///<summary>
///<para>Enables sequential execution by only allowing one lock to be acquired at a time. The locks will be processed in
///FIFO order and supports async operations being performed within the lock.</para>
///<para>NOTE: The caller MUST dispose the returned object in order to release the lock and allows others to get a
/// chance to execute.</para>
/// </summary>
///<example>
///<code>
/// TaskLock _lockQueue = new TaskLock(maxQueueSize: 100);
///
/// using(await _lockQueue.GetLock(cancellationToken))
/// {
/// /* This code will be done under the acquired lock, only one lock will be given out at a time */
/// }
/// </code>
/// </example>
/// <param name="cancelToken">The GetLock will throw a cancellation exception if this token is canceled before the lock is granted</param>
/// <param name="timeout">The GetLock will throw a timeout exception if this timeout occurs before the lock is granted</param>
/// <returns>An exception or the TaskSerialLock which should be disposed by the caller when the lock is no longer needed</returns>
public async Task <TaskLockTracker> GetLock(CancellationToken cancelToken, TimeSpan timeout)
{
var serialLock = new TaskLockTracker(this, cancelToken, timeout);
lock ( _lockedTaskQueue )
{
// If we don't have room in the queue then fail
//
if (_lockedTaskQueue.Count >= MaxQueueSize)
{
throw new IndexOutOfRangeException($"GetLock: failed because maximum queue Size of {MaxQueueSize} reached");
}
;
// If we have no current lock then there is nothing queued so we can just go ahead get the lock now; otherwise,
// we just add our lock request to the queue.
//
if (_currentLock == null)
{
_currentLock = serialLock;
_currentLock.GrantLock();
_lockedTaskQueue.Add(serialLock);
return(serialLock);
}
_lockedTaskQueue.Add(serialLock);
}
try
{
await serialLock.WaitForLockAsync();
return(serialLock);
}
catch
{
// Make sure the lock has been properly disposed as we got an exception in processing the lock.
// The using pattern won't know to call dispose because an exception occurred so we do it here.
//
serialLock.TryDispose();
throw;
}
}
internal void LockNoLongerNeeded(TaskLockTracker lockTracker)
{
// NOTE: We do not need to dispose the _currentLock because LockNoLongerNeeded is only called
// by the dispose method of TaskLockTracker so we count on it already being disposed.
//
lock ( _lockedTaskQueue )
{
// If the given serialLock doesn't match the _currentLock then go ahead and remove it from
// the lock list as it no longer requires a lock.
//
if (!object.ReferenceEquals(_currentLock, lockTracker))
{
_lockedTaskQueue.TryRemove(lockTracker);
return;
}
// The given lockTracker is equal to the current lock so go ahead and release the current lock
// and find the next one available.
//
_currentLock = null;
// Take the first lock we find and make it the current lock
//
while (_lockedTaskQueue.TryTakeFirst(out var nextLock))
{
// If the next lock is canceled or timed out, we just skip it.
//
if (nextLock.IsDisposed || nextLock.CancelToken.IsCancellationRequested)
{
continue;
}
// We found a lock request ready so mark it as our current lock request.
//
_currentLock = nextLock;
nextLock.GrantLock();
return;
}
/* No locks are waiting */
}
}
