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https://issues.apache.org/jira/browse/LANG-762?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Phil Steitz updated LANG-762:
-----------------------------
Attachment: ReflectionToStringBuilderConcurrencyTest.java
Attaching a test that illustrates the problem, which I don't think is solvable
by the [lang] code (so probably this class should not be committed, as it will
never pass).
The problem is that when you circumvent a class' internal synchronization to
protect fields, all bets are off in terms of data integrity or CoMod
exceptions. This should be clearly documented - i.e., users should be warned
that this class should not be used in concurrent applications, or at least
fields protected by synchronization should be excluded.
What is going on in the test case is that there are two different kinds of
threads spawned concurrently - one kind uses the reflection back door opened by
the builder to "inspect" an instance and the other kind mutates the instance
using its synchronized methods. Note that synchronizing the builder using the
private field's monitor will not solve the problem (i.e., the first patch does
not work) because what really needs to happen is that the access by the builder
needs to be synchronized using the instance's monitor. You could try to fix
that by synchronizing on the instance, which would solve this example; but
there is no guarantee that a class may not use its own internal locks, so there
is no generic solution to this problem.
My recommendation is to just document the danger associated with using
reflection to access private fields in the class javadoc.
> Handle or document ReflectionToStringBuilder and ToStringBuilder for
> collections that are not thread safe
> ---------------------------------------------------------------------------------------------------------
>
> Key: LANG-762
> URL: https://issues.apache.org/jira/browse/LANG-762
> Project: Commons Lang
> Issue Type: Bug
> Components: lang.builder.*
> Environment: Apache Maven 3.0.3 (r1075438; 2011-02-28 12:31:09-0500)
> Maven home: C:\Java\apache-maven-3.0.3\bin\..
> Java version: 1.6.0_24, vendor: Sun Microsystems Inc.
> Java home: C:\Program Files\Java\jdk1.6.0_24\jre
> Default locale: en_US, platform encoding: Cp1252
> OS name: "windows 7", version: "6.1", arch: "amd64", family: "windows"
> Reporter: Gary D. Gregory
> Attachments: ReflectionToStringBuilderConcurrencyTest.java,
> patch-LANG762.txt
>
>
> Moving discussion here from https://issues.apache.org/jira/browse/POOL-191
> ConcurrentModificationException in GenericObjectPool LinkedList.
> It is possible to get a {{ConcurrentModificationException}} in a
> {{LinkedList}} from a Commons Pool {{GenericObjectPool}}.
> This happens when I call {{ReflectionToStringBuilder.toString(this)}} from a
> subclass of {{GenericObjectPool}}. My guess is that it would happen with just
> {{ReflectionToStringBuilder.toString(gop)}}. IOW, subclassing does not have
> anything to do with it I would venture.
> For example, in this stack trace {{JmsSessionPool}} is a subclass of
> {{GenericObjectPool}}.
> {noformat}
> java.util.ConcurrentModificationException
> at java.util.LinkedList$ListItr.checkForComodification(LinkedList.java:761)
> at java.util.LinkedList$ListItr.next(LinkedList.java:696)
> at java.util.AbstractCollection.toString(AbstractCollection.java:421)
> at java.lang.String.valueOf(String.java:2826)
> at java.lang.StringBuffer.append(StringBuffer.java:219)
> at
> org.apache.commons.lang3.builder.ToStringStyle.appendDetail(ToStringStyle.java:598)
> at
> org.apache.commons.lang3.builder.ToStringStyle.appendInternal(ToStringStyle.java:473)
> at
> org.apache.commons.lang3.builder.ToStringStyle.append(ToStringStyle.java:436)
> at
> org.apache.commons.lang3.builder.ToStringBuilder.append(ToStringBuilder.java:848)
> at
> org.apache.commons.lang3.builder.ReflectionToStringBuilder.appendFieldsIn(ReflectionToStringBuilder.java:528)
> at
> org.apache.commons.lang3.builder.ReflectionToStringBuilder.toString(ReflectionToStringBuilder.java:692)
> at
> org.apache.commons.lang3.builder.ReflectionToStringBuilder.toString(ReflectionToStringBuilder.java:288)
> at
> org.apache.commons.lang3.builder.ReflectionToStringBuilder.toString(ReflectionToStringBuilder.java:119)
> at
> com.seagullsw.appinterface.comm.jms.JmsSessionPool.toString(JmsSessionPool.java:120)
> at java.lang.String.valueOf(String.java:2826)
> at java.lang.StringBuffer.append(StringBuffer.java:219)
> at
> org.apache.commons.lang3.builder.ToStringStyle.appendDetail(ToStringStyle.java:586)
> at
> org.apache.commons.lang3.builder.ToStringStyle.appendInternal(ToStringStyle.java:550)
> at
> org.apache.commons.lang3.builder.ToStringStyle.append(ToStringStyle.java:436)
> at
> org.apache.commons.lang3.builder.ToStringBuilder.append(ToStringBuilder.java:848)
> at
> org.apache.commons.lang3.builder.ReflectionToStringBuilder.appendFieldsIn(ReflectionToStringBuilder.java:528)
> at
> org.apache.commons.lang3.builder.ReflectionToStringBuilder.toString(ReflectionToStringBuilder.java:689)
> at
> org.apache.commons.lang3.builder.ReflectionToStringBuilder.toString(ReflectionToStringBuilder.java:288)
> at
> org.apache.commons.lang3.builder.ReflectionToStringBuilder.toString(ReflectionToStringBuilder.java:119)
> at
> com.seagullsw.appinterface.server.comm.BasicCommunicationManager.toString(BasicCommunicationManager.java:828)
> at
> com.seagullsw.appinterface.server.comm.BasicCommunicationManager.toString(BasicCommunicationManager.java:817)
> at java.lang.String.valueOf(String.java:2826)
> at java.lang.StringBuilder.append(StringBuilder.java:115)
> at
> com.seagullsw.appinterface.server.AisHelper.waitForCommuncationManagers(AisHelper.java:217)
> at com.seagullsw.appinterface.server.AisHelper.start(AisHelper.java:136)
> at
> com.seagullsw.appinterface.server.AisHelper.startFromResource(AisHelper.java:161)
> at
> com.seagullsw.appinterface.server.AbstractServerJunit4.startServer(AbstractServerJunit4.java:179)
> at
> com.seagullsw.appinterface.server.comm.jms.AbstractJmsRoundtripMaxConcurrencyTestCase.setUpOnce(AbstractJmsRoundtripMaxConcurrencyTestCase.java:141)
> at
> com.seagullsw.appinterface.server.comm.jms.ibmmq.JmsRoundtripMaxConcurrency032TestCase.setUpOnce(JmsRoundtripMaxConcurrency032TestCase.java:40)
> {noformat}
> We should either:
> - Document ReflectionToStringBuilder and ToStringBuilder such that call sites
> use synchronized if the object passed in contains collections that are not
> thread-safe. F
> or example:
> {code:java}
> @Override
> public synchronized String toString() {
> return ReflectionToStringBuilder.toString(this);
> }
> {code}
> - Or have our code in ReflectionToStringBuilder and ToStringBuilder lock
> collections while they are being toString'd.
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