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	/*
	* Copyright (c) 2000, 2021, 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.io.IOException;
	import java.lang.reflect.InvocationTargetException;
	import java.net.ProtocolFamily;
	import java.nio.channels.Channel;
	import java.nio.channels.DatagramChannel;
	import java.nio.channels.Pipe;
	import java.nio.channels.ServerSocketChannel;
	import java.nio.channels.SocketChannel;
	import java.security.AccessController;
	import java.security.PrivilegedAction;
	import java.util.Iterator;
	import java.util.Objects;
	import java.util.ServiceLoader;
	import java.util.ServiceConfigurationError;

	/**
	* Service-provider class for selectors and selectable channels.
	*
	* <p> A selector 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.
	*
	* <p> The system-wide default provider is used by the static {@code open}
	* methods of the {@link java.nio.channels.DatagramChannel#open
	* DatagramChannel}, {@link java.nio.channels.Pipe#open Pipe}, {@link
	* java.nio.channels.Selector#open Selector}, {@link
	* java.nio.channels.ServerSocketChannel#open ServerSocketChannel}, and {@link
	* java.nio.channels.SocketChannel#open SocketChannel} classes. It is also
	* used by the {@link java.lang.System#inheritedChannel System.inheritedChannel()}
	* method. A program may make use of a provider other than the default provider
	* by instantiating that provider and then directly invoking the {@code open}
	* methods defined in this class.
	*
	* <p> All of the methods in this class are safe for use by multiple concurrent
	* threads. </p>
	*
	*
	* @author Mark Reinhold
	* @author JSR-51 Expert Group
	* @since 1.4
	*/

	public abstract class SelectorProvider {

	private static Void checkPermission() {
	@SuppressWarnings("removal")
	SecurityManager sm = System.getSecurityManager();
	if (sm != null)
	sm.checkPermission(new RuntimePermission("selectorProvider"));
	return null;
	}
	private SelectorProvider(Void ignore) { }

	/**
	* Initializes a new instance of this class.
	*
	* @throws SecurityException
	* If a security manager has been installed and it denies
	* {@link RuntimePermission}{@code ("selectorProvider")}
	*/
	protected SelectorProvider() {
	this(checkPermission());
	}

	private static class Holder {
	static final SelectorProvider INSTANCE = provider();

	@SuppressWarnings("removal")
	static SelectorProvider provider() {
	PrivilegedAction<SelectorProvider> pa = () -> {
	SelectorProvider sp;
	if ((sp = loadProviderFromProperty()) != null)
	return sp;
	if ((sp = loadProviderAsService()) != null)
	return sp;
	return sun.nio.ch.DefaultSelectorProvider.get();
	};
	return AccessController.doPrivileged(pa);
	}

	private static SelectorProvider loadProviderFromProperty() {
	String cn = System.getProperty("java.nio.channels.spi.SelectorProvider");
	if (cn == null)
	return null;
	try {
	Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader());
	return (SelectorProvider) clazz.getConstructor().newInstance();
	} catch (ClassNotFoundException \|
	NoSuchMethodException \|
	IllegalAccessException \|
	InvocationTargetException \|
	InstantiationException \|
	SecurityException x) {
	throw new ServiceConfigurationError(null, x);
	}
	}

	private static SelectorProvider loadProviderAsService() {
	ServiceLoader<SelectorProvider> sl =
	ServiceLoader.load(SelectorProvider.class,
	ClassLoader.getSystemClassLoader());
	Iterator<SelectorProvider> i = sl.iterator();
	for (;;) {
	try {
	return i.hasNext() ? i.next() : null;
	} catch (ServiceConfigurationError sce) {
	if (sce.getCause() instanceof SecurityException) {
	// Ignore the security exception, try the next provider
	continue;
	}
	throw sce;
	}
	}
	}
	}

	/**
	* Returns the system-wide default selector provider for this invocation of
	* the Java virtual machine.
	*
	* <p> The first invocation of this method locates the default provider
	* object as follows: </p>
	*
	* <ol>
	*
	* <li><p> If the system property
	* {@systemProperty java.nio.channels.spi.SelectorProvider} 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. </p></li>
	*
	* <li><p> 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.SelectorProvider} 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. </p></li>
	*
	* <li><p> 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. </p></li>
	*
	* </ol>
	*
	* <p> Subsequent invocations of this method return the provider that was
	* returned by the first invocation. </p>
	*
	* @return The system-wide default selector provider
	*/
	public static SelectorProvider provider() {
	return Holder.INSTANCE;
	}

	/**
	* Opens a datagram channel.
	*
	* @return The new channel
	*
	* @throws IOException
	* If an I/O error occurs
	*/
	public abstract DatagramChannel openDatagramChannel()
	throws IOException;

