[rules-users] Rule Compilation - Thread deadlock possibility?

[Krishna Satya]

I have a class DroolsRuleLocator that fetches rules from the database,
compiles and hands me back the RuleBase.  At this time I have just one rule
file with a bunch of rules in them. I do not experience any issues when I
execute that in a single thread.

But when I load test my application and the client is passing in the request
that requires *lookup and compilation of the same rule source in my server
concurrently but on different threads,* it appears that my application is
dead locked trying to compile the rules.

Relevant Rule compilation code:
        RuleBase ruleBase = RuleBaseFactory.newRuleBase();
        try {
            // Rule is a simple java bean containing the rule text.
            for (Rule rule : rules) {
                // ruleDefinition will contain the contents of the drl
source.
                String ruleDefinition = rule.getRuleText();
                PackageBuilder builder = new PackageBuilder();

                // Parse and compile in one step
                builder.addPackageFromDrl(new StringReader(ruleDefinition));
                if (builder.hasErrors()) {
                    throw new RuntimeException("Unable to compile rule
definition: "+ rule.getName());
                }

                // Get the compiled package (which is serializable)
                Package pkg = builder.getPackage();

                // Add the package to the created rulebase (deploy the rule
package).
                ruleBase.addPackage(pkg);
            }
        }

Remote attaching to the tomcat server and suspending the hanging threads
shows the following trace.
Daemon Thread [http-8080-58] (Suspended)
            owns: PhaseInterceptorChain  (id=315)
            waiting for: StandardClassLoader  (id=244)
                        owned by: Daemon Thread [http-8080-62]
(Running)
            StandardClassLoader(ClassLoader).loadClass(String, boolean)
line: not available
            StandardClassLoader(ClassLoader).loadClass(String) line: not
available
            WebappClassLoader.loadClass(String, boolean) line: 1349

            WebappClassLoader.loadClass(String) line: 1208
            ParserContext.checkForDynamicImport(String) line: 121
            ParserContext.hasImport(String) line: 155
            ExpressionCompiler(AbstractParser).createPropertyToken(int, int)
line: 893
            ExpressionCompiler(AbstractParser).nextToken() line:
836
            ExpressionCompiler._compile() line: 80
            ExpressionCompiler.compile(ParserContext) line: 44
            MVELExprAnalyzer.analyzeExpression(RuleBuildContext, String,
Set[], Map) line: 85
            MVELDialect.analyzeExpression(RuleBuildContext, BaseDescr,
Object, Map) line: 320
            MVELDialect.analyzeExpression(RuleBuildContext, BaseDescr,
Object) line: 308
            MVELFromBuilder.build(RuleBuildContext, BaseDescr, Pattern)
line: 71
            MVELFromBuilder.build(RuleBuildContext, BaseDescr) line: 50
            PatternBuilder.build(RuleBuildContext, BaseDescr, Pattern) line:
172
            PatternBuilder.build(RuleBuildContext, BaseDescr) line:
87
            GroupElementBuilder.build(RuleBuildContext, BaseDescr, Pattern)
line: 69
            RuleBuilder.build(RuleBuildContext) line: 53
            PackageBuilder.addRule(RuleDescr) line: 446
            PackageBuilder.addPackage(PackageDescr) line: 304
            PackageBuilder.addPackageFromDrl(Reader) line: 167
            DroolsRuleLocator.findRuleBase(long, String) line: 122

Can someone clarify if this dead lock scenario is a possibility.  Currently
I am sychronizing on the method that compiles and returns the RuleBase to
avoid this situation.

Thanks.
- Krishna
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