| java.lang.Object
 jj2000.j2k.util.ThreadPool
| ThreadPool | | public class ThreadPool (Code) | | This class implements a thread pool. The thread pool contains a set of
threads which can be given work to do.
If the Java Virtual Machine (JVM) uses native threads, then the
different threads will be able to execute in different processors in
parallel on multiprocessors machines. However, under some JVMs and
operating systems using native threads is not sufficient to allow the JVM
access to multiple processors. This is the case when native threads are
implemented using POSIX threads on lightweight processes
(i.e. PTHREAD_SCOPE_PROCESS sopce scheduling), which is the case on most
UNIX operating systems. In order to do provide access to multiple
processors it is necessary to set the concurrency level to the number of
processors or slightly higher. This can be achieved by setting the Java
system property with the name defined by CONCURRENCY_PROP_NAME to some
non-negative number. This will make use of the 'NativeServices' class and
supporting native libraries. See 'NativeServices' for details. See
'CONCURRENCY_PROP_NAME' for the name of the property.
Initially the thread pool contains a user specified number of idle
threads. Idle threads can be given a target which is run. While running the
target the thread temporarily leaves the idle list. When the target
finishes, it joins the idle list again, waiting for a new target. When a
target is finished a thread can be notified on a particular object that is
given as a lock.
Jobs can be submitted using Runnable interfaces, using the 'runTarget()'
methods. When the job is submitted, an idle thread will be obtained, the
'run()' method of the 'Runnable' interface will be executed and when it
completes the thread will be returned to the idle list. In general the
'run()' method should complete in a rather short time, so that the threds
of the pool are not starved.
If using the non-asynchronous calls to 'runTarget()', it is important
that any target's 'run()' method, or any method called from it, does not
use non-asynchronous calls to 'runTarget()' on the same thread pool where
it was started. Otherwise this could create a dead-lock when there are not
enough idle threads.
The pool also has a global error and runtime exception condition (one
for 'Error' and one for 'RuntimeException'). If a target's 'run()' method
throws an 'Error' or 'RuntimeException' the corresponding exception
condition is set and the exception object saved. In any subsequent call to
'checkTargetErrors()' the saved exception object is thrown. Likewise, if a
target's 'run()' method throws any other subclass of 'Throwable' a new
'RuntimeException' is created and saved. It will be thrown on a subsequent
call to 'checkTargetErrors()'. If more than one exception occurs between
calls to 'checkTargetErrors()' only the last one is saved. Any 'Error'
condition has precedence on all 'RuntimeException' conditions. The threads
in the pool are unaffected by any exceptions thrown by targets.
The only exception to the above is the 'ThreadDeath' exception. If a
target's 'run()' method throws the 'ThreadDeath' exception a warning
message is printed and the exception is propagated, which will terminate
the thread in which it occurs. This could lead to instabilities of the
pool. The 'ThreadDeath' exception should never be thrown by the program. It
is thrown by the Java(TM) Virtual Machine when Thread.stop() is
called. This method is deprecated and should never be called.
All the threads in the pool are "daemon" threads and will automatically
terminate when no daemon threads are running.
See Also: NativeServices
See Also: ThreadPool.CONCURRENCY_PROP_NAME
See Also: Runnable
See Also: Thread
See Also: Error
See Also: RuntimeException |
| Inner Class :class ThreadPoolThread extends Thread | |
| Constructor Summary | |
| public | ThreadPool(int size, int priority, String name)
Creates a new thread pool of the given size, thread priority and pool
name.
If the Java system property of the name defined by
'CONCURRENCY_PROP_NAME' is set, then an attempt will be made to load
the library that supports concurrency setting (see
'NativeServices'). |
| Method Summary | |
| public void | checkTargetErrors()
Checks that no error or runtime exception in any target have occurred
so far. | | public void | clearTargetErrors()
Clears the current target error conditions, if any. | | public int | getSize()
Returns the size of the pool. | | public boolean | runTarget(Runnable t, Object l)
Runs the run method of the specified target in an idle thread of this
pool. | | public boolean | runTarget(Runnable t, Object l, boolean async)
Runs the run method of the specified target in an idle thread of this
pool. | | public boolean | runTarget(Runnable t, Object l, boolean async, boolean notifyAll)
Runs the run method of the specified target in an idle thread of this
pool. |
| CONCURRENCY_PROP_NAME | | final public static String CONCURRENCY_PROP_NAME(Code) | | The name of the property that sets the concurrency level:
jj2000.j2k.util.ThreadPool.concurrency
|
| ThreadPool | | public ThreadPool(int size, int priority, String name)(Code) | | Creates a new thread pool of the given size, thread priority and pool
name.
