634 lines
26 KiB
Java
634 lines
26 KiB
Java
/*
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* Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.nio.channels;
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import java.io.Closeable;
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import java.io.IOException;
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import java.nio.channels.spi.SelectorProvider;
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import java.util.Objects;
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import java.util.Set;
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import java.util.function.Consumer;
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/**
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* A multiplexor of {@link SelectableChannel} objects.
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*
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* <p> A selector may be created by invoking the {@link #open open} method of
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* this class, which will use the system's default {@link
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* java.nio.channels.spi.SelectorProvider selector provider} to
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* create a new selector. A selector may also be created by invoking the
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* {@link java.nio.channels.spi.SelectorProvider#openSelector openSelector}
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* method of a custom selector provider. A selector remains open until it is
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* closed via its {@link #close close} method.
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*
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* <a id="ks"></a>
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*
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* <p> A selectable channel's registration with a selector is represented by a
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* {@link SelectionKey} object. A selector maintains three sets of selection
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* keys:
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*
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* <ul>
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*
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* <li><p> The <i>key set</i> contains the keys representing the current
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* channel registrations of this selector. This set is returned by the
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* {@link #keys() keys} method. </p></li>
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*
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* <li><p> The <i>selected-key set</i> is the set of keys such that each
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* key's channel was detected to be ready for at least one of the operations
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* identified in the key's interest set during a prior selection operation
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* that adds keys or updates keys in the set.
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* This set is returned by the {@link #selectedKeys() selectedKeys} method.
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* The selected-key set is always a subset of the key set. </p></li>
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*
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* <li><p> The <i>cancelled-key</i> set is the set of keys that have been
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* cancelled but whose channels have not yet been deregistered. This set is
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* not directly accessible. The cancelled-key set is always a subset of the
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* key set. </p></li>
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*
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* </ul>
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*
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* <p> All three sets are empty in a newly-created selector.
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*
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* <p> A key is added to a selector's key set as a side effect of registering a
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* channel via the channel's {@link SelectableChannel#register(Selector,int)
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* register} method. Cancelled keys are removed from the key set during
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* selection operations. The key set itself is not directly modifiable.
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*
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* <p> A key is added to its selector's cancelled-key set when it is cancelled,
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* whether by closing its channel or by invoking its {@link SelectionKey#cancel
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* cancel} method. Cancelling a key will cause its channel to be deregistered
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* during the next selection operation, at which time the key will be removed
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* from all of the selector's key sets.
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*
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* <a id="sks"></a><p> Keys are added to the selected-key set by selection
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* operations. A key may be removed directly from the selected-key set by
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* invoking the set's {@link java.util.Set#remove(java.lang.Object) remove}
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* method or by invoking the {@link java.util.Iterator#remove() remove} method
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* of an {@link java.util.Iterator iterator} obtained from the set.
