* Due time is negative for first time-out relative to
current time. Period is in ms (10^-3 sec) whereas
the due time is in 100 ns (10^-7 sec) units to be
consistent with a FILETIME. */
hTimer = CreateWaitableTimer (NULL,
FALSE /* "Synchronization timer" */, NULL);
SetWaitableTimer (hTimer, &DueTime, Period,
Beeper, &Count, TRUE);
while (!Exit) {
_tprintf (_T ("Count = %d\n"), Count);
/* Count is increased in the timer routine. */
/* Enter an alertable wait state. */
SleepEx (INFINITE, TRUE);
}
_tprintf (_T ("Shut down. Count = %d"), Count);
CancelWaitableTimer (hTimer);
CloseHandle (hTimer);
return 0;
}
static VOID APIENTRY Beeper (LPVOID lpCount,
DWORD dwTimerLowValue, DWORD dwTimerHighValue)
{
*(LPDWORD) lpCount = *(LPDWORD) lpCount + 1;
_tprintf (_T ("Perform beep number: %d\n"), *(LPDWORD) lpCount);
Beep (1000 /* Frequency. */, 250 /* Duration (ms). */);
return;
}
BOOL WINAPI Handler (DWORD CntrlEvent)
{
Exit = TRUE;
_tprintf (_T ("Shutting Down\n"));
return TRUE;
}
Comments on the Waitable Timer Example
There are four combinations based on timer type and whether you wait on the handle or use a completion routine.
