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package java.nio.channels.spi;

import java.io.IOException;
import java.net.ProtocolFamily;
import java.nio.channels.*;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Iterator;
import java.util.ServiceLoader;
import java.util.ServiceConfigurationError;
import sun.security.action.GetPropertyAction;


Service-provider class for selectors and selectable channels.
 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 provider method. The first invocation of that method will locate the default provider as specified below. 
 The system-wide default provider is used by the static open methods of the 
DatagramChannel, Pipe, Selector, ServerSocketChannel, and SocketChannel classes. It is also used by the 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 open methods defined in this class. 
 All of the methods in this class are safe for use by multiple concurrent
threads.  
Author:
Mark Reinhold, JSR-51 Expert Group
Since:
1.4/**
 * 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 final Object lock = new Object();
    private static SelectorProvider provider = null;

    private static Void checkPermission() {
        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 RuntimePermission("selectorProvider")/**
     * 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 boolean loadProviderFromProperty() {
        String cn = System.getProperty("java.nio.channels.spi.SelectorProvider");
        if (cn == null)
            return false;
        try {
            @SuppressWarnings("deprecation")
            Object tmp = Class.forName(cn, true,
                                       ClassLoader.getSystemClassLoader()).newInstance();
            provider = (SelectorProvider)tmp;
            return true;
        } catch (ClassNotFoundException x) {
            throw new ServiceConfigurationError(null, x);
        } catch (IllegalAccessException x) {
            throw new ServiceConfigurationError(null, x);
        } catch (InstantiationException x) {
            throw new ServiceConfigurationError(null, x);
        } catch (SecurityException x) {
            throw new ServiceConfigurationError(null, x);
        }
    }

    private static boolean loadProviderAsService() {

        ServiceLoader<SelectorProvider> sl =
            ServiceLoader.load(SelectorProvider.class,
                               ClassLoader.getSystemClassLoader());
        Iterator<SelectorProvider> i = sl.iterator();
        for (;;) {
            try {
                if (!i.hasNext())
                    return false;
                provider = i.next();
                return true;
            } 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.
 The first invocation of this method locates the default provider
object as follows: 

  
 If the system property 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. 
  
 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 java.nio.channels.spi.SelectorProvider in the resource directory 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. 
  
 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.  

 Subsequent invocations of this method return the provider that was
returned by the first invocation.  
Returns:
 The system-wide default selector provider/**
     * 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
     *   {@code 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() {
        synchronized (lock) {
            if (provider != null)
                return provider;
            return AccessController.doPrivileged(
                new PrivilegedAction<>() {
                    public SelectorProvider run() {
                            if (loadProviderFromProperty())
                                return provider;
                            if (loadProviderAsService())
                                return provider;
                            provider = sun.nio.ch.DefaultSelectorProvider.create();
                            return provider;
                        }
                    });
        }
    }

    
Opens a datagram channel.
Throws:
IOException – 
         If an I/O error occurs
Returns:
 The new channel/**
     * 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.
Params:
family – 
         The protocol family
Throws:
UnsupportedOperationException – 
         If the specified protocol family is not supported
IOException – 
         If an I/O error occurs
Returns:
 A new datagram channel
Since:
1.7/**
     * 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.
Throws:
IOException – 
         If an I/O error occurs
Returns:
 The new pipe/**
     * Opens a pipe.
     *
     * @return  The new pipe
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    public abstract Pipe openPipe()
        throws IOException;

    
Opens a selector.
Throws:
IOException – 
         If an I/O error occurs
Returns:
 The new selector/**
     * 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.
Throws:
IOException – 
         If an I/O error occurs
Returns:
 The new channel/**
     * 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.
Throws:
IOException – 
         If an I/O error occurs
Returns:
 The new channel/**
     * 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.
 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 (inetd) 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.
 In cases where the inherited channel represents a network socket then the Channel type returned by this method is determined as follows: 

 
 If the inherited channel represents a stream-oriented connected socket then a SocketChannel is returned. The socket channel is, at least initially, in blocking mode, bound to a socket address, and connected to a peer. 
 
 If the inherited channel represents a stream-oriented listening socket then a 
 ServerSocketChannel is returned. The server-socket channel is, at least initially, in blocking mode, and bound to a socket address. 
 
 If the inherited channel is a datagram-oriented socket then a DatagramChannel is returned. The datagram channel is, at least initially, in blocking mode, and bound to a socket address. 

 In addition to the network-oriented channels described, this method
may return other kinds of channels in the future.
 The first invocation of this method creates the channel that is
returned. Subsequent invocations of this method return the same
channel. 
Throws:
IOException – 
         If an I/O error occurs
SecurityException –  If a security manager has been installed and it denies RuntimePermission("inheritedChannel")
Returns:
 The inherited channel, if any, otherwise null.
Since:
1.5/**
     * 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 represents a network socket
     * then the {@link java.nio.channels.Channel Channel} type returned
     * by this method is determined as follows:
     *
     * <ul>
     *
     *  <li><p> If the inherited channel represents a stream-oriented connected
     *  socket then a {@link java.nio.channels.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 represents a stream-oriented listening
     *  socket then a {@link java.nio.channels.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 java.nio.channels.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 addition to the network-oriented channels described, this method
     * may return other kinds of channels 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>
     *
     * @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;
   }

}