601 lines
18 KiB
C#
601 lines
18 KiB
C#
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// Ami Bar
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// amibar@gmail.com
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using System;
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using System.Threading;
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namespace Amib.Threading.Internal
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{
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#region WorkItemsQueue class
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/// <summary>
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/// WorkItemsQueue class.
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/// </summary>
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public class WorkItemsQueue : IDisposable
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{
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#region Member variables
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/// <summary>
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/// Waiters queue (implemented as stack).
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/// </summary>
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private WaiterEntry _headWaiterEntry = new WaiterEntry();
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/// <summary>
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/// Waiters count
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/// </summary>
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private int _waitersCount = 0;
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/// <summary>
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/// Work items queue
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/// </summary>
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private PriorityQueue _workItems = new PriorityQueue();
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/// <summary>
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/// Indicate that work items are allowed to be queued
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/// </summary>
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private bool _isWorkItemsQueueActive = true;
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/// <summary>
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/// Each thread in the thread pool keeps its own waiter entry.
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/// </summary>
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[ThreadStatic]
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private static WaiterEntry _waiterEntry;
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/// <summary>
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/// A flag that indicates if the WorkItemsQueue has been disposed.
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/// </summary>
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private bool _isDisposed = false;
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#endregion
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#region Public properties
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/// <summary>
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/// Returns the current number of work items in the queue
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/// </summary>
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public int Count
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{
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get
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{
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lock(this)
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{
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ValidateNotDisposed();
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return _workItems.Count;
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}
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}
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}
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/// <summary>
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/// Returns the current number of waiters
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/// </summary>
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public int WaitersCount
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{
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get
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{
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lock(this)
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{
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ValidateNotDisposed();
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return _waitersCount;
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}
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}
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}
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#endregion
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#region Public methods
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/// <summary>
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/// Enqueue a work item to the queue.
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/// </summary>
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public bool EnqueueWorkItem(WorkItem workItem)
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{
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// A work item cannot be null, since null is used in the
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// WaitForWorkItem() method to indicate timeout or cancel
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if (null == workItem)
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{
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throw new ArgumentNullException("workItem" , "workItem cannot be null");
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}
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bool enqueue = true;
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// First check if there is a waiter waiting for work item. During
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// the check, timed out waiters are ignored. If there is no
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// waiter then the work item is queued.
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lock(this)
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{
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ValidateNotDisposed();
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if (!_isWorkItemsQueueActive)
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{
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return false;
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}
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while(_waitersCount > 0)
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{
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// Dequeue a waiter.
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WaiterEntry waiterEntry = PopWaiter();
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// Signal the waiter. On success break the loop
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if (waiterEntry.Signal(workItem))
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{
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enqueue = false;
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break;
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}
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}
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if (enqueue)
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{
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// Enqueue the work item
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_workItems.Enqueue(workItem);
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}
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}
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return true;
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}
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/// <summary>
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/// Waits for a work item or exits on timeout or cancel
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/// </summary>
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/// <param name="millisecondsTimeout">Timeout in milliseconds</param>
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/// <param name="cancelEvent">Cancel wait handle</param>
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/// <returns>Returns true if the resource was granted</returns>
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public WorkItem DequeueWorkItem(
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int millisecondsTimeout,
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WaitHandle cancelEvent)
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{
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/// This method cause the caller to wait for a work item.
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/// If there is at least one waiting work item then the
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/// method returns immidiately with true.
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///
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/// If there are no waiting work items then the caller
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/// is queued between other waiters for a work item to arrive.
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///
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/// If a work item didn't come within millisecondsTimeout or
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/// the user canceled the wait by signaling the cancelEvent
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/// then the method returns false to indicate that the caller
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/// didn't get a work item.
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WaiterEntry waiterEntry = null;
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WorkItem workItem = null;
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lock(this)
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{
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ValidateNotDisposed();
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// If there are waiting work items then take one and return.
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if (_workItems.Count > 0)
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{
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workItem = _workItems.Dequeue() as WorkItem;
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return workItem;
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}
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// No waiting work items ...
