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Eclipse Platform
Release 3.5

org.eclipse.core.runtime
Class SubMonitor

java.lang.Object
  extended by 
org.eclipse.core.runtime.SubMonitor
All Implemented Interfaces:
IProgressMonitor, IProgressMonitorWithBlocking

public final class SubMonitor
extends Object
implements IProgressMonitorWithBlocking

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:

  • It is not necessary to call beginTask() or done() on an instance of SubMonitor.
  • SubMonitor has a simpler syntax for creating nested monitors.
  • SubMonitor is more efficient for deep recursion chains.
  • SubMonitor has a setWorkRemining method that allows the remaining space on the monitor to be redistributed without reporting any work.
  • 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.

USAGE:

When implementing a method that accepts an IProgressMonitor:

  • At the start of your method, use SubMonitor.convert(...). to convert the IProgressMonitor into a SubMonitor.
  • Use SubMonitor.newChild(...) whenever you need to call another method that accepts an IProgressMonitor.

DEFAULT BEHAVIOR:

When writing JavaDoc for a method that accepts an IProgressMonitor, you should assume the following default behavior unless the method's JavaDoc says otherwise:

  • It WILL call beginTask on the IProgressMonitor.
  • It WILL NOT accept a null argument.
  • It WILL call done on the IProgressMonitor.

BEST PRACTISES:

We recommend that newly-written methods follow the given contract:

  • It WILL call beginTask on the IProgressMonitor.
  • It WILL accept a null argument, indicating that no progress should be reported and the operation cannot be cancelled.
  • It WILL NOT call done on the IProgressMonitor, leaving this responsibility up to the caller.

If you wish to follow these conventions, you may copy and paste the following text into your method's JavaDoc:

@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 null, indicating that no progress should be
        reported and that the operation cannot be cancelled.

Example: Recommended usage

This example demonstrates how the recommended usage of SubMonitor makes it unnecessary to call IProgressMonitor.done() in most situations.

It is never necessary to call done() on a monitor obtained from convert or progress.newChild(). In this example, there is no guarantee that monitor is an instance of SubMonitor, making it necessary to call monitor.done(). The JavaDoc contract makes this the responsibility of the caller.

      // 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 null, 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)); 
      }
 

Example: Default usage

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:

      // param monitor the progress monitor to use for reporting progress to the user, or null 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();
              }
          } 
      }
 

Example: Branches

This example demonstrates how to smoothly report progress in situations where some of the work is optional.

      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)); 
      }
 

Please beware of the following anti-pattern:

          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);
          }
 

Example: Loops

This example demonstrates how to report progress in a loop.

      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));
      }
 

Example: Infinite progress

This example demonstrates how to report logarithmic progress in situations where the number of ticks cannot be easily computed in advance.

      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;
          }
      }
 

This class can be used without OSGi running.

Since:
org.eclipse.equinox.common 3.3

Field Summary
static int SUPPRESS_ALL_LABELS
          May be passed as a flag to newChild.
static int SUPPRESS_BEGINTASK
          May be passed as a flag to newChild.
static int SUPPRESS_NONE
          May be passed as a flag to newChild.
static int SUPPRESS_SETTASKNAME
          May be passed as a flag to newChild.
static int SUPPRESS_SUBTASK
          May be passed as a flag to newChild.
 
Fields inherited from interface org.eclipse.core.runtime. IProgressMonitor
UNKNOWN
 
