Kilim: Continuations, Fibers, Actors and message passing for the JVM

Kilim is composed of 2 primary components:

The Kilim weaver modifies the bytecode of compiled java classes, enabling a method to save it's state and yield control of it's thread, ie to cooperatively multitask
The Kilim runtime library provides constructs that leverage the weaver to simplify concurrent programming, including Coroutines, Task, Actors, Mailboxes (aka channels), and Generators

Together, these facilities allow for simple concurrency and can scale to millions of concurrent tasks

Usage

Code can be woven:

during compilation by using the maven plugin
during compilation by running kilim.tools.Weaver
at runtime by invoking kilim.tools.Kilim com.yourcompany.yourclass
at runtime by including if (kilim.tools.Kilim.trampoline(false,args)) return; at the start of main()

Writing code with Kilim

Please see docs/manual.txt and docs/kilim_ecoop08.pdf for a brief introduction.

src/kilim/examples contains some simple examples
src/kilim/bench contains some performance benchmarks
kilim streams is a port of java 8 streams to kilim
java empower is a comparison of several async web server techs
- kj/src/main/java/KilimJetty.java shows integrating with jetty async
- kilim/src/main/java/KilimHello.java shows the built-in kilim web server (which in addition to doing async connections also does async io)

"hello world" in kilim

for an example of a project that uses kilim (with the trampoline for runtime weaving) see the battle royale demo in this repository. clone this repository, and from that directory execute mvn package exec:java -Dexec.mainClass=kilim.demo.Battle

Similarity to Java Futures

java.util.concurrent.Future<V> is an interface that can represents the result of an asynchronous computation. kilim pre-dates java futures, and uses a slightly different api, but kilim supports the same notion, ie to block until an async computation finishes:

kilim.Task.joinb() blocks until a Task completes
kilim.Task.isDone() returns true if this Task completed
cancellation isn't explicitly supported
kilim.Mailbox.getb() is also similar

these methods allow synchronizing threads with async computations. however, the real power of kilim is in enabling communication between async computations. for this, use the join() and get() methods which are Pausable

Maven

for an example of a project that uses kilim, see the kilim jetty demo in this repository

the pom.xml specifies kilim as both a dependency and a plugin for ahead-of-time weaving
this version supports java 8, 9, 11, 12 and 13-ea (and 10 if you don't use lambdas)
there are dedicated artifacts for java 7 and 10 (see below)

the dependency:

    <dependency>
        <groupId>org.db4j</groupId>
        <artifactId>kilim</artifactId>
        <version>2.0.1</version>
    </dependency>

weaving with the kilim plugin:

    <plugin>
        <groupId>org.db4j</groupId>
        <artifactId>kilim</artifactId>
        <version>2.0.1</version>
        <executions>
            <execution>
                <goals><goal>weave</goal></goals>
            </execution>
        </executions>
    </plugin>

Overview

java.lang.Runnable: once a java.lang.Task starts running, it takes over the thread until it returns
kilim.Continuation: like java.lang.Runnable, but can yield (relinquish control of the thread) while preserving state. It’s caller must arrange to resume it at some appropriate time. Used for event-driven state machines where the event loop knows when to resume. The programmer is in charge of the event loop.
kilim.Task: like kilim.Continuation, but specifies a reason that it yields, and a scheduler automatically resumes it when the reason is no longer true. Typically used for a system of communicating state machines that communicate using Mailboxes. Releases the programmer from the job of mapping fibers to thread and of managing an event loop and the delivery of events.
kilim.Pausable: a hypothetical exception used to declare intent. a method that declares this to be thrown will trigger the weaver
kilim.Mailbox: a queue with Pausable methods that cause the calling Task method to yield when an operation would otherwise block and to resume automatically when the Mailbox because available for reading or writing
kilim.Fiber: the structure that stores the Continuation (and Task) state

Java Versions

java 8, 11 and 12 are the recommended platforms, but 7, 8, 9, and 10 are regularly tested, and in theory java 6 could probably still be made to work without too much work

java 8, java 9, java 11, java 12 and java 13-ea:

maven central: org.db4j : kilim : 2.0.2
compiled with java 8 bytecode
ASM 7.1 supports all versions of java through java 13-ea (and presumably, java 13 when it's released)

other versions and notes on limitations

java 7:

