/// <summary>
/// Flip a phase in the {@link WriterReaderPhaser} instance, {@link WriterReaderPhaser#flipPhase()}
/// can only be called while holding the readerLock().
/// {@link WriterReaderPhaser#flipPhase()} will return only after all writer critical sections (protected by
/// {@link WriterReaderPhaser#writerCriticalSectionEnter()} ()} and
/// {@link WriterReaderPhaser#writerCriticalSectionExit(long)} ()}) that may have been in flight when the
/// {@link WriterReaderPhaser#flipPhase()} call were made had completed.
/// No actual writer critical section activity is required for {@link WriterReaderPhaser#flipPhase()} to
/// succeed.
/// However, {@link WriterReaderPhaser#flipPhase()} is lock-free with respect to calls to
/// {@link WriterReaderPhaser#writerCriticalSectionEnter()} and
/// {@link WriterReaderPhaser#writerCriticalSectionExit(long)}. It may spin-wait for for active
/// writer critical section code to complete.
/// </summary>
/// <param name="yieldTimeNsec">The amount of time (in nanoseconds) to sleep in each yield if yield loop is needed.</param>
public void FlipPhase(long yieldTimeNsec = 0)
{
if (!Monitor.IsEntered(readerLockObject))
{
throw new ThreadStateException("flipPhase() can only be called while holding the readerLock()");
}
var nextPhaseIsEven = (startEpoch.GetValue() < 0); // Current phase is odd...
long initialStartValue;
// First, clear currently unused [next] phase end epoch (to proper initial value for phase):
if (nextPhaseIsEven)
{
initialStartValue = 0;
evenEndEpoch.SetValue(initialStartValue);
}
else
{
initialStartValue = long.MinValue;
oddEndEpoch.SetValue(initialStartValue);
}
// Next, reset start value, indicating new phase, and retain value at flip:
var startValueAtFlip = startEpoch.GetAndSet(initialStartValue);
// Now, spin until previous phase end value catches up with start value at flip:
bool caughtUp;
do
{
if (nextPhaseIsEven)
{
caughtUp = (oddEndEpoch.GetValue() == startValueAtFlip);
}
else
{
caughtUp = (evenEndEpoch.GetValue() == startValueAtFlip);
}
if (!caughtUp)
{
if (yieldTimeNsec == 0)
{
//TODO: HdrHistogram
Task.Yield();
}
else
{
Thread.Sleep(TimeSpan.FromMilliseconds(yieldTimeNsec / 1000000.0));
}
}
} while (!caughtUp);
}
public void Can_get_and_set()
{
_num.SetValue(32);
_num.GetAndSet(64).Should().Be(32);
_num.GetValue().Should().Be(64);
}
