public
abstract
class
SelectableChannel
extends AbstractInterruptibleChannel
implements
Channel
| java.lang.Object | ||
| ↳ | java.nio.channels.spi.AbstractInterruptibleChannel | |
| ↳ | java.nio.channels.SelectableChannel | |
 Known Direct Subclasses
|
|
Known Indirect Subclasses
|
A channel that can be multiplexed via a 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.
Developers
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.
See also:
Protected constructors | |
|---|---|
SelectableChannel()
Initializes a new instance of this class. |
|
Public methods | |
|---|---|
abstract
Object
|
blockingLock()
Retrieves the object upon which the |
abstract
SelectableChannel
|
configureBlocking(boolean block)
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(Selector sel)
Retrieves the key representing the channel's registration with the given selector. |
abstract
SelectorProvider
|
provider()
Returns the provider that created this channel. |
abstract
SelectionKey
|
register(Selector sel, int ops, Object att)
Registers this channel with the given selector, returning a selection key. |
final
SelectionKey
|
register(Selector sel, int ops)
Registers this channel with the given selector, returning a selection key. |
abstract
int
|
validOps()
Returns an operation set identifying this channel's supported operations. |
Inherited methods | |
|---|---|
From
class
java.nio.channels.spi.AbstractInterruptibleChannel
| |
From
class
java.lang.Object
| |
From
interface
java.nio.channels.Channel
| |
From
interface
java.nio.channels.InterruptibleChannel
| |
From
interface
java.io.Closeable
| |
From
interface
java.lang.AutoCloseable
| |
SelectableChannel ()
Initializes a new instance of this class.
Object blockingLock ()
Retrieves the object upon which the 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.
| Returns | |
|---|---|
Object |
The blocking-mode lock object |
SelectableChannel configureBlocking (boolean block)
Adjusts this channel's blocking mode.
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.
| Parameters | |
|---|---|
block |
boolean:
If true then this channel will be placed in
blocking mode; if false then it will be placed
non-blocking mode |
| Returns | |
|---|---|
SelectableChannel |
This selectable channel |
| Throws | |
|---|---|
ClosedChannelException |
If this channel is closed |
IllegalBlockingModeException |
If block is true and this channel is registered with one or more selectors |
IOException |
If an I/O error occurs |
boolean isBlocking ()
Tells whether or not every I/O operation on this channel will block until it completes. A newly-created channel is always in blocking mode.
If this channel is closed then the value returned by this method is not specified.
| Returns | |
|---|---|
boolean |
true if, and only if, this channel is in blocking mode |
boolean isRegistered ()
Tells whether or not this channel is currently registered with any selectors. A newly-created channel is not registered.
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.
| Returns | |
|---|---|
boolean |
true if, and only if, this channel is registered |
SelectionKey keyFor (Selector sel)
Retrieves the key representing the channel's registration with the given selector.
| Parameters | |
|---|---|
sel |
Selector
|
| Returns | |
|---|---|
SelectionKey |
The key returned when this channel was last registered with the given selector, or null if this channel is not currently registered with that selector |
SelectorProvider provider ()
Returns the provider that created this channel.
| Returns | |
|---|---|
SelectorProvider |
The provider that created this channel |
SelectionKey register (Selector sel, int ops, Object att)
Registers this channel with the given selector, returning a selection key.
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 another invocation of this method or of the configureBlocking method is in progress
then it will first block until the other operation is complete. This
method will then synchronize on the selector's key set and therefore may
block if invoked concurrently with another registration or selection
operation involving the same selector.
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.
| Parameters | |
|---|---|
sel |
Selector:
The selector with which this channel is to be registered |
ops |
int:
The interest set for the resulting key |
att |
Object:
The attachment for the resulting key; may be null |
| Returns | |
|---|---|
SelectionKey |
A key representing the registration of this channel with the given selector |
| Throws | |
|---|---|
ClosedChannelException |
If this channel is closed |
ClosedSelectorException |
If the selector is closed |
IllegalBlockingModeException |
If this channel is in blocking mode |
IllegalSelectorException |
If this channel was not created by the same provider as the given selector |
CancelledKeyException |
If this channel is currently registered with the given selector but the corresponding key has already been cancelled |
IllegalArgumentException |
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 |
SelectionKey register (Selector sel, int ops)
Registers this channel with the given selector, returning a selection key.
An invocation of this convenience method of the form
sc.register(sel, ops)behaves in exactly the same way as the invocation
sc.register(sel, ops, null)
| Parameters | |
|---|---|
sel |
Selector:
The selector with which this channel is to be registered |
ops |
int:
The interest set for the resulting key |
| Returns | |
|---|---|
SelectionKey |
A key representing the registration of this channel with the given selector |
| Throws | |
|---|---|
ClosedChannelException |
If this channel is closed |
ClosedSelectorException |
If the selector is closed |
IllegalBlockingModeException |
If this channel is in blocking mode |
IllegalSelectorException |
If this channel was not created by the same provider as the given selector |
CancelledKeyException |
If this channel is currently registered with the given selector but the corresponding key has already been cancelled |
IllegalArgumentException |
If a bit in ops does not correspond to an operation that is supported by this channel, that is, if set & ~validOps() != 0 |
int validOps ()
Returns an operation set identifying this channel's supported operations. The bits that are set in this integer value denote exactly the operations that are valid for this channel. This method always returns the same value for a given concrete channel class.
| Returns | |
|---|---|
int |
The valid-operation set |