Closeable, AutoCloseable, Channel, InterruptibleChannel
AbstractSelectableChannelpublic abstract class SelectableChannel extends AbstractInterruptibleChannel implements Channel
Selector. In order to be used with a selector, an instance of this class must first be registered via the register method. This method returns a new SelectionKey object that represents the channel's registration with the selector.
Once registered with a selector, a channel remains registered until it is deregistered. This involves deallocating whatever resources were allocated to the channel by the selector.
A channel cannot be deregistered directly; instead, the key representing its registration must be cancelled. Cancelling a key requests that the channel be deregistered during the selector's next selection operation. A key may be cancelled explicitly by invoking its cancel method. All of a channel's keys are cancelled implicitly when the channel is closed, whether by invoking its close method or by interrupting a thread blocked in an I/O operation upon the channel.
If the selector itself is closed then the channel will be deregistered, and the key representing its registration will be invalidated, without further delay.
A channel may be registered at most once with any particular selector.
Whether or not a channel is registered with one or more selectors may be determined by invoking the isRegistered method.
Selectable channels are safe for use by multiple concurrent threads.
isBlocking method. Newly-created selectable channels are always in blocking mode. Non-blocking mode is most useful in conjunction with selector-based multiplexing. A channel must be placed into non-blocking mode before being registered with a selector, and may not be returned to blocking mode until it has been deregistered.
| Modifier | Constructor | Description |
|---|---|---|
protected |
Initializes a new instance of this class. |
| Modifier and Type | Method | Description |
|---|---|---|
abstract Object |
blockingLock() |
Retrieves the object upon which the configureBlocking and register methods synchronize. |
abstract SelectableChannel |
configureBlocking |
Adjusts this channel's blocking mode. |
abstract boolean |
isBlocking() |
Tells whether or not every I/O operation on this channel will block until it completes. |
abstract boolean |
isRegistered() |
Tells whether or not this channel is currently registered with any selectors. |
abstract SelectionKey |
keyFor |
Retrieves the key representing the channel's registration with the given selector. |
abstract SelectorProvider |
provider() |
Returns the provider that created this channel. |
final SelectionKey |
register |
Registers this channel with the given selector, returning a selection key. |
abstract SelectionKey |
register |
Registers this channel with the given selector, returning a selection key. |
abstract int |
validOps() |
Returns an operation set identifying this channel's supported operations. |
begin, close, end, implCloseChannel, isOpen
protected SelectableChannel()
public abstract SelectorProvider provider()
public abstract int validOps()
public abstract boolean isRegistered()
Due to the inherent delay between key cancellation and channel deregistration, a channel may remain registered for some time after all of its keys have been cancelled. A channel may also remain registered for some time after it is closed.
true if, and only if, this channel is registeredpublic abstract SelectionKey keyFor(Selector sel)
sel - The selectornull if this channel is not currently registered with that selectorpublic abstract SelectionKey register(Selector sel, int ops, Object att) throws ClosedChannelException
If this channel is currently registered with the given selector then the selection key representing that registration is returned. The key's interest set will have been changed to ops, as if by invoking the interestOps(int) method. If the att argument is not null then the key's attachment will have been set to that value. A CancelledKeyException will be thrown if the key has already been cancelled.
Otherwise this channel has not yet been registered with the given selector, so it is registered and the resulting new key is returned. The key's initial interest set will be ops and its attachment will be att.
This method may be invoked at any time. If this method is invoked while a selection operation is in progress then it has no effect upon that operation; the new registration or change to the key's interest set will be seen by the next selection operation. If this method is invoked while an invocation of configureBlocking is in progress then it will block until the channel's blocking mode has been adjusted.
If this channel is closed while this operation is in progress then the key returned by this method will have been cancelled and will therefore be invalid.
sel - The selector with which this channel is to be registeredops - The interest set for the resulting keyatt - The attachment for the resulting key; may be null
ClosedChannelException - If this channel is closedClosedSelectorException - If the selector is closedIllegalBlockingModeException - If this channel is in blocking modeIllegalSelectorException - If this channel was not created by the same provider as the given selectorCancelledKeyException - If this channel is currently registered with the given selector but the corresponding key has already been cancelledIllegalArgumentException - If a bit in the ops set does not correspond to an operation that is supported by this channel, that is, if set & ~validOps() != 0
public final SelectionKey register(Selector sel, int ops) throws ClosedChannelException
An invocation of this convenience method of the form
sc.register(sel, ops)sc.register(sel, ops, null)
sel - The selector with which this channel is to be registeredops - The interest set for the resulting keyClosedChannelException - If this channel is closedClosedSelectorException - If the selector is closedIllegalBlockingModeException - If this channel is in blocking modeIllegalSelectorException - If this channel was not created by the same provider as the given selectorCancelledKeyException - If this channel is currently registered with the given selector but the corresponding key has already been cancelledIllegalArgumentException - If a bit in ops does not correspond to an operation that is supported by this channel, that is, if set &
~validOps() != 0
public abstract SelectableChannel configureBlocking(boolean block) throws IOException
If this channel is registered with one or more selectors then an attempt to place it into blocking mode will cause an IllegalBlockingModeException to be thrown.
This method may be invoked at any time. The new blocking mode will only affect I/O operations that are initiated after this method returns. For some implementations this may require blocking until all pending I/O operations are complete.
If this method is invoked while another invocation of this method or of the register method is in progress then it will first block until the other operation is complete.
block - If true then this channel will be placed in blocking mode; if false then it will be placed non-blocking modeClosedChannelException - If this channel is closedIllegalBlockingModeException - If block is true and this channel is registered with one or more selectorsIOException - If an I/O error occurspublic abstract boolean isBlocking()
If this channel is closed then the value returned by this method is not specified.
true if, and only if, this channel is in blocking modepublic abstract Object blockingLock()
configureBlocking and register methods synchronize. This is often useful in the implementation of adaptors that require a specific blocking mode to be maintained for a short period of time.
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/nio/channels/SelectableChannel.html