Dynamic Code Evolution VM for Java 7/8
skybber Merge pull request #156 from przemelek/master
Changes to display JVM installations on macOS/OSX.
Latest commit 6d520d8 Aug 20, 2018



This project is a fork of original DCEVM project.

The purpose of the project is to maintain enhanced class redefinition functionality for OpenJDK HotSpot 7/8.


You can download binaries here.

Dcevm for Java9 and Java10

Dcevm8 is last version supported by this project. New versions are moved to separated projects extended from OpenJDK under HotswapProjects umbrella.

Dcevm patch is hosted in dedicated dcevm branch in each repository.

Supported versions

hotspot/.hg/patches/ contains patches for all supported versions. Each patch is named by concatenating prefix full or light with the OpenJDK HotSpot tag. full patches support full redefenition capabilities (including removal of superclasses, for example). light patches are easier to maintain, but they only support limited functionality (generally, additions to class hierarchies are fine, removals are not).

HotSpot tag is the name of the tag in the corresponding HotSpot Mercurial repository (Java 8/Java 7).


General Requirements

You need the following software to build DCEVM:

  • Java 7 or later. If you intend to run tests, it should be one of the supported versions (see list of patches/)
  • C++ compiler toolchain (gcc). There is no strict version requirement except that it should be supported by HotSpot build scripts.
  • Mercurial with Mercurial Queues Extension enabled.

Mac OS X specific requirements

Currently the build is not compatible with Clang on Mac OS X, you need to install gcc 4.8 using the Homebrew:

brew tap homebrew/versions
brew install gcc48

Then set the following environmental properties:

export CC=/usr/local/bin/gcc-4.8
export CFLAGS=-fobjc-exceptions
export CXX=/usr/local/bin/g++-4.8
export SA_LDFLAGS=-fobjc-exceptions

Compiling DCEVM

  • Configure version you want in gradle.properties.
  • Run ./gradlew patch to retrieve HotSpot sources and patch them.
  • Run ./gradlew compileFastdebug to build fastdebug version or ./gradlew compileProduct to build product version.
  • Compiled libraries are placed in hotspot/build/fastdebug or hotspot/build/product.

Installing DCEVM

  • Replace libjvm.so/jvm.dll/libjvm.dylib in the target JRE.
  • Run java -version, it should include Dynamic Code Evolution string.

Or you can install DCEVM using the gradle script:

  • Run ./gradlew installFastdebug -PtargetJre=$JAVA_HOME/jre or ./gradlew installProduct -PtargetJre=$JAVA_HOME/jre
  • DCEVM will be installed as "alternative" JVM. To use it, add -XXaltjvm=dcevm

Alternatively, on Debian and Ubuntu systems DCEVM can be installed with the openjdk-7-jre-dcevm package and invoked by adding the -dcevm command line parameter:

  • Run apt-get install openjdk-7-jre-dcevm
  • Run java -dcevm -version, it should include Dynamic Code Evolution string.

Testing DCEVM

  • Configure version you want in gradle.properties.
  • Set JAVA_HOME to point to JDK you want to test against (should be compatible with the version you set in gradle.properties).
  • Run ./gradlew patch to retrieve HotSpot sources and patch them.
  • Run ./gradlew test to run tests.
  • Tests reports will be in dcevm/build/reports/tests/index.html

To run tests from IDE, you need:

  • Run ./gradlew agent:build to build redefinition agent code.
  • Add JVM argument to use redefinition agent (-javaagent:agent/build/libs/agent.jar).
  • Add JVM argument to DCEVM VM if installed side-by-side (-XXaltjvm=dcevm).

Hotswap performance tweak (Experimental)

DCEVM executes deoptimization (purge of code cache) after any class redefinition. It leads to decrease JVM's performance (after redefinition). This is especially problem on large scale projects with significant number of classes. Hotswap performance can be improved using an experimental option -XX:HotswapDeoptClassPath=. One or more packages can be specified in comma separated list as parameters. Packages must contain all classes that will be potentially modified (redefined). Classes outside of this list won't be included in the deoptimization. Usually it is sufficient to specify application main or root package. If com.sun.proxy.Proxy is used in the application or by application's framework, then this option should contain package com.sun.proxy as well. If HotswapDeoptClassPath option is not specified, then all classes will be deoptimized after redefinition. It is also recommended to clean all generated byte by reflection. Example:


Known issues