Class AbstractSelector

java.lang.Object

java.nio.channels.Selector

java.nio.channels.spi.AbstractSelector

All Implemented Interfaces:: Closeable, AutoCloseable

public abstract class AbstractSelector extends Selector

Base implementation class for selectors.

This class encapsulates the low-level machinery required to implement the interruption of selection operations. A concrete selector class must invoke the begin and end methods before and after, respectively, invoking an I/O operation that might block indefinitely. In order to ensure that the end method is always invoked, these methods should be used within a try ... finally block:

    try {
        begin();
        // Perform blocking I/O operation here
        ...
    } finally {
        end();
    }

This class also defines methods for maintaining a selector's cancelled-key set and for removing a key from its channel's key set, and declares the abstract register method that is invoked by a selectable channel's register method in order to perform the actual work of registering a channel.

Since:: 1.4

Constructor Summary

AbstractSelector(SelectorProvider provider)

Modifier	Constructor	Description
`protected`	Initializes a new instance of this class.

Method Summary

Modifier and Type	Method	Description
`protected final void`	`begin()`	Marks the beginning of an I/O operation that might block indefinitely.
`protected final Set<SelectionKey>`	`cancelledKeys()`	Retrieves this selector's cancelled-key set.
`final void`	`close()`	Closes this selector.
`protected final void`	`deregister(AbstractSelectionKey key)`	Removes the given key from its channel's key set.
`protected final void`	`end()`	Marks the end of an I/O operation that might block indefinitely.
`protected abstract void`	`implCloseSelector()`	Closes this selector.
`final boolean`	`isOpen()`	Tells whether or not this selector is open.
`final SelectorProvider`	`provider()`	Returns the provider that created this channel.
`protected abstract SelectionKey`	`register(AbstractSelectableChannel ch, int ops, Object att)`	Registers the given channel with this selector.

Methods declared in class Selector

keys, open, select, select, select, select, selectedKeys, selectNow, selectNow, wakeup

Modifier and Type	Method	Description
`abstract Set<SelectionKey>`	`keys()`	Returns this selector's key set.
`static Selector`	`open()`	Opens a selector.
`abstract int`	`select()`	Selects a set of keys whose corresponding channels are ready for I/O operations.
`abstract int`	`select(long timeout)`	Selects a set of keys whose corresponding channels are ready for I/O operations.
`int`	`select(Consumer<SelectionKey> action)`	Selects and performs an action on the keys whose corresponding channels are ready for I/O operations.
`int`	`select(Consumer<SelectionKey> action, long timeout)`	Selects and performs an action on the keys whose corresponding channels are ready for I/O operations.
`abstract Set<SelectionKey>`	`selectedKeys()`	Returns this selector's selected-key set.
`abstract int`	`selectNow()`	Selects a set of keys whose corresponding channels are ready for I/O operations.
`int`	`selectNow(Consumer<SelectionKey> action)`	Selects and performs an action on the keys whose corresponding channels are ready for I/O operations.
`abstract Selector`	`wakeup()`	Causes the first selection operation that has not yet returned to return immediately.

Methods declared in class Object

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

Modifier and Type	Method	Description
`protected Object`	`clone()`	Creates and returns a copy of this object.
`boolean`	`equals(Object obj)`	Indicates whether some other object is "equal to" this one.
`protected void`	`finalize()`	Deprecated, for removal: This API element is subject to removal in a future version. Finalization is deprecated and subject to removal in a future release.
`final Class<?>`	`getClass()`	Returns the runtime class of this `Object`.
`int`	`hashCode()`	Returns a hash code value for this object.
`final void`	`notify()`	Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()`	Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()`	Returns a string representation of the object.
`final void`	`wait()`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
`final void`	`wait(long timeoutMillis)`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis, int nanos)`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

Constructor Details

AbstractSelector

protected AbstractSelector(SelectorProvider provider)

Initializes a new instance of this class.

Parameters:: provider - The provider that created this selector

Method Details

close

public final void close() throws IOException

Closes this selector.

If the selector has already been closed then this method returns immediately. Otherwise it marks the selector as closed and then invokes the implCloseSelector method in order to complete the close operation.

Specified by:: close in interface AutoCloseable
Specified by:: close in interface Closeable
Specified by:: close in class Selector
Throws:: IOException - If an I/O error occurs

implCloseSelector

protected abstract void implCloseSelector() throws IOException

Closes this selector.

This method is invoked by the close method in order to perform the actual work of closing the selector. This method is only invoked if the selector has not yet been closed, and it is never invoked more than once.

An implementation of this method must arrange for any other thread that is blocked in a selection operation upon this selector to return immediately as if by invoking the wakeup method.

Throws:: IOException - If an I/O error occurs while closing the selector

isOpen

public final boolean isOpen()

Description copied from class: Selector

Tells whether or not this selector is open.

Specified by:: isOpen in class Selector
Returns:: true if, and only if, this selector is open

provider

public final SelectorProvider provider()

Returns the provider that created this channel.

Specified by:: provider in class Selector
Returns:: The provider that created this channel

cancelledKeys

protected final Set<SelectionKey> cancelledKeys()

Retrieves this selector's cancelled-key set.

This set should only be used while synchronized upon it.

Returns:: The cancelled-key set

register

protected abstract SelectionKey register(AbstractSelectableChannel ch, int ops, Object att)

Registers the given channel with this selector.

This method is invoked by a channel's register method in order to perform the actual work of registering the channel with this selector.

Parameters:: ch - The channel to be registered; ops - The initial interest set, which must be valid; att - The initial attachment for the resulting key
Returns:: A new key representing the registration of the given channel with this selector

deregister

protected final void deregister(AbstractSelectionKey key)

Removes the given key from its channel's key set.

This method must be invoked by the selector for each channel that it deregisters.

Parameters:: key - The selection key to be removed

begin

protected final void begin()

Marks the beginning of an I/O operation that might block indefinitely.

This method should be invoked in tandem with the end method, using a try ... finally block as shown above, in order to implement interruption for this selector.

Invoking this method arranges for the selector's wakeup method to be invoked if a thread's interrupt method is invoked while the thread is blocked in an I/O operation upon the selector.

end

protected final void end()

Marks the end of an I/O operation that might block indefinitely.

This method should be invoked in tandem with the begin method, using a try ... finally block as shown above, in order to implement interruption for this selector.

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