bundles/org.eclipse.equinox.common/src/org/eclipse/core/runtime/SubMonitor.java

/*******************************************************************************
 * Copyright (c) 2006, 2008 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors:
 *     Stefan Xenos - initial API and implementation
 *     Stefan Xenos - bug 174539 - add a 1-argument convert(...) method     
 *     Stefan Xenos - bug 174040 - SubMonitor#convert doesn't always set task name
 *     Stefan Xenos - bug 206942 - updated javadoc to recommend better constants for infinite progress
 *     IBM Corporation - ongoing maintenance
 *******************************************************************************/
package org.eclipse.core.runtime;

/**
 * <p>A progress monitor that uses a given amount of work ticks from a parent monitor. This is intended as a 
 * safer, easier-to-use alternative to SubProgressMonitor. The main benefits of SubMonitor over 
 * SubProgressMonitor are:</p>
 * <ul>
 * <li>It is not necessary to call beginTask() or done() on an instance of SubMonitor.</li>
 * <li>SubMonitor has a simpler syntax for creating nested monitors.</li>
 * <li>SubMonitor is more efficient for deep recursion chains.</li>      
 * <li>SubMonitor has a setWorkRemining method that allows the remaining space on the monitor to be 
 * redistributed without reporting any work.</li>
 * <li>SubMonitor protects the caller from common progress reporting bugs in a called method. For example, 
 * if a called method fails to call done() on the given monitor or fails to consume all the ticks on 
 * the given monitor, the parent will correct the problem after the method returns.</li>  
 * </ul>
 * <p></p>
 * <p><b>USAGE:</b></p>
 * 
 * <p>When implementing a method that accepts an IProgressMonitor:</p>
 * <ul>
 * <li>At the start of your method, use <code>SubMonitor.convert(...).</code> to convert the IProgressMonitor 
 * into a SubMonitor. </li>
 * <li>Use <code>SubMonitor.newChild(...)</code> whenever you need to call another method that 
 * accepts an IProgressMonitor.</li>
 * </ul>
 * <p></p>
 * <p><b>DEFAULT BEHAVIOR:</b></p>
 * 
 * <p>When writing JavaDoc for a method that accepts an IProgressMonitor, you should assume the 
 * following default behavior unless the method's JavaDoc says otherwise:</p>
 * <ul>
 * <li>It WILL call beginTask on the IProgressMonitor.</li>
 * <li>It WILL NOT accept a null argument.</li>
 * <li>It WILL call done on the IProgressMonitor.</li>
 * </ul>
 * <p></p>
 * <p><b>BEST PRACTISES:</b></p>
 * 
 * <p>We recommend that newly-written methods follow the given contract:</p>
 * <ul>
 * <li>It WILL call beginTask on the IProgressMonitor.</li>
 * <li>It WILL accept a null argument, indicating that no progress should be reported and the operation cannot be cancelled.</li>
 * <li>It WILL NOT call done on the IProgressMonitor, leaving this responsibility up to the caller.</li>
 * </ul>
 * <p>If you wish to follow these conventions, you may copy and paste the following text into your method's JavaDoc:</p>
 * 
 * <pre>@param monitor the progress monitor to use for reporting progress to the user. It is the caller's responsibility
 *        to call done() on the given monitor. Accepts <code>null</code>, indicating that no progress should be
 *        reported and that the operation cannot be cancelled.</pre>
 *
 * <p></p>
 * <p><b>Example: Recommended usage</b></p>
 *
 * <p>This example demonstrates how the recommended usage of <code>SubMonitor</code> makes it unnecessary to call
 * IProgressMonitor.done() in most situations.</p>
 * 
 * <p>It is never necessary to call done() on a monitor obtained from <code>convert</code> or <code>progress.newChild()</code>. 
 * In this example, there is no guarantee that <code>monitor</code> is an instance of <code>SubMonitor</code>, making it 
 * necessary to call <code>monitor.done()</code>. The JavaDoc contract makes this the responsibility of the caller.</p> 
 * 
 * <pre>
 *      // param monitor the progress monitor to use for reporting progress to the user. It is the caller's responsibility
 *      //        to call done() on the given monitor. Accepts <code>null</code>, indicating that no progress should be
 *      //        reported and that the operation cannot be cancelled.
 *      //
 *      void doSomething(IProgressMonitor monitor) {
 *      	// Convert the given monitor into a progress instance 
 *          SubMonitor progress = SubMonitor.convert(monitor, 100);
 *              
 *          // Use 30% of the progress to do some work
 *          doSomeWork(progress.newChild(30));
 *          
 *          // Advance the monitor by another 30%
 *          progress.worked(30);
 *          
