FCL/sftools/ana/dynaanamdw/crashmdw: comparison crashanalysercmd/PerfToolsSharedLibraries/Engine/SymBuildParsingLib/Utils/SymSemaphore.cs

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+/*
+* Copyright (c) 2004-2008 Nokia Corporation and/or its subsidiary(-ies).
+* All rights reserved.
+* This component and the accompanying materials are made available
+* under the terms of "Eclipse Public License v1.0"
+* which accompanies this distribution, and is available
+* at the URL "http://www.eclipse.org/legal/epl-v10.html".
+*
+* Initial Contributors:
+* Nokia Corporation - initial contribution.
+*
+* Contributors:
+*
+* Description:
+*
+*/
+using System;
+using System.Threading;
+namespace SymBuildParsingLib.Utils
+{
+	// <summary>
+	// Author: William Stacey (staceyw@mvps.org)
+	// Date: 06/10/04
+	// The Dijkstra semaphore (also called a counting
+	// semaphore) is used to control access to
+	// a set of resources. A Dijkstra semaphore
+	// has a count associated with it and each
+	// Acquire() call reduces the count. A thread
+	// that tries to Acquire() the semaphore
+	// with a zero count blocks until someone else
+	// calls Release() to increase the count.
+	// <seealso cref="http://www.fawcette.com/javapro/
+	//            2002_02/magazine/features/krangaraju/"/>
+	// <seealso cref="http://www.mcs.drexel.edu/~shartley/
+	//         MCS361/Lectures/designingJavaSemaphore.html"/>
+	// </summary>
+	public sealed class SymSemaphore
+	{
+		#region Constructors
+		// <summary>
+		// Creates semaphore object with a maxCount
+		// and set initial count to maxCount.
+		// </summary>
+		// <param name="maxCount">
+		// Maximum count for the semaphore object.
+		// This value must be greater than zero.
+		// </param>
+		public SymSemaphore(int maxCount) : this(maxCount, maxCount)
+		{
+		}
+		// <summary>
+		// Creates semaphore object with
+		// a maximum count and initial count.
+		// </summary>
+		// <param name="maxCount">
+		// Maximum count for the semaphore object.
+		// This value must be greater than zero.
+		// </param>
+		// <param name="initialCount">
+		// Initial count for the semaphore object.
+		// This value must be zero or greater
+		// and less than or equal to maximumCount.
+		// </param>
+		public SymSemaphore(int initialCount, int maxCount)
+		{
+			if ( initialCount < 0 )
+				throw new
+					ArgumentOutOfRangeException("initialCount must be >= 0.");
+			if ( maxCount < 1 )
+				throw new ArgumentOutOfRangeException("maxCount must be >= 1.");
+			if ( initialCount > maxCount)
+				throw new
+					ArgumentOutOfRangeException("initialCount" +
+					" must be <= maxCount.");
+			count = initialCount;
+			this.maxCount = maxCount;
+			syncLock = new object();
+			starvationLock = new object();
+		}
+		#endregion
+		#region Properties
+		// <summary>
+		// Gets the current available count (or slots)
+		// in the semaphore. A count of zero means that no slots
+		// are available and calls to Acquire will block until
+		// other thread(s) call Release.
+		// Example:
+		// A semaphore with a count of 2 will allow
+		// 2 more Acquire calls before blocking.
+		// </summary>
+		public int Count
+		{
+			get
+			{
+				lock(syncLock)
+				{
+					return count;
+				}
+			}
+		}
+		// <summary>
+		// Gets the maximum count of the semaphore
+		// set during construction.
+		// </summary>
+		public int MaxCount
+		{
+			get { return maxCount; }
+		}
+		#endregion
+		#region Public Methods
+		// <summary>
+		// Acquires semaphore and decrements count by 1.
+		// If count is zero, this will
+		// block indefinitely until another thread executes
+		// a Release() to increase the count.
+		// </summary>
+		// <returns>true if the call returned because
+		// the caller reacquired the lock for the
+		// specified object. This method does not return
+		// if the lock is not reacquired.</returns>
+		public bool Wait()
+		{
+			return Wait(Timeout.Infinite);
+		}
+		// <summary>
+		// Returns a value indicating if Semephore
+		// can be acquired within the timeout period.
