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#include "qelapsedtimer.h"

QT_BEGIN_NAMESPACE

/*!

    \class QElapsedTimer

    \brief The QElapsedTimer class provides a fast way to calculate elapsed times.

    \since 4.7

    \reentrant

    \ingroup tools

    \inmodule QtCore

    The QElapsedTimer class is usually used to quickly calculate how much

    time has elapsed between two events. Its API is similar to that of QTime,

    so code that was using that can be ported quickly to the new class.

    However, unlike QTime, QElapsedTimer tries to use monotonic clocks if

    possible. This means it's not possible to convert QElapsedTimer objects

    to a human-readable time.

    The typical use-case for the class is to determine how much time was

    spent in a slow operation. The simplest example of such a case is for

    debugging purposes, as in the following example:

    \snippet doc/src/snippets/qelapsedtimer/main.cpp 0

    In this example, the timer is started by a call to start() and the

    elapsed timer is calculated by the elapsed() function.

    The time elapsed can also be used to recalculate the time available for

    another operation, after the first one is complete. This is useful when

    the execution must complete within a certain time period, but several

    steps are needed. The \tt{waitFor}-type functions in QIODevice and its

    subclasses are good examples of such need. In that case, the code could

    be as follows:

    \snippet doc/src/snippets/qelapsedtimer/main.cpp 1

    Another use-case is to execute a certain operation for a specific

    timeslice. For this, QElapsedTimer provides the hasExpired() convenience

    function, which can be used to determine if a certain number of

    milliseconds has already elapsed:

    \snippet doc/src/snippets/qelapsedtimer/main.cpp 1

    \section1 Reference clocks

    QElapsedTimer will use the platform's monotonic reference clock in all

    platforms that support it (see QElapsedTimer::isMonotonic()). This has

    the added benefit that QElapsedTimer is immune to time adjustments, such

    as the user correcting the time. Also unlike QTime, QElapsedTimer is

    immune to changes in the timezone settings, such as daylight savings

    periods.

    On the other hand, this means QElapsedTimer values can only be compared

    with other values that use the same reference. This is especially true if

    the time since the reference is extracted from the QElapsedTimer object

    (QElapsedTimer::msecsSinceReference()) and serialised. These values

    should never be exchanged across the network or saved to disk, since

    there's no telling whether the computer node receiving the data is the

    same as the one originating it or if it has rebooted since.

    It is, however, possible to exchange the value with other processes

    running on the same machine, provided that they also use the same

    reference clock. QElapsedTimer will always use the same clock, so it's

    safe to compare with the value coming from another process in the same

    machine. If comparing to values produced by other APIs, you should check

    that the clock used is the same as QElapsedTimer (see

    QElapsedTimer::clockType()).

    \section2 32-bit overflows

    Some of the clocks that QElapsedTimer have a limited range and may

    overflow after hitting the upper limit (usually 32-bit). QElapsedTimer

    deals with this overflow issue and presents a consistent timing. However,

    when extracting the time since reference from QElapsedTimer, two

    different processes in the same machine may have different understanding

    of how much time has actually elapsed.

    The information on which clocks types may overflow and how to remedy that

    issue is documented along with the clock types.

    \sa QTime, QTimer

*/

/*!

    \enum QElapsedTimer::ClockType

    This enum contains the different clock types that QElapsedTimer may use.

    QElapsedTimer will always use the same clock type in a particular

    machine, so this value will not change during the lifetime of a program.

    It is provided so that QElapsedTimer can be used with other non-Qt

    implementations, to guarantee that the same reference clock is being

    used.

    \value SystemTime       The human-readable system time. This clock is not monotonic.

    \value MonotonicClock   The system's monotonic clock, usually found in Unix systems. This clock is monotonic and does not overflow.

    \value TickCounter      The system's tick counter, used on Windows and Symbian systems. This clock may overflow.

    \value MachAbsoluteTime The Mach kernel's absolute time (Mac OS X). This clock is monotonic and does not overflow.

    \section2 SystemTime

    The system time clock is purely the real time, expressed in milliseconds

    since Jan 1, 1970 at 0:00 UTC. It's equivalent to the value returned by

    the C and POSIX \tt{time} function, with the milliseconds added. This

    clock type is currently only used on Unix systems that do not support

    monotonic clocks (see below).

    This is the only non-monotonic clock that QElapsedTimer may use.

    \section2 MonotonicClock

    This is the system's monotonic clock, expressed in milliseconds since an

    arbitrary point in the past. This clock type is used on Unix systems

    which support POSIX monotonic clocks (\tt{_POSIX_MONOTONIC_CLOCK}).

    This clock does not overflow.

    \section2 TickCounter

    The tick counter clock type is based on the system's or the processor's

    tick counter, multiplied by the duration of a tick. This clock type is

    used on Windows and Symbian platforms.

    The TickCounter clock type is the only clock type that may overflow.

    Windows Vista and Windows Server 2008 support the extended 64-bit tick

    counter, which allows avoiding the overflow.

    On Windows systems, the clock overflows after 2^32 milliseconds, which

    corresponds to roughly 49.7 days. This means two processes's reckoning of

    the time since the reference may be different by multiples of 2^32

    milliseconds. When comparing such values, it's recommended that the high

    32 bits of the millisecond count be masked off.

    On Symbian systems, the overflow happens after 2^32 ticks, the duration

    of which can be obtained from the platform HAL using the constant

    HAL::ENanoTickPeriod. When comparing values between processes, it's

    necessary to divide the value by the tick duration and mask off the high

    32 bits.

    \section2 MachAbsoluteTime

    This clock type is based on the absolute time presented by Mach kernels,

    such as that found on Mac OS X. This clock type is presented separately

    from MonotonicClock since Mac OS X is also a Unix system and may support

    a POSIX monotonic clock with values differing from the Mach absolute

    time.

    This clock is monotonic and does not overflow.

    \sa clockType(), isMonotonic()

*/

/*!

    \fn bool QElapsedTimer::operator ==(const QElapsedTimer &other) const

    Returns true if this object and \a other contain the same time.

*/

/*!

    \fn bool QElapsedTimer::operator !=(const QElapsedTimer &other) const

    Returns true if this object and \a other contain different times.

*/

static const qint64 invalidData = Q_INT64_C(0x8000000000000000);

/*!

    Marks this QElapsedTimer object as invalid.

    An invalid object can be checked with isValid(). Calculations of timer

    elapsed since invalid data are undefined and will likely produce bizarre

    results.

    \sa isValid(), start(), restart()

*/

void QElapsedTimer::invalidate()

{

     t1 = t2 = invalidData;

}

/*!

    Returns true if this object was invalidated by a call to invalidate() and

    has not been restarted since.

    \sa invalidate(), start(), restart()

*/

bool QElapsedTimer::isValid() const

{

    return t1 != invalidData && t2 != invalidData;

}

/*!

    Returns true if this QElapsedTimer has already expired by \a timeout

    milliseconds (that is, more than \a timeout milliseconds have elapsed).

    The value of \a timeout can be -1 to indicate that this timer does not

    expire, in which case this function will always return false.

    \sa elapsed()

*/

bool QElapsedTimer::hasExpired(qint64 timeout) const

{

    // if timeout is -1, quint64(timeout) is LLINT_MAX, so this will be

    // considered as never expired

    return quint64(elapsed()) > quint64(timeout);

}

QT_END_NAMESPACE