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Stop trying to discover the system timer resolution on Windows

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Let's take the beginning of the description: WaitForSingleObjectEx can
be up to 16 milliseconds early. This is proven by the fact that there
are tests doing:

    wait(waitTime);
    QVERIFY(timer.elapsed() >= waitTime - systemTimersResolution);

and failing.

Task-number: QTBUG-59337
Change-Id: Iae839f6a131a4f0784bffffd14a9a79523d69d94
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
This commit is contained in:
Thiago Macieira 2017-03-07 17:48:28 +01:00
parent 2d81968c3b
commit 3a1f4b186d
1 changed files with 10 additions and 51 deletions
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61
tests/auto/corelib/thread/qmutex/tst_qmutex.cpp
View File

@ -36,11 +36,6 @@
#include <qthread.h> #include <qthread.h>
#include <qwaitcondition.h> #include <qwaitcondition.h>
#ifdef Q_OS_WIN
#include <private/qsystemlibrary_p.h>
#include <cmath>
#endif
class tst_QMutex : public QObject class tst_QMutex : public QObject
{ {
Q_OBJECT Q_OBJECT
@ -54,7 +49,6 @@ public:
Q_ENUM(TimeUnit); Q_ENUM(TimeUnit);
private slots: private slots:
void initTestCase();
void convertToMilliseconds_data(); void convertToMilliseconds_data();
void convertToMilliseconds(); void convertToMilliseconds();
void tryLock_non_recursive(); void tryLock_non_recursive();
@ -70,8 +64,6 @@ private slots:
void tryLockNegative_data(); void tryLockNegative_data();
void tryLockNegative(); void tryLockNegative();
void moreStress(); void moreStress();
private:
void initializeSystemTimersResolution();
}; };
static const int iterations = 100; static const int iterations = 100;
@ -81,57 +73,24 @@ QMutex normalMutex, recursiveMutex(QMutex::Recursive);
QSemaphore testsTurn; QSemaphore testsTurn;
QSemaphore threadsTurn; QSemaphore threadsTurn;
enum { waitTime = 100 };
uint systemTimersResolution = 1;
#if QT_HAS_INCLUDE(<chrono>)
static Q_CONSTEXPR std::chrono::milliseconds waitTimeAsDuration(waitTime);
#endif
/* /*
Depending on the OS, tryWaits may return early than expected because of the Depending on the OS, tryWaits may return early than expected because of the
resolution of the underlying timer is too coarse. E.g.: on Windows resolution of the underlying timer is too coarse. E.g.: on Windows
WaitForSingleObjectEx does *not* use high resolution multimedia timers, and WaitForSingleObjectEx does *not* use high resolution multimedia timers, and
it's actually very coarse, about 16msec by default. it's actually very coarse, about 16msec by default.
Try to find out the timer resolution in here, so that the tryLock tests can
actually take into account early wakes.
*/ */
void tst_QMutex::initializeSystemTimersResolution() enum {
{
#ifdef Q_OS_WIN #ifdef Q_OS_WIN
// according to MSDN, Windows can default up to this systemTimersResolution = 16,
systemTimersResolution = 16; #else
systemTimersResolution = 1,
#endif
waitTime = 100
};
// private API. There's no way on Windows to otherwise know the #if QT_HAS_INCLUDE(<chrono>)
// actual resolution of the application's timers (you can only set it) static Q_CONSTEXPR std::chrono::milliseconds waitTimeAsDuration(waitTime);
// cf. https://stackoverflow.com/questions/7685762/windows-7-timing-functions-how-to-use-getsystemtimeadjustment-correctly/11743614#11743614 #endif
typedef NTSTATUS (NTAPI *NtQueryTimerResolutionType)(OUT PULONG MinimumResolution,
OUT PULONG MaximumResolution,
OUT PULONG ActualResolution);
const NtQueryTimerResolutionType NtQueryTimerResolutionPtr =
reinterpret_cast<NtQueryTimerResolutionType>(QSystemLibrary::resolve(QStringLiteral("ntdll"), "NtQueryTimerResolution"));
if (!NtQueryTimerResolutionPtr)
return;
ULONG minimumResolution;
ULONG maximumResolution;
ULONG actualResolution;
if (!NtQueryTimerResolutionPtr(&minimumResolution, &maximumResolution, &actualResolution)) {
// the result is in 100ns units => adjust to msec
const double actualResolutionMsec = actualResolution / 10000.0;
systemTimersResolution = static_cast<int>(std::ceil(actualResolutionMsec));
}
#endif // Q_OS_WIN
}
void tst_QMutex::initTestCase()
{
initializeSystemTimersResolution();
}
void tst_QMutex::convertToMilliseconds_data() void tst_QMutex::convertToMilliseconds_data()
{ {