+		// </summary>
+		// <returns>true if the lock was acquired before
+		// the specified time elapsed; otherwise, false.</returns>
+		// <exception cref="ArgumentOutOfRangeException">
+		// The value of the millisecondsTimeout parameter
+		// is negative, and is not equal to Infinite.
+		// </exception>
+		public bool Wait(int millisecondsTimeout)
+		{
+			lock(syncLock)
+			{
+				// Use spin lock instead of an if test, to handle
+				// rogue/barging threads that can enter
+				// syncLock before a thread that was notified by a pulse.
+				// That rogue thread would
+				// decrease the count, then our "Pulsed" thread
+				// would regain the lock and continue and
+				// decrease the count to -1 which is an error.
+				// The while loop/test prevents this.
+				while ( count == 0 )
+					try
+					{
+						if (!Monitor.Wait(syncLock, millisecondsTimeout))
+							return false;
+					}
+					catch
+					{
+						// If we get interupted or aborted,
+						// we may have been pulsed before.
+						// If we just exit, that pulse would get lost and
+						// possibly result in a "live" lock
+						// where other threads are waiting
+						// on syncLock, and never get a pulse.
+						// Regenerate a Pulse as we consumed it.
+						// Even if we did not get
+						// pulsed, this does not hurt as any thread
+						// will check again for count = 0.
+						Monitor.Pulse(syncLock);
+						// Rethrow the exception for caller.
+						// Now semaphore state is same as if
+						// this call never happened. Caller must
+						// decide how to handle exception.
+						throw;
+					}
+				count--;
+				if ( count == 0 )
+					lock(starvationLock) { Monitor.PulseAll(starvationLock); }
+				return true;
+			}
+		}
+		// <summary>
+		// Acquires all the semaphores and brings
+		// count to zero. This has the effect
+		// of block other threads until we release one or more slots.
+		// <seealso cref="Acquire()"/>
+		// <seealso cref="ReleaseAll()"/>
+		// </summary>
+		// <returns>true if the acquired maxCount slots.
+		// This method does not return until
+		// all slots are acquired.</returns>
+		public bool WaitAll()
+		{
+			// Aquires all slots or blocks for Timeout.Infinite.
+			return WaitAll(Timeout.Infinite);
+		}
+		// <summary>
+		// Tries to acquire (maxCount) slots
+		// in semaphore. If any single attempt to
+		// acquire a semaphore slot exceeds
+		// millisecondsTimeout, then return is false.
+		// Return is true if we acquire maxCount slots.
+		// Normally this method would be paired
+		// with the ReleaseAll method.
+		// </summary>
+		// <param name="millisecondsTimeout"></param>
+		// <returns>true if maxCount slots are acquired
+		// before the specified time elapsed;
+		// otherwise, false.</returns>
+		public bool WaitAll(int millisecondsTimeout)
+		{
+			int slotsGot = 0;
+			int elapsedMS = 0;
+			DateTime start = DateTime.Now;
+			int timeout = millisecondsTimeout;
+			for (int i = 0; i < maxCount; i++)
+			{
+				try
+				{
+					if (! Wait(timeout) )
+					{
+						// Could not acquire all slots,
+						// release any we may already have got.
+						if ( slotsGot > 0 )
+							Signal(slotsGot);
+						return false;
+					}
+					else
+					{
+						elapsedMS = (int)((TimeSpan)
+							(DateTime.Now - start)).TotalMilliseconds;
+						timeout = millisecondsTimeout - elapsedMS;
+						// Next wait will be a smaller timeout.
+						if ( timeout < 0 )
+							timeout = 0;
+						// Next Acquire will return
+						// false if we have to wait;
+						slotsGot++;
+						// If we get all remaining slots
+						// with no timeout, we just keep going.
+					}
+				}
+				catch
+				{
+					// Catch any exception during Acquire wait.
+					if ( slotsGot > 0 )
+						Signal(slotsGot);
+					throw;
+				}
+			} // end for.
+			// Count is not zero, so notify any/all starvation consumers.