If the Java system property of the name defined by
'CONCURRENCY_PROP_NAME' is set, then an attempt will be made to load
the library that supports concurrency setting (see
'NativeServices'). If that succeds the concurrency level will be set to
the specified value. Otherwise a warning is printed.
Parameters:
size - The size of the pool (number of threads to create in thepool).
Parameters:
priority - The priority to give to the threads in the pool. Ifless than 'Thread.MIN_PRIORITY' it will be the same as the priority ofthe calling thread.
Parameters:
name - The name of the pool. If null a default generic name ischosen.
See Also: NativeServices
See Also: ThreadPool.CONCURRENCY_PROP_NAME |
| checkTargetErrors | | public void checkTargetErrors()(Code) | | Checks that no error or runtime exception in any target have occurred
so far. If an error or runtime exception has occurred in a target's run
method they are thrown by this method.
exception:
Error - If an error condition has been thrown by a target'run()' method.
exception:
RuntimeException - If a runtime exception has been thrown by atarget 'run()' method. |
| clearTargetErrors | | public void clearTargetErrors()(Code) | | Clears the current target error conditions, if any. Note that a thread
in the pool might have set the error conditions since the last check
and that those error conditions will be lost. Likewise, before
returning from this method another thread might set the error
conditions. There is no guarantee that no error conditions exist when
returning from this method.
In order to ensure that no error conditions exist when returning
from this method cooperation from the targets and the thread using this
pool is necessary (i.e. currently no targets running or waiting to
run).
|
| getSize | | public int getSize()(Code) | | Returns the size of the pool. That is the number of threads in this
pool (idle + busy).
The pool's size. |
| runTarget | | public boolean runTarget(Runnable t, Object l)(Code) | | Runs the run method of the specified target in an idle thread of this
pool. When the target's run method completes, the thread waiting on the
lock object is notified, if any. If there is currently no idle thread
the method will block until a thread of the pool becomes idle or the
calling thread is interrupted.
This method is the same as runTarget(t,l,true,false).
Parameters:
t - The target. The 'run()' method of this object will be run inan idle thread of the pool.
Parameters:
l - The lock object. A thread waiting on the lock of the 'l'object will be notified, through the 'notify()' call, when the target'srun method completes. If null no thread is notified. True if the target was submitted to some thread. False if noidle thread could be found and the target was not submitted forexecution. |
| runTarget | | public boolean runTarget(Runnable t, Object l, boolean async)(Code) | | Runs the run method of the specified target in an idle thread of this
pool. When the target's run method completes, the thread waiting on the
lock object is notified, if any. If there is currently no idle thread
and the asynchronous mode is not used the method will block until a
thread of the pool becomes idle or the calling thread is
interrupted. If the asynchronous mode is used then the method will not
block and will return false.
This method is the same as runTarget(t,l,async,false).
Parameters:
t - The target. The 'run()' method of this object will be run inan idle thread of the pool.
Parameters:
l - The lock object. A thread waiting on the lock of the 'l'object will be notified, through the 'notify()' call, when the target'srun method completes. If null no thread is notified.
Parameters:
async - If true the asynchronous mode will be used. True if the target was submitted to some thread. False if noidle thread could be found and the target was not submitted forexecution. |
| runTarget | | public boolean runTarget(Runnable t, Object l, boolean async, boolean notifyAll)(Code) | | Runs the run method of the specified target in an idle thread of this
pool. When the target's run method completes, the thread waiting on the
lock object is notified, if any. If there is currently no idle thread
and the asynchronous mode is not used the method will block until a
thread of the pool becomes idle or the calling thread is
interrupted. If the asynchronous mode is used then the method will not
block and will return false.
Parameters:
t - The target. The 'run()' method of this object will be run inan idle thread of the pool.
Parameters:
l - The lock object. A thread waiting on the lock of the 'l'object will be notified, through the 'notify()' call, when the target'srun method completes. If null no thread is notified.
Parameters:
async - If true the asynchronous mode will be used.
Parameters:
notifyAll - If true, threads waiting on the lock of the 'l' objectwill be notified trough the 'notifyAll()' instead of the normal'notify()' call. This is not normally needed. True if the target was submitted to some thread. False if noidle thread could be found and the target was not submitted forexecution. |
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