gettimeofday.c

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/*
 * gettimeofday.c
 *    Win32 gettimeofday() replacement
 *
 * src/port/gettimeofday.c
 *
 * Copyright (c) 2003 SRA, Inc.
 * Copyright (c) 2003 SKC, Inc.
 *
 * Permission to use, copy, modify, and distribute this software and
 * its documentation for any purpose, without fee, and without a
 * written agreement is hereby granted, provided that the above
 * copyright notice and this paragraph and the following two
 * paragraphs appear in all copies.
 *
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE TO ANY PARTY FOR DIRECT,
 * INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
 * LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
 * DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * THE AUTHOR SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS
 * IS" BASIS, AND THE AUTHOR HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE,
 * SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 */

#include "c.h"

#include <sys/time.h>

/* FILETIME of Jan 1 1970 00:00:00, the PostgreSQL epoch */
static const unsigned __int64 epoch = UINT64CONST(116444736000000000);

/*
 * FILETIME represents the number of 100-nanosecond intervals since
 * January 1, 1601 (UTC).
 */
#define FILETIME_UNITS_PER_SEC  10000000L
#define FILETIME_UNITS_PER_USEC 10

/*
 * Both GetSystemTimeAsFileTime and GetSystemTimePreciseAsFileTime share a
 * signature, so we can just store a pointer to whichever we find. This
 * is the pointer's type.
 */
typedef VOID(WINAPI * PgGetSystemTimeFn) (LPFILETIME);

/* One-time initializer function, must match that signature. */
static void WINAPI init_gettimeofday(LPFILETIME lpSystemTimeAsFileTime);

/* Storage for the function we pick at runtime */
static PgGetSystemTimeFn pg_get_system_time = &init_gettimeofday;

/*
 * One time initializer.  Determine whether GetSystemTimePreciseAsFileTime
 * is available and if so, plan to use it; if not, fall back to
 * GetSystemTimeAsFileTime.
 */
static void WINAPI
init_gettimeofday(LPFILETIME lpSystemTimeAsFileTime)
{
    /*
     * Because it's guaranteed that kernel32.dll will be linked into our
     * address space already, we don't need to LoadLibrary it and worry about
     * closing it afterwards, so we're not using Pg's dlopen/dlsym() wrapper.
     *
     * We'll just look up the address of GetSystemTimePreciseAsFileTime if
     * present.
     *
     * While we could look up the Windows version and skip this on Windows
     * versions below Windows 8 / Windows Server 2012 there isn't much point,
     * and determining the windows version is its self somewhat Windows
     * version and development SDK specific...
     */
    pg_get_system_time = (PgGetSystemTimeFn) GetProcAddress(GetModuleHandle(TEXT("kernel32.dll")),
                                                            "GetSystemTimePreciseAsFileTime");
    if (pg_get_system_time == NULL)
    {
        /*
         * The expected error from GetLastError() is ERROR_PROC_NOT_FOUND, if
         * the function isn't present. No other error should occur.
         *
         * We can't report an error here because this might be running in
         * frontend code; and even if we're in the backend, it's too early to
         * elog(...) if we get some unexpected error.  Also, it's not a
         * serious problem, so just silently fall back to
         * GetSystemTimeAsFileTime irrespective of why the failure occurred.
         */
        pg_get_system_time = &GetSystemTimeAsFileTime;
    }

    (*pg_get_system_time) (lpSystemTimeAsFileTime);
}

/*
 * timezone information is stored outside the kernel so tzp isn't used anymore.
 *
 * Note: this function is not for Win32 high precision timing purposes. See
 * elapsed_time().
 */
int
gettimeofday(struct timeval *tp, struct timezone *tzp)
{
    FILETIME    file_time;
    ULARGE_INTEGER ularge;

    (*pg_get_system_time) (&file_time);
    ularge.LowPart = file_time.dwLowDateTime;
    ularge.HighPart = file_time.dwHighDateTime;

    tp->tv_sec = (long) ((ularge.QuadPart - epoch) / FILETIME_UNITS_PER_SEC);
    tp->tv_usec = (long) (((ularge.QuadPart - epoch) % FILETIME_UNITS_PER_SEC)
                          / FILETIME_UNITS_PER_USEC);

    return 0;
}