 *          // Use the remaining 40% of the progress to do some more work
 *          doSomeWork(progress.newChild(40)); 
 *      }
 * </pre>
 *
 *
 * <p></p>
 * <p><b>Example: Default usage</b></p>
 * 
 * <p>You will often need to implement a method that does not explicitly stipulate that calling done() is the responsibility
 * of the caller. In this case, you should use the following pattern:</p>
 * 
 * <pre>
 *      // param monitor the progress monitor to use for reporting progress to the user, or <code>null</code> indicating
 *      //        that no progress should be reported and the operation cannot be cancelled.
 *      //
 *      void doSomething(IProgressMonitor monitor) {
 *          // Convert the given monitor into a progress instance 
 *          SubMonitor progress = SubMonitor.convert(monitor, 100);
 *          try {
 *              // Use 30% of the progress to do some work
 *              doSomeWork(progress.newChild(30));
 *          
 *              // Advance the monitor by another 30%
 *              progress.worked(30);
 *          
 *              // Use the remaining 40% of the progress to do some more work
 *              doSomeWork(progress.newChild(40));
 *                            
 *          } finally {
 *              if (monitor != null) {
 *              	monitor.done();
 *              }
 *          } 
 *      }
 * </pre>
 * 
 * <p></p>
 * <p><b>Example: Branches</b></p>
 *
 * <p>This example demonstrates how to smoothly report progress in situations where some of the work is optional.</p>
 * 
 * <pre>
 *      void doSomething(IProgressMonitor monitor) {
 *          SubMonitor progress = SubMonitor.convert(monitor, 100);
 *           
 *          if (condition) {
 *              // Use 50% of the progress to do some work
 *          	doSomeWork(progress.newChild(50));
 *          }
 *          
 *          // Don't report any work, but ensure that we have 50 ticks remaining on the progress monitor.
 *          // If we already consumed 50 ticks in the above branch, this is a no-op. Otherwise, the remaining
 *          // space in the monitor is redistributed into 50 ticks.
 *          
 *          progress.setWorkRemaining(50);
 *          
 *          // Use the remainder of the progress monitor to do the rest of the work
 *          doSomeWork(progress.newChild(50)); 
 *      }
 * </pre>
 * 
 * <p>Please beware of the following anti-pattern:</p>
 *
 * <pre>
 *          if (condition) {
 *              // Use 50% of the progress to do some work
 *          	doSomeWork(progress.newChild(50));
 *          } else {
 *              // Bad: Causes the progress monitor to appear to start at 50%, wasting half of the
 *              // space in the monitor.
 *              progress.worked(50);
 *          }
 * </pre>
 * 
 * 
 * <p></p>
 * <p><b>Example: Loops</b></p>
 *
 * <p>This example demonstrates how to report progress in a loop.</p> 
 * 
 * <pre>
 *      void doSomething(IProgressMonitor monitor, Collection someCollection) {
 *          SubMonitor progress = SubMonitor.convert(monitor, 100);
 *
 *          // Create a new progress monitor that uses 70% of the total progress and will allocate one tick
 *          // for each element of the given collection. 
 *          SubMonitor loopProgress = progress.newChild(70).setWorkRemaining(someCollection.size());
 *          
 *          for (Iterator iter = someCollection.iterator(); iter.hasNext();) {
 *          	Object next = iter.next();
 *              
 *              doWorkOnElement(next, loopProgress.newChild(1));
 *          }
 *          
 *          // Use the remaining 30% of the progress monitor to do some work outside the loop
 *          doSomeWork(progress.newChild(30));
 *      }
 * </pre>
 *
 *
 * <p></p>
 * <p><b>Example: Infinite progress</b></p>
 * 
 * <p>This example demonstrates how to report logarithmic progress in situations where the number of ticks
 * cannot be easily computed in advance.</p>
 * 
 * <pre>
 *      void doSomething(IProgressMonitor monitor, LinkedListNode node) {
 *          SubMonitor progress = SubMonitor.convert(monitor);
 *
 *			while (node != null) {
 *              // Regardless of the amount of progress reported so far,
 *              // use 0.01% of the space remaining in the monitor to process the next node.
 *              progress.setWorkRemaining(10000);
 *              
 *				doWorkOnElement(node, progress.newChild(1));
 *
 *              node = node.next;
 *          }
 *      }
 * </pre>  
 * 
 * <p>
 * This class can be used without OSGi running.
 * </p>
 * 
 * @since org.eclipse.equinox.common 3.3
 */
public final class SubMonitor implements IProgressMonitorWithBlocking {