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* All keys may be removed from the selected-key set by invoking the set's
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* {@link java.util.Set#clear() clear} method. Keys may not be added directly
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* to the selected-key set. </p>
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*
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* <a id="selop"></a>
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* <h2>Selection</h2>
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*
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* <p> A selection operation queries the underlying operating system for an
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* update as to the readiness of each registered channel to perform any of the
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* operations identified by its key's interest set. There are two forms of
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* selection operation:
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*
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* <ol>
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*
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* <li><p> The {@link #select()}, {@link #select(long)}, and {@link #selectNow()}
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* methods add the keys of channels ready to perform an operation to the
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* selected-key set, or update the ready-operation set of keys already in the
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* selected-key set. </p></li>
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*
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* <li><p> The {@link #select(Consumer)}, {@link #select(Consumer, long)}, and
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* {@link #selectNow(Consumer)} methods perform an <i>action</i> on the key
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* of each channel that is ready to perform an operation. These methods do
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* not add to the selected-key set. </p></li>
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*
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* </ol>
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*
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* <h3>Selection operations that add to the selected-key set</h3>
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*
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* <p> During each selection operation, keys may be added to and removed from a
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* selector's selected-key set and may be removed from its key and
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* cancelled-key sets. Selection is performed by the {@link #select()}, {@link
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* #select(long)}, and {@link #selectNow()} methods, and involves three steps:
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* </p>
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*
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* <ol>
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*
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* <li><p> Each key in the cancelled-key set is removed from each key set of
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* which it is a member, and its channel is deregistered. This step leaves
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* the cancelled-key set empty. </p></li>
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*
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* <li><p> The underlying operating system is queried for an update as to the
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* readiness of each remaining channel to perform any of the operations
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* identified by its key's interest set as of the moment that the selection
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* operation began. For a channel that is ready for at least one such
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* operation, one of the following two actions is performed: </p>
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*
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* <ol>
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*
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* <li><p> If the channel's key is not already in the selected-key set then
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* it is added to that set and its ready-operation set is modified to
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* identify exactly those operations for which the channel is now reported
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* to be ready. Any readiness information previously recorded in the ready
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* set is discarded. </p></li>
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*
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* <li><p> Otherwise the channel's key is already in the selected-key set,
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* so its ready-operation set is modified to identify any new operations
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* for which the channel is reported to be ready. Any readiness
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* information previously recorded in the ready set is preserved; in other
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* words, the ready set returned by the underlying system is
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* bitwise-disjoined into the key's current ready set. </p></li>
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*
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* </ol>
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*
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* If all of the keys in the key set at the start of this step have empty
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* interest sets then neither the selected-key set nor any of the keys'
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* ready-operation sets will be updated.
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*
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* <li><p> If any keys were added to the cancelled-key set while step (2) was
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* in progress then they are processed as in step (1). </p></li>
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*
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* </ol>
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*
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* <p> Whether or not a selection operation blocks to wait for one or more
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* channels to become ready, and if so for how long, is the only essential
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* difference between the three selection methods. </p>
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*
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*
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* <h3>Selection operations that perform an action on selected keys</h3>
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*
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* <p> During each selection operation, keys may be removed from the selector's
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* key, selected-key, and cancelled-key sets. Selection is performed by the
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* {@link #select(Consumer)}, {@link #select(Consumer,long)}, and {@link
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* #selectNow(Consumer)} methods, and involves three steps: </p>
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*
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* <ol>
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*
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* <li><p> Each key in the cancelled-key set is removed from each key set of
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* which it is a member, and its channel is deregistered. This step leaves
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* the cancelled-key set empty. </p></li>
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*
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* <li><p> The underlying operating system is queried for an update as to the
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* readiness of each remaining channel to perform any of the operations
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* identified by its key's interest set as of the moment that the selection
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* operation began.
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*
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* <p> For a channel that is ready for at least one such operation, the
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* ready-operation set of the channel's key is set to identify exactly the
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* operations for which the channel is ready and the <i>action</i> specified
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* to the {@code select} method is invoked to consume the channel's key. Any
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* readiness information previously recorded in the ready set is discarded
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* prior to invoking the <i>action</i>.
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*
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* <p> Alternatively, where a channel is ready for more than one operation,
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* the <i>action</i> may be invoked more than once with the channel's key and
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* ready-operation set modified to a subset of the operations for which the
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* channel is ready. Where the <i>action</i> is invoked more than once for
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* the same key then its ready-operation set never contains operation bits
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* that were contained in the set at previous calls to the <i>action</i>
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* in the same selection operation. </p></li>
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*
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* <li><p> If any keys were added to the cancelled-key set while step (2) was
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* in progress then they are processed as in step (1). </p></li>
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*
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* </ol>
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*
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*
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* <h2>Concurrency</h2>
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*
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* <p> A Selector and its key set are safe for use by multiple concurrent
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* threads. Its selected-key set and cancelled-key set, however, are not.
