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BEGIN LICENSE BLOCK ***** Version: CPL 1.0/GPL 2.0/LGPL 2.1 The contents of this file are subject to the Common Public License Version 1.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at Software distributed under the License is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for the specific language governing rights and limitations under the License. Copyright (C) 2002-2004 Anders Bengtsson <> Copyright (C) 2004 Charles O Nutter <> Copyright (C) 2004 Stefan Matthias Aust <> Copyright (C) 2006 Miguel Covarrubias <> Alternatively, the contents of this file may be used under the terms of either of the GNU General Public License Version 2 or later (the "GPL"), or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"), in which case the provisions of the GPL or the LGPL are applicable instead of those above. If you wish to allow use of your version of this file only under the terms of either the GPL or the LGPL, and not to allow others to use your version of this file under the terms of the CPL, indicate your decision by deleting the provisions above and replace them with the notice and other provisions required by the GPL or the LGPL. If you do not delete the provisions above, a recipient may use your version of this file under the terms of any one of the CPL, the GPL or the LGPL. END LICENSE BLOCK ***
 package org.jruby.internal.runtime;
 import java.util.List;
 import java.util.Map;
 import org.jruby.Ruby;
ThreadService maintains lists ofall the JRuby-specific thread data structures needed for Ruby's threading API and for JRuby's execution. The main structures are:
  • ThreadContext, which contains frames, scopes, etc needed for Ruby execution
  • RubyThread, the Ruby object representation of a thread's state
  • RubyThreadGroup, which represents a group of Ruby threads
  • NativeThread, used to wrap native Java threads
  • FutureThread, used to wrap java.util.concurrent.Future
In order to ensure these structures do not linger after the thread has terminated, most of them are either weakly or softly referenced. The references associated with these structures are:
  • ThreadService has a hard reference to a ThreadLocal, which holds a soft reference to a ThreadContext. So the thread's locals softly reference ThreadContext. We use a soft reference to keep ThreadContext instances from going away too quickly when a Java thread leaves Ruby space completely, which would otherwise result in a lot of ThreadContext object churn.
  • ThreadService maintains a weak map from the actual java.lang.Thread (or java.util.concurrent.Future) instance to the associated RubyThread. The map is weak-keyyed, so it will not prevent the collection of the associated Thread or Future. The associated RubyThread will remain alive as long as the Thread/Future and this ThreadService instance are both alive, maintaining the external thread's identity in Ruby-land.
  • RubyThread has a weak reference to its to ThreadContext.
  • ThreadContext has a hard reference to its associated RubyThread. Ignoring other references, this will usually mean RubyThread is softly reachable via the soft threadlocal reference to ThreadContext in ThreadService.
  • RubyThreadGroup has hard references to threads it owns. The thread removes itself on termination (if it's a Ruby thread) or when the ThreadContext is collected (as in the case of "adopted" Java threads.
These data structures can come to life in one of two ways:
  • A Ruby thread is started. This constructs a new RubyThread object, which calls to ThreadService to initialize a ThreadContext and appropriate mappings in all ThreadService's structures. The body of the thread is wrapped with a finally block that will forcibly unregister the thread and all related structures from ThreadService.
  • A Java thread enters Ruby by doing a call. The thread is "adopted", and gains a RubyThread instance, a ThreadContext instance, and all associated mappings in ThreadService. Since we don't know when the thread has "left" Ruby permanently, no forcible unregistration is attempted for the various structures and maps. However, they should not be hard-rooted; the ThreadContext is only softly reachable at best if no calls are in-flight, so it will collect. Its collection will release the reference to RubyThread, and its finalizer will unregister that RubyThread from its RubyThreadGroup. With the RubyThread gone, the Thread-to-RubyThread map will eventually clear, releasing the hard reference to the Thread itself.
public class ThreadService {
    private Ruby runtime;
A hard reference to the "main" context, so we always have one waiting for "main" thread execution.
    private ThreadContext mainContext;

A thread-local soft reference to the current thread's ThreadContext. We use a soft reference so that the ThreadContext is still collectible but will not immediately disappear once dereferenced, to avoid churning through ThreadContext instances every time a Java thread enters and exits Ruby space.
The Java thread group into which we register all Ruby threads. This is distinct from the RubyThreadGroup, which is simply a mutable collection of threads.
    private ThreadGroup rubyThreadGroup;