	/**
	 * Minimum number of ticks to allocate when calling beginTask on an unknown IProgressMonitor.
	 * Pick a number that is big enough such that, no matter where progress is being displayed,
	 * the user would be unlikely to notice if progress were to be reported with higher accuracy.
	 */
	private static final int MINIMUM_RESOLUTION = 1000;

	/**
	 * The RootInfo holds information about the root progress monitor. A SubMonitor and
	 * its active descendents share the same RootInfo.
	 */
	private static final class RootInfo {
		private final IProgressMonitor root;

		/**
		 * Remembers the last task name. Prevents us from setting the same task name multiple
		 * times in a row.
		 */
		private String taskName = null;

		/**
		 * Remembers the last subtask name. Prevents the SubMonitor from setting the same
		 * subtask string more than once in a row.
		 */
		private String subTask = null;

		/**
		 * Creates a RootInfo struct that delegates to the given progress 
		 * monitor. 
		 * 
		 * @param root progress monitor to delegate to
		 */
		public RootInfo(IProgressMonitor root) {
			this.root = root;
		}

		public boolean isCanceled() {
			return root.isCanceled();
		}

		public void setCanceled(boolean value) {
			root.setCanceled(value);
		}

		public void setTaskName(String taskName) {
			if (eq(taskName, this.taskName)) {
				return;
			}
			this.taskName = taskName;
			root.setTaskName(taskName);
		}

		public void subTask(String name) {
			if (eq(subTask, name)) {
				return;
			}

			this.subTask = name;
			root.subTask(name);
		}

		public void worked(int i) {
			root.worked(i);
		}

		public void clearBlocked() {
			if (root instanceof IProgressMonitorWithBlocking)
				((IProgressMonitorWithBlocking) root).clearBlocked();
		}

		public void setBlocked(IStatus reason) {
			if (root instanceof IProgressMonitorWithBlocking)
				((IProgressMonitorWithBlocking) root).setBlocked(reason);
		}

	}

	/**
	 * Total number of ticks that this progress monitor is permitted to consume
	 * from the root.
	 */
	private int totalParent;

	/**
	 * Number of ticks that this progress monitor has already reported in the root.
	 */
	private int usedForParent = 0;

	/**
	 * Number of ticks that have been consumed by this instance's children.
	 */
	private double usedForChildren = 0.0;

	/**
	 * Number of ticks allocated for this instance's children. This is the total number
	 * of ticks that may be passed into worked(int) or newChild(int). 
	 */
	private int totalForChildren;

	/**
	 * Children created by newChild will be completed automatically the next time
	 * the parent progress monitor is touched. This points to the last incomplete child 
	 * created with newChild.
	 */
	private IProgressMonitor lastSubMonitor = null;

	/**
	 * Used to communicate with the root of this progress monitor tree
	 */
	private final RootInfo root;

	/**
	 * A bitwise combination of the SUPPRESS_* flags.
	 */
	private final int flags;

	/**
	 * May be passed as a flag to newChild. Indicates that the calls
	 * to subTask on the child should be ignored. Without this flag,
	 * calling subTask on the child will result in a call to subTask
	 * on its parent.
	 */
	public static final int SUPPRESS_SUBTASK = 0x0001;

	/**
	 * May be passed as a flag to newChild. Indicates that strings
	 * passed into beginTask should be ignored. If this flag is
	 * specified, then the progress monitor instance will accept null 
	 * as the first argument to beginTask. Without this flag, any 
	 * string passed to beginTask will result in a call to
	 * setTaskName on the parent.
	 */
	public static final int SUPPRESS_BEGINTASK = 0x0002;

	/**
	 * May be passed as a flag to newChild. Indicates that strings
	 * passed into setTaskName should be ignored. If this string
	 * is omitted, then a call to setTaskName on the child will 
	 * result in a call to setTaskName on the parent.
	 */
	public static final int SUPPRESS_SETTASKNAME = 0x0004;

