Thread safety issue in TableDescriptor
--------------------------------------
Key: DERBY-2861
URL: https://issues.apache.org/jira/browse/DERBY-2861
Project: Derby
Issue Type: Bug
Environment: Tested on a dual-core 3GHz Pentium machine running
Windows Vista Business, using JDK 1.4.2_13 and Derby trunk revision 548822.
Reporter: Jeff Clary
Attachments: TestEmbeddedMultiThreading.java
A NullPointerException occurs in
org.apache.derby.iapi.sql.dictionary.TableDescriptor.getObjectName when
accessing the same object on many threads (each with its own connection). The
attached test program starts N threads each creating and then dropping a
separate view against the same source view, repeated M times. I can reproduce
the problem with N=100 and M=100 on my machine, but not every run.
An instance member named referencedColumnMap is checked for null at the top of
the getObjectName method, but later when it is dereferenced it is null, because
it was set to null by another thread. I am not sure what getObjectName is used
for other than error reporting. I have considered a fix of just saving the
non-null reference as a method variable, to avoid the later
NullPointerException. But I don't know what unintended consequences this may
have.
When the test program does show the exception, the stack trace looks like this:
java.lang.NullPointerException
at
org.apache.derby.iapi.sql.dictionary.TableDescriptor.getObjectName(TableDescriptor.java:758)
at
org.apache.derby.impl.sql.depend.BasicDependencyManager.getPersistentProviderInfos(BasicDependencyManager.java:677)
at
org.apache.derby.impl.sql.compile.CreateViewNode.bindViewDefinition(CreateViewNode.java:287)
at
org.apache.derby.impl.sql.compile.CreateViewNode.bind(CreateViewNode.java:183)
at
org.apache.derby.impl.sql.GenericStatement.prepMinion(GenericStatement.java:345)
at
org.apache.derby.impl.sql.GenericStatement.prepare(GenericStatement.java:119)
at
org.apache.derby.impl.sql.conn.GenericLanguageConnectionContext.prepareInternalStatement(GenericLanguageConnectionContext.java:745)
at org.apache.derby.impl.jdbc.EmbedStatement.execute(EmbedStatement.java:568)
at org.apache.derby.impl.jdbc.EmbedStatement.execute(EmbedStatement.java:517)
at
TestEmbeddedMultiThreading.executeStatement(TestEmbeddedMultiThreading.java:109)
at TestEmbeddedMultiThreading.access$100(TestEmbeddedMultiThreading.java:10)
at
TestEmbeddedMultiThreading$ViewCreatorDropper.run(TestEmbeddedMultiThreading.java:173)
at java.lang.Thread.run(Thread.java:534)
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