public abstract class AsynchronousChannelGroup extends Object
An asynchronous channel group encapsulates the mechanics required to
handle the completion of I/O operations initiated by asynchronous channels that are bound to the group. A group has an associated
thread pool to which tasks are submitted to handle I/O events and dispatch to
completion-handlers that consume the result of
asynchronous operations performed on channels in the group. In addition to
handling I/O events, the pooled threads may also execute other tasks required
to support the execution of asynchronous I/O operations.
An asynchronous channel group is created by invoking the withFixedThreadPool or withCachedThreadPool methods defined here. Channels are bound to a group by
specifying the group when constructing the channel. The associated thread
pool is owned by the group; termination of the group results in the
shutdown of the associated thread pool.
In addition to groups created explicitly, the Java virtual machine
maintains a system-wide default group that is constructed
automatically. Asynchronous channels that do not specify a group at
construction time are bound to the default group. The default group has an
associated thread pool that creates new threads as needed. The default group
may be configured by means of system properties defined in the table below.
Where the ThreadFactory for the
default group is not configured then the pooled threads of the default group
are daemon threads.
| System property | Description |
|---|---|
java.nio.channels.DefaultThreadPool.threadFactory |
The value of this property is taken to be the fully-qualified name
of a concrete ThreadFactory
class. The class is loaded using the system class loader and instantiated.
The factory's newThread method is invoked to create each thread for the default
group's thread pool. If the process to load and instantiate the value
of the property fails then an unspecified error is thrown during the
construction of the default group. |
java.nio.channels.DefaultThreadPool.initialSize |
The value of the initialSize parameter for the default
group (see withCachedThreadPool).
The value of the property is taken to be the String
representation of an Integer that is the initial size parameter.
If the value cannot be parsed as an Integer it causes an
unspecified error to be thrown during the construction of the default
group. |
The completion handler for an I/O operation initiated on a channel bound to a group is guaranteed to be invoked by one of the pooled threads in the group. This ensures that the completion handler is run by a thread with the expected identity.
Where an I/O operation completes immediately, and the initiating thread
is one of the pooled threads in the group then the completion handler may
be invoked directly by the initiating thread. To avoid stack overflow, an
implementation may impose a limit as to the number of activations on the
thread stack. Some I/O operations may prohibit invoking the completion
handler directly by the initiating thread (see accept).
Shutdown and Termination
The shutdown method is used to initiate an orderly
shutdown of a group. An orderly shutdown marks the group as shutdown;
further attempts to construct a channel that binds to the group will throw
ShutdownChannelGroupException. Whether or not a group is shutdown can
be tested using the isShutdown method. Once shutdown,
the group terminates when all asynchronous channels that are bound to
the group are closed, all actively executing completion handlers have run to
completion, and resources used by the group are released. No attempt is made
to stop or interrupt threads that are executing completion handlers. The
isTerminated method is used to test if the group has
terminated, and the awaitTermination method can be
used to block until the group has terminated.
The shutdownNow method can be used to initiate a
forceful shutdown of the group. In addition to the actions performed
by an orderly shutdown, the shutdownNow method closes all open channels
in the group as if by invoking the close
method.
| Modifier | Constructor and Description |
|---|---|
protected |
AsynchronousChannelGroup(AsynchronousChannelProvider provider)
Initialize a new instance of this class.
|
| Modifier and Type | Method and Description |
|---|---|
abstract boolean |
awaitTermination(long timeout,
TimeUnit unit)
Awaits termination of the group.
|
abstract boolean |
isShutdown()
Tells whether or not this asynchronous channel group is shutdown.
|
abstract boolean |
isTerminated()
Tells whether or not this group has terminated.
|
AsynchronousChannelProvider |
provider()
Returns the provider that created this channel group.
|
abstract void |
shutdown()
Initiates an orderly shutdown of the group.
|
abstract void |
shutdownNow()
Shuts down the group and closes all open channels in the group.
|
static AsynchronousChannelGroup |
withCachedThreadPool(ExecutorService executor,
int initialSize)
Creates an asynchronous channel group with a given thread pool that
creates new threads as needed.
|
static AsynchronousChannelGroup |
withFixedThreadPool(int nThreads,
ThreadFactory threadFactory)
Creates an asynchronous channel group with a fixed thread pool.
