/**
* Auxiliary methods
*/
/**
* Returns the list of all pending async acquires that can be satisfied with
* the current number of permits owned by the semaphore.
*
* Note: Tis method is called when the current thread owns the lock.
*/
private List <AsyncAcquire> SatisfyPendingAsyncAcquires()
{
List <AsyncAcquire> satisfied = null;
while (asyncAcquires.Count > 0)
{
AsyncAcquire acquire = asyncAcquires.First.Value;
// Check if available permits allow satisfy this request
if (acquire.acquires > permits)
{
break;
}
// Remove the request from the queue
asyncAcquires.RemoveFirst();
// Try lock the request and complete it if succeeded
if (acquire.TryLock())
{
permits -= acquire.acquires;
if (satisfied == null)
{
satisfied = new List <AsyncAcquire>(1);
}
satisfied.Add(acquire);
}
}
return(satisfied);
}
/**
* Auxiliary methods
*/
/**
* Returns the list of all pending async acquires that can be satisfied with
* the number of permits currently owned by the semaphore.
*
* Note: This method is called when the current thread owns the lock.
*/
private List <AsyncAcquire> SatisfyPendingAsyncAcquires()
{
List <AsyncAcquire> satisfied = null;
while (asyncAcquires.Count > 0)
{
AsyncAcquire acquire = asyncAcquires.First.Value;
// Check if available permits allow satisfy this async request
if (acquire.acquires > permits)
{
break;
}
// Remove the async request from the queue
asyncAcquires.RemoveFirst();
// Update permits and mark acquire as done
permits -= acquire.acquires;
acquire.done = true;
// Add the async acquire to the result list
if (satisfied == null)
{
satisfied = new List <AsyncAcquire>(1);
}
satisfied.Add(acquire);
}
return(satisfied);
}
/**
* Asynchronous Task-based Asynchronous Pattern (TAP) interface.
*/
/**
* Acquires one or more permits asynchronously enabling, optionally,
* a timeout and/or cancellation.
*/
public Task <bool> AcquireAsync(int acquires = 1, int timeout = Timeout.Infinite,
CancellationToken cToken = default(CancellationToken))
{
lock (theLock)
{
if (asyncAcquires.Count == 0 && permits >= acquires)
{
permits -= acquires;
return(trueTask);
}
// if the acquire was specified as immediate, return failure
if (timeout == 0)
{
return(falseTask);
}
// If a cancellation was already requested return a task in the Canceled state
if (cToken.IsCancellationRequested)
{
return(Task.FromCanceled <bool>(cToken));
}
// Create a request node and insert it in requests queue
AsyncAcquire acquire = new AsyncAcquire(acquires, cToken);
LinkedListNode <AsyncAcquire> acquireNode = asyncAcquires.AddLast(acquire);
/**
* Activate the specified cancelers owning the lock.
*/
/**
* Since the timeout handler, that runs on a thread pool's worker thread,
* acquires the lock before access the "acquirer.timer" and "acquirer.cTokenRegistration"
* these assignements will be visible to timer handler.
*/
if (timeout != Timeout.Infinite)
{
acquire.timer = new Timer(timeoutHandler, acquireNode, timeout, Timeout.Infinite);
}
/**
* If the cancellation token is already in the canceled state, the cancellation
* handler will run immediately and synchronously, which *causes no damage* because
* this processing is terminal and the implicit locks can be acquired recursively.
*/
if (cToken.CanBeCanceled)
{
acquire.cTokenRegistration = cToken.Register(cancellationHandler, acquireNode);
}
// Return the Task<bool> that represents the async acquire
return(acquire.Task);
}
}
/**
* Try to cancel an async acquire request
*/
private void AcquireCancellationHandler(object _acquireNode, bool canceling)
{
LinkedListNode <AsyncAcquire> acquireNode = (LinkedListNode <AsyncAcquire>)_acquireNode;
AsyncAcquire acquire = acquireNode.Value;
bool complete = false;
List <AsyncAcquire> satisfied = null;
// To access shared mutable state we must acquire the lock
lock (theLock) {
/**
* Here, the async request can be already satisfied or cancelled.
*/
if (!acquire.done)
{
// Remove the async acquire request from queue and mark it as done.
asyncAcquires.Remove(acquireNode);
complete = acquire.done = true;
// If after removing the async acquire is possible to satisfy any
// pending async acquire(s) do it
if (asyncAcquires.Count > 0 && permits >= asyncAcquires.First.Value.acquires)
{
satisfied = SatisfyPendingAsyncAcquires();
}
}
}
// If we cancelled the async acquire, release the resources associated with it,
// and complete the underlying task.
if (complete)
{
// Complete any satisfied async acquires
if (satisfied != null)
{
CompleteSatisfiedAsyncAcquires(satisfied);
}
// Dispose the resources associated with the cancelled async acquire
acquire.Dispose(canceling);
// Complete the TaskCompletionSource to RanToCompletion with false (timeout)
// or Canceled final state (cancellation).
if (canceling)
{
acquire.SetCanceled(); // cancelled
}
else
{
acquire.SetResult(false); // timeout
}
}
}
/**
* Synchronous interface implemented using the asynchronous TAP interface.
*/
/**
* Try to cancel an asynchronous acquire request identified by its task.
*
* Note: This method is needed to implement the synchronous interface.
