Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Base / System / Windows / Threading / DispatcherOperation.cs / 1407647 / DispatcherOperation.cs
using System; using System.Security; using System.Security.Permissions; using System.Threading; using MS.Internal.WindowsBase; namespace System.Windows.Threading { ////// DispatcherOperation represents a delegate that has been /// posted to the Dispatcher queue. /// public sealed class DispatcherOperation { ////// Critical: This code calls into InvokeInSecurityContext which can be used to process input /// TreatAsSafe: This is ok to expose since the operation itself is ok . But this will /// `blow up if something untowards is done in the operation that violates trust boundaries /// .Essentially although this lets you execute arbitrary code that code cannot be doing /// any untrusted operation /// [SecurityCritical,SecurityTreatAsSafe] static DispatcherOperation() { _invokeInSecurityContext = new ContextCallback(InvokeInSecurityContext); } ////// Critical: accesses _executionContext /// [SecurityCritical] internal DispatcherOperation( Dispatcher dispatcher, Delegate method, DispatcherPriority priority, // NOTE: should be Priority object args, int numArgs) { _dispatcher = dispatcher; _method = method; _priority = priority; _numArgs = numArgs; _args = args; _executionContext = ExecutionContext.Capture(); } ////// Internal constructor used to generate a Dispatcher operation /// when the dispatcher has shut down /// /// /// /// internal DispatcherOperation( Dispatcher dispatcher, Delegate method, DispatcherPriority priority ) { _dispatcher = dispatcher; _method = method; _priority = priority; _status = DispatcherOperationStatus.Aborted; } ////// Returns the Dispatcher that this operation was posted to. /// public Dispatcher Dispatcher { get { return _dispatcher; } } ////// Gets or sets the priority of this operation within the /// Dispatcher queue. /// public DispatcherPriority Priority // NOTE: should be Priority { get { return _priority; } set { Dispatcher.ValidatePriority(value, "value"); if(value != _priority && _dispatcher.SetPriority(this, value)) { _priority = value; } } } ////// The status of this operation. /// public DispatcherOperationStatus Status { get { return _status; } } ////// Waits for this operation to complete. /// ////// The status of the operation. To obtain the return value /// of the invoked delegate, use the the Result property. /// public DispatcherOperationStatus Wait() { return Wait(TimeSpan.FromMilliseconds(-1)); } ////// Waits for this operation to complete. /// /// /// The maximum amount of time to wait. /// ////// The status of the operation. To obtain the return value /// of the invoked delegate, use the the Result property. /// ////// Critical: This code calls into PushFrame which has a link demand /// PublicOk: The act of setting a timeline for an operation to complete is a safe one /// [SecurityCritical] public DispatcherOperationStatus Wait(TimeSpan timeout) { if((_status == DispatcherOperationStatus.Pending || _status == DispatcherOperationStatus.Executing) && timeout.TotalMilliseconds != 0) { if(_dispatcher.Thread == Thread.CurrentThread) { if(_status == DispatcherOperationStatus.Executing) { // We are the dispatching thread, and the current operation state is // executing, which means that the operation is in the middle of // executing (on this thread) and is trying to wait for the execution // to complete. Unfortunately, the thread will now deadlock, so // we throw an exception instead. throw new InvalidOperationException(SR.Get(SRID.ThreadMayNotWaitOnOperationsAlreadyExecutingOnTheSameThread)); } // We are the dispatching thread for this operation, so // we can't block. We will push a frame instead. DispatcherOperationFrame frame = new DispatcherOperationFrame(this, timeout); Dispatcher.PushFrame(frame); } else { // We are some external thread, so we can just block. Of // course this means that the Dispatcher (queue)for this // thread (if any) is now blocked. The COM STA model // suggests that we should pump certain messages so that // back-communication can happen. Underneath us, the CLR // will pump the STA apartment for us, and we will allow // the UI thread for a context to call // Invoke(Priority.Max, ...) without going through the // blocked queue. DispatcherOperationEvent wait = new DispatcherOperationEvent(this, timeout); wait.WaitOne(); } } return _status; } ////// Aborts this operation. /// ////// False if the operation could not be aborted (because the /// operation was already in progress) /// public bool Abort() { bool removed = false; if (_dispatcher != null) { removed = _dispatcher.Abort(this); if (removed) { // Raise the Aborted so anyone who is waiting will wake up. EventHandler aborted = _aborted; if (aborted != null) { aborted(this, EventArgs.Empty); } } } return removed; } ////// Name of this operation. /// ////// Returns a string representation of the operation to be invoked. /// internal String Name { get { return _method.Method.DeclaringType + "." + _method.Method.Name; } } ////// Returns the result of the operation if it has completed. /// public object Result { get { return _result; } } ////// An event that is raised when the operation is aborted. /// public event EventHandler Aborted { add { lock (DispatcherLock) { _aborted = (EventHandler) Delegate.Combine(_aborted, value); } } remove { lock(DispatcherLock) { _aborted = (EventHandler) Delegate.Remove(_aborted, value); } } } ////// An event that is raised when the operation completes. /// public event EventHandler Completed { add { lock (DispatcherLock) { _completed = (EventHandler) Delegate.Combine(_completed, value); } } remove { lock(DispatcherLock) { _completed = (EventHandler) Delegate.Remove(_completed, value); } } } // Note: this is called by the Dispatcher to actually invoke the operation. // Invoke --> InvokeInSecurityContext --> InvokeImpl ////// Critical: This code calls into ExecutionContext.Run which is link demand protected /// accesses _executionContext /// [SecurityCritical] internal object Invoke() { // Mark this operation as executing. _status = DispatcherOperationStatus.Executing; // Continue