Class ThreadPoolExecutor
- All Implemented Interfaces:
Executor
,ExecutorService
ExecutorService
that executes each submitted task using
one of possibly several pooled threads, normally configured
using Executors
factory methods.
Thread pools address two different problems: they usually
provide improved performance when executing large numbers of
asynchronous tasks, due to reduced per-task invocation overhead,
and they provide a means of bounding and managing the resources,
including threads, consumed when executing a collection of tasks.
Each ThreadPoolExecutor
also maintains some basic
statistics, such as the number of completed tasks.
To be useful across a wide range of contexts, this class
provides many adjustable parameters and extensibility
hooks. However, programmers are urged to use the more convenient
Executors
factory methods Executors.newCachedThreadPool()
(unbounded thread pool, with
automatic thread reclamation), Executors.newFixedThreadPool(int)
(fixed size thread pool) and Executors.newSingleThreadExecutor()
(single background thread), that
preconfigure settings for the most common usage
scenarios. Otherwise, use the following guide when manually
configuring and tuning this class:
- Core and maximum pool sizes
- A
ThreadPoolExecutor
will automatically adjust the pool size (seegetPoolSize()
) according to the bounds set by corePoolSize (seegetCorePoolSize()
) and maximumPoolSize (seegetMaximumPoolSize()
). When a new task is submitted in methodexecute(Runnable)
, if fewer than corePoolSize threads are running, a new thread is created to handle the request, even if other worker threads are idle. Else if fewer than maximumPoolSize threads are running, a new thread will be created to handle the request only if the queue is full. By setting corePoolSize and maximumPoolSize the same, you create a fixed-size thread pool. By setting maximumPoolSize to an essentially unbounded value such asInteger.MAX_VALUE
, you allow the pool to accommodate an arbitrary number of concurrent tasks. Most typically, core and maximum pool sizes are set only upon construction, but they may also be changed dynamically usingsetCorePoolSize(int)
andsetMaximumPoolSize(int)
. - On-demand construction
- By default, even core threads are initially created and
started only when new tasks arrive, but this can be overridden
dynamically using method
prestartCoreThread()
orprestartAllCoreThreads()
. You probably want to prestart threads if you construct the pool with a non-empty queue. - Creating new threads
- New threads are created using a
ThreadFactory
. If not otherwise specified, aExecutors.defaultThreadFactory()
is used, that creates threads to all be in the sameThreadGroup
and with the sameNORM_PRIORITY
priority and non-daemon status. By supplying a different ThreadFactory, you can alter the thread's name, thread group, priority, daemon status, etc. If aThreadFactory
fails to create a thread when asked by returning null fromnewThread
, the executor will continue, but might not be able to execute any tasks. Threads should possess the "modifyThread"RuntimePermission
. If worker threads or other threads using the pool do not possess this permission, service may be degraded: configuration changes may not take effect in a timely manner, and a shutdown pool may remain in a state in which termination is possible but not completed. - Keep-alive times
- If the pool currently has more than corePoolSize threads,
excess threads will be terminated if they have been idle for more
than the keepAliveTime (see
getKeepAliveTime(TimeUnit)
). This provides a means of reducing resource consumption when the pool is not being actively used. If the pool becomes more active later, new threads will be constructed. This parameter can also be changed dynamically using methodsetKeepAliveTime(long, TimeUnit)
. Using a value ofLong.MAX_VALUE
TimeUnit.NANOSECONDS
effectively disables idle threads from ever terminating prior to shut down. By default, the keep-alive policy applies only when there are more than corePoolSize threads, but methodallowCoreThreadTimeOut(boolean)
can be used to apply this time-out policy to core threads as well, so long as the keepAliveTime value is non-zero. - Queuing
- Any
BlockingQueue
may be used to transfer and hold submitted tasks. The use of this queue interacts with pool sizing:- If fewer than corePoolSize threads are running, the Executor always prefers adding a new thread rather than queuing.
- If corePoolSize or more threads are running, the Executor always prefers queuing a request rather than adding a new thread.
- If a request cannot be queued, a new thread is created unless this would exceed maximumPoolSize, in which case, the task will be rejected.
