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Release v1.1.10


  • (#951) Set the Ruby compatibility version at 2.2
  • (#939, #933) The caller_runs fallback policy no longer blocks reads from the job queue by worker threads
  • (#938, #761, #652) You can now explicitly prune_pool a thread pool (Sylvain Joyeux)
  • (#937, #757, #670) We switched the Yahoo stock API for demos to Alpha Vantage (Gustavo Caso)
  • (#932, #931) We changed how SafeTaskExecutor handles local jump errors (Aaron Jensen)
  • (#927) You can use keyword arguments in your initialize when using Async (Matt Larraz)
  • (#926, #639) We removed timeout from TimerTask because it wasn't sound, and now it's a no-op with a warning (Jacob Atzen)
  • (#919) If you double-lock a re-entrant read-write lock, we promote to locked for writing (zp yuan)
  • (#915) monotonic_time now accepts an optional unit parameter, as Ruby's clock_gettime (Jean Boussier)

Release v1.1.9 (5 Jun 2021)


  • (#866) Child promise state not set to :pending immediately after #execute when parent has completed
  • (#905, #872) Fix RubyNonConcurrentPriorityQueue#delete method
  • (2df0337d) Make sure locks are not shared on shared when objects are dup/cloned
  • (#900, #906, #796, #847, #911) Fix Concurrent::Set tread-safety issues on CRuby
  • (#907) Add new ConcurrentMap backend for TruffleRuby

Release v1.1.8 (20 January 2021)


  • (#885) Fix race condition in TVar for stale reads
  • (#884) RubyThreadLocalVar: Do not iterate over hash which might conflict with new pair addition

Release v1.1.7 (6 August 2020)


  • (#879) Consider falsy value on Concurrent::Map#compute_if_absent for fast non-blocking path
  • (#876) Reset Async queue on forking, makes Async fork-safe
  • (#856) Avoid running problematic code in RubyThreadLocalVar on MRI that occasionally results in segfault
  • (#853) Introduce ThreadPoolExecutor without a Queue

Release v1.1.6, edge v0.6.0 (10 Feb 2020)


  • (#841) Concurrent.disable_at_exit_handlers! is no longer needed and was deprecated.
  • (#841) AbstractExecutorService#auto_terminate= was deprecated and has no effect. Set :auto_terminate option instead when executor is initialized.

Release v1.1.6.pre1, edge v0.6.0.pre1 (26 Jan 2020)


  • (#828) Allow to name executors, the name is also used to name their threads
  • (#838) Implement #dup and #clone for structs
  • (#821) Safer finalizers for thread local variables
  • Documentation fixes
  • (#814) Use Ruby's Etc.nprocessors if available
  • (#812) Fix directory structure not to mess with packaging tools
  • (#840) Fix termination of pools on JRuby


  • Add WrappingExecutor (#830)

Release v1.1.5, edge v0.5.0 (10 Mar 2019)


  • fix potential leak of context on JRuby and Java 7


  • Add finalized Concurrent::Cancellation
  • Add finalized Concurrent::Throttle
  • Add finalized Concurrent::Promises::Channel
  • Add new Concurrent::ErlangActor

Release v1.1.4 (14 Dec 2018)

  • (#780) Remove java_alias of 'submit' method of Runnable to let executor service work on java 11
  • (#776) Fix NameError on defining a struct with a name which is already taken in an ancestor

Release v1.1.3 (7 Nov 2018)

  • (#775) fix partial require of the gem (although not officially supported)

Release v1.1.2 (6 Nov 2018)

  • (#773) more defensive 1.9.3 support

Release v1.1.1, edge v0.4.1 (1 Nov 2018)

  • (#768) add support for 1.9.3 back

Release v1.1.0, edge v0.4.0 (31 OCt 2018) (yanked)

  • (#768) yanked because of issues with removed 1.9.3 support

Release v1.1.0.pre2, edge v0.4.0.pre2 (18 Sep 2018)


