Lock contention in Groovy Shell interpreter under high load

We are evaluating GroovyShell interpreter (v2.4) in our application for dynamically executing standard Java syntax.

Earlier, we were using Java BeanShell Interpreter for it, but it has an issue under high load which prompted us to look for an alternative such as Groovy.

Sample Java Code

static String script = "int y = x * x; System.out.println(\"** value of y ** :: \" + y ); ";

GroovyShell gs = new GroovyShell();
Script evalScript = gs.parse("void evalMethod() {" + script + "}");
// bind variables
Binding binding = new Binding();
binding.setVariable("x", 5);
evalScript.setBinding(binding);
// invoke eval method
evalScript.invokeMethod("evalMethod", null);

We are seeing thread lock contention when multiple threads execute above code simultaneously. We have multiple threads in the blocked state which is degrading application performance.

Blocked Thread Call Stack

java.lang.Thread.State: BLOCKED (on object monitor)
at java.lang.ClassLoader.loadClass(ClassLoader.java:404)
- waiting to lock <0x00000007bc425e40> (a java.lang.Object)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:411)
- locked <0x00000007bd369ba8> (a groovy.lang.GroovyClassLoader)
at groovy.lang.GroovyClassLoader.loadClass(GroovyClassLoader.java:677)
at groovy.lang.GroovyClassLoader.loadClass(GroovyClassLoader.java:545)
at org.codehaus.groovy.control.ClassNodeResolver.tryAsLoaderClassOrScript(ClassNodeResolver.java:185)
at org.codehaus.groovy.control.ClassNodeResolver.findClassNode(ClassNodeResolver.java:170)
at org.codehaus.groovy.control.ClassNodeResolver.resolveName(ClassNodeResolver.java:126)
at org.codehaus.groovy.control.ResolveVisitor.resolveToOuter(ResolveVisitor.java:676)
at org.codehaus.groovy.control.ResolveVisitor.resolve(ResolveVisitor.java:313)
at org.codehaus.groovy.control.ResolveVisitor.transformPropertyExpression(ResolveVisitor.java:845)
at org.codehaus.groovy.control.ResolveVisitor.transform(ResolveVisitor.java:696)
at org.codehaus.groovy.control.ResolveVisitor.transformMethodCallExpression(ResolveVisitor.java:1081)
at org.codehaus.groovy.control.ResolveVisitor.transform(ResolveVisitor.java:702)
at org.codehaus.groovy.ast.ClassCodeExpressionTransformer.visitExpressionStatement(ClassCodeExpressionTransformer.java:142)
at org.codehaus.groovy.ast.stmt.ExpressionStatement.visit(ExpressionStatement.java:42)
at org.codehaus.groovy.ast.CodeVisitorSupport.visitBlockStatement(CodeVisitorSupport.java:37)
at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitBlockStatement(ClassCodeVisitorSupport.java:166)
at org.codehaus.groovy.control.ResolveVisitor.visitBlockStatement(ResolveVisitor.java:1336)
at org.codehaus.groovy.ast.stmt.BlockStatement.visit(BlockStatement.java:71)
at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitClassCodeContainer(ClassCodeVisitorSupport.java:104)
at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitConstructorOrMethod(ClassCodeVisitorSupport.java:115)
at org.codehaus.groovy.ast.ClassCodeExpressionTransformer.visitConstructorOrMethod(ClassCodeExpressionTransformer.java:53)
at org.codehaus.groovy.control.ResolveVisitor.visitConstructorOrMethod(ResolveVisitor.java:201)
at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitMethod(ClassCodeVisitorSupport.java:126)
at org.codehaus.groovy.ast.ClassNode.visitContents(ClassNode.java:1081)
at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitClass(ClassCodeVisitorSupport.java:53)
at org.codehaus.groovy.control.ResolveVisitor.visitClass(ResolveVisitor.java:1279)
at org.codehaus.groovy.control.ResolveVisitor.startResolving(ResolveVisitor.java:176)
at org.codehaus.groovy.control.CompilationUnit$12.call(CompilationUnit.java:663)
at org.codehaus.groovy.control.CompilationUnit.applyToSourceUnits(CompilationUnit.java:943)
at org.codehaus.groovy.control.CompilationUnit.doPhaseOperation(CompilationUnit.java:605)
at org.codehaus.groovy.control.CompilationUnit.compile(CompilationUnit.java:554)
at groovy.lang.GroovyClassLoader.doParseClass(GroovyClassLoader.java:298)
at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:268)
- locked <0x00000007bd372240> (a java.util.HashMap)
at groovy.lang.GroovyShell.parseClass(GroovyShell.java:688)
at groovy.lang.GroovyShell.parse(GroovyShell.java:700)
at groovy.lang.GroovyShell.parse(GroovyShell.java:736)
at groovy.lang.GroovyShell.parse(GroovyShell.java:727)

My questions are:

Has anyone experienced such problem? If yes, can you please suggest any possible resolution for it? I googled around for this problem and few blogs suggested to cache groovy Script object. Is Script object thread-safe? Moreover, I need to bind variables to Script object (via groovy Binding object, which is different for each execution in different threads), so I don't think caching groovy Script object is a viable option.
Are there any best practices that I need to follow while using Groovy Shell interpreter with Java?
Any other library that we can consider? My requirement is to dynamically execute standard Java syntax.

Solution

groovy parse&compile is a quite heavy part

if your script is static - then you have to parse it just once

if the scripts always different but repeating - you can cache compiled groovy scripts into

ConcurrentHashMap<String, Class<groovy.lang.Script>>

after

Script evalScript = gs.parse(...);

just put evalScript.getClass() into cache of compiled scripts.

and before gs.parse(...) check if you have compiled script and just take a new instance of the cached class if it exists.

check the following examples and execution speed

String script = "int y = x * x; System.out.println(\"** value of y ** :: \" + y ); ";

def ts = System.currentTimeMillis()
for(int i=0;i<100;i++){
    GroovyShell gs = new GroovyShell();
    Script evalScript = gs.parse("void evalMethod() {" + script + "}");
    // bind variables
    Binding binding = new Binding();
    binding.setVariable("x", i);
    evalScript.setBinding(binding);
    // invoke eval method
    evalScript.invokeMethod("evalMethod", null);
}
println ">> ${System.currentTimeMillis() - ts} millis"

1165 millis

String script = "int y = x * x; System.out.println(\"** value of y ** :: \" + y ); ";
GroovyShell gs = new GroovyShell();
Class<Script> scriptClass = gs.parse("void evalMethod() {" + script + "}").getClass();

def ts = System.currentTimeMillis()
for(int i=0;i<100;i++){
    Script evalScript = scriptClass.newInstance();
    // bind variables
    Binding binding = new Binding();
    binding.setVariable("x", i);
    evalScript.setBinding(binding);
    // invoke eval method
    evalScript.invokeMethod("evalMethod", null);
}
println ">> ${System.currentTimeMillis() - ts} millis"

6 millis