- Direct handoffs. A good default choice for a work
queue is a
SynchronousQueue
that hands off tasks to threads without otherwise holding them. Here, an attempt to queue a task will fail if no threads are immediately available to run it, so a new thread will be constructed. This policy avoids lockups when handling sets of requests that might have internal dependencies. Direct handoffs generally require unbounded maximumPoolSizes to avoid rejection of new submitted tasks. This in turn admits the possibility of unbounded thread growth when commands continue to arrive on average faster than they can be processed. - Unbounded queues. Using an unbounded queue (for
example a
LinkedBlockingQueue
without a predefined capacity) will cause new tasks to wait in the queue when all corePoolSize threads are busy. Thus, no more than corePoolSize threads will ever be created. (And the value of the maximumPoolSize therefore doesn't have any effect.) This may be appropriate when each task is completely independent of others, so tasks cannot affect each others execution; for example, in a web page server. While this style of queuing can be useful in smoothing out transient bursts of requests, it admits the possibility of unbounded work queue growth when commands continue to arrive on average faster than they can be processed. - Bounded queues. A bounded queue (for example, an
ArrayBlockingQueue
) helps prevent resource exhaustion when used with finite maximumPoolSizes, but can be more difficult to tune and control. Queue sizes and maximum pool sizes may be traded off for each other: Using large queues and small pools minimizes CPU usage, OS resources, and context-switching overhead, but can lead to artificially low throughput. If tasks frequently block (for example if they are I/O bound), a system may be able to schedule time for more threads than you otherwise allow. Use of small queues generally requires larger pool sizes, which keeps CPUs busier but may encounter unacceptable scheduling overhead, which also decreases throughput.
- Rejected tasks
- New tasks submitted in method
execute(Runnable)
will be rejected when the Executor has been shut down, and also when the Executor uses finite bounds for both maximum threads and work queue capacity, and is saturated. In either case, theexecute
method invokes theThreadPoolExecutor.RejectedExecutionHandler.rejectedExecution(Runnable, ThreadPoolExecutor)
method of itsThreadPoolExecutor.RejectedExecutionHandler
. Four predefined handler policies are provided:- In the default
ThreadPoolExecutor.AbortPolicy
, the handler throws a runtimeRejectedExecutionException
upon rejection. - In
ThreadPoolExecutor.CallerRunsPolicy
, the thread that invokesexecute
itself runs the task. This provides a simple feedback control mechanism that will slow down the rate that new tasks are submitted. - In
ThreadPoolExecutor.DiscardPolicy
, a task that cannot be executed is simply dropped. This policy is designed only for those rare cases in which task completion is never relied upon. - In
ThreadPoolExecutor.DiscardOldestPolicy
, if the executor is not shut down, the task at the head of the work queue is dropped, and then execution is retried (which can fail again, causing this to be repeated.) This policy is rarely acceptable. In nearly all cases, you should also cancel the task to cause an exception in any component waiting for its completion, and/or log the failure, as illustrated inThreadPoolExecutor.DiscardOldestPolicy
documentation.
ThreadPoolExecutor.RejectedExecutionHandler
classes. Doing so requires some care especially when policies are designed to work only under particular capacity or queuing policies. - In the default
- Hook methods
- This class provides
protected
overridablebeforeExecute(Thread, Runnable)
andafterExecute(Runnable, Throwable)
methods that are called before and after execution of each task. These can be used to manipulate the execution environment; for example, reinitializing ThreadLocals, gathering statistics, or adding log entries. Additionally, methodterminated()
can be overridden to perform any special processing that needs to be done once the Executor has fully terminated.If hook, callback, or BlockingQueue methods throw exceptions, internal worker threads may in turn fail, abruptly terminate, and possibly be replaced.
