Minor Description
I wrote an object provider for injecting web services into another service.
This hivemind fragment shows it declaration:
<service-point id="PingHolder" interface="de.compeople.spirit.communication.base.mikrokernel.objectprovider.IPingHolder">
<invoke-factory>
<construct class="de.compeople.spirit.communication.base.mikrokernel.objectprovider.PingHolder" autowire-services="false">
<object>web-service:Ping</object>
</construct>
</invoke-factory>
</service-point>
A web service has a logical name (Ping) and its type is derived from the injected property/contructor parameter.
This provider works quite well, but while debugging I recognised that the provideObject() method within the object provider
is called twice. From eclipse I have the two stacktraces where it stops (breakpoint) in the object provider:
Thread [main] (Suspended (breakpoint at line 42 in de.compeople.spirit.communication.base.microkernel.objectprovider.WebServiceObjectProvider))
de.compeople.spirit.communication.base.microkernel.objectprovider.WebServiceObjectProvider.provideObject(org.apache.hivemind.internal.Module, java.lang.Class, java.lang.String, org.apache.hivemind.Location) line: 42
$ObjectProvider_1027bec98d2.provideObject(org.apache.hivemind.internal.Module, java.lang.Class, java.lang.String, org.apache.hivemind.Location) line: not available
org.apache.hivemind.service.impl.ObjectTranslator.translate(org.apache.hivemind.internal.Module, java.lang.Class, java.lang.String, org.apache.hivemind.Location) line: 75
$Translator_1027bec98c2.translate(org.apache.hivemind.internal.Module, java.lang.Class, java.lang.String, org.apache.hivemind.Location) line: not available
org.apache.hivemind.service.impl.BuilderPropertyFacet.getFacetValue(org.apache.hivemind.ServiceImplementationFactoryParameters, java.lang.Class) line: 41
org.apache.hivemind.service.impl.BuilderFactoryLogic.instantiateExplicitConstructorInstance(java.lang.Class, java.util.List) line: 135
===========
org.apache.hivemind.service.impl.BuilderFactoryLogic.instantiateCoreServiceInstance() line: 112
org.apache.hivemind.service.impl.BuilderFactoryLogic.createService() line: 77
org.apache.hivemind.service.impl.BuilderFactory.createCoreServiceImplementation(org.apache.hivemind.ServiceImplementationFactoryParameters) line: 42
org.apache.hivemind.impl.InvokeFactoryServiceConstructor.constructCoreServiceImplementation() line: 84
org.apache.hivemind.impl.servicemodel.SingletonServiceModel(org.apache.hivemind.impl.servicemodel.AbstractServiceModelImpl).constructCoreServiceImplementation() line: 106
org.apache.hivemind.impl.servicemodel.SingletonServiceModel(org.apache.hivemind.impl.servicemodel.AbstractServiceModelImpl).constructNewServiceImplementation() line: 156
org.apache.hivemind.impl.servicemodel.SingletonServiceModel(org.apache.hivemind.impl.servicemodel.AbstractServiceModelImpl).constructServiceImplementation() line: 138
org.apache.hivemind.impl.servicemodel.SingletonServiceModel.getActualServiceImplementation() line: 68
$IPingHolder_1027bec98eb._service() line: not available
$IPingHolder_1027bec98eb.getPing() line: not available
$IPingHolder_1027bec98ea.getPing() line: not available
de.compeople.spirit.communication.base.mikrokernel.objectprovider.WebServiceObjectProviderUsageTest.testBuildWebServiceWithoutTimeoutAndConstructorInjection() line: 39
sun.reflect.NativeMethodAccessorImpl.invoke0(java.lang.reflect.Method, java.lang.Object, java.lang.Object[]) line: not available [native method]
sun.reflect.NativeMethodAccessorImpl.invoke(java.lang.Object, java.lang.Object[]) line: 39
sun.reflect.DelegatingMethodAccessorImpl.invoke(java.lang.Object, java.lang.Object[]) line: 25
java.lang.reflect.Method.invoke(java.lang.Object, java.lang.Object...) line: 585
de.compeople.spirit.communication.base.mikrokernel.objectprovider.WebServiceObjectProviderUsageTest(junit.framework.TestCase).runTest() line: 154
de.compeople.spirit.communication.base.mikrokernel.objectprovider.WebServiceObjectProviderUsageTest(junit.framework.TestCase).runBare() line: 127
junit.framework.TestResult$1.protect() line: 106
junit.framework.TestResult.runProtected(junit.framework.Test, junit.framework.Protectable) line: 124
junit.framework.TestResult.run(junit.framework.TestCase) line: 109
de.compeople.spirit.communication.base.mikrokernel.objectprovider.WebServiceObjectProviderUsageTest(junit.framework.TestCase).run(junit.framework.TestResult) line: 118
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(java.lang.String[], java.lang.String) line: 598
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run() line: 354
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(java.lang.String[]) line: 219
Thread [main] (Suspended (breakpoint at line 42 in de.compeople.spirit.communication.base.microkernel.objectprovider.WebServiceObjectProvider))
de.compeople.spirit.communication.base.microkernel.objectprovider.WebServiceObjectProvider.provideObject(org.apache.hivemind.internal.Module, java.lang.Class, java.lang.String, org.apache.hivemind.Location) line: 42