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*
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* <p> The selection operations synchronize on the selector itself, on the
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* selected-key set, in that order. They also synchronize on the cancelled-key
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* set during steps (1) and (3) above.
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*
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* <p> Changes made to the interest sets of a selector's keys while a
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* selection operation is in progress have no effect upon that operation; they
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* will be seen by the next selection operation.
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*
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* <p> Keys may be cancelled and channels may be closed at any time. Hence the
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* presence of a key in one or more of a selector's key sets does not imply
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* that the key is valid or that its channel is open. Application code should
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* be careful to synchronize and check these conditions as necessary if there
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* is any possibility that another thread will cancel a key or close a channel.
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*
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* <p> A thread blocked in a selection operation may be interrupted by some
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* other thread in one of three ways:
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*
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* <ul>
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*
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* <li><p> By invoking the selector's {@link #wakeup wakeup} method,
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* </p></li>
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*
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* <li><p> By invoking the selector's {@link #close close} method, or
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* </p></li>
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*
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* <li><p> By invoking the blocked thread's {@link
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* java.lang.Thread#interrupt() interrupt} method, in which case its
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* interrupt status will be set and the selector's {@link #wakeup wakeup}
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* method will be invoked. </p></li>
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*
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* </ul>
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*
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* <p> The {@link #close close} method synchronizes on the selector and its
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* selected-key set in the same order as in a selection operation.
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*
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* <a id="ksc"></a>
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* <p> A Selector's key set is safe for use by multiple concurrent threads.
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* Retrieval operations from the key set do not generally block and so may
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* overlap with new registrations that add to the set, or with the cancellation
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* steps of selection operations that remove keys from the set. Iterators and
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* spliterators return elements reflecting the state of the set at some point at
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* or since the creation of the iterator/spliterator. They do not throw
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* {@link java.util.ConcurrentModificationException ConcurrentModificationException}.
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*
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* <a id="sksc"></a>
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* <p> A selector's selected-key set is not, in general, safe for use by
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* multiple concurrent threads. If such a thread might modify the set directly
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* then access should be controlled by synchronizing on the set itself. The
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* iterators returned by the set's {@link java.util.Set#iterator() iterator}
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* methods are <i>fail-fast:</i> If the set is modified after the iterator is
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* created, in any way except by invoking the iterator's own {@link
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* java.util.Iterator#remove() remove} method, then a {@link
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* java.util.ConcurrentModificationException} will be thrown. </p>
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*
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* @author Mark Reinhold
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* @author JSR-51 Expert Group
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* @since 1.4
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*
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* @see SelectableChannel
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* @see SelectionKey
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*/
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public abstract class Selector implements Closeable {
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/**
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* Initializes a new instance of this class.
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*/
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protected Selector() { }
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/**
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* Opens a selector.
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*
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* <p> The new selector is created by invoking the {@link
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* java.nio.channels.spi.SelectorProvider#openSelector openSelector} method
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* of the system-wide default {@link
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* java.nio.channels.spi.SelectorProvider} object. </p>
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*
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* @return A new selector
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*
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* @throws IOException
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* If an I/O error occurs
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*/
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public static Selector open() throws IOException {
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return SelectorProvider.provider().openSelector();
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}
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/**
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* Tells whether or not this selector is open.
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*
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* @return {@code true} if, and only if, this selector is open
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*/
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public abstract boolean isOpen();
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/**
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* Returns the provider that created this channel.
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*
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* @return The provider that created this channel
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*/
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public abstract SelectorProvider provider();
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/**
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* Returns this selector's key set.
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*
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* <p> The key set is not directly modifiable. A key is removed only after
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* it has been cancelled and its channel has been deregistered. Any
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* attempt to modify the key set will cause an {@link
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* UnsupportedOperationException} to be thrown.
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*
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* <p> The set is <a href="#ksc">safe</a> for use by multiple concurrent
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* threads. </p>
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*
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* @return This selector's key set
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*
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* @throws ClosedSelectorException
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* If this selector is closed
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*/
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public abstract Set<SelectionKey> keys();
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/**
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* Returns this selector's selected-key set.