- Queue maintenance
- Method
getQueue()
allows access to the work queue for purposes of monitoring and debugging. Use of this method for any other purpose is strongly discouraged. Two supplied methods,remove(Runnable)
andpurge()
are available to assist in storage reclamation when large numbers of queued tasks become cancelled. - Reclamation
- A pool that is no longer referenced in a program AND
has no remaining threads may be reclaimed (garbage collected)
without being explicitly shutdown. You can configure a pool to
allow all unused threads to eventually die by setting appropriate
keep-alive times, using a lower bound of zero core threads and/or
setting
allowCoreThreadTimeOut(boolean)
.
Extension example. Most extensions of this class override one or more of the protected hook methods. For example, here is a subclass that adds a simple pause/resume feature:
class PausableThreadPoolExecutor extends ThreadPoolExecutor {
private boolean isPaused;
private ReentrantLock pauseLock = new ReentrantLock();
private Condition unpaused = pauseLock.newCondition();
public PausableThreadPoolExecutor(...) { super(...); }
protected void beforeExecute(Thread t, Runnable r) {
super.beforeExecute(t, r);
pauseLock.lock();
try {
while (isPaused) unpaused.await();
} catch (InterruptedException ie) {
t.interrupt();
} finally {
pauseLock.unlock();
}
}
public void pause() {
pauseLock.lock();
try {
isPaused = true;
} finally {
pauseLock.unlock();
}
}
public void resume() {
pauseLock.lock();
try {
isPaused = false;
unpaused.signalAll();
} finally {
pauseLock.unlock();
}
}
}
- Since:
- 1.5
- Author:
- Doug Lea
-
Nested Class Summary
Modifier and TypeClassDescriptionstatic class
A handler for rejected tasks that throws aRejectedExecutionException
.static class
A handler for rejected tasks that runs the rejected task directly in the calling thread of theexecute
method, unless the executor has been shut down, in which case the task is discarded.static class
A handler for rejected tasks that discards the oldest unhandled request and then retriesexecute
, unless the executor is shut down, in which case the task is discarded.static class
A handler for rejected tasks that silently discards the rejected task.static interface
-
Field Summary
-
Constructor Summary
ConstructorDescriptionThreadPoolExecutor
(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) Creates a newThreadPoolExecutor
with the given initial parameters, the default thread factory and the default rejected execution handler.ThreadPoolExecutor
(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory) Creates a newThreadPoolExecutor
with the given initial parameters and the default rejected execution handler.ThreadPoolExecutor
(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory, ThreadPoolExecutor.RejectedExecutionHandler handler) Creates a newThreadPoolExecutor
with the given initial parameters.ThreadPoolExecutor
(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadPoolExecutor.RejectedExecutionHandler handler) Creates a newThreadPoolExecutor
with the given initial parameters and the default thread factory. -
Method Summary
Modifier and TypeMethodDescriptionprotected void
afterExecute
(Runnable r, Throwable t) Method invoked upon completion of execution of the given Runnable.void
allowCoreThreadTimeOut
(boolean value) Sets the policy governing whether core threads may time out and terminate if no tasks arrive within the keep-alive time, being replaced if needed when new tasks arrive.boolean
Returns true if this pool allows core threads to time out and terminate if no tasks arrive within the keepAlive time, being replaced if needed when new tasks arrive.boolean
awaitTermination
(long timeout, TimeUnit unit) protected void
beforeExecute
(Thread t, Runnable r) Method invoked prior to executing the given Runnable in the given thread.void
protected boolean
void
void
Deprecated.This will be removed in Tomcat 10.1.x onwardsint
Returns the approximate number of threads that are actively executing tasks.long
Returns the approximate total number of tasks that have completed execution.int
Returns the core number of threads.long
getKeepAliveTime
(TimeUnit unit) Returns the thread keep-alive time, which is the amount of time that threads may remain idle before being terminated.int
Returns the largest number of threads that have ever simultaneously been in the pool.int
Returns the maximum allowed number of threads.int
Returns the current number of threads in the pool.protected int
Returns the current number of threads in the pool.getQueue()
Returns the task queue used by this executor.Returns the current handler for unexecutable tasks.int
long
Returns the approximate total number of tasks that have ever been scheduled for execution.Returns the thread factory used to create new threads.long
boolean
boolean
boolean
Returns true if this executor is in the process of terminating aftershutdown()
orshutdownNow()