$ObjectProvider_1027bec98d3.provideObject(org.apache.hivemind.internal.Module, java.lang.Class, java.lang.String, org.apache.hivemind.Location) line: not available
$ObjectProvider_1027bec98d2.provideObject(org.apache.hivemind.internal.Module, java.lang.Class, java.lang.String, org.apache.hivemind.Location) line: not available
org.apache.hivemind.service.impl.ObjectTranslator.translate(org.apache.hivemind.internal.Module, java.lang.Class, java.lang.String, org.apache.hivemind.Location) line: 75
$Translator_1027bec98c2.translate(org.apache.hivemind.internal.Module, java.lang.Class, java.lang.String, org.apache.hivemind.Location) line: not available
org.apache.hivemind.service.impl.BuilderPropertyFacet.getFacetValue(org.apache.hivemind.ServiceImplementationFactoryParameters, java.lang.Class) line: 41
org.apache.hivemind.service.impl.BuilderPropertyFacet.isAssignableToType(org.apache.hivemind.ServiceImplementationFactoryParameters, java.lang.Class) line: 54
org.apache.hivemind.service.impl.BuilderFactoryLogic.instantiateExplicitConstructorInstance(java.lang.Class, java.util.List) line: 132
===========
org.apache.hivemind.service.impl.BuilderFactoryLogic.instantiateCoreServiceInstance() line: 112
org.apache.hivemind.service.impl.BuilderFactoryLogic.createService() line: 77
org.apache.hivemind.service.impl.BuilderFactory.createCoreServiceImplementation(org.apache.hivemind.ServiceImplementationFactoryParameters) line: 42
org.apache.hivemind.impl.InvokeFactoryServiceConstructor.constructCoreServiceImplementation() line: 84
org.apache.hivemind.impl.servicemodel.SingletonServiceModel(org.apache.hivemind.impl.servicemodel.AbstractServiceModelImpl).constructCoreServiceImplementation() line: 106
org.apache.hivemind.impl.servicemodel.SingletonServiceModel(org.apache.hivemind.impl.servicemodel.AbstractServiceModelImpl).constructNewServiceImplementation() line: 156
org.apache.hivemind.impl.servicemodel.SingletonServiceModel(org.apache.hivemind.impl.servicemodel.AbstractServiceModelImpl).constructServiceImplementation() line: 138
org.apache.hivemind.impl.servicemodel.SingletonServiceModel.getActualServiceImplementation() line: 68
$IPingHolder_1027bec98eb._service() line: not available
$IPingHolder_1027bec98eb.getPing() line: not available
$IPingHolder_1027bec98ea.getPing() line: not available
de.compeople.spirit.communication.base.mikrokernel.objectprovider.WebServiceObjectProviderUsageTest.testBuildWebServiceWithoutTimeoutAndConstructorInjection() line: 39
sun.reflect.NativeMethodAccessorImpl.invoke0(java.lang.reflect.Method, java.lang.Object, java.lang.Object[]) line: not available [native method]
sun.reflect.NativeMethodAccessorImpl.invoke(java.lang.Object, java.lang.Object[]) line: 39
sun.reflect.DelegatingMethodAccessorImpl.invoke(java.lang.Object, java.lang.Object[]) line: 25
java.lang.reflect.Method.invoke(java.lang.Object, java.lang.Object...) line: 585
de.compeople.spirit.communication.base.mikrokernel.objectprovider.WebServiceObjectProviderUsageTest(junit.framework.TestCase).runTest() line: 154
de.compeople.spirit.communication.base.mikrokernel.objectprovider.WebServiceObjectProviderUsageTest(junit.framework.TestCase).runBare() line: 127
junit.framework.TestResult$1.protect() line: 106
junit.framework.TestResult.runProtected(junit.framework.Test, junit.framework.Protectable) line: 124
junit.framework.TestResult.run(junit.framework.TestCase) line: 109
de.compeople.spirit.communication.base.mikrokernel.objectprovider.WebServiceObjectProviderUsageTest(junit.framework.TestCase).run(junit.framework.TestResult) line: 118
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(java.lang.String[], java.lang.String) line: 598
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run() line: 354
org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(java.lang.String[]) line: 219
As you can see the object provider is reached from two different points within BuilderFactoryLogic.instantiateExplicitConstructorInstance at line 132 and line 135 (marked with ===== in the stacktraces). Everything ´before´ is the same.
Achim Huegen commented this:
The reason is that BuilderFactoryLogic checks the provider value
for compliance with the constructor parameter type, before assigning
the value. For this check the current value is retrieved from the
provider and after the check the value is retrieved again for assignment.
That could be prevented by introducing some caching in
BuilderPropertyFacet, but I'm not quite sure how this contradicts
the dynamic nature of an object provider (that is the value could change
over time).
Hmmmhhh ... thinking longer about this I would even say it is quite
dangerous not to cache the retrieved value.
If the value changes during the construction process of a single
service, the BuilderFactory will work with inconsistent data.
Moreover the getFacetValue method is called quite often if multiple
constructor candidates exists.