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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.*;
import java.security.AccessController;
import java.security.PrivilegedAction;

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 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/**
 * Service-provider class for asynchronous channels.
 *
 * <p> 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.
 *
 * <p> All of the methods in this class are safe for use by multiple concurrent
 * threads.  </p>
 *
 * @since 1.7
 */

public abstract class AsynchronousChannelProvider {
    private static Void checkPermission() {
        SecurityManager sm = System.getSecurityManager();
        if (sm != null)
            sm.checkPermission(new RuntimePermission("asynchronousChannelProvider"));
        return null;
    }
    private AsynchronousChannelProvider(Void ignore) { }

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

    // lazy initialization of default provider
    private static class ProviderHolder {
        static final AsynchronousChannelProvider provider = load();

        private static AsynchronousChannelProvider load() {
            return AccessController
                .doPrivileged(new PrivilegedAction<>() {
                    public AsynchronousChannelProvider run() {
                        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 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 AsynchronousChannelProvider loadProviderAsService() {
            ServiceLoader<AsynchronousChannelProvider> sl =
                ServiceLoader.load(AsynchronousChannelProvider.class,
                                   ClassLoader.getSystemClassLoader());
            Iterator<AsynchronousChannelProvider> 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 asynchronous channel 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.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.  
  
 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.AsynchronousChannelProvider 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 AsynchronousChannel provider/**
     * Returns the system-wide default asynchronous channel 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.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.  </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.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.  </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 AsynchronousChannel provider
     */
    public static AsynchronousChannelProvider provider() {
        return ProviderHolder.provider;
    }

    
Constructs a new asynchronous channel group with a fixed thread pool.
Params:
nThreads – 
         The number of threads in the pool
threadFactory – 
         The factory to use when creating new threads
Throws:
IllegalArgumentException –  If nThreads <= 0
IOException – 
         If an I/O error occurs
See Also:
AsynchronousChannelGroup.withFixedThreadPool
Returns:
 A new asynchronous channel group/**
     * 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.
Params:
executor – 
         The thread pool
initialSize –  A value >=0 or a negative value for implementation specific default
Throws:
IOException – 
         If an I/O error occurs
See Also:
AsynchronousChannelGroup.withCachedThreadPool
Returns:
 A new asynchronous channel group/**
     * 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.
Params:
group –  The group to which the channel is bound, or null to bind to the default group
Throws:
IllegalChannelGroupException – 
         If the provider that created the group differs from this provider
ShutdownChannelGroupException – 
         The group is shutdown
IOException – 
         If an I/O error occurs
Returns:
 The new channel/**
     * 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.
Params:
group –  The group to which the channel is bound, or null to bind to the default group
Throws:
IllegalChannelGroupException – 
         If the provider that created the group differs from this provider
ShutdownChannelGroupException – 
         The group is shutdown
IOException – 
         If an I/O error occurs
Returns:
 The new channel/**
     * 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;
}