but has not completely terminated.int
Starts all core threads, causing them to idly wait for work.boolean
Starts a core thread, causing it to idly wait for work.void
purge()
Tries to remove from the work queue allFuture
tasks that have been cancelled.boolean
Removes this task from the executor's internal queue if it is present, thus causing it not to be run if it has not already started.void
setCorePoolSize
(int corePoolSize) Sets the core number of threads.void
setKeepAliveTime
(long time, TimeUnit unit) Sets the thread keep-alive time, which is the amount of time that threads may remain idle before being terminated.void
setMaximumPoolSize
(int maximumPoolSize) Sets the maximum allowed number of threads.void
Sets a new handler for unexecutable tasks.void
setThreadFactory
(ThreadFactory threadFactory) Sets the thread factory used to create new threads.void
setThreadRenewalDelay
(long threadRenewalDelay) void
shutdown()
Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution.protected void
If the current thread was started before the last time when a context was stopped, an exception is thrown so that the current thread is stopped.protected void
Method invoked when the Executor has terminated.toString()
Returns a string identifying this pool, as well as its state, including indications of run state and estimated worker and task counts.Methods inherited from class java.util.concurrent.AbstractExecutorService
invokeAll, invokeAll, invokeAny, invokeAny, newTaskFor, newTaskFor, submit, submit, submit
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Field Details
-
sm
-
-
Constructor Details
-
ThreadPoolExecutor
public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) Creates a newThreadPoolExecutor
with the given initial parameters, the default thread factory and the default rejected execution handler.It may be more convenient to use one of the
Executors
factory methods instead of this general purpose constructor.- Parameters:
corePoolSize
- the number of threads to keep in the pool, even if they are idle, unlessallowCoreThreadTimeOut
is setmaximumPoolSize
- the maximum number of threads to allow in the poolkeepAliveTime
- when the number of threads is greater than the core, this is the maximum time that excess idle threads will wait for new tasks before terminating.unit
- the time unit for thekeepAliveTime
argumentworkQueue
- the queue to use for holding tasks before they are executed. This queue will hold only theRunnable
tasks submitted by theexecute
method.- Throws:
IllegalArgumentException
- if one of the following holds:
corePoolSize < 0
keepAliveTime < 0
maximumPoolSize <= 0
maximumPoolSize < corePoolSize
NullPointerException
- ifworkQueue
is null
-
ThreadPoolExecutor
public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory) Creates a newThreadPoolExecutor
with the given initial parameters and the default rejected execution handler.- Parameters:
corePoolSize
- the number of threads to keep in the pool, even if they are idle, unlessallowCoreThreadTimeOut
is setmaximumPoolSize
- the maximum number of threads to allow in the poolkeepAliveTime
- when the number of threads is greater than the core, this is the maximum time that excess idle threads will wait for new tasks before terminating.unit
- the time unit for thekeepAliveTime
argumentworkQueue
- the queue to use for holding tasks before they are executed. This queue will hold only theRunnable
tasks submitted by theexecute
method.threadFactory
- the factory to use when the executor creates a new thread- Throws:
IllegalArgumentException
- if one of the following holds:
corePoolSize < 0
keepAliveTime < 0
maximumPoolSize <= 0
maximumPoolSize < corePoolSize
NullPointerException
- ifworkQueue
orthreadFactory
is null
-
ThreadPoolExecutor
public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadPoolExecutor.RejectedExecutionHandler handler) Creates a newThreadPoolExecutor
with the given initial parameters and the default thread factory.- Parameters:
corePoolSize
- the number of threads to keep in the pool, even if they are idle, unlessallowCoreThreadTimeOut
is setmaximumPoolSize
- the maximum number of threads to allow in the poolkeepAliveTime
- when the number of threads is greater than the core, this is the maximum time that excess idle threads will wait for new tasks before terminating.unit
- the time unit for thekeepAliveTime
argumentworkQueue
- the queue to use for holding tasks before they are executed. This queue will hold only theRunnable
tasks submitted by theexecute
method.handler
- the handler to use when execution is blocked because the thread bounds and queue capacities are reached- Throws:
IllegalArgumentException
- if one of the following holds:
corePoolSize < 0
keepAliveTime < 0
maximumPoolSize <= 0
maximumPoolSize < corePoolSize
NullPointerException
- ifworkQueue
orhandler
is null
-
ThreadPoolExecutor