	/**
	 * May be passed as a flag to newChild. Indicates that strings
	 * passed to setTaskName, subTask, and beginTask should all be ignored.
	 */
	public static final int SUPPRESS_ALL_LABELS = SUPPRESS_SETTASKNAME | SUPPRESS_BEGINTASK | SUPPRESS_SUBTASK;

	/**
	 * May be passed as a flag to newChild. Indicates that strings
	 * passed to setTaskName, subTask, and beginTask should all be propagated
	 * to the parent.
	 */
	public static final int SUPPRESS_NONE = 0;

	/**
	 * Creates a new SubMonitor that will report its progress via
	 * the given RootInfo.
	 * @param rootInfo the root of this progress monitor tree
	 * @param totalWork total work to perform on the given progress monitor
	 * @param availableToChildren number of ticks allocated for this instance's children
	 * @param flags a bitwise combination of the SUPPRESS_* constants
	 */
	private SubMonitor(RootInfo rootInfo, int totalWork, int availableToChildren, int flags) {
		root = rootInfo;
		totalParent = (totalWork > 0) ? totalWork : 0;
		this.totalForChildren = availableToChildren;
		this.flags = flags;
	}

	/**
	 * <p>Converts an unknown (possibly null) IProgressMonitor into a SubMonitor. It is 
	 * not necessary to call done() on the result, but the caller is responsible for calling 
	 * done() on the argument. Calls beginTask on the argument.</p>
	 * 
	 * <p>This method should generally be called at the beginning of a method that accepts
	 * an IProgressMonitor in order to convert the IProgressMonitor into a SubMonitor.</p> 
	 * 
	 * @param monitor monitor to convert to a SubMonitor instance or null. Treats null
	 * as a new instance of <code>NullProgressMonitor</code>.
	 * @return a SubMonitor instance that adapts the argument
	 */
	public static SubMonitor convert(IProgressMonitor monitor) {
		return convert(monitor, "", 0); //$NON-NLS-1$
	}

	/**
	 * <p>Converts an unknown (possibly null) IProgressMonitor into a SubMonitor allocated
	 * with the given number of ticks. It is not necessary to call done() on the result,
	 * but the caller is responsible for calling done() on the argument. Calls beginTask
	 * on the argument.</p>
	 * 
	 * <p>This method should generally be called at the beginning of a method that accepts
	 * an IProgressMonitor in order to convert the IProgressMonitor into a SubMonitor.</p> 
	 * 
	 * @param monitor monitor to convert to a SubMonitor instance or null. Treats null
	 * as a new instance of <code>NullProgressMonitor</code>.
	 * @param work number of ticks that will be available in the resulting monitor
	 * @return a SubMonitor instance that adapts the argument
	 */
	public static SubMonitor convert(IProgressMonitor monitor, int work) {
		return convert(monitor, "", work); //$NON-NLS-1$
	}

	/**
	 * <p>Converts an unknown (possibly null) IProgressMonitor into a SubMonitor allocated
	 * with the given number of ticks. It is not necessary to call done() on the result,
	 * but the caller is responsible for calling done() on the argument. Calls beginTask
	 * on the argument.</p>
	 * 
	 * <p>This method should generally be called at the beginning of a method that accepts
	 * an IProgressMonitor in order to convert the IProgressMonitor into a SubMonitor.</p> 
	 *  
	 * @param monitor to convert into a SubMonitor instance or null. If given a null argument,
	 * the resulting SubMonitor will not report its progress anywhere.
	 * @param taskName user readable name to pass to monitor.beginTask. Never null. 
	 * @param work initial number of ticks to allocate for children of the SubMonitor
	 * @return a new SubMonitor instance that is a child of the given monitor
	 */
	public static SubMonitor convert(IProgressMonitor monitor, String taskName, int work) {
		if (monitor == null)
			monitor = new NullProgressMonitor();

		// Optimization: if the given monitor already a SubMonitor, no conversion is necessary
		if (monitor instanceof SubMonitor) {
			monitor.beginTask(taskName, work);
			return (SubMonitor) monitor;
		}

		monitor.beginTask(taskName, MINIMUM_RESOLUTION);
		return new SubMonitor(new RootInfo(monitor), MINIMUM_RESOLUTION, work, SUPPRESS_NONE);
	}