  • fixed documentation and README links
  • fix Set for TruffleRuby and Rubinius
  • use properly supported TruffleRuby APIs


  • add Promises.zip_futures_over_on

Release v1.1.0.pre1, edge v0.4.0.pre1 (15 Aug 2018)


  • requires at least Ruby 2.0
  • Promises are moved from concurrent-ruby-edge to concurrent-ruby
  • Add support for TruffleRuby
    • (#734) Fix Array/Hash/Set construction broken on TruffleRuby
    • AtomicReference fixed
  • CI stabilization
  • remove sharp dependency edge -> core
  • remove warnings
  • documentation updates
  • Exchanger is no longer documented as edge since it was already available in concurrent-ruby
  • (#644) Fix Map#each and #each_pair not returning enumerator outside of MRI
  • (#659) Edge promises fail during error handling
  • (#741) Raise on recursive Delay#value call
  • (#727) #717 fix global IO executor on JRuby
  • (#740) Drop support for CRuby 1.9, JRuby 1.7, Rubinius.
  • (#737) Move AtomicMarkableReference out of Edge
  • (#708) Prefer platform specific memory barriers
  • (#735) Fix wrong expected exception in channel spec assertion
  • (#729) Allow executor option in Promise#then
  • (#725) fix timeout check to use timeout_interval
  • (#719) update engine detection
  • (#660) Add specs for Promise#zip/ ordering
  • (#654) execution changes
  • (#666) Add thread safe set implementation
  • (#651) #699 #to_s, #inspect should not output negative object IDs.
  • (#685) Avoid RSpec warnings about raise_error
  • (#680) Avoid RSpec monkey patching, persist spec results locally, use RSpec v3.7.0
  • (#665) Initialize the monitor for new subarrays on Rubinius
  • (#661) Fix error handling in edge promises


  • (#659) Edge promises fail during error handling
  • Edge files clearly separated in lib-edge
  • added ReInclude

Release v1.0.5, edge v0.3.1 (26 Feb 2017)


  • Documentation for Event and Semaphore
  • Use Unsafe#fullFence and #loadFence directly since the shortcuts were removed in JRuby
  • Do not depend on org.jruby.util.unsafe.UnsafeHolder


  • (#620) Actors on Pool raise an error
  • (#624) Delayed promises did not interact correctly with flatting
    • Fix arguments yielded by callback methods
  • Overridable default executor in promises factory methods
  • Asking actor to terminate will always resolve to true

Release v1.0.4, edge v0.3.0 (27 Dec 2016)


  • Nothing


  • New promises' API renamed, lots of improvements, edge bumped to 0.3.0
    • Incompatible with previous 0.2.3 version
    • see #522

Release v1.0.3 (17 Dec 2016)

  • Trigger execution of flattened delayed futures
  • Avoid forking for processor_count if possible
  • Semaphore Mutex and JRuby parity
  • Adds Map#each as alias to Map#each_pair
  • Fix uninitialized instance variables
  • Make Fixnum, Bignum merger ready
  • Allows Promise#then to receive an executor
  • TimerSet now survives a fork
  • Reject promise on any exception
  • Allow ThreadLocalVar to be initialized with a block
  • Support Alpha with Concurrent::processor_count
  • Fixes format-security error when compiling ruby_193_compatible.h
  • Concurrent::Atom#swap fixed: reraise the exceptions from block

Release v1.0.2 (2 May 2016)

  • Fix bug with Concurrent::Map MRI backend #inspect method
  • Fix bug with Concurrent::Map MRI backend using Hash#value?
  • Improved documentation and examples
  • Minor updates to Edge

Release v1.0.1 (27 February 2016)

  • Fix "uninitialized constant Concurrent::ReentrantReadWriteLock" error.
  • Better handling of autoload vs. require.
  • Improved API for Edge Future zipping.
  • Fix reference leak in Edge Future constructor .
  • Fix bug which prevented thread pools from surviving a fork.
  • Fix bug in which TimerTask did not correctly specify all its dependencies.
  • Improved support for JRuby+Truffle
  • Improved error messages.
  • Improved documentation.