public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory, ThreadPoolExecutor.RejectedExecutionHandler handler) Creates a newThreadPoolExecutor
with the given initial parameters.- Parameters:
corePoolSize
- the number of threads to keep in the pool, even if they are idle, unlessallowCoreThreadTimeOut
is setmaximumPoolSize
- the maximum number of threads to allow in the poolkeepAliveTime
- when the number of threads is greater than the core, this is the maximum time that excess idle threads will wait for new tasks before terminating.unit
- the time unit for thekeepAliveTime
argumentworkQueue
- the queue to use for holding tasks before they are executed. This queue will hold only theRunnable
tasks submitted by theexecute
method.threadFactory
- the factory to use when the executor creates a new threadhandler
- the handler to use when execution is blocked because the thread bounds and queue capacities are reached- Throws:
IllegalArgumentException
- if one of the following holds:
corePoolSize < 0
keepAliveTime < 0
maximumPoolSize <= 0
maximumPoolSize < corePoolSize
NullPointerException
- ifworkQueue
orthreadFactory
orhandler
is null
-
-
Method Details
-
execute
-
execute
Deprecated.This will be removed in Tomcat 10.1.x onwardsExecutes the given command at some time in the future. The command may execute in a new thread, in a pooled thread, or in the calling thread, at the discretion of theExecutor
implementation. If no threads are available, it will be added to the work queue. If the work queue is full, the system will wait for the specified time and it throw a RejectedExecutionException if the queue is still full after that.- Parameters:
command
- the runnable tasktimeout
- A timeout for the completion of the taskunit
- The timeout time unit- Throws:
RejectedExecutionException
- if this task cannot be accepted for execution - the queue is fullNullPointerException
- if command or unit is null
-
shutdown
public void shutdown()Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. Invocation has no additional effect if already shut down.This method does not wait for previously submitted tasks to complete execution. Use
awaitTermination
to do that.- Throws:
SecurityException
-
shutdownNow
Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution. These tasks are drained (removed) from the task queue upon return from this method.This method does not wait for actively executing tasks to terminate. Use
awaitTermination
to do that.There are no guarantees beyond best-effort attempts to stop processing actively executing tasks. This implementation interrupts tasks via
Thread.interrupt()
; any task that fails to respond to interrupts may never terminate.- Throws:
SecurityException
-
isShutdown
public boolean isShutdown() -
isTerminating
public boolean isTerminating()Returns true if this executor is in the process of terminating aftershutdown()
orshutdownNow()
but has not completely terminated. This method may be useful for debugging. A return oftrue
reported a sufficient period after shutdown may indicate that submitted tasks have ignored or suppressed interruption, causing this executor not to properly terminate.- Returns:
true
if terminating but not yet terminated
-
isTerminated
public boolean isTerminated() -
awaitTermination
- Throws:
InterruptedException
-
setThreadFactory
Sets the thread factory used to create new threads.- Parameters:
threadFactory
- the new thread factory- Throws:
NullPointerException
- if threadFactory is null- See Also:
-
getThreadFactory
Returns the thread factory used to create new threads.- Returns:
- the current thread factory
- See Also:
-
setRejectedExecutionHandler
Sets a new handler for unexecutable tasks.- Parameters:
handler
- the new handler- Throws:
NullPointerException
- if handler is null- See Also:
-
getRejectedExecutionHandler
Returns the current handler for unexecutable tasks.- Returns:
- the current handler
- See Also:
-
setCorePoolSize
public void setCorePoolSize(int corePoolSize) Sets the core number of threads. This overrides any value set in the constructor. If the new value is smaller than the current value, excess existing threads will be terminated when they next become idle. If larger, new threads will, if needed, be started to execute any queued tasks.- Parameters:
corePoolSize
- the new core size- Throws:
IllegalArgumentException
- ifcorePoolSize < 0
orcorePoolSize
is greater than the maximum pool size- See Also:
-
getCorePoolSize
public int getCorePoolSize()Returns the core number of threads.- Returns:
- the core number of threads
- See Also:
-
prestartCoreThread
public boolean prestartCoreThread()Starts a core thread, causing it to idly wait for work. This overrides the default policy of starting core threads only when new tasks are executed. This method will returnfalse
if all core threads have already been started.- Returns:
true
if a thread was started
-
prestartAllCoreThreads