	/**
	 * <p>Sets the work remaining for this SubMonitor instance. This is the total number
	 * of ticks that may be reported by all subsequent calls to worked(int), newChild(int), etc.
	 * This may be called many times for the same SubMonitor instance. When this method 
	 * is called, the remaining space on the progress monitor is redistributed into the given 
	 * number of ticks.</p>
	 * 
	 * <p>It doesn't matter how much progress has already been reported with this SubMonitor
	 * instance. If you call setWorkRemaining(100), you will be able to report 100 more ticks of 
	 * work before the progress meter reaches 100%.</p>
	 * 
	 * @param workRemaining total number of remaining ticks
	 * @return the receiver
	 */
	public SubMonitor setWorkRemaining(int workRemaining) {
		// Ensure we don't try to allocate negative ticks
		workRemaining = Math.max(0, workRemaining);

		// Ensure we don't cause division by zero
		if (totalForChildren > 0 && totalParent > usedForParent) {
			// Note: We want the following value to remain invariant after this method returns
			double remainForParent = totalParent * (1.0d - (usedForChildren / totalForChildren));
			usedForChildren = (workRemaining * (1.0d - remainForParent / (totalParent - usedForParent)));
		} else
			usedForChildren = 0.0d;

		totalParent = totalParent - usedForParent;
		usedForParent = 0;
		totalForChildren = workRemaining;
		return this;
	}

	/**
	 * Consumes the given number of child ticks, given as a double. Must only 
	 * be called if the monitor is in floating-point mode.
	 *  
	 * @param ticks the number of ticks to consume
	 * @return ticks the number of ticks to be consumed from parent
	 */
	private int consume(double ticks) {
		if (totalParent == 0 || totalForChildren == 0) // this monitor has no available work to report
			return 0;

		usedForChildren += ticks;

		if (usedForChildren > totalForChildren)
			usedForChildren = totalForChildren;
		else if (usedForChildren < 0.0)
			usedForChildren = 0.0;

		int parentPosition = (int) (totalParent * usedForChildren / totalForChildren);
		int delta = parentPosition - usedForParent;

		usedForParent = parentPosition;
		return delta;
	}

	/* (non-Javadoc)
	 * @see org.eclipse.core.runtime.IProgressMonitor#isCanceled()
	 */
	public boolean isCanceled() {
		return root.isCanceled();
	}

	/* (non-Javadoc)
	 * @see org.eclipse.core.runtime.IProgressMonitor#setTaskName(java.lang.String)
	 */
	public void setTaskName(String name) {
		if ((flags & SUPPRESS_SETTASKNAME) == 0)
			root.setTaskName(name);
	}

	/**
	 * Starts a new main task. The string argument is ignored
	 * if and only if the SUPPRESS_BEGINTASK flag has been set on this SubMonitor
	 * instance. 
	 * 
	 * <p>This method is equivalent calling setWorkRemaining(...) on the receiver. Unless 
	 * the SUPPRESS_BEGINTASK flag is set, this will also be equivalent to calling 
	 * setTaskName(...) on the parent.</p>
	 * 
	 * @param name new main task name
	 * @param totalWork number of ticks to allocate
	 * 
	 * @see org.eclipse.core.runtime.IProgressMonitor#beginTask(java.lang.String, int)
	 */
	public void beginTask(String name, int totalWork) {
		if ((flags & SUPPRESS_BEGINTASK) == 0 && name != null)
			root.setTaskName(name);
		setWorkRemaining(totalWork);
	}

	/* (non-Javadoc)
	 * @see org.eclipse.core.runtime.IProgressMonitor#done()
	 */
	public void done() {
		cleanupActiveChild();
		int delta = totalParent - usedForParent;
		if (delta > 0)
			root.worked(delta);

		totalParent = 0;
		usedForParent = 0;
		totalForChildren = 0;
		usedForChildren = 0.0d;
	}

	/* (non-Javadoc)
	 * @see org.eclipse.core.runtime.IProgressMonitor#internalWorked(double)
	 */
	public void internalWorked(double work) {
		cleanupActiveChild();

		int delta = consume((work > 0.0d) ? work : 0.0d);
		if (delta != 0)
			root.worked(delta);
	}

	/* (non-Javadoc)
	 * @see org.eclipse.core.runtime.IProgressMonitor#subTask(java.lang.String)
	 */
	public void subTask(String name) {
		if ((flags & SUPPRESS_SUBTASK) == 0)
			root.subTask(name);
	}