Release v1.0.0 (13 November 2015)

  • Rename attr_volatile_with_cas to attr_atomic
  • Add clear_each to LockFreeStack
  • Update AtomicReference documentation
  • Further updates and improvements to the synchronization layer.
  • Performance and memory usage performance with Actor logging.
  • Fixed ThreadPoolExecutor task count methods.
  • Improved Async performance for both short and long-lived objects.
  • Fixed bug in LockFreeLinkedSet.
  • Fixed bug in which Agent#await triggered a validation failure.
  • Further Channel updates.
  • Adopted a project Code of Conduct
  • Cleared interpreter warnings
  • Fixed bug in ThreadPoolExecutor task count methods
  • Fixed bug in 'LockFreeLinkedSet'
  • Improved Java extension loading
  • Handle Exception children in Edge::Future
  • Continued improvements to channel
  • Removed interpreter warnings.
  • Shared constants now in lib/concurrent/constants.rb
  • Refactored many tests.
  • Improved synchronization layer/memory model documentation.
  • Bug fix in Edge Future#flat
  • Brand new Channel implementation in Edge gem.
  • Simplification of RubySingleThreadExecutor
  • Async improvements
    • Each object uses its own SingleThreadExecutor instead of the global thread pool.
    • No longers supports executor injection
    • Much better documentation
  • Atom updates
    • No longer Dereferenceable
    • Now Observable
    • Added a #reset method
  • Brand new Agent API and implementation. Now functionally equivalent to Clojure.
  • Continued improvements to the synchronization layer
  • Merged in the thread_safe gem
    • Concurrent::Array
    • Concurrent::Hash
    • Concurrent::Map (formerly ThreadSafe::Cache)
    • Concurrent::Tuple
  • Minor improvements to Concurrent::Map
  • Complete rewrite of Exchanger
  • Removed all deprecated code (classes, methods, constants, etc.)
  • Updated Agent, MutexAtomic, and BufferedChannel to inherit from Synchronization::Object.
  • Many improved tests
  • Some internal reorganization

Release v0.9.1 (09 August 2015)

  • Fixed a Rubiniux bug in synchronization object
  • Fixed all interpreter warnings (except circular references)
  • Fixed require statements when requiring Atom alone
  • Significantly improved ThreadLocalVar on non-JRuby platforms
  • Fixed error handling in Edge
  • AtomicFixnum methods #increment and #decrement now support optional delta
  • New AtomicFixnum#update method
  • Minor optimizations in ReadWriteLock
  • New ReentrantReadWriteLock class
  • ThreadLocalVar#bind method is now public
  • Refactored many tests

Release v0.9.0 (10 July 2015)