public int prestartAllCoreThreads()Starts all core threads, causing them to idly wait for work. This overrides the default policy of starting core threads only when new tasks are executed.- Returns:
- the number of threads started
-
allowsCoreThreadTimeOut
public boolean allowsCoreThreadTimeOut()Returns true if this pool allows core threads to time out and terminate if no tasks arrive within the keepAlive time, being replaced if needed when new tasks arrive. When true, the same keep-alive policy applying to non-core threads applies also to core threads. When false (the default), core threads are never terminated due to lack of incoming tasks.- Returns:
true
if core threads are allowed to time out, elsefalse
- Since:
- 1.6
-
allowCoreThreadTimeOut
public void allowCoreThreadTimeOut(boolean value) Sets the policy governing whether core threads may time out and terminate if no tasks arrive within the keep-alive time, being replaced if needed when new tasks arrive. When false, core threads are never terminated due to lack of incoming tasks. When true, the same keep-alive policy applying to non-core threads applies also to core threads. To avoid continual thread replacement, the keep-alive time must be greater than zero when settingtrue
. This method should in general be called before the pool is actively used.- Parameters:
value
-true
if should time out, elsefalse
- Throws:
IllegalArgumentException
- if value istrue
and the current keep-alive time is not greater than zero- Since:
- 1.6
-
setMaximumPoolSize
public void setMaximumPoolSize(int maximumPoolSize) Sets the maximum allowed number of threads. This overrides any value set in the constructor. If the new value is smaller than the current value, excess existing threads will be terminated when they next become idle.- Parameters:
maximumPoolSize
- the new maximum- Throws:
IllegalArgumentException
- if the new maximum is less than or equal to zero, or less than the core pool size- See Also:
-
getMaximumPoolSize
public int getMaximumPoolSize()Returns the maximum allowed number of threads.- Returns:
- the maximum allowed number of threads
- See Also:
-
setKeepAliveTime
Sets the thread keep-alive time, which is the amount of time that threads may remain idle before being terminated. Threads that wait this amount of time without processing a task will be terminated if there are more than the core number of threads currently in the pool, or if this pool allows core thread timeout. This overrides any value set in the constructor.- Parameters:
time
- the time to wait. A time value of zero will cause excess threads to terminate immediately after executing tasks.unit
- the time unit of thetime
argument- Throws:
IllegalArgumentException
- iftime
less than zero or iftime
is zero andallowsCoreThreadTimeOut
- See Also:
-
getKeepAliveTime
Returns the thread keep-alive time, which is the amount of time that threads may remain idle before being terminated. Threads that wait this amount of time without processing a task will be terminated if there are more than the core number of threads currently in the pool, or if this pool allows core thread timeout.- Parameters:
unit
- the desired time unit of the result- Returns:
- the time limit
- See Also:
-
getThreadRenewalDelay
public long getThreadRenewalDelay() -
setThreadRenewalDelay
public void setThreadRenewalDelay(long threadRenewalDelay) -
getQueue
Returns the task queue used by this executor. Access to the task queue is intended primarily for debugging and monitoring. This queue may be in active use. Retrieving the task queue does not prevent queued tasks from executing.- Returns:
- the task queue
-
remove
Removes this task from the executor's internal queue if it is present, thus causing it not to be run if it has not already started.This method may be useful as one part of a cancellation scheme. It may fail to remove tasks that have been converted into other forms before being placed on the internal queue. For example, a task entered using
submit
might be converted into a form that maintainsFuture
status. However, in such cases, methodpurge()
may be used to remove those Futures that have been cancelled.- Parameters:
task
- the task to remove- Returns:
true
if the task was removed
-
purge
public void purge()Tries to remove from the work queue allFuture
tasks that have been cancelled. This method can be useful as a storage reclamation operation, that has no other impact on functionality. Cancelled tasks are never executed, but may accumulate in work queues until worker threads can actively remove them. Invoking this method instead tries to remove them now. However, this method may fail to remove tasks in the presence of interference by other threads. -
contextStopping
public void contextStopping() -
getPoolSize
public int getPoolSize()Returns the current number of threads in the pool.- Returns:
- the number of threads
-
getPoolSizeNoLock
protected int getPoolSizeNoLock()Returns the current number of threads in the pool.