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else
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{
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// Get the wait entry for the waiters queue
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waiterEntry = GetThreadWaiterEntry();
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// Put the waiter with the other waiters
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PushWaiter(waiterEntry);
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}
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}
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// Prepare array of wait handle for the WaitHandle.WaitAny()
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WaitHandle [] waitHandles = new WaitHandle [] {
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waiterEntry.WaitHandle,
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cancelEvent };
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// Wait for an available resource, cancel event, or timeout.
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// During the wait we are supposes to exit the synchronization
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// domain. (Placing true as the third argument of the WaitAny())
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// It just doesn't work, I don't know why, so I have lock(this)
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// statments insted of one.
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int index = WaitHandle.WaitAny(
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waitHandles,
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millisecondsTimeout,
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true);
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lock(this)
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{
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// success is true if it got a work item.
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bool success = (0 == index);
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// The timeout variable is used only for readability.
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// (We treat cancel as timeout)
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bool timeout = !success;
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// On timeout update the waiterEntry that it is timed out
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if (timeout)
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{
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// The Timeout() fails if the waiter has already been signaled
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timeout = waiterEntry.Timeout();
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// On timeout remove the waiter from the queue.
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// Note that the complexity is O(1).
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if(timeout)
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{
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RemoveWaiter(waiterEntry, false);
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}
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// Again readability
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success = !timeout;
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}
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// On success return the work item
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if (success)
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{
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workItem = waiterEntry.WorkItem;
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if (null == workItem)
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{
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workItem = _workItems.Dequeue() as WorkItem;
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}
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}
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}
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// On failure return null.
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return workItem;
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}
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/// <summary>
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/// Cleanup the work items queue, hence no more work
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/// items are allowed to be queue
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/// </summary>
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protected virtual void Cleanup()
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{
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lock(this)
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{
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// Deactivate only once
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if (!_isWorkItemsQueueActive)
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{
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return;
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}
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// Don't queue more work items
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_isWorkItemsQueueActive = false;
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foreach(WorkItem workItem in _workItems)
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{
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workItem.DisposeOfState();
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}
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// Clear the work items that are already queued
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_workItems.Clear();
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// Note:
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// I don't iterate over the queue and dispose of work items's states,
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// since if a work item has a state object that is still in use in the
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// application then I must not dispose it.
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// Tell the waiters that they were timed out.
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// It won't signal them to exit, but to ignore their
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// next work item.
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while(_waitersCount > 0)
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{
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WaiterEntry waiterEntry = PopWaiter();
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waiterEntry.Timeout();
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}
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}
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}
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#endregion
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#region Private methods
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/// <summary>
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/// Returns the WaiterEntry of the current thread
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/// </summary>
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/// <returns></returns>
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/// In order to avoid creation and destuction of WaiterEntry
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/// objects each thread has its own WaiterEntry object.
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private WaiterEntry GetThreadWaiterEntry()
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{
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if (null == _waiterEntry)
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{
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_waiterEntry = new WaiterEntry();
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}
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_waiterEntry.Reset();
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return _waiterEntry;
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}
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#region Waiters stack methods
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/// <summary>
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/// Push a new waiter into the waiter's stack
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/// </summary>
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/// <param name="newWaiterEntry">A waiter to put in the stack</param>
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public void PushWaiter(WaiterEntry newWaiterEntry)
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{
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// Remove the waiter if it is already in the stack and
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// update waiter's count as needed
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RemoveWaiter(newWaiterEntry, false);
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// If the stack is empty then newWaiterEntry is the new head of the stack
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if (null == _headWaiterEntry._nextWaiterEntry)
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{
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_headWaiterEntry._nextWaiterEntry = newWaiterEntry;
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newWaiterEntry._prevWaiterEntry = _headWaiterEntry;
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}
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// If the stack is not empty then put newWaiterEntry as the new head
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// of the stack.
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else
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{
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// Save the old first waiter entry
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WaiterEntry oldFirstWaiterEntry = _headWaiterEntry._nextWaiterEntry;
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// Update the links
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_headWaiterEntry._nextWaiterEntry = newWaiterEntry;
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newWaiterEntry._nextWaiterEntry = oldFirstWaiterEntry;
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newWaiterEntry._prevWaiterEntry = _headWaiterEntry;
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oldFirstWaiterEntry._prevWaiterEntry = newWaiterEntry;
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}
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// Increment the number of waiters
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++_waitersCount;
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}
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/// <summary>
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/// Pop a waiter from the waiter's stack
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/// </summary>
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/// <returns>Returns the first waiter in the stack</returns>
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private WaiterEntry PopWaiter()
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{
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// Store the current stack head
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WaiterEntry oldFirstWaiterEntry = _headWaiterEntry._nextWaiterEntry;
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// Store the new stack head
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WaiterEntry newHeadWaiterEntry = oldFirstWaiterEntry._nextWaiterEntry;
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// Update the old stack head list links and decrement the number
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// waiters.
