timer.c

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/*-------------------------------------------------------------------------
 *
 * timer.c
 *    Microsoft Windows Win32 Timer Implementation
 *
 *    Limitations of this implementation:
 *
 *    - Does not support interval timer (value->it_interval)
 *    - Only supports ITIMER_REAL
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/backend/port/win32/timer.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
 
/* Communication area for inter-thread communication */
typedef struct timerCA
{
    struct itimerval value;
    HANDLE      event;
    CRITICAL_SECTION crit_sec;
} timerCA;
 
static timerCA timerCommArea;
static HANDLE timerThreadHandle = INVALID_HANDLE_VALUE;
 
 
/* Timer management thread */
static DWORD WINAPI
pg_timer_thread(LPVOID param)
{
    DWORD       waittime;
 
    Assert(param == NULL);
 
    waittime = INFINITE;
 
    for (;;)
    {
        int         r;
 
        r = WaitForSingleObjectEx(timerCommArea.event, waittime, FALSE);
        if (r == WAIT_OBJECT_0)
        {
            /* Event signaled from main thread, change the timer */
            EnterCriticalSection(&timerCommArea.crit_sec);
            if (timerCommArea.value.it_value.tv_sec == 0 &&
                timerCommArea.value.it_value.tv_usec == 0)
                waittime = INFINITE;    /* Cancel the interrupt */
            else
            {
                /* WaitForSingleObjectEx() uses milliseconds, round up */
                waittime = (timerCommArea.value.it_value.tv_usec + 999) / 1000 +
                    timerCommArea.value.it_value.tv_sec * 1000;
            }
            ResetEvent(timerCommArea.event);
            LeaveCriticalSection(&timerCommArea.crit_sec);
        }
        else if (r == WAIT_TIMEOUT)
        {
            /* Timeout expired, signal SIGALRM and turn it off */
            pg_queue_signal(SIGALRM);
            waittime = INFINITE;
        }
        else
        {
            /* Should never happen */
            Assert(false);
        }
    }
 
    return 0;
}
 
/*
 * Win32 setitimer emulation by creating a persistent thread
 * to handle the timer setting and notification upon timeout.
 */
int
setitimer(int which, const struct itimerval *value, struct itimerval *ovalue)
{
    Assert(value != NULL);
    Assert(value->it_interval.tv_sec == 0 && value->it_interval.tv_usec == 0);
    Assert(which == ITIMER_REAL);
 
    if (timerThreadHandle == INVALID_HANDLE_VALUE)
    {
        /* First call in this backend, create event and the timer thread */
        timerCommArea.event = CreateEvent(NULL, TRUE, FALSE, NULL);
        if (timerCommArea.event == NULL)
            ereport(FATAL,
                    (errmsg_internal("could not create timer event: error code %lu",
                                     GetLastError())));
 
        MemSet(&timerCommArea.value, 0, sizeof(struct itimerval));
 
        InitializeCriticalSection(&timerCommArea.crit_sec);
 
        timerThreadHandle = CreateThread(NULL, 0, pg_timer_thread, NULL, 0, NULL);
        if (timerThreadHandle == INVALID_HANDLE_VALUE)
            ereport(FATAL,
                    (errmsg_internal("could not create timer thread: error code %lu",
                                     GetLastError())));
    }
 
    /* Request the timer thread to change settings */
    EnterCriticalSection(&timerCommArea.crit_sec);
    if (ovalue)
        *ovalue = timerCommArea.value;
    timerCommArea.value = *value;
    LeaveCriticalSection(&timerCommArea.crit_sec);
    SetEvent(timerCommArea.event);
 
    return 0;
}