/**
 * Lists all ThreadGroups and Threads in a program.
 * from _Java_in_a_Nutshell_ by David Flanagan, p. 162-163
 */

import java.io.*;

public class ThreadLister {

// Display thread info
private static void print_thread_info( PrintStream out, Thread t,
                                       String indent ) {
    if ( t == null ) return;
    out.println( indent + "Thread: " + t.getName() +
                 " Priority: " + t.getPriority() +
                 (t.isDaemon()  ?  " Daemon"  :  "") +
                 (t.isAlive()  ?  ""  :  " Not Alive" ) );
}

// Display info about a thread group and its threads and groups
private static void list_group( PrintStream out, ThreadGroup g,
                                String indent ) {
    if ( g == null ) return;
    int num_threads = g.activeCount();
    int num_groups = g.activeGroupCount();
    Thread[] threads = new Thread[ num_threads ];
    ThreadGroup[] groups = new ThreadGroup[ num_groups ];

    g.enumerate( threads, false );
    g.enumerate( groups, false );

    out.println( indent + "Thread Group: " + g.getName() +
                 " Max Priority: " + g.getMaxPriority() +
                 (g.isDaemon() ?  " Daemon"  :  "") +
                 " ; has " + (g.activeCount() - g.activeGroupCount()) +
                 " active Thread(s)" );

    for ( int i = 0; i < num_threads; i++ )
        print_thread_info( out, threads[ i ], indent + "    " );
    for ( int i = 0; i < num_groups; i++ )
        list_group( out, groups[ i ], indent + "    " );
}

/**
 * Find the root thread group and list it recursively
 *
 * @param out PrintStream to output to
 */
public static void listAllThreads( PrintStream out ) {
    ThreadGroup current_thread_group;
    ThreadGroup root_thread_group;
    ThreadGroup parent;

    // Get the current thread group
    current_thread_group = Thread.currentThread().getThreadGroup();

    // Now go find the root thread group
    root_thread_group = current_thread_group;
    parent = root_thread_group.getParent();
    while ( parent != null ) {
        root_thread_group = parent;
        parent = parent.getParent();
    }

    // And list it, recursively
    list_group( out, root_thread_group, "" );
}

}


// EOF