private static int GetRemainingTimeout(int millisecondsTimeout, long initialTicks)
{
return(millisecondsTimeout == Timeout.Infinite ? Timeout.Infinite :
(int)Math.Max(0, millisecondsTimeout -
(TimeUtils.GetTimestampTicks(true) - initialTicks) / 10000));
}
/// <summary>
/// Tries to asynchronously enter the lock in write mode, with an optional integer time-out.
/// </summary>
/// <param name="millisecondsTimeout">The number of milliseconds to wait, or -1
/// (<see cref="Timeout.Infinite"/>) to wait indefinitely.</param>
/// <param name="cancellationToken">The <see cref="CancellationToken"/> to observe.</param>
/// <returns>A task that will complete with a result of <c>true</c> if the lock has been entered,
/// otherwise with a result of <c>false</c>.</returns>
/// <exception cref="ArgumentOutOfRangeException"><paramref name="millisecondsTimeout"/> is a negative number
/// other than -1, which represents an infinite time-out.</exception>
/// <exception cref="OperationCanceledException"><paramref name="cancellationToken"/> was canceled.</exception>
/// <exception cref="ObjectDisposedException">The current instance has already been disposed.</exception>
public async Task <bool> TryEnterWriteLockAsync(
int millisecondsTimeout = 0,
CancellationToken cancellationToken = default)
{
DenyIfDisposed();
if (millisecondsTimeout < Timeout.Infinite)
{
throw new ArgumentOutOfRangeException(nameof(millisecondsTimeout));
}
cancellationToken.ThrowIfCancellationRequested();
long initialTicks = millisecondsTimeout == Timeout.Infinite ? 0 :
TimeUtils.GetTimestampTicks(true);
// Enter the write lock semaphore before doing anything else.
if (!EnterWriteLockPreface(out bool waitForReadLocks))
{
bool writeLockWaitResult = false;
try
{
writeLockWaitResult = await this.writeLockSemaphore.WaitAsync(
millisecondsTimeout,
cancellationToken);
}
finally
{
EnterWriteLockPostface(writeLockWaitResult, out waitForReadLocks);
}
if (!writeLockWaitResult)
{
return(false);
}
}
// After we set the write lock state, we might need to wait for existing read
// locks to be released.
// In this state, no new read locks can be entered until we release the write
// lock state.
// We only wait one time since only the last active read lock will release
// the semaphore.
if (waitForReadLocks)
{
bool waitResult = false;
try
{
// This may throw an OperationCanceledException.
waitResult = await this.readLockReleaseSemaphore.WaitAsync(
GetRemainingTimeout(millisecondsTimeout, initialTicks),
cancellationToken);
}
finally
{
if (!waitResult)
{
// Timeout has been exceeded or a OperationCancelledException has
// been thrown.
HandleEnterWriteLockWaitFailure();
}
}
if (!waitResult)
{
return(false); // Timeout exceeded
}
}
return(true);
}