	/* (non-Javadoc)
	 * @see org.eclipse.core.runtime.IProgressMonitor#worked(int)
	 */
	public void worked(int work) {
		internalWorked(work);
	}

	/* (non-Javadoc)
	 * @see org.eclipse.core.runtime.IProgressMonitor#setCanceled(boolean)
	 */
	public void setCanceled(boolean b) {
		root.setCanceled(b);
	}

	/**
	 * <p>Creates a sub progress monitor that will consume the given number of ticks from the 
	 * receiver. It is not necessary to call <code>beginTask</code> or <code>done</code> on the
	 * result. However, the resulting progress monitor will not report any work after the first 
	 * call to done() or before ticks are allocated. Ticks may be allocated by calling beginTask
	 * or setWorkRemaining.</p>
	 * 
	 * <p>Each SubMonitor only has one active child at a time. Each time newChild() is called, the
	 * result becomes the new active child and any unused progress from the previously-active child is
	 * consumed.</p>
	 * 
	 * <p>This is property makes it unnecessary to call done() on a SubMonitor instance, since child
	 * monitors are automatically cleaned up the next time the parent is touched.</p> 
	 * 
	 * <code><pre> 
	 *      ////////////////////////////////////////////////////////////////////////////
	 *      // Example 1: Typical usage of newChild
	 *      void myMethod(IProgressMonitor parent) {
	 *          SubMonitor progress = SubMonitor.convert(parent, 100); 
	 *          doSomething(progress.newChild(50));
	 *          doSomethingElse(progress.newChild(50));
	 *      }
	 *      
	 *      ////////////////////////////////////////////////////////////////////////////
	 *      // Example 2: Demonstrates the function of active children. Creating children
	 *      // is sufficient to smoothly report progress, even if worked(...) and done()
	 *      // are never called.
	 *      void myMethod(IProgressMonitor parent) {
	 *          SubMonitor progress = SubMonitor.convert(parent, 100);
	 *          
	 *          for (int i = 0; i < 100; i++) {
	 *              // Creating the next child monitor will clean up the previous one,
	 *              // causing progress to be reported smoothly even if we don't do anything
	 *              // with the monitors we create
	 *          	progress.newChild(1);
	 *          }
	 *      }
	 *      
	 *      ////////////////////////////////////////////////////////////////////////////
	 *      // Example 3: Demonstrates a common anti-pattern
	 *      void wrongMethod(IProgressMonitor parent) {
	 *          SubMonitor progress = SubMonitor.convert(parent, 100);
	 *          
	 *          // WRONG WAY: Won't have the intended effect, as only one of these progress
	 *          // monitors may be active at a time and the other will report no progress.
	 *          callMethod(progress.newChild(50), computeValue(progress.newChild(50)));
	 *      }
	 *      
	 *      void rightMethod(IProgressMonitor parent) {
	 *          SubMonitor progress = SubMonitor.convert(parent, 100);
	 *          
	 *          // RIGHT WAY: Break up method calls so that only one SubMonitor is in use at a time.
	 *          Object someValue = computeValue(progress.newChild(50));
	 *          callMethod(progress.newChild(50), someValue);
	 *      }
	 * </pre></code>
	 * 
	 * @param totalWork number of ticks to consume from the receiver
	 * @return new sub progress monitor that may be used in place of a new SubMonitor
	 */
	public SubMonitor newChild(int totalWork) {
		return newChild(totalWork, SUPPRESS_BEGINTASK);
	}