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RemoveWaiter(oldFirstWaiterEntry, true);
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// Update the new stack head
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_headWaiterEntry._nextWaiterEntry = newHeadWaiterEntry;
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if (null != newHeadWaiterEntry)
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{
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newHeadWaiterEntry._prevWaiterEntry = _headWaiterEntry;
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}
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// Return the old stack head
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return oldFirstWaiterEntry;
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}
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/// <summary>
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/// Remove a waiter from the stack
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/// </summary>
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/// <param name="waiterEntry">A waiter entry to remove</param>
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/// <param name="popDecrement">If true the waiter count is always decremented</param>
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private void RemoveWaiter(WaiterEntry waiterEntry, bool popDecrement)
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{
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// Store the prev entry in the list
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WaiterEntry prevWaiterEntry = waiterEntry._prevWaiterEntry;
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// Store the next entry in the list
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WaiterEntry nextWaiterEntry = waiterEntry._nextWaiterEntry;
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// A flag to indicate if we need to decrement the waiters count.
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// If we got here from PopWaiter then we must decrement.
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// If we got here from PushWaiter then we decrement only if
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// the waiter was already in the stack.
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bool decrementCounter = popDecrement;
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// Null the waiter's entry links
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waiterEntry._prevWaiterEntry = null;
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waiterEntry._nextWaiterEntry = null;
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// If the waiter entry had a prev link then update it.
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// It also means that the waiter is already in the list and we
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// need to decrement the waiters count.
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if (null != prevWaiterEntry)
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{
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prevWaiterEntry._nextWaiterEntry = nextWaiterEntry;
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decrementCounter = true;
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}
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// If the waiter entry had a next link then update it.
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// It also means that the waiter is already in the list and we
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// need to decrement the waiters count.
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if (null != nextWaiterEntry)
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{
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nextWaiterEntry._prevWaiterEntry = prevWaiterEntry;
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decrementCounter = true;
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}
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// Decrement the waiters count if needed
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if (decrementCounter)
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{
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--_waitersCount;
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}
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}
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#endregion
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#endregion
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#region WaiterEntry class
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// A waiter entry in the _waiters queue.
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public class WaiterEntry : IDisposable
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{
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|
#region Member variables
|
||
|
|
|
||
|
|
/// <summary>
|
||
|
|
/// Event to signal the waiter that it got the work item.
|
||
|
|
/// </summary>
|
||
|
|
private AutoResetEvent _waitHandle = new AutoResetEvent(false);
|
||
|
|
|
||
|
|
/// <summary>
|
||
|
|
/// Flag to know if this waiter already quited from the queue
|
||
|
|
/// because of a timeout.
|
||
|
|
/// </summary>
|
||
|
|
private bool _isTimedout = false;
|
||
|
|
|
||
|
|
/// <summary>
|
||
|
|
/// Flag to know if the waiter was signaled and got a work item.
|
||
|
|
/// </summary>
|
||
|
|
private bool _isSignaled = false;
|
||
|
|
|
||
|
|
/// <summary>
|
||
|
|
/// A work item that passed directly to the waiter withou going
|
||
|
|
/// through the queue
|
||
|
|
/// </summary>
|
||
|
|
private WorkItem _workItem = null;
|
||
|
|
|
||
|
|
private bool _isDisposed = false;
|
||
|
|
|
||
|
|
// Linked list members
|
||
|
|
internal WaiterEntry _nextWaiterEntry = null;
|
||
|
|
internal WaiterEntry _prevWaiterEntry = null;
|
||
|
|
|
||
|
|
#endregion
|
||
|
|
|
||
|
|
#region Construction
|
||
|
|
|
||
|
|
public WaiterEntry()
|
||
|
|
{
|
||
|
|
Reset();
|
||
|
|
}
|
||
|
|
|
||
|
|
#endregion
|
||
|
|
|
||
|
|
#region Public methods
|
||
|
|
|
||
|
|
public WaitHandle WaitHandle
|
||
|
|
{
|
||
|
|
get { return _waitHandle; }
|
||
|
|
}
|
||
|
|
|
||
|
|
public WorkItem WorkItem
|
||
|
|
{
|
||
|
|
get
|
||
|
|
{
|
||
|
|
lock(this)
|
||
|
|
{
|
||
|
|
return _workItem;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
/// <summary>
|
||
|
|
/// Signal the waiter that it got a work item.
