orthotweezers
Class CancelThread

java.lang.Object
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  +--java.lang.Thread
        |
        +--orthotweezers.CancelThread

All Implemented Interfaces:

java.lang.Runnable

public class CancelThread

extends java.lang.Thread

A CancelThread extends Thread and allows a mechanism to cleanly pause or cancel the thread. When the thread is created its state is ENABLED (not to be confused with the interrupted or alive state). If the pause() or cancel() method is called, the state is set to PAUSED or CANCELLED, respectively. A thread may call CancelThread.check() and if pause() has been called (by another thread), check() will loop until the other thread calls unpause() or cancel(). If cancelled, check() throws a CancelException.

Field Summary

static int	CANCELLED
static int	ENABLED
static int	PAUSE_REQUEST
static int	PAUSED

Fields inherited from class java.lang.Thread

MAX_PRIORITY, MIN_PRIORITY, NORM_PRIORITY

Constructor Summary

CancelThread(java.lang.Runnable runnable)
Creates a new CancelThread as in Thread(Runnable target)

Method Summary

void	cancel() This sets the state to CANCELLED so that the next call to check() from the running thread will throw a CancelException, or if check() is looping in the PAUSED state then it will also throw a CancelException.
static void	check() If this thread state is still ENABLED, simply return.
boolean	isPaused() Return true if the state of this thread is PAUSED.
void	pause() This sets the state to PAUSE_REQUEST so that the next call to check() from the running thread will convert the state to PAUSED and loop until unpause() or cancel() is called.
void	unpause() If the state is PAUSED, this sets the state back to ENABLED so that the check() method in which the other thread is looping can exit and allow the thread to resume.

Methods inherited from class java.lang.Thread

activeCount, checkAccess, countStackFrames, currentThread, destroy, dumpStack, enumerate, getContextClassLoader, getName, getPriority, getThreadGroup, interrupt, interrupted, isAlive, isDaemon, isInterrupted, join, join, join, resume, run, setContextClassLoader, setDaemon, setName, setPriority, sleep, sleep, start, stop, stop, suspend, toString, yield

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

ENABLED

public static int ENABLED

PAUSE_REQUEST

public static int PAUSE_REQUEST

PAUSED

public static int PAUSED

CANCELLED

public static int CANCELLED

Constructor Detail

CancelThread

public CancelThread(java.lang.Runnable runnable)

Creates a new CancelThread as in Thread(Runnable target)

Method Detail

cancel

public void cancel()

This sets the state to CANCELLED so that the next call to check() from the running thread will throw a CancelException, or if check() is looping in the PAUSED state then it will also throw a CancelException. Once the CancelException is thrown, the run() method should exit causing the thread to stop running. This also uses isAlive() to wait until the cancelled thread is dead, so you know that when cancel() returns the cancelled thread is really dead. Note that if for some reason, the cancelled thread does not die, this method may not return.

See Also:

check()

pause

public void pause()

This sets the state to PAUSE_REQUEST so that the next call to check() from the running thread will convert the state to PAUSED and loop until unpause() or cancel() is called. However, if the state is already PAUSED or CANCELLED, this simply returns without doing anything. This waits until the check() method responds and converts the PAUSE_REQUEST to PAUSED, so you know that when this returns, the paused thread is really pausing. Note that if for some reason, the other thread does not call check() in order to become paused, this method may not return.

See Also:

check(), unpause(), cancel()

unpause

public void unpause()

If the state is PAUSED, this sets the state back to ENABLED so that the check() method in which the other thread is looping can exit and allow the thread to resume. If the state is alreay ENABLED, this does nothing. Also, if the state is already CANCELLED, this also does nothing because you can't unpause a cancelled thread.

See Also:

check(), pause()

check

public static void check()
                  throws CancelException

If this thread state is still ENABLED, simply return. If the state is CANCELLED (because another thread called cancel()) then this throws a CancelException. If the state is PAUSED or PAUSE_REQUEST (because another thread called pause()) then this will loop until the state becomes ENABLED (because another thread called unpause()) or CANCELLED.

This is a static method and queries Thread.currentThread() to see if the current thread is an instanceof CancelThread. If not, it simply returns, but if it is, then it looks at the state as described.

Throws:

CancelException - if this object is no longer enabled

See Also:

cancel(), pause(), unpause()

isPaused

public boolean isPaused()

Return true if the state of this thread is PAUSED. Note: to find out if the thread is cancelled, use the isAlive() method inherited from the Thread class.