Method Summary
 void beginTask ( String name, int totalWork)
          Starts a new main task.
 void clearBlocked ()
          Clears the blocked state of the running operation.
static  SubMonitor convert ( IProgressMonitor monitor)
          Converts an unknown (possibly null) IProgressMonitor into a SubMonitor.
static  SubMonitor convert ( IProgressMonitor monitor, int work)
          Converts an unknown (possibly null) IProgressMonitor into a SubMonitor allocated with the given number of ticks.
static  SubMonitor convert ( IProgressMonitor monitor, String taskName, int work)
          Converts an unknown (possibly null) IProgressMonitor into a SubMonitor allocated with the given number of ticks.
 void done ()
          Notifies that the work is done; that is, either the main task is completed or the user canceled it.
protected static boolean eq ( Object o1, Object o2)
           
 void internalWorked (double work)
          Internal method to handle scaling correctly.
 boolean isCanceled ()
          Returns whether cancelation of current operation has been requested.
  SubMonitor newChild (int totalWork)
          Creates a sub progress monitor that will consume the given number of ticks from the receiver.
  SubMonitor newChild (int totalWork, int suppressFlags)
          Creates a sub progress monitor that will consume the given number of ticks from the receiver.
 void setBlocked ( IStatus reason)
          Indicates that this operation is blocked by some background activity.
 void setCanceled (boolean b)
          Sets the cancel state to the given value.
 void setTaskName ( String name)
          Sets the task name to the given value.
  SubMonitor setWorkRemaining (int workRemaining)
          Sets the work remaining for this SubMonitor instance.
 void subTask ( String name)
          Notifies that a subtask of the main task is beginning.
 void worked (int work)
          Notifies that a given number of work unit of the main task has been completed.
 
Methods inherited from class java.lang. Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

SUPPRESS_SUBTASK

public static final int SUPPRESS_SUBTASK
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.

See Also:
Constant Field Values

SUPPRESS_BEGINTASK

public static final int SUPPRESS_BEGINTASK
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.

See Also:
Constant Field Values

SUPPRESS_SETTASKNAME

public static final int SUPPRESS_SETTASKNAME
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.

See Also:
Constant Field Values

SUPPRESS_ALL_LABELS

public static final int SUPPRESS_ALL_LABELS
May be passed as a flag to newChild. Indicates that strings passed to setTaskName, subTask, and beginTask should all be ignored.

See Also:
Constant Field Values

SUPPRESS_NONE

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

See Also:
Constant Field Values
Method Detail

convert

public static 
SubMonitor convert(
IProgressMonitor monitor)

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.

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.

Parameters:
monitor - monitor to convert to a SubMonitor instance or null. Treats null as a new instance of NullProgressMonitor.
Returns:
a SubMonitor instance that adapts the argument

convert

public static 
SubMonitor convert(
IProgressMonitor monitor,
                                 int work)

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.

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.

Parameters:
monitor - monitor to convert to a SubMonitor instance or null. Treats null as a new instance of NullProgressMonitor.
work - number of ticks that will be available in the resulting monitor
Returns:
a SubMonitor instance that adapts the argument

convert

public static 
SubMonitor convert(
IProgressMonitor monitor,
                                 
String taskName,
                                 int work)

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.

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.

Parameters:
monitor - to convert into a SubMonitor instance or null. If given a null argument, the resulting SubMonitor will not report its progress anywhere.
taskName - user readable name to pass to monitor.beginTask. Never null.
work - initial number of ticks to allocate for children of the SubMonitor
Returns:
a new SubMonitor instance that is a child of the given monitor

setWorkRemaining

public 
SubMonitor setWorkRemaining(int workRemaining)

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.

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%.

Parameters:
workRemaining - total number of remaining ticks
Returns:
the receiver

isCanceled

public boolean isCanceled()
Description copied from interface: IProgressMonitor
Returns whether cancelation of current operation has been requested. Long-running operations should poll to see if cancelation has been requested.

Specified by:
isCanceled in interface IProgressMonitor
Returns:
true if cancellation has been requested, and false otherwise
See Also:
IProgressMonitor.setCanceled(boolean)

setTaskName

public void setTaskName(
String name)
Description copied from interface: IProgressMonitor
Sets the task name to the given value. This method is used to restore the task label after a nested operation was executed. Normally there is no need for clients to call this method.

Specified by:
setTaskName in interface IProgressMonitor
Parameters:
name - the name (or description) of the main task
See Also:
IProgressMonitor.beginTask(java.lang.String, int)

beginTask

public void beginTask(
String name,
                      int totalWork)
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.