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*
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* <p> Keys may be removed from, but not directly added to, the
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* selected-key set. Any attempt to add an object to the key set will
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* cause an {@link UnsupportedOperationException} to be thrown.
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*
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* <p> The selected-key set is <a href="#sksc">not thread-safe</a>. </p>
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*
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* @return This selector's selected-key set
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*
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* @throws ClosedSelectorException
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* If this selector is closed
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*/
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public abstract Set<SelectionKey> selectedKeys();
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/**
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* Selects a set of keys whose corresponding channels are ready for I/O
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* operations.
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*
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* <p> This method performs a non-blocking <a href="#selop">selection
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* operation</a>. If no channels have become selectable since the previous
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* selection operation then this method immediately returns zero.
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*
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* <p> Invoking this method clears the effect of any previous invocations
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* of the {@link #wakeup wakeup} method. </p>
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*
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* @return The number of keys, possibly zero, whose ready-operation sets
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* were updated by the selection operation
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*
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* @throws IOException
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* If an I/O error occurs
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*
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* @throws ClosedSelectorException
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* If this selector is closed
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*/
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public abstract int selectNow() throws IOException;
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/**
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* Selects a set of keys whose corresponding channels are ready for I/O
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* operations.
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*
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* <p> This method performs a blocking <a href="#selop">selection
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* operation</a>. It returns only after at least one channel is selected,
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* this selector's {@link #wakeup wakeup} method is invoked, the current
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* thread is interrupted, or the given timeout period expires, whichever
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* comes first.
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*
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* <p> This method does not offer real-time guarantees: It schedules the
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* timeout as if by invoking the {@link Object#wait(long)} method. </p>
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*
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* @param timeout If positive, block for up to {@code timeout}
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* milliseconds, more or less, while waiting for a
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* channel to become ready; if zero, block indefinitely;
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* must not be negative
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*
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* @return The number of keys, possibly zero,
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* whose ready-operation sets were updated
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*
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* @throws IOException
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* If an I/O error occurs
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*
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* @throws ClosedSelectorException
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* If this selector is closed
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*
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* @throws IllegalArgumentException
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* If the value of the timeout argument is negative
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*/
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public abstract int select(long timeout) throws IOException;
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/**
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* Selects a set of keys whose corresponding channels are ready for I/O
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* operations.
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*
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* <p> This method performs a blocking <a href="#selop">selection
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* operation</a>. It returns only after at least one channel is selected,
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* this selector's {@link #wakeup wakeup} method is invoked, or the current
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* thread is interrupted, whichever comes first. </p>
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*
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* @return The number of keys, possibly zero,
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* whose ready-operation sets were updated
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*
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* @throws IOException
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* If an I/O error occurs
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*
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* @throws ClosedSelectorException
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* If this selector is closed
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*/
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public abstract int select() throws IOException;
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/**
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* Selects and performs an action on the keys whose corresponding channels
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* are ready for I/O operations.
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*
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* <p> This method performs a blocking <a href="#selop">selection
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* operation</a>. It wakes up from querying the operating system only when
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* at least one channel is selected, this selector's {@link #wakeup wakeup}
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* method is invoked, the current thread is interrupted, or the given
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* timeout period expires, whichever comes first.
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*
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* <p> The specified <i>action</i>'s {@link Consumer#accept(Object) accept}
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* method is invoked with the key for each channel that is ready to perform
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* an operation identified by its key's interest set. The {@code accept}
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* method may be invoked more than once for the same key but with the
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* ready-operation set containing a subset of the operations for which the
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* channel is ready (as described above). The {@code accept} method is
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* invoked while synchronized on the selector and its selected-key set.