  • Updated AtomicReference
    • AtomicReference#try_update now simply returns instead of raising exception
    • AtomicReference#try_update! was added to raise exceptions if an update fails. Note: this is the same behavior as the old try_update
  • Pure Java implementations of
    • AtomicBoolean
    • AtomicFixnum
    • Semaphore
  • Fixed bug when pruning Ruby thread pools
  • Fixed bug in time calculations within ScheduledTask
  • Default count in CountDownLatch to 1
  • Use monotonic clock for all timers via Concurrent.monotonic_time
    • Use Process.clock_gettime(Process::CLOCK_MONOTONIC) when available
    • Fallback to java.lang.System.nanoTime() on unsupported JRuby versions
    • Pure Ruby implementation for everything else
    • Effects Concurrent.timer, Concurrent.timeout, TimerSet, TimerTask, and ScheduledTask
  • Deprecated all clock-time based timer scheduling
    • Only support scheduling by delay
    • Effects Concurrent.timer, TimerSet, and ScheduledTask
  • Added new ReadWriteLock class
  • Consistent at_exit behavior for Java and Ruby thread pools.
  • Added at_exit handler to Ruby thread pools (already in Java thread pools)
    • Ruby handler stores the object id and retrieves from ObjectSpace
    • JRuby disables ObjectSpace by default so that handler stores the object reference
  • Added a :stop_on_exit option to thread pools to enable/disable at_exit handler
  • Updated thread pool docs to better explain shutting down thread pools
  • Simpler :executor option syntax for all abstractions which support this option
  • Added Executor#auto_terminate? predicate method (for thread pools)
  • Added at_exit handler to TimerSet
  • Simplified auto-termination of the global executors
    • Can now disable auto-termination of global executors
    • Added shutdown/kill/wait_for_termination variants for global executors
  • Can now disable auto-termination for all executors (the nuclear option)
  • Simplified auto-termination of the global executors
  • Deprecated terms "task pool" and "operation pool"
    • New terms are "io executor" and "fast executor"
    • New functions added with new names
    • Deprecation warnings added to functions referencing old names
  • Moved all thread pool related functions from Concurrent::Configuration to Concurrent
    • Old functions still exist with deprecation warnings
    • New functions have updated names as appropriate
  • All high-level abstractions default to the "io executor"
  • Fixed bug in Actor causing it to prematurely warm global thread pools on gem load
    • This also fixed a RejectedExecutionError bug when running with minitest/autorun via JRuby
  • Moved global logger up to the Concurrent namespace and refactored the code
  • Optimized the performance of Delay
    • Fixed a bug in which no executor option on construction caused block execution on a global thread pool
  • Numerous improvements and bug fixes to TimerSet
  • Fixed deadlock of Future when the handler raises Exception
  • Added shared specs for more classes
  • New concurrency abstractions including:
    • Atom
    • Maybe
    • ImmutableStruct
    • MutableStruct
    • SettableStruct
  • Created an Edge gem for unstable abstractions including
    • Actor
    • Agent
    • Channel
    • Exchanger
    • LazyRegister
    • new Future Framework - unified implementation of Futures and Promises which combines Features of previous Future, Promise, IVar, Event, Probe, dataflow, Delay, TimerTask into single framework. It uses extensively new synchronization layer to make all the paths lock-free with exception of blocking threads on #wait. It offers better performance and does not block threads when not required.
  • Actor framework changes:
    • fixed reset loop in Pool
    • Pool can use any actor as a worker, abstract worker class is no longer needed.
    • Actor events not have format [:event_name, *payload] instead of just the Symbol.
    • Actor now uses new Future/Promise Framework instead of IVar for better interoperability
    • Behaviour definition array was simplified to [BehaviourClass1, [BehaviourClass2, *initialization_args]]
    • Linking behavior responds to :linked message by returning array of linked actors
    • Supervised behavior is removed in favour of just Linking
    • RestartingContext is supervised by default now, supervise: true is not required any more
    • Events can be private and public, so far only difference is that Linking will pass to linked actors only public messages. Adding private :restarting and :resetting events which are send before the actor restarts or resets allowing to add callbacks to cleanup current child actors.
    • Print also object_id in Reference to_s
    • Add AbstractContext#default_executor to be able to override executor class wide
    • Add basic IO example
    • Documentation somewhat improved
    • All messages should have same priority. It's now possible to send actor << job1 << job2 << :terminate! and be sure that both jobs are processed first.
  • Refactored Channel to use newer synchronization objects
  • Added #reset and #cancel methods to TimerSet
  • Added #cancel method to Future and ScheduledTask
  • Refactored TimerSet to use ScheduledTask
  • Updated Async with a factory that initializes the object
  • Deprecated Concurrent.timer and Concurrent.timeout
  • Reduced max threads on pure-Ruby thread pools (abends around 14751 threads)
  • Moved many private/internal classes/modules into "namespace" modules
  • Removed brute-force killing of threads in tests
  • Fixed a thread pool bug when the operating system cannot allocate more threads

Release v0.8.0 (25 January 2015)

