Indexer is not thread safe

While looking through logs, found that build expiry was throwing exceptions:

2008-01-12 00:00:23,686 ERROR [QuartzScheduler_Worker-0] [JobRunShell] Job DEFAULT.removeExpiredBuilds threw an unhandled Exception:
org.apache.lucene.store.AlreadyClosedException: this IndexReader is closed
at org.apache.lucene.index.IndexReader.ensureOpen(IndexReader.java:128)
at org.apache.lucene.index.IndexReader.termDocs(IndexReader.java:579)
at org.apache.lucene.search.TermQuery$TermWeight.scorer(TermQuery.java:64)
at org.apache.lucene.search.BooleanQuery$BooleanWeight.scorer(BooleanQuery.java:233)
at org.apache.lucene.search.IndexSearcher.search(IndexSearcher.java:143)
at org.apache.lucene.search.IndexSearcher.search(IndexSearcher.java:113)
at org.apache.lucene.search.Hits.getMoreDocs(Hits.java:74)
at org.apache.lucene.search.Hits.hitDoc(Hits.java:154)
at org.apache.lucene.search.Hits.id(Hits.java:131)
at org.apache.lucene.search.Hit.getId(Hit.java:77)
at com.atlassian.bamboo.index.DefaultBuildResultsIndexer.deIndexBuildResults(DefaultBuildResultsIndexer.java:328)
at com.atlassian.bamboo.resultsummary.BuildResultsSummaryManagerImpl.removeBuildResult(BuildResultsSummaryManagerImpl.java:190)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:304)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:182)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
at com.atlassian.bamboo.security.acegi.intercept.aopalliance.AuthorityOverrideMethodSecurityInterceptor.invoke(AuthorityOverrideMethodSecurityInterceptor.java:30)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:106)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
at $Proxy10.removeBuildResult(Unknown Source)
at com.atlassian.bamboo.build.expiry.BuildExpiryBean.expireBuild(BuildExpiryBean.java:172)
at com.atlassian.bamboo.build.expiry.BuildExpiryBean.expireAllBuilds(BuildExpiryBean.java:88)
at com.atlassian.bamboo.build.expiry.ExpiredBuildCleaner.execute(ExpiredBuildCleaner.java:25)
at org.quartz.core.JobRunShell.run(JobRunShell.java:203)
at com.atlassian.bamboo.quartz.SystemAuthorizedThreadPool$1.run(SystemAuthorizedThreadPool.java:36)
at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)
2008-01-12 00:00:23,791 ERROR [QuartzScheduler_Worker-0] [ErrorLogger] Job (DEFAULT.removeExpiredBuilds threw an exception.
org.quartz.SchedulerException: Job threw an unhandled exception. [See nested exception: org.apache.lucene.store.AlreadyClosedException: this IndexReader is closed]
at org.quartz.core.JobRunShell.run(JobRunShell.java:214)
at com.atlassian.bamboo.quartz.SystemAuthorizedThreadPool$1.run(SystemAuthorizedThreadPool.java:36)
at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)

• Nested Exception (Underlying Cause) ---------------
  org.apache.lucene.store.AlreadyClosedException: this IndexReader is closed
  at org.apache.lucene.index.IndexReader.ensureOpen(IndexReader.java:128)
  at org.apache.lucene.index.IndexReader.termDocs(IndexReader.java:579)
  at org.apache.lucene.search.TermQuery$TermWeight.scorer(TermQuery.java:64)
  at org.apache.lucene.search.BooleanQuery$BooleanWeight.scorer(BooleanQuery.java:233)
  at org.apache.lucene.search.IndexSearcher.search(IndexSearcher.java:143)
  at org.apache.lucene.search.IndexSearcher.search(IndexSearcher.java:113)
  at org.apache.lucene.search.Hits.getMoreDocs(Hits.java:74)
  at org.apache.lucene.search.Hits.hitDoc(Hits.java:154)
  at org.apache.lucene.search.Hits.id(Hits.java:131)
  at org.apache.lucene.search.Hit.getId(Hit.java:77)
  at com.atlassian.bamboo.index.DefaultBuildResultsIndexer.deIndexBuildResults(DefaultBuildResultsIndexer.java:328)
  at com.atlassian.bamboo.resultsummary.BuildResultsSummaryManagerImpl.removeBuildResult(BuildResultsSummaryManagerImpl.java:190)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
  at java.lang.reflect.Method.invoke(Method.java:585)
  at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:304)
  at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:182)
  at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
  at com.atlassian.bamboo.security.acegi.intercept.aopalliance.AuthorityOverrideMethodSecurityInterceptor.invoke(AuthorityOverrideMethodSecurityInterceptor.java:30)
  at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
  at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:106)
  at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
  at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
  at $Proxy10.removeBuildResult(Unknown Source)
  at com.atlassian.bamboo.build.expiry.BuildExpiryBean.expireBuild(BuildExpiryBean.java:172)
  at com.atlassian.bamboo.build.expiry.BuildExpiryBean.expireAllBuilds(BuildExpiryBean.java:88)
  at com.atlassian.bamboo.build.expiry.ExpiredBuildCleaner.execute(ExpiredBuildCleaner.java:25)
  at org.quartz.core.JobRunShell.run(JobRunShell.java:203)
  at com.atlassian.bamboo.quartz.SystemAuthorizedThreadPool$1.run(SystemAuthorizedThreadPool.java:36)
  at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)