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Monitor.Pulse Method

Notifies a thread in the waiting queue of a change in the locked object's state.

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

public static void Pulse(
	Object obj
)

Parameters

obj
Type: System.Object

The object a thread is waiting for.

ExceptionCondition
ArgumentNullException

The obj parameter is null.

SynchronizationLockException

The calling thread does not own the lock for the specified object.

Only the current owner of the lock can signal a waiting object using Pulse.

The thread that currently owns the lock on the specified object invokes this method to signal the next thread in line for the lock. Upon receiving the pulse, the waiting thread is moved to the ready queue. When the thread that invoked Pulse releases the lock, the next thread in the ready queue (which is not necessarily the thread that was pulsed) acquires the lock.

Important noteImportant Note:

The Monitor class does not maintain state indicating that the Pulse method has been called. Thus, if you call Pulse when no threads are waiting, the next thread that calls Wait blocks as if Pulse had never been called. If two threads are using Pulse and Wait to interact, this could result in a deadlock. Contrast this with the behavior of the AutoResetEvent class: If you signal an AutoResetEvent by calling its Set method, and there are no threads waiting, the AutoResetEvent remains in a signaled state until a thread calls WaitOne, WaitAny, or WaitAll. The AutoResetEvent releases that thread and returns to the unsignaled state.

Note that a synchronized object holds several references, including a reference to the thread that currently holds the lock, a reference to the ready queue, which contains the threads that are ready to obtain the lock, and a reference to the waiting queue, which contains the threads that are waiting for notification of a change in the object's state.

The Pulse, PulseAll, and Wait methods must be invoked from within a synchronized block of code.

To signal multiple threads, use the PulseAll method.

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

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

namespace MonitorCS1
{
	class MonitorSample
	{
		const int MAX_LOOP_TIME = 1000;
		Queue	m_smplQueue;

		public MonitorSample()
		{
			m_smplQueue = new Queue(); 
		}
		public void FirstThread()
		{
			int counter = 0;
			lock(m_smplQueue)
			{
				while(counter < MAX_LOOP_TIME)
				{
					//Wait, if the queue is busy.
					Monitor.Wait(m_smplQueue);
					//Push one element.
					m_smplQueue.Enqueue(counter);
					//Release the waiting thread.
					Monitor.Pulse(m_smplQueue);	

					counter++;
				}
			}
		}
		public void SecondThread()
		{
			lock(m_smplQueue)
			{
				//Release the waiting thread.
				Monitor.Pulse(m_smplQueue);
				//Wait in the loop, while the queue is busy. 
				//Exit on the time-out when the first thread stops.  
				while(Monitor.Wait(m_smplQueue,1000))
				{
					//Pop the first element. 
					int counter = (int)m_smplQueue.Dequeue();
					//Print the first element.
					Console.WriteLine(counter.ToString());
					//Release the waiting thread.
					Monitor.Pulse(m_smplQueue);
				}
			}
		}
		//Return the number of queue elements. 
		public int GetQueueCount()
		{
			return m_smplQueue.Count;
		}

		static void Main(string[] args)
		{
			//Create the MonitorSample object.
			MonitorSample test = new MonitorSample();			
			//Create the first thread.
			Thread tFirst = new Thread(new ThreadStart(test.FirstThread));
			//Create the second thread.
			Thread tSecond = new Thread(new ThreadStart(test.SecondThread));
			//Start threads.
			tFirst.Start();
			tSecond.Start();
			//wait to the end of the two threads
			tFirst.Join();
			tSecond.Join();			
			//Print the number of queue elements.
			Console.WriteLine("Queue Count = " + test.GetQueueCount().ToString());
		}
	}
}

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

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

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

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