  • C extension for MRI have been extracted into the concurrent-ruby-ext companion gem. Please see the README for more detail.
  • Better variable isolation in Promise and Future via an :args option
  • Continued to update intermittently failing tests

Release v0.7.2 (24 January 2015)

  • New Semaphore class based on java.util.concurrent.Semaphore
  • New Promise.all? and Promise.any? class methods
  • Renamed :overflow_policy on thread pools to :fallback_policy
  • Thread pools still accept the :overflow_policy option but display a warning
  • Thread pools now implement fallback_policy behavior when not running (rather than universally rejecting tasks)
  • Fixed minor set_deref_options constructor bug in Promise class
  • Fixed minor require bug in ThreadLocalVar class
  • Fixed race condition bug in TimerSet class
  • Fixed race condition bug in TimerSet class
  • Fixed signal bug in TimerSet#post method
  • Numerous non-functional updates to clear warning when running in debug mode
  • Fixed more intermittently failing tests
  • Tests now run on new Travis build environment
  • Multiple documentation updates

Release v0.7.1 (4 December 2014)

Please see the roadmap for more information on the next planned release.

  • Added flat_map method to Promise
  • Added zip method to Promise
  • Fixed bug with logging in Actor
  • Improvements to Promise tests
  • Removed actor-experimental warning
  • Added an IndirectImmediateExecutor class
  • Allow disabling auto termination of global executors
  • Fix thread leaking in ThreadLocalVar (uses Ref gem on non-JRuby systems)
  • Fix thread leaking when pruning pure-Ruby thread pools
  • Prevent Actor from using an ImmediateExecutor (causes deadlock)
  • Added missing synchronizations to TimerSet
  • Fixed bug with return value of Concurrent::Actor::Utils::Pool#ask
  • Fixed timing bug in TimerTask
  • Fixed bug when creating a JavaThreadPoolExecutor with minimum pool size of zero
  • Removed confusing warning when not using native extenstions
  • Improved documentation

Release v0.7.0 (13 August 2014)

  • Merge the atomic gem
    • Pure Ruby MutexAtomic atomic reference class
    • Platform native atomic reference classes CAtomic, JavaAtomic, and RbxAtomic
    • Automated build process
    • Fat binary releases for multiple platforms including Windows (32/64), Linux (32/64), OS X (64-bit), Solaris (64-bit), and JRuby
  • C native CAtomicBoolean
  • C native CAtomicFixnum
  • Refactored intermittently failing tests
  • Added dataflow! and dataflow_with! methods to match Future#value! method
  • Better handling of timeout in Agent
  • Actor Improvements
    • Fine-grained implementation using chain of behaviors. Each behavior is responsible for single aspect like: Termination, Pausing, Linking, Supervising, etc. Users can create custom Actors easily based on their needs.
    • Supervision was added. RestartingContext will pause on error waiting on its supervisor to decide what to do next ( options are :terminate!, :resume!, :reset!, :restart!). Supervising behavior also supports strategies :one_for_one and :one_for_all.
    • Linking was added to be able to monitor actor's events like: :terminated, :paused, :restarted, etc.
    • Dead letter routing added. Rejected envelopes are collected in a configurable actor (default: Concurrent::Actor.root.ask!(:dead_letter_routing))
    • Old Actor class removed and replaced by new implementation previously called Actress. Actress was kept as an alias for Actor to keep compatibility.
    • Utils::Broadcast actor which allows Publish–subscribe pattern.
  • More executors for managing serialized operations
    • SerializedExecution mixin module
    • SerializedExecutionDelegator for serializing any executor
  • Updated Async with serialized execution
  • Updated ImmediateExecutor and PerThreadExecutor with full executor service lifecycle
  • Added a Delay to root Actress initialization
  • Minor bug fixes to thread pools
  • Refactored many intermittently failing specs
  • Removed Java interop warning executor.rb:148 warning: ambiguous Java methods found, using submit(java.lang.Runnable)
  • Fixed minor bug in RubyCachedThreadPool overflow policy
  • Updated tests to use RSpec 3.0
  • Removed deprecated Actor class
  • Better support for Rubinius

