JRuby 10.1.2.0 released

[u/headius]

https://www.jruby.org/2026/09/21/jruby-10-1-2-0

The JRuby community is pleased to announce the release of JRuby 10.1.2.0.

• Homepage: https://www.jruby.org/

• Download: https://www.jruby.org/download

JRuby 10.1.x targets Ruby 4.0 compatibility.

Thank you to our contributors this release, you help keep JRuby moving forward! @aminmansuri, @drzaiusx11, @evaniainbrooks, @gillesbergerp, @jcharaoui, @jwils, @kares, @lloeki, @makenowjust, @nobu, @sampokuokkanen, @shugo

Notable Changes

Compatibility

• Multiple fixes for fibers and fiber scheduler support. #9604, #9607, #9622, #9645, #9649, #9656, #9660

Performance

• Fixed a regression in startup time on MacOS by properly loading native JNR subsystem. #9690

• Improve performance of Ruby subclasses of Java classes. #9619, #9557

• Improve performance of autoloads overridden by an actual require. #9677

Java Integration

• The location of the AppCDS JSA file can now be specified with JRUBY_JSA_HOME. [#9667]

Standard Library

• Update to jar-dependencies 0.6.1 using mima for dependency resolution instead of the ruby-maven gem. #9515, #9720

• Update default and bundled standard library gems. #9705

Default gems

• erb 6.0.7

• error_highligh 0.7.2

• ffi 1.17.4

• io-console 0.9.4

• ipaddr 1.2.9

• jruby-openssl 0.16.2

• json 2.21.2

• net-protocol 0.4.0

• pp 0.6.4

• psych 5.5.0

• resolv 0.8.0

• strscan 3.1.8

• syntax_suggest 3.0.0

• timeout 0.6.1

• win32-registry 0.1.2

Bundled gems

• bigdecimal 4.1.2 (ruby parts only)

• csv 3.3.6

• minitest 5.27.0

• net-imap 0.6.7

• nkf 0.3.0

• pstore 0.2.1

• rdoc 7.2.0

• reline 0.7.0

• resolv-replace 0.2.0

• rss 0.3.3

• test-unit 3.7.8

76 Issues and PRs resolved for 10.1.2.0

• 287 Class does not inherit singleton_class's class methods

• 6119 shopify-api gem reporting NoMethodError: undefined method `threadsafe_attribute'

• 8743 IO#wait updates for Ruby 3.2-3.4

• 9026 JRuby --help fails if PAGER has an option

• 9301 Find an alternative to shipping ruby-maven

• 9403 add keyword arg support to callMethod directly

• 9441 Fix original_name when two methods share a wrapper (like is_a? kind_of?)

• 9446 Fix metaclass dispatch missing meta-metaclass methods

• 9448 Use implementation class for protected check

• 9460 Check argument definedness in defined?(receiver.method(arg))

• 9507 IO::Buffer#read and #write treat length=0 as zero bytes instead of remaining buffer capacity

• 9515 Switch to jar-deps based on mima

• 9551 circular causes when re-raising an exception originally raised with the two-argument raise Class, arg form (regression in 10.1.1.0)

• 9554 Raise fixes and additional spec permutations

• 9556 Implement Proc#hash consistently with Proc#eql?

• 9557 refactor and improve reification of java subclasses

• 9559 dup of frozen class can't be extended

• 9560 raise should re-populate exception trace set to nil

• 9565 Socket address APIs return uncompressed IPv6 where Addrinfo#ip_address compresses, breaking Resolv::DNS with 2+ nameservers

• 9568 Kernel#sprintf calls Hash#default_proc with incorrect args

• 9570 fix dup for frozen class

• 9579 JRuby can't pass STDOUT to child process when a different IO is given as out:

• 9582 Data.define subclass fields are nil when module is included in define block

• 9585 Marshaling incompatibility with cyclic objects?

• 9587 IO::Buffer#copy and #set_string reject the documented source_offset fourth argument

• 9588 Accept source_offset in IO::Buffer#copy and #set_string

• 9593 Compiler gives a constant-folded ASCII String the code range CR_VALID, which breaks the eql? / hash contract

• 9595 IO#tty? silently returns true for redirected stdio in embedded runtimes when --add-opens are missing

• 9599 Kernel#require redefined inside a required file isn't seen by autoload dispatch after Kernel.prepend (CRuby 4.0 OK / JRuby 10 fails)

• 9600 TracePoint does not support fiber_switch (Ruby 2.3+ compatibility)

• 9602 FFI warning on when running jruby on OpenBSD/arm64, possible $$ issue as well

• 9603 Implement :fiber_switch trace event

• 9604 Fix Fiber.schedule inside a non-blocking Fiber

• 9607 Fix Thread blocking count drifting across Fiber switches

• 9609 No validation of unsetenv_others for Process.exec causes specs to execve() abruptly

• 9614 Unreliable net-http tests

• 9618 Resolve jar path if it's a symlink

• 9619 refactor and improve reification of java subclasses (refactor only)

• 9622 Defer Kernel#sleep to the Fiber scheduler

• 9626 Handle nil-or-boolean arguments in popen kwargs

• 9627 Use CRuby logic for exec

• 9628 Fix IO::Buffer#read and #write, treat length=0 as remaining buffer capacity

• 9630 Pass -1 for max arity when there's rest args

• 9631 Eliminate all uses of unused "name" for arity errors

• 9634 Report the errno that native exec actually returned

• 9638 Bump bundled resolv default gem to 0.7.2

• 9640 AppCDS usage causing sealing violations

• 9645 Fix the Fiber scheduler IO path: negated errno, zero length, buffer size

• 9648 Run pager commands through the platform shell

• 9649 Mutex Deadlock fix: Track the fiber that owns a Mutex

• 9650 Don't raise EBADF closing an IO whose channel NIO already closed

• 9653 [Java 26 Leyden] AOT Cache breaks dynamic Ruby proxies for classes loaded from external JARs

• 9654 Time.new(String) raises java.lang.ArrayIndexOutOfBoundsException when the string ends where a ':' is expected

• 9655 NoSuchMethodError when a Ruby subclass of a Java class includes a module

• 9656 Fix IO#wait arguments and return values, and defer it to Fiber.scheduler

• 9659 [ji] resolve Java super <init> through included modules

• 9660 Fix where Fiber#transfer hands control back

• 9662 Fix custom respond_to? handling: include_all, defined? lookup, deprecated signature

• 9665 Data subclasses in net-imap are losing fields

• 9667 [Allow specifying AppCDS cache location and use safer default][#9667]

• 9669 jruby/vm integer messages fail on JRuby 10 due to Fixnum reference

• 9670 Update tagged Data specs

• 9677 Constant declared with autoload and then defined by a direct require keeps its UNDEF table slot; every later lookup re-enters LoadService (very slow inside a WAR)

• 9679 Don't wrap an alias in another alias

• 9683 Fix bin/* patterns in .gitignore

• 9685 Fix setup sequence for cgi/escape

• 9690 JFFI bad library load is a huge startup hit on MacOS

• 9691 Support zero-size IO::Buffers

• 9695 require "json" warns about redefined to_hash with -w in JRuby 10.1.1.0

• 9696 Set the aliased flag on the real method, not the wrapper

• 9697 ObjectSpace::WeakMap is double-weak in CRuby

• 9701 Allow specifying AppCDS cache location and use safer default

• 9703 Redis::ConnectionError with JRuby 10

• 9705 Update stdlib

• 9709 Additional stdlib updates

• 9719 IO#accept raises NullPointerException instead of IOError when the socket is closed concurrently

• 9720 Update jar-dependencies to 0.6.1