	/**
	 * <p>Creates a sub progress monitor that will consume the given number of ticks from the 
	 * receiver. It is not necessary to call <code>beginTask</code> or <code>done</code> on the
	 * result. However, the resulting progress monitor will not report any work after the first 
	 * call to done() or before ticks are allocated. Ticks may be allocated by calling beginTask
	 * or setWorkRemaining.</p>
	 * 
	 * <p>Each SubMonitor only has one active child at a time. Each time newChild() is called, the
	 * result becomes the new active child and any unused progress from the previously-active child is
	 * consumed.</p>
	 * 
	 * <p>This is property makes it unnecessary to call done() on a SubMonitor instance, since child
	 * monitors are automatically cleaned up the next time the parent is touched.</p> 
	 * 
	 * <code><pre> 
	 *      ////////////////////////////////////////////////////////////////////////////
	 *      // Example 1: Typical usage of newChild
	 *      void myMethod(IProgressMonitor parent) {
	 *          SubMonitor progress = SubMonitor.convert(parent, 100); 
	 *          doSomething(progress.newChild(50));
	 *          doSomethingElse(progress.newChild(50));
	 *      }
	 *      
	 *      ////////////////////////////////////////////////////////////////////////////
	 *      // Example 2: Demonstrates the function of active children. Creating children
	 *      // is sufficient to smoothly report progress, even if worked(...) and done()
	 *      // are never called.
	 *      void myMethod(IProgressMonitor parent) {
	 *          SubMonitor progress = SubMonitor.convert(parent, 100);
	 *          
	 *          for (int i = 0; i < 100; i++) {
	 *              // Creating the next child monitor will clean up the previous one,
	 *              // causing progress to be reported smoothly even if we don't do anything
	 *              // with the monitors we create
	 *          	progress.newChild(1);
	 *          }
	 *      }
	 *      
	 *      ////////////////////////////////////////////////////////////////////////////
	 *      // Example 3: Demonstrates a common anti-pattern
	 *      void wrongMethod(IProgressMonitor parent) {
	 *          SubMonitor progress = SubMonitor.convert(parent, 100);
	 *          
	 *          // WRONG WAY: Won't have the intended effect, as only one of these progress
	 *          // monitors may be active at a time and the other will report no progress.
	 *          callMethod(progress.newChild(50), computeValue(progress.newChild(50)));
	 *      }
	 *      
	 *      void rightMethod(IProgressMonitor parent) {
	 *          SubMonitor progress = SubMonitor.convert(parent, 100);
	 *          
	 *          // RIGHT WAY: Break up method calls so that only one SubMonitor is in use at a time.
	 *          Object someValue = computeValue(progress.newChild(50));
	 *          callMethod(progress.newChild(50), someValue);
	 *      }
	 * </pre></code>
	 * 
	 * @param totalWork number of ticks to consume from the receiver
	 * @return new sub progress monitor that may be used in place of a new SubMonitor
	 */
	public SubMonitor newChild(int totalWork, int suppressFlags) {
		double totalWorkDouble = (totalWork > 0) ? totalWork : 0.0d;
		totalWorkDouble = Math.min(totalWorkDouble, totalForChildren - usedForChildren);
		cleanupActiveChild();

		// Compute the flags for the child. We want the net effect to be as though the child is
		// delegating to its parent, even though it is actually talking directly to the root.
		// This means that we need to compute the flags such that - even if a label isn't 
		// suppressed by the child - if that same label would have been suppressed when the
		// child delegated to its parent, the child must explicitly suppress the label. 
		int childFlags = SUPPRESS_NONE;

		if ((flags & SUPPRESS_SETTASKNAME) != 0) {
			// If the parent was ignoring labels passed to setTaskName, then the child will ignore
			// labels passed to either beginTask or setTaskName - since both delegate to setTaskName
			// on the parent
			childFlags |= SUPPRESS_SETTASKNAME | SUPPRESS_BEGINTASK;
		}

		if ((flags & SUPPRESS_SUBTASK) != 0) {
			// If the parent was suppressing labels passed to subTask, so will the child.
			childFlags |= SUPPRESS_SUBTASK;
		}

		// Note: the SUPPRESS_BEGINTASK flag does not affect the child since there
		// is no method on the child that would delegate to beginTask on the parent.
		childFlags |= suppressFlags;

		SubMonitor result = new SubMonitor(root, consume(totalWorkDouble), (int) totalWorkDouble, childFlags);
		lastSubMonitor = result;
		return result;
	}

	private void cleanupActiveChild() {
		if (lastSubMonitor == null)
			return;

		IProgressMonitor child = lastSubMonitor;
		lastSubMonitor = null;
		child.done();
	}

	/* (non-Javadoc)
	 * @see org.eclipse.core.runtime.IProgressMonitorWithBlocking#clearBlocked()
	 */
	public void clearBlocked() {
		root.clearBlocked();
	}

	/* (non-Javadoc)
	 * @see org.eclipse.core.runtime.IProgressMonitorWithBlocking#setBlocked(org.eclipse.core.runtime.IStatus)
	 */
	public void setBlocked(IStatus reason) {
		root.setBlocked(reason);
	}

	protected static boolean eq(Object o1, Object o2) {
		if (o1 == null)
			return (o2 == null);
		if (o2 == null)
			return false;
		return o1.equals(o2);
	}
}