|
static AsynchronousChannelGroup |
withThreadPool(ExecutorService executor)
Creates an asynchronous channel group with a given thread pool.
|
protected AsynchronousChannelGroup(AsynchronousChannelProvider provider)
provider - The asynchronous channel provider for this grouppublic final AsynchronousChannelProvider provider()
public static AsynchronousChannelGroup withFixedThreadPool(int nThreads, ThreadFactory threadFactory) throws IOException
The resulting asynchronous channel group reuses a fixed number of
threads. At any point, at most nThreads threads will be active
processing tasks that are submitted to handle I/O events and dispatch
completion results for operations initiated on asynchronous channels in
the group.
The group is created by invoking the openAsynchronousChannelGroup(int,ThreadFactory) method of the system-wide
default AsynchronousChannelProvider object.
nThreads - The number of threads in the poolthreadFactory - The factory to use when creating new threadsIllegalArgumentException - If nThreads <= 0IOException - If an I/O error occurspublic static AsynchronousChannelGroup withCachedThreadPool(ExecutorService executor, int initialSize) throws IOException
The executor parameter is an ExecutorService that
creates new threads as needed to execute tasks that are submitted to
handle I/O events and dispatch completion results for operations initiated
on asynchronous channels in the group. It may reuse previously constructed
threads when they are available.
The initialSize parameter may be used by the implementation
as a hint as to the initial number of tasks it may submit. For
example, it may be used to indictae the initial number of threads that
wait on I/O events.
The executor is intended to be used exclusively by the resulting
asynchronous channel group. Termination of the group results in the
orderly shutdown of the executor
service. Shutting down the executor service by other means results in
unspecified behavior.
The group is created by invoking the openAsynchronousChannelGroup(ExecutorService,int) method of the system-wide
default AsynchronousChannelProvider object.
executor - The thread pool for the resulting groupinitialSize - A value >=0 or a negative value for implementation
specific defaultIOException - If an I/O error occursExecutors.newCachedThreadPool()public static AsynchronousChannelGroup withThreadPool(ExecutorService executor) throws IOException
The executor parameter is an ExecutorService that
executes tasks submitted to dispatch completion results for operations
initiated on asynchronous channels in the group.
Care should be taken when configuring the executor service. It
should support direct handoff or unbounded queuing of
submitted tasks, and the thread that invokes the execute method should never invoke the task
directly. An implementation may mandate additional constraints.
The executor is intended to be used exclusively by the resulting
asynchronous channel group. Termination of the group results in the
orderly shutdown of the executor
service. Shutting down the executor service by other means results in
unspecified behavior.
The group is created by invoking the openAsynchronousChannelGroup(ExecutorService,int) method of the system-wide
default AsynchronousChannelProvider object with an initialSize of 0.
executor - The thread pool for the resulting groupIOException - If an I/O error occurspublic abstract boolean isShutdown()
true if this asynchronous channel group is shutdown or
has been marked for shutdown.public abstract boolean isTerminated()
Where this method returns true, then the associated thread
pool has also terminated.
true if this group has terminatedpublic abstract void shutdown()
This method marks the group as shutdown. Further attempts to construct
channel that binds to this group will throw ShutdownChannelGroupException.
The group terminates when all asynchronous channels in the group are
closed, all actively executing completion handlers have run to completion,
and all resources have been released. This method has no effect if the
group is already shutdown.
public abstract void shutdownNow()
throws IOException
In addition to the actions performed by the shutdown
method, this method invokes the close
method on all open channels in the group. This method does not attempt to
stop or interrupt threads that are executing completion handlers. The
group terminates when all actively executing completion handlers have run
to completion and all resources have been released. This method may be
invoked at any time. If some other thread has already invoked it, then
another invocation will block until the first invocation is complete,
after which it will return without effect.
IOException - If an I/O error occurspublic abstract boolean awaitTermination(long timeout,
TimeUnit unit)
throws InterruptedException
This method blocks until the group has terminated, or the timeout occurs, or the current thread is interrupted, whichever happens first.
timeout - The maximum time to wait, or zero or less to not waitunit - The time unit of the timeout argumenttrue if the group has terminated; false if the
timeout elapsed before terminationInterruptedException - If interrupted while waiting