NOTE: this method only used inTaskQueue.offer(Runnable)
, where operations are frequent, can greatly reduce unnecessary performance overhead by a lock-free way.- Returns:
- the number of threads
-
getActiveCount
public int getActiveCount()Returns the approximate number of threads that are actively executing tasks.- Returns:
- the number of threads
-
getLargestPoolSize
public int getLargestPoolSize()Returns the largest number of threads that have ever simultaneously been in the pool.- Returns:
- the number of threads
-
getTaskCount
public long getTaskCount()Returns the approximate total number of tasks that have ever been scheduled for execution. Because the states of tasks and threads may change dynamically during computation, the returned value is only an approximation.- Returns:
- the number of tasks
-
getCompletedTaskCount
public long getCompletedTaskCount()Returns the approximate total number of tasks that have completed execution. Because the states of tasks and threads may change dynamically during computation, the returned value is only an approximation, but one that does not ever decrease across successive calls.- Returns:
- the number of tasks
-
getSubmittedCount
public int getSubmittedCount() -
toString
Returns a string identifying this pool, as well as its state, including indications of run state and estimated worker and task counts. -
beforeExecute
Method invoked prior to executing the given Runnable in the given thread. This method is invoked by threadt
that will execute taskr
, and may be used to re-initialize ThreadLocals, or to perform logging.This implementation does nothing, but may be customized in subclasses. Note: To properly nest multiple overridings, subclasses should generally invoke
super.beforeExecute
at the end of this method.- Parameters:
t
- the thread that will run taskr
r
- the task that will be executed
-
afterExecute
Method invoked upon completion of execution of the given Runnable. This method is invoked by the thread that executed the task. If non-null, the Throwable is the uncaughtRuntimeException
orError
that caused execution to terminate abruptly.This implementation does nothing, but may be customized in subclasses. Note: To properly nest multiple overridings, subclasses should generally invoke
super.afterExecute
at the beginning of this method.Note: When actions are enclosed in tasks (such as
FutureTask
) either explicitly or via methods such assubmit
, these task objects catch and maintain computational exceptions, and so they do not cause abrupt termination, and the internal exceptions are not passed to this method. If you would like to trap both kinds of failures in this method, you can further probe for such cases, as in this sample subclass that prints either the direct cause or the underlying exception if a task has been aborted:class ExtendedExecutor extends ThreadPoolExecutor { // ... protected void afterExecute(Runnable r, Throwable t) { super.afterExecute(r, t); if (t == null && r instanceof Future<?> && ((Future<?>)r).isDone()) { try { Object result = ((Future<?>) r).get(); } catch (CancellationException ce) { t = ce; } catch (ExecutionException ee) { t = ee.getCause(); } catch (InterruptedException ie) { // ignore/reset Thread.currentThread().interrupt(); } } if (t != null) System.out.println(t); } }
- Parameters:
r
- the runnable that has completedt
- the exception that caused termination, or null if execution completed normally
-
stopCurrentThreadIfNeeded
protected void stopCurrentThreadIfNeeded()If the current thread was started before the last time when a context was stopped, an exception is thrown so that the current thread is stopped. -
currentThreadShouldBeStopped
protected boolean currentThreadShouldBeStopped() -
terminated
protected void terminated()Method invoked when the Executor has terminated. Default implementation does nothing. Note: To properly nest multiple overridings, subclasses should generally invokesuper.terminated
within this method.
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