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Monitor.TryEnter Method (Object)

Attempts to acquire an exclusive lock on the specified object.

Namespace: System.Threading
Assembly: mscorlib (in mscorlib.dll)

public static bool TryEnter (
	Object obj
)
public static boolean TryEnter (
	Object obj
)
public static function TryEnter (
	obj : Object
) : boolean

Parameters

obj

The object on which to acquire the lock.

Return Value

true if the current thread acquires the lock; otherwise, false.

Exception typeCondition

ArgumentNullException

The obj parameter is a null reference (Nothing in Visual Basic).

ArgumentException

The obj parameter is a value type.

If successful, this method acquires an exclusive lock on the obj parameter. This method returns immediately, whether or not the lock is available.

This method is similar to Enter, but it will never block. If the thread cannot enter without blocking, the method returns false, and the thread does not enter the critical section.

NoteNote

Use Monitor to lock objects (that is, reference types), not value types. For details, see Enter and the conceptual topic Monitors.

The following code example demonstrates how to use the TryEnter method.

using System;
using System.Collections;
using System.Threading;

namespace MonitorCS2
{
	/// <summary>
	/// Summary description for Class1.
	/// </summary>
	class MonitorSample
	{
		//Define the queue to safe thread access.
		private Queue m_inputQueue;

		public MonitorSample()
		{
			m_inputQueue = new Queue(); 
		}

		//Add an element to the queue and obtain the monitor lock for the queue object.
		public void AddElement(object qValue)
		{
			//Lock the queue.
			Monitor.Enter(m_inputQueue);
			//Add element
			m_inputQueue.Enqueue(qValue);
			//Unlock the queue.
			Monitor.Exit(m_inputQueue);
		}

		//Try to add an element to the queue.
		//Add the element to the queue only if the queue object is unlocked.
		public bool AddElementWithoutWait(object qValue)
		{
			//Determine whether the queue is locked 
			if(!Monitor.TryEnter(m_inputQueue))
				return false;
			m_inputQueue.Enqueue(qValue);

			Monitor.Exit(m_inputQueue);
			return true;
		}

		//Try to add an element to the queue. 
		//Add the element to the queue only if during the specified time the queue object will be unlocked.
		public bool WaitToAddElement(object qValue, int waitTime)
		{
			//Wait while the queue is locked.
			if(!Monitor.TryEnter(m_inputQueue,waitTime))
				return false;
			m_inputQueue.Enqueue(qValue);
			Monitor.Exit(m_inputQueue);

			return true;
		}
		
		//Delete all elements that equal the given object and obtain the monitor lock for the queue object.
		public void DeleteElement(object qValue)
		{
			//Lock the queue.
			Monitor.Enter(m_inputQueue);
			int counter = m_inputQueue.Count;
			while(counter > 0)
			{	
				//Check each element.
				object elm = m_inputQueue.Dequeue();
				if(!elm.Equals(qValue))
				{
					m_inputQueue.Enqueue(elm);
				}
				--counter;
			}
			//Unlock the queue.
			Monitor.Exit(m_inputQueue);
		}
		
		//Print all queue elements.
		public void PrintAllElements()
		{
			//Lock the queue.
			Monitor.Enter(m_inputQueue);			
			IEnumerator elmEnum = m_inputQueue.GetEnumerator();
			while(elmEnum.MoveNext())
			{
				//Print the next element.
				Console.WriteLine(elmEnum.Current.ToString());
			}
			//Unlock the queue.
			Monitor.Exit(m_inputQueue);	
		}

		static void Main(string[] args)
		{
			MonitorSample sample = new MonitorSample();
			
			for(int i = 0; i < 30; i++)
				sample.AddElement(i);
			sample.PrintAllElements();
			sample.DeleteElement(0);
			sample.DeleteElement(10);
			sample.DeleteElement(20);
			sample.PrintAllElements();

		}
	}
}


package MonitorJSL2;

import System.*;
import System.Collections.*;
import System.Threading.*;

/// <summary>
/// Summary description for Class1.
/// </summary>
    
class MonitorSample
{
    //Define the queue to safe thread access.
    private Queue mInputQueue;

    public MonitorSample()
    {
        mInputQueue = new Queue();
    } //MonitorSample

    // Add an element to the queue and obtain the monitor lock for the 
    // queue object.
    public void AddElement(Object qValue)
    {
        //Lock the queue.
        Monitor.Enter(mInputQueue);

        //Add element
        mInputQueue.Enqueue(qValue);

        //Unlock the queue.
        Monitor.Exit(mInputQueue);
    } //AddElement

    //Try to add an element to the queue.
    //Add the element to the queue only if the queue object is unlocked.
    public boolean AddElementWithoutWait(Object qValue)
    {
        //Determine whether the queue is locked 
        if (!(Monitor.TryEnter(mInputQueue))) {
            return false;
        }
        mInputQueue.Enqueue(qValue);
        Monitor.Exit(mInputQueue);
        return true;
    } //AddElementWithoutWait

    //Try to add an element to the queue. 
    //Add the element to the queue only if during the specified time the 
    //queue object will be unlocked.
    public boolean WaitToAddElement(Object qValue, int waitTime)
    {
        //Wait while the queue is locked.
        if (!(Monitor.TryEnter(mInputQueue, waitTime))) {
            return false;
        }
        mInputQueue.Enqueue(qValue);
        Monitor.Exit(mInputQueue);

        return true;
    } //WaitToAddElement

    //Delete all elements that equal the given object and obtain the 
    //monitor lock for the queue object.
    public void DeleteElement(Object qValue)
    {
        //Lock the queue.
        Monitor.Enter(mInputQueue);
        int counter = mInputQueue.get_Count();
        while (counter > 0) {
            //Check each element.
            Object elm = mInputQueue.Dequeue();
            if (!(elm.Equals(qValue))) {
                mInputQueue.Enqueue(elm);
            }
            --counter;
        }

        //Unlock the queue.
        Monitor.Exit(mInputQueue);
    } //DeleteElement

    //Print all queue elements.
    public void PrintAllElements()
    {
        //Lock the queue.
        Monitor.Enter(mInputQueue);
        IEnumerator elmEnum = mInputQueue.GetEnumerator();
        while (elmEnum.MoveNext()) {
            //Print the next element.
            Console.WriteLine(elmEnum.get_Current().ToString());
        }

        //Unlock the queue.
        Monitor.Exit(mInputQueue);
    } //PrintAllElements

    public static void main(String[] args)
    {
        MonitorSample sample = new MonitorSample();

        for (int i = 0; i < 30; i++) {
            sample.AddElement((Int32)i);
        }
        sample.PrintAllElements();
        sample.DeleteElement((Int32)0);
        sample.DeleteElement((Int32)10);
        sample.DeleteElement((Int32)20);
        sample.PrintAllElements();
    } //main 
} //MonitorSample

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0

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