org.jruby.internal.runtime

Class ThreadService

java.lang.Object

org.jruby.internal.runtime.ThreadService

public class ThreadService
extends Object

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.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ThreadService.Event Deprecated.

Constructor Summary

Constructors

Constructor and Description
ThreadService(Ruby runtime)

Method Summary

Methods

Modifier and Type	Method and Description
void	associateThread(Object threadOrFuture, RubyThread rubyThread)
void	deliverEvent(RubyThread sender, RubyThread target, ThreadService.Event event) Deprecated.
void	disposeCurrentThread()
void	dissociateThread(Object threadOrFuture)
RubyThread[]	getActiveRubyThreads()
boolean	getCritical()
ThreadContext	getCurrentContext() In order to provide an appropriate execution context for a given thread, we store ThreadContext instances in a threadlocal.
RubyThread	getMainThread()
boolean	getPolling()
ThreadGroup	getRubyThreadGroup()
Map<Object,RubyThread>	getRubyThreadMap() Get the map from threadlike objects to RubyThread instances.
ThreadContext	getThreadContextForThread(RubyThread thread)
void	initMainThread()
ThreadContext	registerNewThread(RubyThread thread)
void	setCritical(boolean critical)
void	setCurrentContext(ThreadContext context)
void	setMainThread(Thread thread, RubyThread rubyThread)
void	unregisterThread(RubyThread thread)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ThreadService

public ThreadService(Ruby runtime)

Method Detail

disposeCurrentThread

public void disposeCurrentThread()

initMainThread

public void initMainThread()

getCurrentContext

public ThreadContext getCurrentContext()

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).

Returns:

The ThreadContext instance for the current thread, or a new one if none has previously been created or the old ThreadContext has been collected.

setCurrentContext

public void setCurrentContext(ThreadContext context)

getMainThread

public RubyThread getMainThread()

setMainThread

public void setMainThread(Thread thread,
                 RubyThread rubyThread)

getPolling

public boolean getPolling()

getActiveRubyThreads

public RubyThread[] getActiveRubyThreads()

getRubyThreadGroup

public ThreadGroup getRubyThreadGroup()

getThreadContextForThread

public ThreadContext getThreadContextForThread(RubyThread thread)

registerNewThread

public ThreadContext registerNewThread(RubyThread thread)

associateThread

public void associateThread(Object threadOrFuture,
                   RubyThread rubyThread)

dissociateThread

public void dissociateThread(Object threadOrFuture)

unregisterThread

public void unregisterThread(RubyThread thread)

setCritical

public void setCritical(boolean critical)

getCritical

public boolean getCritical()

getRubyThreadMap

public Map<Object,RubyThread> getRubyThreadMap()

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

Returns:

The ruby thread map

deliverEvent

@Deprecated
public void deliverEvent(RubyThread sender,
                           RubyThread target,
                           ThreadService.Event event)

Deprecated.