+			lock(starvationLock) { Monitor.PulseAll(starvationLock); }
+			return true;
+		}
+		// <summary>
+		// Increases the count of the semaphore object by one.
+		// </summary>
+		public void Signal()
+		{
+			Signal(1);
+		}
+		// <summary>
+		// Increases the count of the semaphore
+		// object by a specified amount.
+		// </summary>
+		// <param name="count">Amount by which the semaphore
+		// object's current count is to be increased.</param>
+		// <exception cref="ArgumentOutOfRangeException">
+		// The releaseCount must be one or greater.
+		// </exception>
+		// <exception cref="ArgumentOutOfRangeException">
+		// The releaseCount would cause
+		// the semaphore's count to exceed maxCount.
+		// </exception>
+		public void Signal(int releaseCount)
+		{
+			if ( releaseCount < 1 )
+				throw new
+					ArgumentOutOfRangeException("releaseCount must be >= 1.");
+			lock(syncLock)
+			{
+				if ( (count + releaseCount) > maxCount )
+					throw new
+						ArgumentOutOfRangeException("releaseCount" +
+						" would cause the semaphore's count to exceed maxCount.");
+				count += releaseCount;
+				Monitor.PulseAll(syncLock);
+			}
+		}
+		// <summary>
+		// Returns indication if we could
+		// release one slot in the semaphore.
+		// </summary>
+		// <returns>true if we released
+		// one slot; otherwise false.</returns>
+		public bool TryRelease()
+		{
+			return TryRelease(1);
+		}
+		// <summary>
+		// Returns indication if we could release
+		// releaseCount slots in the semaphore.
+		// </summary>
+		// <param name="releaseCount"></param>
+		// <returns>true if we released releaseCount
+		// slots; otherwise false.</returns>
+		public bool TryRelease(int releaseCount)
+		{
+			if ( releaseCount <= 0 )
+				return false;
+			lock(syncLock)
+			{
+				if ( (count + releaseCount) > maxCount )
+					return false;
+				else
+					count += releaseCount;
+				Monitor.PulseAll(syncLock);
+				return true;
+			}
+		}
+		// <summary>
+		// Releases all remaining semaphores
+		// not currently owned. This would normally be
+		// called by a thread that previously
+		// called AcquireAll(). Note:  Be carefull when
+		// using this method as it will release
+		// all threads waiting on an Aquire method,
+		// which may or may not be what you want.
+		// An alternative would be to spin on
+		// TryRelease() until it returns false.
+		// </summary>
+		public void ReleaseAll()
+		{
+			lock(syncLock)
+			{
+				count = maxCount;
+				Monitor.PulseAll(syncLock);
+				// We PulseAll instead of calling pulse
+				// with exact number of times needed.
+				// This can be slightly inefficient,
+				// but is safe and simple.
+				// See http://www.mcs.drexel.edu/~shartley/
+				//   MCS361/Lectures/designingJavaSemaphore.html
+			}
+		}
+		// <summary>
+		// This method blocks the calling thread
+		// until the semaphore count drops to zero.
+		// A drop to zero will not be recognized
+		// if a release happens before this call.
+		// You can use this to get notified when
+		// semephore's count reaches zero.  This
+		// is also known as a "reverse-sensing" semaphore.
+		// </summary>
+		public void WaitForStarvation()
+		{
+			lock(starvationLock)
+			{
+				// We will block until count is 0.
+				// We use Interlocked just to be sure
+				// we test for zero correctly as we
+				// are not in the syncLock context.
+				if ( Interlocked.CompareExchange(ref count, 0, 0) != 0 )
+					Monitor.Wait(starvationLock);
+				// Any Exception during wait will
+				// just go to caller.  Do not need to signal
+				// any other threads as PulseAll(starvationLock) is used.
+				// Also note we don't do a spin
+				// while() test as we only care that
+				// count *did go to zero at some instant.
+			}
+		}
+		#endregion
+		#region Data members
+		// Current count available.
+		private int count;
+		// Max slots in the semaphore.
+		private int maxCount;
+		// Object used for sync.
+		private readonly object syncLock;
+		// Object used for starvation sync.
+		private readonly object starvationLock;
+		#endregion
+	}
+}