using the execution context that was active when the operation // was begun. if(_executionContext != null) { ExecutionContext.Run(_executionContext, _invokeInSecurityContext, this); } else { // _executionContext can be null if someone called // ExecutionContext.SupressFlow before calling BeginInvoke/Invoke. // In this case we'll just call the invokation directly. // SupressFlow is a privileged operation, so this is not a // security hole. _invokeInSecurityContext(this); } // This block of code needs to be synchronized with the constructor of // DispatcherOperationEvent which may be called through // Dispatcher.Invoke on a separate thread. EventHandler completed; lock(DispatcherLock) { // Mark this operation as completed. _status = DispatcherOperationStatus.Completed; // Read the Completed event handler. completed = _completed; } // Raise the Completed so anyone who is waiting will wake up. if(completed != null) { completed(this, EventArgs.Empty); } return _result; } // Invoke --> InvokeInSecurityContext --> InvokeImpl ////// Critical: This code can execute arbitrary code /// [SecurityCritical] private static void InvokeInSecurityContext(Object state) { DispatcherOperation operation = (DispatcherOperation) state; operation.InvokeImpl(); } // Invoke --> InvokeInSecurityContext --> InvokeImpl ////// Critical: This code calls into SynchronizationContext.SetSynchronizationContext which link demands /// [SecurityCritical] private void InvokeImpl() { SynchronizationContext oldSynchronizationContext = SynchronizationContext.Current; bool setSynchronizationContext = oldSynchronizationContext != _dispatcher._dispatcherSynchronizationContext; try { // We are executing under the "foreign" execution context, but the // SynchronizationContext must be for the correct dispatcher. if(setSynchronizationContext) { SynchronizationContext.SetSynchronizationContext(_dispatcher._dispatcherSynchronizationContext); } // Invoke the delegate that does the work for this operation. _result = _dispatcher.WrappedInvoke(_method, _args, _numArgs); } finally { if(setSynchronizationContext) { SynchronizationContext.SetSynchronizationContext(oldSynchronizationContext); } } } private class DispatcherOperationFrame : DispatcherFrame { // Note: we pass "exitWhenRequested=false" to the base // DispatcherFrame construsctor because we do not want to exit // this frame if the dispatcher is shutting down. This is // because we may need to invoke operations during the shutdown process. public DispatcherOperationFrame(DispatcherOperation op, TimeSpan timeout) : base(false) { _operation = op; // We will exit this frame once the operation is completed or aborted. _operation.Aborted += new EventHandler(OnCompletedOrAborted); _operation.Completed += new EventHandler(OnCompletedOrAborted); // We will exit the frame if the operation is not completed within // the requested timeout. if(timeout.TotalMilliseconds > 0) { _waitTimer = new Timer(new TimerCallback(OnTimeout), null, timeout, TimeSpan.FromMilliseconds(-1)); } // Some other thread could have aborted the operation while we were // setting up the handlers. We check the state again and mark the // frame as "should not continue" if this happened. if(_operation._status != DispatcherOperationStatus.Pending) { Exit(); } } private void OnCompletedOrAborted(object sender, EventArgs e) { Exit(); } private void OnTimeout(object arg) { Exit(); } private void Exit() { Continue = false; if(_waitTimer != null) { _waitTimer.Dispose(); } _operation.Aborted -= new EventHandler(OnCompletedOrAborted); _operation.Completed -= new EventHandler(OnCompletedOrAborted); } private DispatcherOperation _operation; private Timer _waitTimer; } private class DispatcherOperationEvent { public DispatcherOperationEvent(DispatcherOperation op, TimeSpan timeout) { _operation = op; _timeout = timeout; _event = new ManualResetEvent(false); _eventClosed = false; lock(DispatcherLock) { // We will set our event once the operation is completed or aborted. _operation.Aborted += new EventHandler(OnCompletedOrAborted); _operation.Completed += new EventHandler(OnCompletedOrAborted); // Since some other thread is dispatching this operation, it could // have been dispatched while we were setting up the handlers. // We check the state again and set the event ourselves if this // happened. if(_operation._status != DispatcherOperationStatus.Pending && _operation._status != DispatcherOperationStatus.Executing) { _event.Set(); } } } private void OnCompletedOrAborted(object sender, EventArgs e) { lock(DispatcherLock) { if(!_eventClosed) { _event.Set(); } } } public void WaitOne() { _event.WaitOne(_timeout, false); lock(DispatcherLock) { if(!_eventClosed) { // Cleanup the events. _operation.Aborted -= new EventHandler(OnCompletedOrAborted); _operation.Completed -= new EventHandler(OnCompletedOrAborted); // Close the event immediately instead of waiting for a GC // because the Dispatcher is a a high-activity component and // we could run out of events. _event.Close(); _eventClosed = true; } } } private object DispatcherLock { get { return _operation.DispatcherLock; } } private DispatcherOperation _operation; private TimeSpan _timeout; private ManualResetEvent _event; private bool _eventClosed; } private object DispatcherLock { get { return _dispatcher._instanceLock; } } ////// Obtained under an elevation. /// [SecurityCritical] private ExecutionContext _executionContext; private static ContextCallback _invokeInSecurityContext; private Dispatcher _dispatcher; private DispatcherPriority _priority; private Delegate _method; private object _args; private int _numArgs; internal DispatcherOperationStatus _status; // set from Dispatcher private object _result; internal PriorityItem_item; // The Dispatcher sets this when it enques/deques the item. EventHandler _aborted; EventHandler _completed; } /// /// A convenient delegate to use for dispatcher operations. /// public delegate object DispatcherOperationCallback(object arg); } // File provided for Reference Use Only by Microsoft Corporation (c) 2007. // Copyright (c) Microsoft Corporation. All rights reserved.
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