Release v0.6.1 (14 June 2014)

Release v0.6.0 (25 May 2014)

  • Added Concurrent::Observable to encapsulate our thread safe observer sets
  • Improvements to new Channel
  • Major improvements to CachedThreadPool and FixedThreadPool
  • Added SingleThreadExecutor
  • Added Current::timer function
  • Added TimerSet executor
  • Added AtomicBoolean
  • ScheduledTask refactoring
  • Pure Ruby and JRuby-optimized PriorityQueue classes
  • Updated Agent behavior to more closely match Clojure
  • Observer sets support block callbacks to the add_observer method
  • New algorithm for thread creation in RubyThreadPoolExecutor
  • Minor API updates to Event
  • Rewritten TimerTask now an Executor instead of a Runnable
  • Fixed many brittle specs
  • Renamed FixedThreadPool and CachedThreadPool to RubyFixedThreadPool and RubyCachedThreadPool
  • Created JRuby optimized JavaFixedThreadPool and JavaCachedThreadPool
  • Consolidated fixed thread pool tests into spec/concurrent/fixed_thread_pool_shared.rb and spec/concurrent/cached_thread_pool_shared.rb
  • FixedThreadPool now subclasses RubyFixedThreadPool or JavaFixedThreadPool as appropriate
  • CachedThreadPool now subclasses RubyCachedThreadPool or JavaCachedThreadPool as appropriate
  • New Delay class
  • Concurrent::processor_count helper function
  • New Async module
  • Renamed NullThreadPool to PerThreadExecutor
  • Deprecated Channel (we are planning a new implementation based on Go)
  • Added gem-level configuration
  • Deprecated $GLOBAL_THREAD_POOL in lieu of gem-level configuration
  • Removed support for Ruby 1.9.2
  • New RubyThreadPoolExecutor and JavaThreadPoolExecutor classes
  • All thread pools now extend the appropriate thread pool executor classes
  • All thread pools now support :overflow_policy (based on Java's reject policies)
  • Deprecated UsesGlobalThreadPool in lieu of explicit :executor option (dependency injection) on Future, Promise, and Agent
  • Added Concurrent::dataflow_with(executor, *inputs) method to support executor dependency injection for dataflow
  • Software transactional memory with TVar and Concurrent::atomically
  • First implementation of new, high-performance Channel
  • Actor is deprecated in favor of new experimental actor implementation #73. To avoid namespace collision it is living in Actress namespace until Actor is removed in next release.

Release v0.5.0

This is the most significant release of this gem since its inception. This release includes many improvements and optimizations. It also includes several bug fixes. The major areas of focus for this release were:

  • Stability improvements on Ruby versions with thread-level parallelism (JRuby and Rubinius)
  • Creation of new low-level concurrency abstractions
  • Internal refactoring to use the new low-level abstractions

Most of these updates had no effect on the gem API. There are a few notable exceptions which were unavoidable. Please read the release notes for more information.

Specific changes include:

  • New class IVar
  • New class MVar
  • New class ThreadLocalVar
  • New class AtomicFixnum
  • New class method dataflow
  • New class Condition
  • New class CountDownLatch
  • New class DependencyCounter
  • New class SafeTaskExecutor
  • New class CopyOnNotifyObserverSet
  • New class CopyOnWriteObserverSet
  • Future updated with execute API
  • ScheduledTask updated with execute API
  • New Promise API
  • Future now extends IVar
  • Postable#post? now returns an IVar
  • Thread safety fixes to Dereferenceable
  • Thread safety fixes to Obligation
  • Thread safety fixes to Supervisor
  • Thread safety fixes to Event
  • Various other thread safety (race condition) fixes
  • Refactored brittle tests
  • Implemented pending tests
  • Added JRuby and Rubinius as Travis CI build targets
  • Added CodeClimate code review
  • Improved YARD documentation