*/
private bool TryCancelAcquireAsyncByTask(Task <bool> acquireTask)
{
AsyncAcquire acquire = null;
List <AsyncAcquire> satisfied = null;
// To access the shared mutable state we must acquire the lock
lock (theLock) {
foreach (AsyncAcquire _acquire in asyncAcquires)
{
if (_acquire.Task == acquireTask)
{
acquire = _acquire;
asyncAcquires.Remove(_acquire);
acquire.done = true;
if (asyncAcquires.Count > 0 && permits >= asyncAcquires.First.Value.acquires)
{
satisfied = SatisfyPendingAsyncAcquires();
}
break;
}
}
}
// If we canceled the async acquire, process the cancellation
if (acquire != null)
{
// After release the lock, complete any satisfied acquires
if (satisfied != null)
{
CompleteSatisfiedAsyncAcquires(satisfied);
}
// Dispose the resources associated with this async acquire and complete
// its task to the Canceled state.
acquire.Dispose();
acquire.SetCanceled();
return(true);
}
return(false);
}
/**
* Try to cancel an async acquire request
*/
private void AcquireCancellationHandler(object _acquireNode, bool canceling)
{
LinkedListNode <AsyncAcquire> acquireNode = (LinkedListNode <AsyncAcquire>)_acquireNode;
AsyncAcquire acquire = acquireNode.Value;
if (acquire.TryLock())
{
List <AsyncAcquire> satisfied = null;
// To access shared mutable state we must acquire the lock
lock (theLock)
{
if (acquireNode.List != null)
{
asyncAcquires.Remove(acquireNode);
}
if (asyncAcquires.Count > 0 && permits >= asyncAcquires.First.Value.acquires)
{
satisfied = SatisfyPendingAsyncAcquires();
}
}
// Complete the satisfied async acquires
CompleteSatisfiedAsyncAcquires(satisfied);
// Release the resources associated with the async acquire.
acquire.Dispose(canceling);
// Complete the TaskCompletionSource to RanToCompletion (timeout)
// or Canceled final state.
if (canceling)
{
acquire.SetCanceled();
}
else
{
acquire.SetResult(false);
}
}
}
/**
* Synchronous interface implemented using the asynchronous TAP interface.
*/
/**
* Try to cancel an asynchronous request identified by its task.
*
* Note: This is used to implement the synchronous interface.
*/
private bool CancelAcquireByTask(Task <bool> acquireTask)
{
AsyncAcquire acquire = null;
List <AsyncAcquire> satisfied = null;
// To access the shared mutable state we must acquire the lock
lock (theLock)
{
foreach (AsyncAcquire _acquire in asyncAcquires)
{
if (_acquire.Task == acquireTask)
{
if (_acquire.TryLock())
{
acquire = _acquire;
asyncAcquires.Remove(_acquire);
}
break;
}
}
// If the new state od semaphore allows waiting acquires, satisfy them
if (asyncAcquires.Count > 0 && permits >= asyncAcquires.First.Value.acquires)
{
satisfied = SatisfyPendingAsyncAcquires();
}
}
CompleteSatisfiedAsyncAcquires(satisfied);
if (acquire != null)
{
// Dispose the resources associated with this async acquire and complete
// its task to the Canceled state.
acquire.Dispose();
acquire.SetCanceled();
}
return(acquire != null);
}
/**
* Asynchronous Task-based Asynchronous Pattern (TAP) interface.
*/
/**
* Acquires one or more permits asynchronously enabling, optionally,
* a timeout and/or cancellation.
*/
public Task <bool> AcquireAsync(int acquires = 1, int timeout = Timeout.Infinite,
CancellationToken cToken = default(CancellationToken))
{
// Validate the argument "acquires"
if (acquires < 1 || acquires > maxPermits)
{
return(argExceptionTask);
}
lock (theLock) {
// If the queue is empty ans sufficiente authorizations are available,
// the acquire can be satisfied immediatelly; so, the field permits is
// updated and a completed task is returned with a result of true.
if (asyncAcquires.Count == 0 && permits >= acquires)
{
permits -= acquires;
return(trueTask);
}
// If the acquire was specified as immediate, return completed task with
// a result of false, which means timeout.
if (timeout == 0)
{
return(falseTask);
}
// If the cancellation was already requested return a a completed task in
// the Canceled state
if (cToken.IsCancellationRequested)
{
return(Task.FromCanceled <bool>(cToken));
}
// Create a request node and insert it in requests queue
AsyncAcquire acquire = new AsyncAcquire(acquires, cToken);
LinkedListNode <AsyncAcquire> acquireNode = asyncAcquires.AddLast(acquire);
/**
* Activate the specified cancelers when owning the lock.
*/
/**
* Since the timeout handler, that runs on a thread pool's worker thread,
* that acquires the lock before access the fields "acquirer.timer" and
* "acquirer.cTokenRegistration" these assignements will be visible to the
* timeout handler.
*/
if (timeout != Timeout.Infinite)
{
acquire.timer = new Timer(timeoutHandler, acquireNode, timeout, Timeout.Infinite);
}
/**
* If the cancellation token is already in the canceled state, the cancellation
* handler will run immediately and synchronously, which *causes no damage* because
* this processing is terminal and the implicit locks can be acquired recursively.
*/
if (cToken.CanBeCanceled)
{
acquire.cTokenRegistration = cToken.Register(cancellationHandler, acquireNode);
}
// Return the Task<bool> that represents the async acquire
return(acquire.Task);
}
}
/****************************************************************************/
public async Task <Acquire> AcquireAsync()
{
AsyncAcquire acquire = new AsyncAcquire(this);
return(await acquire.Open());
}