|
||
|
|
/// </summary>
|
||
|
|
/// <returns>Return true on success</returns>
|
||
|
|
/// The method fails if Timeout() preceded its call
|
||
|
|
public bool Signal(WorkItem workItem)
|
||
|
|
{
|
||
|
|
lock(this)
|
||
|
|
{
|
||
|
|
if (!_isTimedout)
|
||
|
|
{
|
||
|
|
_workItem = workItem;
|
||
|
|
_isSignaled = true;
|
||
|
|
_waitHandle.Set();
|
||
|
|
return true;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
return false;
|
||
|
|
}
|
||
|
|
|
||
|
|
/// <summary>
|
||
|
|
/// Mark the wait entry that it has been timed out
|
||
|
|
/// </summary>
|
||
|
|
/// <returns>Return true on success</returns>
|
||
|
|
/// The method fails if Signal() preceded its call
|
||
|
|
public bool Timeout()
|
||
|
|
{
|
||
|
|
lock(this)
|
||
|
|
{
|
||
|
|
// Time out can happen only if the waiter wasn't marked as
|
||
|
|
// signaled
|
||
|
|
if (!_isSignaled)
|
||
|
|
{
|
||
|
|
// We don't remove the waiter from the queue, the DequeueWorkItem
|
||
|
|
// method skips _waiters that were timed out.
|
||
|
|
_isTimedout = true;
|
||
|
|
return true;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
return false;
|
||
|
|
}
|
||
|
|
|
||
|
|
/// <summary>
|
||
|
|
/// Reset the wait entry so it can be used again
|
||
|
|
/// </summary>
|
||
|
|
public void Reset()
|
||
|
|
{
|
||
|
|
_workItem = null;
|
||
|
|
_isTimedout = false;
|
||
|
|
_isSignaled = false;
|
||
|
|
_waitHandle.Reset();
|
||
|
|
}
|
||
|
|
|
||
|
|
/// <summary>
|
||
|
|
/// Free resources
|
||
|
|
/// </summary>
|
||
|
|
public void Close()
|
||
|
|
{
|
||
|
|
if (null != _waitHandle)
|
||
|
|
{
|
||
|
|
_waitHandle.Close();
|
||
|
|
_waitHandle = null;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
#endregion
|
||
|
|
|
||
|
|
#region IDisposable Members
|
||
|
|
|
||
|
|
public void Dispose()
|
||
|
|
{
|
||
|
|
if (!_isDisposed)
|
||
|
|
{
|
||
|
|
Close();
|
||
|
|
_isDisposed = true;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
~WaiterEntry()
|
||
|
|
{
|
||
|
|
Dispose();
|
||
|
|
}
|
||
|
|
|
||
|
|
#endregion
|
||
|
|
}
|
||
|
|
|
||
|
|
#endregion
|
||
|
|
|
||
|
|
#region IDisposable Members
|
||
|
|
|
||
|
|
public void Dispose()
|
||
|
|
{
|
||
|
|
if (!_isDisposed)
|
||
|
|
{
|
||
|
|
Cleanup();
|
||
|
|
_isDisposed = true;
|
||
|
|
GC.SuppressFinalize(this);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
~WorkItemsQueue()
|
||
|
|
{
|
||
|
|
Cleanup();
|
||
|
|
}
|
||
|
|
|
||
|
|
private void ValidateNotDisposed()
|
||
|
|
{
|
||
|
|
if(_isDisposed)
|
||
|
|
{
|
||
|
|
throw new ObjectDisposedException(GetType().ToString(), "The SmartThreadPool has been shutdown");
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
#endregion
|
||
|
|
}
|
||
|
|
|
||
|
|
#endregion
|
||
|
|
}
|
||
|
|
|