/* * Copyright (c) 2007, 2024, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.nio.channels.spi; import java.nio.channels.*; import java.io.IOException; import java.util.Iterator; import java.util.ServiceLoader; import java.util.ServiceConfigurationError; import java.util.concurrent.*; /** * Service-provider class for asynchronous channels. * *

An asynchronous channel provider is a concrete subclass of this class that * has a zero-argument constructor and implements the abstract methods specified * below. A given invocation of the Java virtual machine maintains a single * system-wide default provider instance, which is returned by the {@link * #provider() provider} method. The first invocation of that method will locate * the default provider as specified below. * *

All of the methods in this class are safe for use by multiple concurrent * threads.

* * @since 1.7 */ public abstract class AsynchronousChannelProvider { /** * Initializes a new instance of this class. */ protected AsynchronousChannelProvider() { } // lazy initialization of default provider private static class ProviderHolder { static final AsynchronousChannelProvider provider = load(); private static AsynchronousChannelProvider load() { AsynchronousChannelProvider p; p = loadProviderFromProperty(); if (p != null) return p; p = loadProviderAsService(); if (p != null) return p; return sun.nio.ch.DefaultAsynchronousChannelProvider.create(); } private static AsynchronousChannelProvider loadProviderFromProperty() { String cn = System.getProperty("java.nio.channels.spi.AsynchronousChannelProvider"); if (cn == null) return null; try { @SuppressWarnings("deprecation") Object tmp = Class.forName(cn, true, ClassLoader.getSystemClassLoader()).newInstance(); return (AsynchronousChannelProvider)tmp; } catch (ClassNotFoundException | InstantiationException | IllegalAccessException x) { throw new ServiceConfigurationError(null, x); } } private static AsynchronousChannelProvider loadProviderAsService() { ServiceLoader sl = ServiceLoader.load(AsynchronousChannelProvider.class, ClassLoader.getSystemClassLoader()); return sl.findFirst().orElse(null); } } /** * Returns the system-wide default asynchronous channel provider for this * invocation of the Java virtual machine. * *

The first invocation of this method locates the default provider * object as follows:

* *
    * *

  1. If the system property * {@systemProperty java.nio.channels.spi.AsynchronousChannelProvider} is * defined then it is taken to be the fully-qualified name of a concrete * provider class. The class is loaded and instantiated; if this process * fails then an unspecified error is thrown.

    2. * *

  2. If a provider class has been installed in a jar file that is * visible to the system class loader, and that jar file contains a * provider-configuration file named * {@code java.nio.channels.spi.AsynchronousChannelProvider} in the resource * directory {@code META-INF/services}, then the first class name * specified in that file is taken. The class is loaded and * instantiated; if this process fails then an unspecified error is * thrown.

    3. * *

  3. Finally, if no provider has been specified by any of the above * means then the system-default provider class is instantiated and the * result is returned.

    4. * *
* *

Subsequent invocations of this method return the provider that was * returned by the first invocation.

* * @return The system-wide default AsynchronousChannel provider */ public static AsynchronousChannelProvider provider() { return ProviderHolder.provider; } /** * Constructs a new asynchronous channel group with a fixed thread pool. * * @param nThreads * The number of threads in the pool * @param threadFactory * The factory to use when creating new threads * * @return A new asynchronous channel group * * @throws IllegalArgumentException * If {@code nThreads <= 0} * @throws IOException * If an I/O error occurs * * @see AsynchronousChannelGroup#withFixedThreadPool */ public abstract AsynchronousChannelGroup openAsynchronousChannelGroup(int nThreads, ThreadFactory threadFactory) throws IOException; /** * Constructs a new asynchronous channel group with the given thread pool. * * @param executor * The thread pool * @param initialSize * A value {@code >=0} or a negative value for implementation * specific default * * @return A new asynchronous channel group * * @throws IOException * If an I/O error occurs * * @see AsynchronousChannelGroup#withCachedThreadPool */ public abstract AsynchronousChannelGroup openAsynchronousChannelGroup(ExecutorService executor, int initialSize) throws IOException; /** * Opens an asynchronous server-socket channel. * * @param group * The group to which the channel is bound, or {@code null} to * bind to the default group * * @return The new channel * * @throws IllegalChannelGroupException * If the provider that created the group differs from this provider * @throws ShutdownChannelGroupException * The group is shutdown * @throws IOException * If an I/O error occurs */ public abstract AsynchronousServerSocketChannel openAsynchronousServerSocketChannel (AsynchronousChannelGroup group) throws IOException; /** * Opens an asynchronous socket channel. * * @param group * The group to which the channel is bound, or {@code null} to * bind to the default group * * @return The new channel * * @throws IllegalChannelGroupException * If the provider that created the group differs from this provider * @throws ShutdownChannelGroupException * The group is shutdown * @throws IOException * If an I/O error occurs */ public abstract AsynchronousSocketChannel openAsynchronousSocketChannel (AsynchronousChannelGroup group) throws IOException; }