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* Great care must be taken to avoid deadlocking with other threads that
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* also synchronize on these objects. Selection operations are not reentrant
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* in general and consequently the <i>action</i> should take great care not
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* to attempt a selection operation on the same selector. The behavior when
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* attempting a reentrant selection operation is implementation specific and
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* therefore not specified. If the <i>action</i> closes the selector then
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* {@code ClosedSelectorException} is thrown when the action completes.
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* The <i>action</i> is not prohibited from closing channels registered with
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* the selector, nor prohibited from cancelling keys or changing a key's
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* interest set. If a channel is selected but its key is cancelled or its
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* interest set changed before the <i>action</i> is performed on the key
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* then it is implementation specific as to whether the <i>action</i> is
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* invoked (it may be invoked with an {@link SelectionKey#isValid() invalid}
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* key). Exceptions thrown by the action are relayed to the caller.
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*
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* <p> This method does not offer real-time guarantees: It schedules the
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* timeout as if by invoking the {@link Object#wait(long)} method.
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*
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* @implSpec The default implementation removes all keys from the
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* selected-key set, invokes {@link #select(long) select(long)} with the
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* given timeout and then performs the action for each key added to the
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* selected-key set. The default implementation does not detect the action
|
|
* performing a reentrant selection operation. The selected-key set may
|
|
* or may not be empty on completion of the default implementation.
|
|
*
|
|
* @param action The action to perform
|
|
*
|
|
* @param timeout If positive, block for up to {@code timeout}
|
|
* milliseconds, more or less, while waiting for a
|
|
* channel to become ready; if zero, block indefinitely;
|
|
* must not be negative
|
|
*
|
|
* @return The number of unique keys consumed, possibly zero
|
|
*
|
|
* @throws IOException
|
|
* If an I/O error occurs
|
|
*
|
|
* @throws ClosedSelectorException
|
|
* If this selector is closed or is closed by the action
|
|
*
|
|
* @throws IllegalArgumentException
|
|
* If the value of the timeout argument is negative
|
|
*
|
|
* @since 11
|
|
*/
|
|
public int select(Consumer<SelectionKey> action, long timeout)
|
|
throws IOException
|
|
{
|
|
if (timeout < 0)
|
|
throw new IllegalArgumentException("Negative timeout");
|
|
return doSelect(Objects.requireNonNull(action), timeout);
|
|
}
|
|
|
|
/**
|
|
* Selects and performs an action on the keys whose corresponding channels
|
|
* are ready for I/O operations.
|
|
*
|
|
* <p> This method performs a blocking <a href="#selop">selection
|
|
* operation</a>. It wakes up from querying the operating system only when
|
|
* at least one channel is selected, this selector's {@link #wakeup wakeup}
|
|
* method is invoked, or the current thread is interrupted, whichever comes
|
|
* first.
|
|
*
|
|
* <p> This method is equivalent to invoking the 2-arg
|
|
* {@link #select(Consumer, long) select} method with a timeout of {@code 0}
|
|
* to block indefinitely. </p>
|
|
*
|
|
* @implSpec The default implementation invokes the 2-arg {@code select}
|
|
* method with a timeout of {@code 0}.
|
|
*
|
|
* @param action The action to perform
|
|
*
|
|
* @return The number of unique keys consumed, possibly zero
|
|
*
|
|
* @throws IOException
|
|
* If an I/O error occurs
|
|
*
|
|
* @throws ClosedSelectorException
|
|
* If this selector is closed or is closed by the action
|
|
*
|
|
* @since 11
|
|
*/
|
|
public int select(Consumer<SelectionKey> action) throws IOException {
|
|
return select(action, 0);
|
|
}
|
|
|
|
/**
|
|
* Selects and performs an action on the keys whose corresponding channels
|
|
* are ready for I/O operations.
|
|
*
|
|
* <p> This method performs a non-blocking <a href="#selop">selection
|
|
* operation</a>.
