Code:
/ DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / clr / src / BCL / System / Threading / SynchronizationContext.cs / 2 / SynchronizationContext.cs
// ==++== // // Copyright (c) Microsoft Corporation. All rights reserved. // /*============================================================ ** ** Class: SynchronizationContext ** ** ** Purpose: Capture synchronization semantics for asynchronous callbacks ** ** ===========================================================*/ namespace System.Threading { using Microsoft.Win32.SafeHandles; using System.Security.Permissions; using System.Runtime.InteropServices; using System.Runtime.CompilerServices; using System.Runtime.ConstrainedExecution; using System.Reflection; internal struct SynchronizationContextSwitcher : IDisposable { internal SynchronizationContext savedSC; internal SynchronizationContext currSC; internal ExecutionContext _ec; public override bool Equals(Object obj) { if (obj == null || !(obj is SynchronizationContextSwitcher)) return false; SynchronizationContextSwitcher sw = (SynchronizationContextSwitcher)obj; return (this.savedSC == sw.savedSC && this.currSC == sw.currSC && this._ec == sw._ec); } public override int GetHashCode() { return ToString().GetHashCode(); } public static bool operator ==(SynchronizationContextSwitcher c1, SynchronizationContextSwitcher c2) { return c1.Equals(c2); } public static bool operator !=(SynchronizationContextSwitcher c1, SynchronizationContextSwitcher c2) { return !c1.Equals(c2); } ///void IDisposable.Dispose() { Undo(); } [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)] internal bool UndoNoThrow() { if (_ec == null) { return true; } try { Undo(); } catch { return false; } return true; } [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)] public void Undo() { if (_ec == null) { return; } ExecutionContext executionContext = Thread.CurrentThread.GetExecutionContextNoCreate(); if (_ec != executionContext) { throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_SwitcherCtxMismatch")); } if (currSC != _ec.SynchronizationContext) { throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_SwitcherCtxMismatch")); } BCLDebug.Assert(executionContext != null, " ExecutionContext can't be null"); // restore the Saved Sync context as current executionContext.SynchronizationContext = savedSC; // can't reuse this anymore _ec = null; } } public delegate void SendOrPostCallback(Object state); [Flags] enum SynchronizationContextProperties { None = 0, RequireWaitNotification = 0x1 }; [SecurityPermissionAttribute(SecurityAction.InheritanceDemand, Flags =SecurityPermissionFlag.ControlPolicy|SecurityPermissionFlag.ControlEvidence)] public class SynchronizationContext { SynchronizationContextProperties _props = SynchronizationContextProperties.None; public SynchronizationContext() { } // protected so that only the derived sync context class can enable these flags protected void SetWaitNotificationRequired() { // Prepare the method so that it can be called in a reliable fashion when a wait is needed. // This will obviously only make the Wait reliable if the Wait method is itself reliable. The only thing // preparing the method here does is to ensure there is no failure point before the method execution begins. RuntimeHelpers.PrepareDelegate(new WaitDelegate(this.Wait)); _props |= SynchronizationContextProperties.RequireWaitNotification; } public bool IsWaitNotificationRequired() { return ((_props & SynchronizationContextProperties.RequireWaitNotification) != 0); } public virtual void Send(SendOrPostCallback d, Object state) { d(state); } public virtual void Post(SendOrPostCallback d, Object state) { ThreadPool.QueueUserWorkItem(new WaitCallback(d), state); } /// /// Optional override for subclasses, for responding to notification that operation is starting. /// public virtual void OperationStarted() { } ////// Optional override for subclasses, for responding to notification that operation has completed. /// public virtual void OperationCompleted() { } // Method called when the CLR does a wait operation [CLSCompliant(false)] [PrePrepareMethod] [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags =SecurityPermissionFlag.ControlPolicy|SecurityPermissionFlag.ControlEvidence)] public virtual int Wait(IntPtr[] waitHandles, bool waitAll, int millisecondsTimeout) { if (waitHandles == null) { throw new ArgumentNullException("waitHandles"); } return WaitHelper(waitHandles, waitAll, millisecondsTimeout); } // Static helper to which the above method can delegate to in order to get the default // COM behavior. [CLSCompliant(false)] [PrePrepareMethod] [MethodImplAttribute(MethodImplOptions.InternalCall)] [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags =SecurityPermissionFlag.ControlPolicy|SecurityPermissionFlag.ControlEvidence), ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)] protected static extern int WaitHelper(IntPtr[] waitHandles, bool waitAll, int millisecondsTimeout); // set SynchronizationContext on the current thread [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags =SecurityPermissionFlag.ControlPolicy|SecurityPermissionFlag.ControlEvidence)] public static void SetSynchronizationContext(SynchronizationContext syncContext) { SetSynchronizationContext(syncContext, Thread.CurrentThread.ExecutionContext.SynchronizationContext); } internal static SynchronizationContextSwitcher SetSynchronizationContext(SynchronizationContext syncContext, SynchronizationContext prevSyncContext) { // get current execution context ExecutionContext ec = Thread.CurrentThread.ExecutionContext; // create a swticher SynchronizationContextSwitcher scsw = new SynchronizationContextSwitcher(); RuntimeHelpers.PrepareConstrainedRegions(); try { // attach the switcher to the exec context scsw._ec = ec; // save the current sync context using the passed in value scsw.savedSC = prevSyncContext; // save the new sync context also scsw.currSC = syncContext; // update the current sync context to the new context ec.SynchronizationContext = syncContext; } catch { // Any exception means we just restore the old SyncCtx scsw.UndoNoThrow(); //No exception will be thrown in this Undo() throw; } // return switcher return scsw; } // Get the current SynchronizationContext on the current thread public static SynchronizationContext Current { get { ExecutionContext ec = Thread.CurrentThread.GetExecutionContextNoCreate(); if (ec != null) return ec.SynchronizationContext; return null; } } // helper to Clone this SynchronizationContext, public virtual SynchronizationContext CreateCopy() { // the CLR dummy has an empty clone function - no member data return new SynchronizationContext(); } private static int InvokeWaitMethodHelper(SynchronizationContext syncContext, IntPtr[] waitHandles, bool waitAll, int millisecondsTimeout) { return syncContext.Wait(waitHandles, waitAll, millisecondsTimeout); } } }
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