James Daugherty created GROOVY-12557:
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Summary: Indy: casting a GroovyObject calls getMetaClass() on the
value being cast
Key: GROOVY-12557
URL: https://issues.apache.org/jira/browse/GROOVY-12557
Project: Groovy
Issue Type: Bug
Affects Versions: 4.0.33, 5.1.3, 6.0.0
Reporter: James Daugherty
With invokedynamic, a cast of a {{GroovyObject}} that already has the target
type, such as {{Widget widget = value}}, calls {{value.getMetaClass()}}: once
to build the call site's guard and again on each call through it. With classic
call sites the same cast calls nothing on the value.
That is observable whenever {{getMetaClass()}} is not a plain field read. A
Spring class-based (CGLIB) proxy of a Groovy class forwards every public
method, {{getMetaClass()}} included, to its target. For a step-, job-, request-
or session-scoped bean the target exists only while the scope is active, so
merely assigning the proxy to a typed variable outside the scope fails:
{noformat}
org.springframework.beans.factory.support.ScopeNotActiveException: Error
creating bean with name 'scopedTarget.widget': Scope 'step' is not active for
the current thread
at
org.springframework.aop.target.SimpleBeanTargetSource.getTarget(SimpleBeanTargetSource.java:35)
at
org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:698)
at Widget$$SpringCGLIB$$0.getMetaClass
at org.codehaus.groovy.vmplugin.v8.Selector$MethodSelector.setGuards
at org.codehaus.groovy.vmplugin.v8.Selector$CastSelector.castAndSetGuards
at org.codehaus.groovy.vmplugin.v8.Selector$CastSelector.setCallSiteTarget
at org.codehaus.groovy.vmplugin.v8.IndyInterface.fallback
{noformat}
A Grails application moving from classic call sites to invokedynamic (the
Grails 9 default) meets this in code that handles scoped proxies dynamically.
*Reproducer:*
https://github.com/jdaugherty/groovy-indy-cast-getmetaclass-reproducer
({{./run.sh 4.0.33 5.1.3 6.0.0}}). With indy the cast {{Watched typed = value}}
makes 2 {{getMetaClass()}} calls on the value and fails when {{getMetaClass()}}
throws; with classic call sites it makes none. Reproduced on 4.0.33, 5.1.3 and
6.0.0.
*Cause:* {{Selector.CastSelector.castAndSetGuards()}} reuses
{{MethodSelector.setGuards(args[0])}}, which calls {{getMetaClass()}} on a
{{GroovyObject}} receiver to bind a {{SAME_MC}} guard. Only a cast to boolean
selects a method ({{asBoolean}}) through the metaclass; every other cast is
decided by the class of the value, which the argument guards and the class
SwitchPoint already cover.
*Proposed fix:* keep the receiver metaclass guard for the {{asBoolean}} path
only, so a cast decided by the value's class never calls into the value, as
with classic call sites. A patch with tests follows as a pull request against
master, with backports for the 6.0.x and 5.1.x lines.
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