[CXF-7083] Maven Plugins: System properties handling in ClassLoaderSwitcher breaks thread safety

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.7.18
• Fix Version/s: 3.0.13, 3.1.11, 3.2.0
• Component/s: Tooling

Environment

Apache Maven 3.3.9 (bb52d8502b132ec0a5a3f4c09453c07478323dc5; 2015-11-10T17:41:47+01:00)
Maven home: /usr/maven/default
Java version: 1.8.0_102, vendor: Oracle Corporation
Java home: /usr/java/jdk1.8.0_102/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "linux", version: "2.6.32-431.29.2.el6.x86_64", arch: "amd64", family: "unix"

• Estimated Complexity: Unknown
• Assignee: Daniel Kulp
• Reporter: Falko Modler
• Created: 11/Oct/16 14:38
• Updated: 10/Apr/17 19:04
• Resolved: 31/Mar/17 19:34

Description

We got a rather large Maven project with a couble of modules that execute cxf-codegen-plugin. Our builds runs in parallel mode via -Tx and according to the JavaDoc the plugin should be fine with that:

https://github.com/apache/cxf/blob/cxf-2.7.18/maven-plugins/codegen-plugin/src/main/java/org/apache/cxf/maven_plugin/wsdl2java/WSDL2JavaMojo.java

/**
 * @goal wsdl2java
 * @phase generate-sources
 * @description CXF WSDL To Java Tool
 * @requiresDependencyResolution test
 * @threadSafe
 */
public class WSDL2JavaMojo extends AbstractCodegenMoho {
...

But from time to time (maybe 5% of our builds) we see following exception causing the respective build to fail:

[ERROR] Failed to execute goal org.apache.cxf:cxf-codegen-plugin:2.7.18:wsdl2java (exampleExec) on project example-module: Execution exampleService of goal org.apache.cxf:cxf-codegen-plugin:2.7.18:wsdl2java failed. ConcurrentModificationException -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.cxf:cxf-codegen-plugin:2.7.18:wsdl2java (exampleExec) on project example-module: Execution exampleService of goal org.apache.cxf:cxf-codegen-plugin:2.7.18:wsdl2java failed.
	at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:212)
	at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
	at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
	at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:116)
	at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call(MultiThreadedBuilder.java:185)
	at org.apache.maven.lifecycle.internal.builder.multithreaded.MultiThreadedBuilder$1.call(MultiThreadedBuilder.java:181)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.maven.plugin.PluginExecutionException: Execution exampleService of goal org.apache.cxf:cxf-codegen-plugin:2.7.18:wsdl2java failed.
	at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:145)
	at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:207)
	... 11 more
Caused by: java.util.ConcurrentModificationException
	at java.util.Hashtable$Enumerator.next(Hashtable.java:1378)
	at java.util.HashMap.putMapEntries(HashMap.java:511)
	at java.util.HashMap.<init>(HashMap.java:489)
	at org.apache.cxf.maven_plugin.ClassLoaderSwitcher.restoreClassLoader(ClassLoaderSwitcher.java:129)
	at org.apache.cxf.maven_plugin.AbstractCodegenMoho.execute(AbstractCodegenMoho.java:326)
	at org.apache.cxf.maven_plugin.wsdl2java.WSDL2JavaMojo.execute(WSDL2JavaMojo.java:524)
	at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134)
	... 12 more
[ERROR] 
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/PluginExecutionException

There seems to be a write access from another thread while ClassLoaderSwitcher tries to copy the system properties:

https://github.com/apache/cxf/blob/cxf-2.7.18/maven-plugins/wadl2java-plugin/src/main/java/org/apache/cxf/maven_plugin/common/ClassLoaderSwitcher.java#L131

        if (origProps != null) {
            Map<Object, Object> newProps = new HashMap<Object, Object>(System.getProperties());
            for (Object o : newProps.keySet()) {
                if (!origProps.containsKey(o)) {
                    System.clearProperty(o.toString());
                }
            }
            System.getProperties().putAll(origProps);
}

Possible solutions:

• synchronize on System.getProperties() in the entire block (lines 129-135)
• create a clone

  (Properties) System.getProperties().clone()
  

  and instead of .putAll() use .setProperties(...)

I haven't checked ClassLoaderSwitcher .switchClassLoader() but I guess something similar needs to be done there.