	/**
	* Opens a datagram channel.
	*
	* @param family
	* The protocol family
	*
	* @return A new datagram channel
	*
	* @throws UnsupportedOperationException
	* If the specified protocol family is not supported
	* @throws IOException
	* If an I/O error occurs
	*
	* @since 1.7
	*/
	public abstract DatagramChannel openDatagramChannel(ProtocolFamily family)
	throws IOException;

	/**
	* Opens a pipe.
	*
	* @return The new pipe
	*
	* @throws IOException
	* If an I/O error occurs
	*/
	public abstract Pipe openPipe()
	throws IOException;

	/**
	* Opens a selector.
	*
	* @return The new selector
	*
	* @throws IOException
	* If an I/O error occurs
	*/
	public abstract AbstractSelector openSelector()
	throws IOException;

	/**
	* Opens a server-socket channel.
	*
	* @return The new channel
	*
	* @throws IOException
	* If an I/O error occurs
	*/
	public abstract ServerSocketChannel openServerSocketChannel()
	throws IOException;

	/**
	* Opens a socket channel.
	*
	* @return The new channel
	*
	* @throws IOException
	* If an I/O error occurs
	*/
	public abstract SocketChannel openSocketChannel()
	throws IOException;

	/**
	* Returns the channel inherited from the entity that created this
	* Java virtual machine.
	*
	* <p> On many operating systems a process, such as a Java virtual
	* machine, can be started in a manner that allows the process to
	* inherit a channel from the entity that created the process. The
	* manner in which this is done is system dependent, as are the
	* possible entities to which the channel may be connected. For example,
	* on UNIX systems, the Internet services daemon (<i>inetd</i>) is used to
	* start programs to service requests when a request arrives on an
	* associated network port. In this example, the process that is started,
	* inherits a channel representing a network socket.
	*
	* <p> In cases where the inherited channel is for an <i>Internet protocol</i>
	* socket then the {@link Channel Channel} type returned
	* by this method is determined as follows:
	*
	* <ul>
	*
	* <li><p> If the inherited channel is for a stream-oriented connected
	* socket then a {@link SocketChannel SocketChannel} is returned. The
	* socket channel is, at least initially, in blocking mode, bound
	* to a socket address, and connected to a peer.
	* </p></li>
	*
	* <li><p> If the inherited channel is for a stream-oriented listening
	* socket then a {@link ServerSocketChannel ServerSocketChannel} is returned.
	* The server-socket channel is, at least initially, in blocking mode,
	* and bound to a socket address.
	* </p></li>
	*
	* <li><p> If the inherited channel is a datagram-oriented socket then a
	* {@link DatagramChannel DatagramChannel} is returned. The datagram channel
	* is, at least initially, in blocking mode, and bound to a socket address.
	* </p></li>
	*
	* </ul>
	*
	* <p> In cases where the inherited channel is for a <i>Unix domain</i>
	* socket then the {@link Channel} type returned is the same as for
	* <i>Internet protocol</i> sockets as described above, except that
	* datagram-oriented sockets are not supported.
	*
	* <p> In addition to the two types of socket just described, this method
	* may return other types in the future.
	*
	* <p> The first invocation of this method creates the channel that is
	* returned. Subsequent invocations of this method return the same
	* channel. </p>
	*
	* @implSpec The default implementation of this method returns
	* {@code null}.
	*
	* @return The inherited channel, if any, otherwise {@code null}.
	*
	* @throws IOException
	* If an I/O error occurs
	*
	* @throws SecurityException
	* If a security manager has been installed and it denies
	* {@link RuntimePermission}{@code ("inheritedChannel")}
	*
	* @since 1.5
	*/
	public Channel inheritedChannel() throws IOException {
	return null;
	}

	/**
	* Opens a socket channel.
	*
	* @implSpec The default implementation of this method first checks that
	* the given protocol {@code family} is not {@code null},
	* then throws {@link UnsupportedOperationException}.
	*
	* @param family
	* The protocol family
	*
	* @return The new channel
	*
	* @throws UnsupportedOperationException
	* If the specified protocol family is not supported
	* @throws IOException
	* If an I/O error occurs
	*
	* @since 15
	*/
	public SocketChannel openSocketChannel(ProtocolFamily family) throws IOException {
	Objects.requireNonNull(family);
	throw new UnsupportedOperationException("Protocol family not supported");
	}

	/**
	* Opens a server-socket channel.
	*
	* @implSpec The default implementation of this method first checks that
	* the given protocol {@code family} is not {@code null},
	* then throws {@link UnsupportedOperationException}.
	*
	* @param family
	* The protocol family
	*
	* @return The new channel
	*
	* @throws UnsupportedOperationException
	* If the specified protocol family is not supported
	* @throws IOException
	* If an I/O error occurs
	*
	* @since 15
	*/
	public ServerSocketChannel openServerSocketChannel(ProtocolFamily family) throws IOException {
	Objects.requireNonNull(family);
	throw new UnsupportedOperationException("Protocol family not supported");
	}
	}

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