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.

Specified by:
beginTask in interface IProgressMonitor
Parameters:
name - new main task name
totalWork - number of ticks to allocate
See Also:
IProgressMonitor.beginTask(java.lang.String, int)

done

public void done()
Description copied from interface: IProgressMonitor
Notifies that the work is done; that is, either the main task is completed or the user canceled it. This method may be called more than once (implementations should be prepared to handle this case).

Specified by:
done in interface IProgressMonitor

internalWorked

public void internalWorked(double work)
Description copied from interface: IProgressMonitor
Internal method to handle scaling correctly. This method must not be called by a client. Clients should always use the method worked(int).

Specified by:
internalWorked in interface IProgressMonitor
Parameters:
work - the amount of work done

subTask

public void subTask(
String name)
Description copied from interface: IProgressMonitor
Notifies that a subtask of the main task is beginning. Subtasks are optional; the main task might not have subtasks.

Specified by:
subTask in interface IProgressMonitor
Parameters:
name - the name (or description) of the subtask

worked

public void worked(int work)
Description copied from interface: IProgressMonitor
Notifies that a given number of work unit of the main task has been completed. Note that this amount represents an installment, as opposed to a cumulative amount of work done to date.

Specified by:
worked in interface IProgressMonitor
Parameters:
work - a non-negative number of work units just completed

setCanceled

public void setCanceled(boolean b)
Description copied from interface: IProgressMonitor
Sets the cancel state to the given value.

Specified by:
setCanceled in interface IProgressMonitor
Parameters:
b - true indicates that cancelation has been requested (but not necessarily acknowledged); false clears this flag
See Also:
IProgressMonitor.isCanceled()

newChild

public 
SubMonitor newChild(int totalWork)

Creates a sub progress monitor that will consume the given number of ticks from the receiver. It is not necessary to call beginTask or done 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.

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.

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.

 
      ////////////////////////////////////////////////////////////////////////////
      // 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);
      }
 

Parameters:
totalWork - number of ticks to consume from the receiver
Returns:
new sub progress monitor that may be used in place of a new SubMonitor

newChild

public 
SubMonitor newChild(int totalWork,
                           int suppressFlags)

Creates a sub progress monitor that will consume the given number of ticks from the receiver. It is not necessary to call beginTask or done 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.

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.

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.

 
      ////////////////////////////////////////////////////////////////////////////
      // 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);
      }
 

Parameters:
totalWork - number of ticks to consume from the receiver
Returns:
new sub progress monitor that may be used in place of a new SubMonitor

clearBlocked

public void clearBlocked()
Description copied from interface: IProgressMonitorWithBlocking
Clears the blocked state of the running operation. If a running operation ever calls setBlocked, it must eventually call clearBlocked before the operation completes.

Specified by:
clearBlocked in interface IProgressMonitorWithBlocking
See Also:
IProgressMonitorWithBlocking.setBlocked(IStatus)

setBlocked

public void setBlocked(
IStatus reason)
Description copied from interface: IProgressMonitorWithBlocking
Indicates that this operation is blocked by some background activity. If a running operation ever calls setBlocked, it must eventually call clearBlocked before the operation completes.

If the caller is blocked by a currently executing job, this method will return an IJobStatus indicating the job that is currently blocking the caller. If this blocking job is not known, this method will return a plain informational IStatus object.

Specified by:
setBlocked in interface IProgressMonitorWithBlocking
Parameters:
reason - an optional status object whose message describes the reason why this operation is blocked, or null if this information is not available.
See Also:
IProgressMonitorWithBlocking.clearBlocked()

eq

protected static boolean eq(
Object o1,
                            
Object o2)

Eclipse Platform
Release 3.5

Guidelines for using Eclipse APIs.

Copyright (c) Eclipse contributors and others 2000, 2008. All rights reserved.


 
 
  Published under the terms of the Eclipse Public License Version 1.0 ("EPL") Design by Interspire