|
|
*
|
|
* <p> Invoking this method clears the effect of any previous invocations
|
|
* of the {@link #wakeup wakeup} method. </p>
|
|
*
|
|
* @implSpec The default implementation removes all keys from the
|
|
* selected-key set, invokes {@link #selectNow() selectNow()} and then
|
|
* performs the action for each key added to the selected-key set. The
|
|
* default implementation does not detect the action performing a reentrant
|
|
* selection operation. The selected-key set may or may not be empty on
|
|
* completion of the default implementation.
|
|
*
|
|
* @param action The action to perform
|
|
*
|
|
* @return The number of unique keys consumed, possibly zero
|
|
*
|
|
* @throws IOException
|
|
* If an I/O error occurs
|
|
*
|
|
* @throws ClosedSelectorException
|
|
* If this selector is closed or is closed by the action
|
|
*
|
|
* @since 11
|
|
*/
|
|
public int selectNow(Consumer<SelectionKey> action) throws IOException {
|
|
return doSelect(Objects.requireNonNull(action), -1);
|
|
}
|
|
|
|
/**
|
|
* Default implementation of select(Consumer) and selectNow(Consumer).
|
|
*/
|
|
private int doSelect(Consumer<SelectionKey> action, long timeout)
|
|
throws IOException
|
|
{
|
|
synchronized (this) {
|
|
Set<SelectionKey> selectedKeys = selectedKeys();
|
|
synchronized (selectedKeys) {
|
|
selectedKeys.clear();
|
|
int numKeySelected;
|
|
if (timeout < 0) {
|
|
numKeySelected = selectNow();
|
|
} else {
|
|
numKeySelected = select(timeout);
|
|
}
|
|
|
|
// copy selected-key set as action may remove keys
|
|
Set<SelectionKey> keysToConsume = Set.copyOf(selectedKeys);
|
|
assert keysToConsume.size() == numKeySelected;
|
|
selectedKeys.clear();
|
|
|
|
// invoke action for each selected key
|
|
keysToConsume.forEach(k -> {
|
|
action.accept(k);
|
|
if (!isOpen())
|
|
throw new ClosedSelectorException();
|
|
});
|
|
|
|
return numKeySelected;
|
|
}
|
|
}
|
|
}
|
|
|
|
|
|
/**
|
|
* Causes the first selection operation that has not yet returned to return
|
|
* immediately.
|
|
*
|
|
* <p> If another thread is currently blocked in a selection operation then
|
|
* that invocation will return immediately. If no selection operation is
|
|
* currently in progress then the next invocation of a selection operation
|
|
* will return immediately unless {@link #selectNow()} or {@link
|
|
* #selectNow(Consumer)} is invoked in the meantime. In any case the value
|
|
* returned by that invocation may be non-zero. Subsequent selection
|
|
* operations will block as usual unless this method is invoked again in the
|
|
* meantime.
|
|
*
|
|
* <p> Invoking this method more than once between two successive selection
|
|
* operations has the same effect as invoking it just once. </p>
|
|
*
|
|
* @return This selector
|
|
*/
|
|
public abstract Selector wakeup();
|
|
|
|
/**
|
|
* Closes this selector.
|
|
*
|
|
* <p> If a thread is currently blocked in one of this selector's selection
|
|
* methods then it is interrupted as if by invoking the selector's {@link
|
|
* #wakeup wakeup} method.
|
|
*
|
|
* <p> Any uncancelled keys still associated with this selector are
|
|
* invalidated, their channels are deregistered, and any other resources
|
|
* associated with this selector are released.
|
|
*
|
|
* <p> If this selector is already closed then invoking this method has no
|
|
* effect.
|
|
*
|
|
* <p> After a selector is closed, any further attempt to use it, except by
|
|
* invoking this method or the {@link #wakeup wakeup} method, will cause a
|
|
* {@link ClosedSelectorException} to be thrown. </p>
|
|
*
|
|
* @throws IOException
|
|
* If an I/O error occurs
|
|
*/
|
|
public abstract void close() throws IOException;
|
|
}
|