Imported Upstream version 4.0.0~alpha1

Former-commit-id: 806294f5ded97629b74c85c09952f2a74fe182d9

external/referencesource/System.ServiceModel.Internals/System/Runtime/SignalGate.cs

@@ -0,0 +1,126 @@
+//-----------------------------------------------------------------------------
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+//-----------------------------------------------------------------------------
+
+namespace System.Runtime
+{
+    using System;
+    using System.Threading;
+
+    [Fx.Tag.SynchronizationPrimitive(Fx.Tag.BlocksUsing.NonBlocking)]
+    class SignalGate
+    {
+        [Fx.Tag.SynchronizationObject(Blocking = false, Kind = Fx.Tag.SynchronizationKind.InterlockedNoSpin)]
+        int state;
+
+        public SignalGate()
+        {
+        }
+
+        internal bool IsLocked
+        {
+            get
+            {
+                return this.state == GateState.Locked;
+            }
+        }
+
+        internal bool IsSignalled
+        {
+            get
+            {
+                return this.state == GateState.Signalled;
+            }
+        }
+
+        // Returns true if this brings the gate to the Signalled state.
+        // Transitions - Locked -> SignalPending | Completed before it was unlocked
+        //               Unlocked -> Signaled
+        public bool Signal()
+        {
+            int lastState = this.state;
+            if (lastState == GateState.Locked)
+            {
+                lastState = Interlocked.CompareExchange(ref this.state, GateState.SignalPending, GateState.Locked);
+            }
+            if (lastState == GateState.Unlocked)
+            {
+                this.state = GateState.Signalled;
+                return true;
+            }
+
+            if (lastState != GateState.Locked)
+            {
+                ThrowInvalidSignalGateState();
+            }
+            return false;
+        }
+
+        // Returns true if this brings the gate to the Signalled state.
+        // Transitions - SignalPending -> Signaled | return the AsyncResult since the callback already 
+        //                                         | completed and provided the result on its thread
+        //               Locked -> Unlocked
+        public bool Unlock()
+        {
+            int lastState = this.state;
+            if (lastState == GateState.Locked)
+            {
+                lastState = Interlocked.CompareExchange(ref this.state, GateState.Unlocked, GateState.Locked);
+            }
+            if (lastState == GateState.SignalPending)
+            {
+                this.state = GateState.Signalled;
+                return true;
+            }
+
+            if (lastState != GateState.Locked)
+            {
+                ThrowInvalidSignalGateState();
+            }
+            return false;
+        }
+
+        // This is factored out to allow Signal and Unlock to be inlined.
+        void ThrowInvalidSignalGateState()
+        {
+            throw Fx.Exception.AsError(new InvalidOperationException(InternalSR.InvalidSemaphoreExit));
+        }
+
+        static class GateState
+        {
+            public const int Locked = 0;
+            public const int SignalPending = 1;
+            public const int Unlocked = 2;
+            public const int Signalled = 3;
+        }
+    }
+
+    [Fx.Tag.SynchronizationPrimitive(Fx.Tag.BlocksUsing.NonBlocking)]
+    class SignalGate<T> : SignalGate
+    {
+        T result;
+
+        public SignalGate()
+            : base()
+        {
+        }
+
+        public bool Signal(T result)
+        {
+            this.result = result;
+            return Signal();
+        }
+
+        public bool Unlock(out T result)
+        {
+            if (Unlock())
+            {
+                result = this.result;
+                return true;
+            }
+
+            result = default(T);
+            return false;
+        }
+    }
+}