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. |
Threading
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.
-
Constructor Summary
ModifierConstructorDescriptionprotected
Initialize a new instance of this class. -
Method Summary
Modifier and TypeMethodDescriptionabstract boolean
awaitTermination(long timeout, TimeUnit unit)
Awaits termination of the group.abstract boolean
Tells whether or not this asynchronous channel group is shutdown.abstract boolean
Tells whether or not this group has terminated.provider()
Returns the provider that created this channel group.abstract void
shutdown()
Initiates an orderly shutdown of the group.abstract void
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.
-
Constructor Details
-
AsynchronousChannelGroup
Initialize a new instance of this class.- Parameters:
provider
- The asynchronous channel provider for this group
-
-
Method Details
-
provider
Returns the provider that created this channel group.- Returns:
- The provider that created this channel group
-
withFixedThreadPool
public static AsynchronousChannelGroup withFixedThreadPool(int nThreads, ThreadFactory threadFactory) throws IOExceptionCreates an asynchronous channel group with a fixed thread pool.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 defaultAsynchronousChannelProvider
object.- Parameters:
nThreads
- The number of threads in the poolthreadFactory
- The factory to use when creating new threads- Returns:
- A new asynchronous channel group
- Throws:
IllegalArgumentException
- IfnThreads <= 0
IOException
- If an I/O error occurs
-
withCachedThreadPool
public static AsynchronousChannelGroup withCachedThreadPool(ExecutorService executor, int initialSize) throws IOExceptionCreates an asynchronous channel group with a given thread pool that creates new threads as needed.The
executor
parameter is anExecutorService
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 indicate 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 defaultAsynchronousChannelProvider
object.- Parameters:
executor
- The thread pool for the resulting groupinitialSize
- A value>=0
or a negative value for implementation specific default- Returns:
- A new asynchronous channel group
- Throws:
IOException
- If an I/O error occurs- See Also:
Executors.newCachedThreadPool()
-
withThreadPool
Creates an asynchronous channel group with a given thread pool.The
executor
parameter is anExecutorService
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 defaultAsynchronousChannelProvider
object with aninitialSize
of0
.- Parameters:
executor
- The thread pool for the resulting group- Returns:
- A new asynchronous channel group
- Throws:
IOException
- If an I/O error occurs
-
isShutdown
public abstract boolean isShutdown()Tells whether or not this asynchronous channel group is shutdown.- Returns:
true
if this asynchronous channel group is shutdown or has been marked for shutdown.
-
isTerminated
public abstract boolean isTerminated()Tells whether or not this group has terminated.Where this method returns
true
, then the associated thread pool has alsoterminated
.- Returns:
true
if this group has terminated
-
shutdown
public abstract void shutdown()Initiates an orderly shutdown of the group.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. -
shutdownNow
Shuts down the group and closes all open channels in the group.In addition to the actions performed by the
shutdown
method, this method invokes theclose
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.- Throws:
IOException
- If an I/O error occurs
-
awaitTermination
Awaits termination of the group.This method blocks until the group has terminated, or the timeout occurs, or the current thread is interrupted, whichever happens first.
- Parameters:
timeout
- The maximum time to wait, or zero or less to not waitunit
- The time unit of the timeout argument- Returns:
true
if the group has terminated;false
if the timeout elapsed before termination- Throws:
InterruptedException
- If interrupted while waiting
-