Modification exception in ImmutableClassNode.enableWriteProtection(...)

[bradbeck]

Environment

• groovy 2.4.3
• groovy-eclipse-compiler 2.9.2-01
• groovy-eclipse-batch 2.4.3-01
• takari-smart-builder 0.4.0
• maven 3.3.3

Description

Running a parallel maven build with "mvn --builder smart -T1C clean install -DskipTests" occasionally causes the following error:

[ERROR] /*
[ERROR] ^
[ERROR] General error during class generation: java.lang.UnsupportedOperationException
[ERROR] 
[ERROR] java.lang.UnsupportedOperationException
[ERROR] at java.util.Collections$UnmodifiableMap.put(Collections.java:1457)
[ERROR] at org.codehaus.groovy.ast.ImmutableClassNode.enableWriteProtection(ImmutableClassNode.java:128)
[ERROR] at org.codehaus.groovy.ast.ImmutableClassNode.getDeclaredMethods(ImmutableClassNode.java:120)
[ERROR] at org.codehaus.groovy.ast.ClassNode.getMethods(ClassNode.java:1004)
[ERROR] at org.codehaus.groovy.classgen.ClassCompletionVerifier.checkMethodForWeakerAccessPrivileges(ClassCompletionVerifier.java:369)
[ERROR] at org.codehaus.groovy.classgen.ClassCompletionVerifier.checkMethodsForWeakerAccess(ClassCompletionVerifier.java:266)
[ERROR] at org.codehaus.groovy.classgen.ClassCompletionVerifier.visitClass(ClassCompletionVerifier.java:66)
[ERROR] at org.codehaus.groovy.control.CompilationUnit$6.call(CompilationUnit.java:857)
[ERROR] at org.codehaus.groovy.control.CompilationUnit$6.call(CompilationUnit.java:909)
[ERROR] at org.codehaus.groovy.control.CompilationUnit.applyToPrimaryClassNodes(CompilationUnit.java:1221)
[ERROR] at org.codehaus.groovy.control.CompilationUnit.doPhaseOperation(CompilationUnit.java:651)
[ERROR] at org.codehaus.groovy.control.CompilationUnit.processPhaseOperations(CompilationUnit.java:629)
[ERROR] at org.codehaus.groovy.control.CompilationUnit.compile(CompilationUnit.java:606)
[ERROR] at org.codehaus.jdt.groovy.internal.compiler.ast.GroovyCompilationUnitDeclaration.processToPhase(GroovyCompilationUnitDeclaration.java:202)
[ERROR] at org.codehaus.jdt.groovy.internal.compiler.ast.GroovyCompilationUnitDeclaration.generateCode(GroovyCompilationUnitDeclaration.java:1711)
[ERROR] at org.eclipse.jdt.internal.compiler.Compiler.process(Compiler.java:838)
[ERROR] at org.eclipse.jdt.internal.compiler.ProcessTaskManager.run(ProcessTaskManager.java:137)
[ERROR] at java.lang.Thread.run(Thread.java:745)

ImmutableClassNode.java:128

It appears that at least two threads think that writeProtected == false and both try to enter the synchronized enableWriteProtection() method. One will block
while the other is creating the unmodifiableMap. But when the blocked thread then executes the enableWriteProtection() method it will generate the above error.

One solution is to make writeProtected volatile and check it again inside the enableWriteProtection() method.

[bradbeck]

Proposed fix: #133