43  * handling I/O events, the pooled threads may also execute other tasks required
  44  * to support the execution of asynchronous I/O operations.
  45  *
  46  * <p> An asynchronous channel group is created by invoking the {@link
  47  * #withFixedThreadPool withFixedThreadPool} or {@link #withCachedThreadPool
  48  * withCachedThreadPool} methods defined here. Channels are bound to a group by
  49  * specifying the group when constructing the channel. The associated thread
  50  * pool is <em>owned</em> by the group; termination of the group results in the
  51  * shutdown of the associated thread pool.
  52  *
  53  * <p> In addition to groups created explicitly, the Java virtual machine
  54  * maintains a system-wide <em>default group</em> that is constructed
  55  * automatically. Asynchronous channels that do not specify a group at
  56  * construction time are bound to the default group. The default group has an
  57  * associated thread pool that creates new threads as needed. The default group
  58  * may be configured by means of system properties defined in the table below.
  59  * Where the {@link java.util.concurrent.ThreadFactory ThreadFactory} for the
  60  * default group is not configured then the pooled threads of the default group
  61  * are {@link Thread#isDaemon daemon} threads.
  62  *
  63  * <table border summary="System properties">


  64  *   <tr>
  65  *     <th>System property</th>
  66  *     <th>Description</th>
  67  *   </tr>


  68  *   <tr>
  69  *     <td> {@code java.nio.channels.DefaultThreadPool.threadFactory} </td>
  70  *     <td> The value of this property is taken to be the fully-qualified name
  71  *     of a concrete {@link java.util.concurrent.ThreadFactory ThreadFactory}
  72  *     class. The class is loaded using the system class loader and instantiated.
  73  *     The factory's {@link java.util.concurrent.ThreadFactory#newThread
  74  *     newThread} method is invoked to create each thread for the default
  75  *     group's thread pool. If the process to load and instantiate the value
  76  *     of the property fails then an unspecified error is thrown during the
  77  *     construction of the default group. </td>
  78  *   </tr>
  79  *   <tr>
  80  *     <td> {@code java.nio.channels.DefaultThreadPool.initialSize} </td>
  81  *     <td> The value of the {@code initialSize} parameter for the default
  82  *     group (see {@link #withCachedThreadPool withCachedThreadPool}).
  83  *     The value of the property is taken to be the {@code String}
  84  *     representation of an {@code Integer} that is the initial size parameter.
  85  *     If the value cannot be parsed as an {@code Integer} it causes an
  86  *     unspecified error to be thrown during the construction of the default
  87  *     group. </td>
  88  *   </tr>

  89  * </table>
  90  *
  91  * <a id="threading"></a><h2>Threading</h2>
  92  *
  93  * <p> The completion handler for an I/O operation initiated on a channel bound
  94  * to a group is guaranteed to be invoked by one of the pooled threads in the
  95  * group. This ensures that the completion handler is run by a thread with the
  96  * expected <em>identity</em>.
  97  *
  98  * <p> Where an I/O operation completes immediately, and the initiating thread
  99  * is one of the pooled threads in the group then the completion handler may
 100  * be invoked directly by the initiating thread. To avoid stack overflow, an
 101  * implementation may impose a limit as to the number of activations on the
 102  * thread stack. Some I/O operations may prohibit invoking the completion
 103  * handler directly by the initiating thread (see {@link
 104  * AsynchronousServerSocketChannel#accept(Object,CompletionHandler) accept}).
 105  *
 106  * <a id="shutdown"></a><h2>Shutdown and Termination</h2>
 107  *
 108  * <p> The {@link #shutdown() shutdown} method is used to initiate an <em>orderly

  43  * handling I/O events, the pooled threads may also execute other tasks required
  44  * to support the execution of asynchronous I/O operations.
  45  *
  46  * <p> An asynchronous channel group is created by invoking the {@link
  47  * #withFixedThreadPool withFixedThreadPool} or {@link #withCachedThreadPool
  48  * withCachedThreadPool} methods defined here. Channels are bound to a group by
  49  * specifying the group when constructing the channel. The associated thread
  50  * pool is <em>owned</em> by the group; termination of the group results in the
  51  * shutdown of the associated thread pool.
  52  *
  53  * <p> In addition to groups created explicitly, the Java virtual machine
  54  * maintains a system-wide <em>default group</em> that is constructed
  55  * automatically. Asynchronous channels that do not specify a group at
  56  * construction time are bound to the default group. The default group has an
  57  * associated thread pool that creates new threads as needed. The default group
  58  * may be configured by means of system properties defined in the table below.
  59  * Where the {@link java.util.concurrent.ThreadFactory ThreadFactory} for the
  60  * default group is not configured then the pooled threads of the default group
  61  * are {@link Thread#isDaemon daemon} threads.
  62  *
  63  * <table class="striped">
  64  * <caption style="display:none:">System properties</caption>
  65  *   <thead>
  66  *   <tr>
  67  *     <th>System property</th>
  68  *     <th>Description</th>
  69  *   </tr>
  70  *   </thead>
  71  *   <tbody>
  72  *   <tr>
  73  *     <td> {@code java.nio.channels.DefaultThreadPool.threadFactory} </td>
  74  *     <td> The value of this property is taken to be the fully-qualified name
  75  *     of a concrete {@link java.util.concurrent.ThreadFactory ThreadFactory}
  76  *     class. The class is loaded using the system class loader and instantiated.
  77  *     The factory's {@link java.util.concurrent.ThreadFactory#newThread
  78  *     newThread} method is invoked to create each thread for the default
  79  *     group's thread pool. If the process to load and instantiate the value
  80  *     of the property fails then an unspecified error is thrown during the
  81  *     construction of the default group. </td>
  82  *   </tr>
  83  *   <tr>
  84  *     <td> {@code java.nio.channels.DefaultThreadPool.initialSize} </td>
  85  *     <td> The value of the {@code initialSize} parameter for the default
  86  *     group (see {@link #withCachedThreadPool withCachedThreadPool}).
  87  *     The value of the property is taken to be the {@code String}
  88  *     representation of an {@code Integer} that is the initial size parameter.
  89  *     If the value cannot be parsed as an {@code Integer} it causes an
  90  *     unspecified error to be thrown during the construction of the default
  91  *     group. </td>
  92  *   </tr>
  93  *   </tbody>
  94  * </table>
  95  *
  96  * <a id="threading"></a><h2>Threading</h2>
  97  *
  98  * <p> The completion handler for an I/O operation initiated on a channel bound
  99  * to a group is guaranteed to be invoked by one of the pooled threads in the
 100  * group. This ensures that the completion handler is run by a thread with the
 101  * expected <em>identity</em>.
 102  *
 103  * <p> Where an I/O operation completes immediately, and the initiating thread
 104  * is one of the pooled threads in the group then the completion handler may
 105  * be invoked directly by the initiating thread. To avoid stack overflow, an
 106  * implementation may impose a limit as to the number of activations on the
 107  * thread stack. Some I/O operations may prohibit invoking the completion
 108  * handler directly by the initiating thread (see {@link
 109  * AsynchronousServerSocketChannel#accept(Object,CompletionHandler) accept}).
 110  *
 111  * <a id="shutdown"></a><h2>Shutdown and Termination</h2>
 112  *
 113  * <p> The {@link #shutdown() shutdown} method is used to initiate an <em>orderly