Interlocked.Exchange Method (Int32%, Int32)
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Sets a 32-bit signed integer to a specified value and returns the original value, as an atomic operation.
Assembly: mscorlib (in mscorlib.dll)
Parameters
- location1
- Type:
System.Int32
%
The variable to set to the specified value.
- value
- Type: System.Int32
The value to which the location1 parameter is set.
| Exception | Condition |
|---|---|
| ArgumentNullException | The address of location1 is a null pointer. |
The following example shows a thread-safe resource locking mechanism.
Note: |
|---|
To run this example, see Building examples that have static TextBlock controls for Windows Phone 8. |
using System; using System.Threading; class Example { private static System.Windows.Controls.TextBlock outputBlock; //0 for false, 1 for true. private static int usingResource = 0; private const int numThreadIterations = 5; private const int numThreads = 10; public static void Demo(System.Windows.Controls.TextBlock outputBlock) { Example.outputBlock = outputBlock; // Run the demo on a separate thread because it uses Sleep, which makes // the user interface unresponsive. Thread ct = new Thread(ControlThread); ct.Start(); } private static void ControlThread() { Thread myThread; Random rnd = new Random(); int i; for(i = 0; i < numThreads; i++) { myThread = new Thread(MyThreadProc); myThread.Name = String.Format("Thread{0}", i + 1); //Wait a random amount of time before starting next thread. Thread.Sleep(rnd.Next(0, 1000)); myThread.Start(); } } private static void MyThreadProc() { int i; for(i = 0; i < numThreadIterations; i++) { UseResource(); //Wait 1 second before next attempt. Thread.Sleep(1000); } } //A simple method that denies reentrancy. public static bool UseResource() { //0 indicates that the method is not in use. if (0 == Interlocked.Exchange(ref usingResource, 1)) { Output(String.Format("{0} acquired the lock\n", Thread.CurrentThread.Name)); //Code to access a resource that is not thread safe would go here. //Simulate some work Thread.Sleep(500); Output(String.Format("{0} exiting lock\n", Thread.CurrentThread.Name)); //Release the lock Interlocked.Exchange(ref usingResource, 0); return true; } else { Output(String.Format(" {0} was denied the lock\n", Thread.CurrentThread.Name)); return false; } } // Helper methods: // In order to update the TextBlock object, which is on the UI thread, you must // make a cross-thread call by using the Dispatcher object that is associated // with the TextBlock. The DisplayOutput helper method and its delegate, // displayHelper, are used by the BeginInvoke method of the Dispatcher object // to append text to the TextBlock. // private static void Output(string msg) { outputBlock.Dispatcher.BeginInvoke(displayHelper, msg); } private static Action<string> displayHelper = new Action<string>(DisplayOutput); private static void DisplayOutput(string msg) { outputBlock.Text += msg; } } /* This example produces output similar to the following: Thread1 acquired the lock Thread2 was denied the lock Thread1 exiting lock Thread3 acquired the lock Thread4 was denied the lock Thread2 was denied the lock Thread1 was denied the lock Thread3 exiting lock Thread6 acquired the lock Thread7 was denied the lock Thread4 was denied the lock Thread2 was denied the lock Thread5 was denied the lock Thread6 exiting lock ... */
Show:
Note: