Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Web/Util/ReadWriteObjectLock.cs

@@ -0,0 +1,94 @@
+//------------------------------------------------------------------------------
+// <copyright file="ReadWriteObjectLock.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>                                                                
+//------------------------------------------------------------------------------
+
+/*
+ * ReadWriteObjectLock
+ * 
+ * Copyright (c) 1998-1999, Microsoft Corporation
+ * 
+ */
+
+namespace System.Web.Util {
+
+    using System.Runtime.Serialization.Formatters;
+    using System.Threading;
+
+    class ReadWriteObjectLock {
+        // Assumption:
+        // -1 = a writer has the lock
+        //  0 = no one has the lock
+        // >0 = number of readers using the lock
+        private int _lock;
+
+        internal ReadWriteObjectLock() {
+        }
+
+        internal virtual void AcquireRead() {
+            lock(this) {
+                while (_lock == -1) {
+                    try {
+                        Monitor.Wait(this);
+                    }
+                    catch (ThreadInterruptedException) {
+                        // Just keep looping
+                    }
+                }
+
+                _lock++;
+            }                   
+        }
+
+        internal virtual void ReleaseRead() {
+            lock(this) {
+                Debug.Assert(_lock > 0);
+
+                _lock--;
+                if (_lock == 0) {
+                    Monitor.PulseAll(this);
+                }
+            }
+        }
+
+        internal virtual void AcquireWrite() {
+            lock(this) {
+                while (_lock != 0) {
+                    try {
+                        Monitor.Wait(this);
+                    }
+                    catch (ThreadInterruptedException) {
+                        // Just keep looping
+                    }
+                }
+
+                _lock = -1;
+            }                   
+        }
+
+        internal virtual void ReleaseWrite() {
+            lock(this) {
+                Debug.Assert(_lock == -1);
+
+                _lock = 0;
+                Monitor.PulseAll(this);
+            }
+        }
+/*
+        internal virtual void AssertReadLock() {
+#if DBG
+            Debug.Assert(_lock > 0);
+#endif
+        }
+
+
+        internal virtual void AssertWriteLock() {
+#if DBG
+            Debug.Assert(_lock == -1);
+#endif
+        }
+*/
+    }
+
+}