A map from a Java Thread or Future to its RubyThread instance. This is a synchronized WeakHashMap, so it weakly references its keys; this means that when the Thread/Future goes away, eventually its entry in this map will follow.
    private final Map<ObjectRubyThreadrubyThreadMap;
    private final ReentrantLock criticalLock = new ReentrantLock();
    public ThreadService(Ruby runtime) {
        this. = runtime;
        this. = new ThreadLocal<SoftReference<ThreadContext>>();
        try {
            this. = new ThreadGroup("Ruby Threads#" + runtime.hashCode());
        } catch(SecurityException e) {
            this. = Thread.currentThread().getThreadGroup();
        this. = Collections.synchronizedMap(new WeakHashMap<ObjectRubyThread>());
    public void disposeCurrentThread() {
    public void initMainThread() {
        this. = ThreadContext.newContext();
        // Must be called from main thread (it is currently, but this bothers me)

In order to provide an appropriate execution context for a given thread, we store ThreadContext instances in a threadlocal. This method is a utility to get at that threadlocal context from anywhere in the program it may not be immediately available. This method should be used sparingly, and if it is possible to pass ThreadContext on the argument list, it is preferable. Description of behavior The threadlocal does not actually contain the ThreadContext directly; instead, it contains a SoftReference that holds the ThreadContext. This is to allow new threads to enter the system and execute Ruby code with a valid context, but still allow that context to garbage collect if the thread stays alive much longer. We use SoftReference here because WeakReference is collected too quickly, resulting in very expensive ThreadContext churn (and this originally lead to JRUBY-2261's leak of adopted RubyThread instances).

The ThreadContext instance for the current thread, or a new one if none has previously been created or the old ThreadContext has been collected.
    public ThreadContext getCurrentContext() {
        SoftReference sr = null;
        ThreadContext context = null;
        while (context == null) {
            // loop until a context is available, to clean up softrefs that might have been collected
            if ((sr = (SoftReference).get()) == null) {
                sr = adoptCurrentThread();
                context = (ThreadContext)sr.get();
            } else {
                context = (ThreadContext)sr.get();
            // context is null, wipe out the SoftReference (this could be done with a reference queue)
            if (context == null) {
        return context;
     * Used only for Fiber context management
    public void setCurrentContext(ThreadContext context) {
        .set(new SoftReference<ThreadContext>(context));
    private SoftReference adoptCurrentThread() {
        Thread current = Thread.currentThread();
        RubyThread.adopt(.getThread(), current);
        return (SoftReference.get();
    public RubyThread getMainThread() {
        return .getThread();
    public void setMainThread(Thread threadRubyThread rubyThread) {
    public synchronized RubyThread[] getActiveRubyThreads() {
    	// all threads in ruby thread group plus main thread
        synchronized() {
            List<RubyThreadrtList = new ArrayList<RubyThread>(.size());
            for (Map.Entry<ObjectRubyThreadentry : .entrySet()) {
                Object key = entry.getKey();
                if (key == nullcontinue;
                if (key instanceof Thread) {
                    Thread t = (Thread)key;
                    // thread is not alive, skip it
                    if (!t.isAlive()) continue;
                } else if (key instanceof Future) {
                    Future f = (Future)key;
                    // future is done or cancelled, skip it
                    if (f.isDone() || f.isCancelled()) continue;
            RubyThread[] rubyThreads = new RubyThread[rtList.size()];
            return rubyThreads;
    public ThreadGroup getRubyThreadGroup() {
    	return ;
        return thread.getContext();
    public synchronized ThreadContext registerNewThread(RubyThread thread) {
        ThreadContext context = ThreadContext.newContext();
        .set(new SoftReference(context));
        return context;
    public synchronized void associateThread(Object threadOrFutureRubyThread rubyThread) {
    public synchronized void dissociateThread(Object threadOrFuture) {
    public synchronized void unregisterThread(RubyThread thread) {
    public void setCritical(boolean critical) {
        if (critical && !.isHeldByCurrentThread()) {
        } else if (!critical && .isHeldByCurrentThread()) {
    private void acquireCritical() {
    private void releaseCritical() {
    public boolean getCritical() {
        return .isHeldByCurrentThread();
    public static class Event {
        public enum Type { KILL, RAISE, WAKEUP }
        public final RubyThread sender;
        public final RubyThread target;
        public final Type type;
        public final IRubyObject exception;
        public Event(RubyThread senderRubyThread targetType type) {
        public Event(RubyThread senderRubyThread targetType typeIRubyObject exception) {
            this. = sender;
            this. = target;
            this. = type;
            this. = exception;
    public synchronized void deliverEvent(Event event) {
        // first, check if the sender has unreceived mail
        // then deliver mail to the target;

Get the map from threadlike objects to RubyThread instances. Used mainly for testing purposes.

The ruby thread map
    public Map<ObjectRubyThreadgetRubyThreadMap() {
        return ;
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