currenttime.cpp

linux下开源浏览器WebKit的源码,市面上的很多商用浏览器都是移植自WebKit

/*
 * Copyright (C) 2006 Apple Computer, Inc.  All rights reserved.
 * Copyright (C) 2008 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "config.h"
#include "CurrentTime.h"

#if PLATFORM(WIN_OS)
// Windows is first since we want to use hires timers, despite PLATFORM(CF)
// being defined.
// If defined, WIN32_LEAN_AND_MEAN disables timeBeginPeriod/timeEndPeriod.
#undef WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <math.h>
#include <stdint.h>
#include <sys/timeb.h>
#include <sys/types.h>
#include <time.h>
#elif PLATFORM(CF)
#include <CoreFoundation/CFDate.h>
#elif PLATFORM(GTK)
#include <glib.h>
#elif PLATFORM(WX)
#include <wx/datetime.h>
#else // Posix systems relying on the gettimeofday()
#include <sys/time.h>
#endif

namespace WTF {

const double msPerSecond = 1000.0;

#if PLATFORM(WIN_OS)

static LARGE_INTEGER qpcFrequency;
static bool syncedTime;

static double highResUpTime()
{
    // We use QPC, but only after sanity checking its result, due to bugs:
    // http://support.microsoft.com/kb/274323
    // http://support.microsoft.com/kb/895980
    // http://msdn.microsoft.com/en-us/library/ms644904.aspx ("...you can get different results on different processors due to bugs in the basic input/output system (BIOS) or the hardware abstraction layer (HAL)."

    static LARGE_INTEGER qpcLast;
    static DWORD tickCountLast;
    static bool inited;

    LARGE_INTEGER qpc;
    QueryPerformanceCounter(&qpc);
    DWORD tickCount = GetTickCount();

    if (inited) {
        __int64 qpcElapsed = ((qpc.QuadPart - qpcLast.QuadPart) * 1000) / qpcFrequency.QuadPart;
        __int64 tickCountElapsed;
        if (tickCount >= tickCountLast)
            tickCountElapsed = (tickCount - tickCountLast);
        else {
#if COMPILER(MINGW)
            __int64 tickCountLarge = tickCount + 0x100000000ULL;
#else
            __int64 tickCountLarge = tickCount + 0x100000000I64;
#endif
            tickCountElapsed = tickCountLarge - tickCountLast;
        }

        // force a re-sync if QueryPerformanceCounter differs from GetTickCount by more than 500ms.
        // (500ms value is from http://support.microsoft.com/kb/274323)
        __int64 diff = tickCountElapsed - qpcElapsed;
        if (diff > 500 || diff < -500)
            syncedTime = false;
    } else
        inited = true;

    qpcLast = qpc;
    tickCountLast = tickCount;

    return (1000.0 * qpc.QuadPart) / static_cast<double>(qpcFrequency.QuadPart);
}

static double lowResUTCTime()
{
#if PLATFORM(WIN_CE)
    SYSTEMTIME systemTime;
    GetSystemTime(&systemTime);
    struct tm tmtime;
    tmtime.tm_year = systemTime.wYear - 1900;
    tmtime.tm_mon = systemTime.wMonth - 1;
    tmtime.tm_mday = systemTime.wDay;
    tmtime.tm_wday = systemTime.wDayOfWeek;
    tmtime.tm_hour = systemTime.wHour;
    tmtime.tm_min = systemTime.wMinute;
    tmtime.tm_sec = systemTime.wSecond;
    time_t timet = mktime(&tmtime);
    return timet * msPerSecond + systemTime.wMilliseconds;
#else // PLATFORM(WIN_CE)
    struct _timeb timebuffer;
    _ftime(&timebuffer);
    return timebuffer.time * msPerSecond + timebuffer.millitm;
#endif // PLATFORM(WIN_CE)
}

static bool qpcAvailable()
{
    static bool available;
    static bool checked;

    if (checked)
        return available;

    available = QueryPerformanceFrequency(&qpcFrequency);
    checked = true;
    return available;
}

double currentTime()
{
    // Use a combination of ftime and QueryPerformanceCounter.
    // ftime returns the information we want, but doesn't have sufficient resolution.
    // QueryPerformanceCounter has high resolution, but is only usable to measure time intervals.
    // To combine them, we call ftime and QueryPerformanceCounter initially. Later calls will use QueryPerformanceCounter
    // by itself, adding the delta to the saved ftime.  We periodically re-sync to correct for drift.
    static bool started;
    static double syncLowResUTCTime;
    static double syncHighResUpTime;
    static double lastUTCTime;

    double lowResTime = lowResUTCTime();

    if (!qpcAvailable())
        return lowResTime / 1000.0;

    double highResTime = highResUpTime();

    if (!syncedTime) {
        timeBeginPeriod(1); // increase time resolution around low-res time getter
        syncLowResUTCTime = lowResTime = lowResUTCTime();
        timeEndPeriod(1); // restore time resolution
        syncHighResUpTime = highResTime;
        syncedTime = true;
    }

    double highResElapsed = highResTime - syncHighResUpTime;
    double utc = syncLowResUTCTime + highResElapsed;

    // force a clock re-sync if we've drifted
    double lowResElapsed = lowResTime - syncLowResUTCTime;
    const double maximumAllowedDriftMsec = 15.625 * 2.0; // 2x the typical low-res accuracy
    if (fabs(highResElapsed - lowResElapsed) > maximumAllowedDriftMsec)
        syncedTime = false;

    // make sure time doesn't run backwards (only correct if difference is < 2 seconds, since DST or clock changes could occur)
    const double backwardTimeLimit = 2000.0;
    if (utc < lastUTCTime && (lastUTCTime - utc) < backwardTimeLimit)
        return lastUTCTime / 1000.0;
    lastUTCTime = utc;
    return utc / 1000.0;
}

#elif PLATFORM(CF)

double currentTime()
{
    return CFAbsoluteTimeGetCurrent() + kCFAbsoluteTimeIntervalSince1970;
}

#elif PLATFORM(GTK)

// Note: GTK on Windows will pick up the PLATFORM(WIN) implementation above which provides
// better accuracy compared with Windows implementation of g_get_current_time:
// (http://www.google.com/codesearch/p?hl=en#HHnNRjks1t0/glib-2.5.2/glib/gmain.c&q=g_get_current_time).
// Non-Windows GTK builds could use gettimeofday() directly but for the sake of consistency lets use GTK function.
double currentTime()
{
    GTimeVal now;
    g_get_current_time(&now);
    return static_cast<double>(now.tv_sec) + static_cast<double>(now.tv_usec / 1000000.0);
}

#elif PLATFORM(WX)

double currentTime()
{
    wxDateTime now = wxDateTime::UNow();
    return (double)now.GetTicks() + (double)(now.GetMillisecond() / 1000.0);
}

#else // Other Posix systems rely on the gettimeofday().

double currentTime()
{
    struct timeval now;
    struct timezone zone;

    gettimeofday(&now, &zone);
    return static_cast<double>(now.tv_sec) + (double)(now.tv_usec / 1000000.0);
}

#endif

} // namespace WTF