JAVA_HOME=path/to/java7 ant clean weave jar
see demos/java7 for usage examples
some features are not available, eg jetty integration and lambdas
this version is incompatible with lambdas in later java versions because default interface methods aren't supported
maven central: 2.0.1-jdk7

java 9:

the java 8 compiled version supports java 9
see demos/battle/pom9.xml for a usage example
kilim does not explicitly support modules, but works with the builtin fallback support, see below
JShell works - see demos/jshell

java 10:

java 10 has a bug and refuses to load some valid lambdas
https://bugs.java.com/bugdatabase/view_bug.do?bug_id=JDK-8209112
this is already fixed in java 11 but will not be fixed in java 10 due to the new release cycle
throws java.lang.NoClassDefFoundError when attempting to load a woven fiber-less lambda
workaround: use lambdas that take an explicit last parameter Fiber dummy and a corresponding default method without that last parameter
the Fiber argument should not be accessed in the lambda
to call a Pausable lambda, call the default method
github tag: java10
all lambdas that will be loaded need to be woven with this java10 "fiber-included" flavor of kilim
this will work fine with java 8 or 9 as well, however it exposes the fiber to the user and makes it harder to detect unwoven Pausable methods, so it's use is discouraged unless you need to support java 10
maven central: 2.0.0-28-jdk10

    interface Lambda {
        void execute(Fiber fiber) throws Pausable, Exception;
        default void execute() throws Pausable, Exception {}
    }
    static void dummy() throws Pausable, Exception {
        Lambda lambda = dummy -> {
            Task.sleep(1000);
            System.out.println("hello world");
        };
        lambda.execute();
    }

java 11:

constant dynamics and preview classes are not yet supported - they will be when usage in the wild is seen
JEP 330 single-file source invocation works with java 11
- the JEP 330 class loader has some limitations which must be worked around
- for java 11, use the kilim jar as a -javaagent (fixed in java 12)
- see demos/java11

specific java features

lambdas:

working
serialization of woven lambdas is problematic and possibly cannot be supported generally
http://mail.openjdk.java.net/pipermail/core-libs-dev/2014-July/027726.html

jshell:

working
see demos/jshell for an example of automatic weaving

JEP-330 single file source invocation

working
see demos/java11 for an example
for java 11, a java agent (included) is needed, see above (this is fixed in java 12)
call Kilim.trampoline in main to enable weaving
eg for java 12:

    public static void main(String[] args) {
        if (kilim.tools.Kilim.trampoline(new Object() {},false,args)) return;
    ...

modules:

kilim works with java 9 and later using the builtin fallback support
no module-info.java is provided
- if you have a demo project that you can share that "depends" on modules, create an issue and it will be investigated

Project Loom:

Project Loom is not yet released and is not yet supported by kilim
- some testing has been done
Loom attempts to run a much larger subset of the java language than kilim, at least initially at the expense of performance
when it is released, kilim will integrate with Loom fibers in whatever capacity makes sense

Building

summary:

maven and ant are used cooperatively
maven is used for downloading dependencies (or manually copy them to ./libs - see pom.xml)
- only needs to be done once (until dependencies change)
- mvn initialize (but any pom-based mvn command should work too)
- and cleaner to delete the copied jars
maven can also be used for building, but tests are disabled
there's a kilim maven plugin, but it's not used here to avoid a circular dependency - the weaver is run directly instead (using ant)
the plugin is only built during the maven build, but once built will be packaged by ant as well, eg mvn package && ant jar

simple: mvn install

build with tests: ant clean testjit test jar doc

details:

testjit runs the tests (after compiling) using the runtime weaver
test runs the tests using the compile-time weaver, as well as some tests that don't require weaving
doc generates sources.jar and javadoc.jar
mvn install:install-file -DpomFile=pom.xml -Dfile=$(target/kilim*.jar) -Dsources=target/sources.jar -Djavadoc=target/javadoc.jar

Support

public support:

nqzero is currently the primary maintainer. he's focused on making Kilim easy to use and reliable and is actively using Kilim

Sriram is the original author (in 2006 !) and deserves a great deal of thanks for his excellent work. He continues to provide guidance on kilim and is especially interested in theory and performance, but is not actively using kilim today. He can be reached at kilim at malhar.net

Users

a number of companies (or their employees) appear to have been using Kilim recently and have contributed

Copyright and License

Kilim v2.0

This software is released under an MIT-style license (please see the License file). Unless otherwise noted, all files in this distribution are offered under these terms, and files that explicitly refer to the "MIT License" refer to this license

nqzero/kilim