Reported by RV-Predict (a dynamic race detector) when running the test suite:
Data race on field org.apache.catalina.core.AsyncContextImpl.request: {{{
    Concurrent read in thread T1 (locks held: {})
 ---->  at org.apache.catalina.core.AsyncContextImpl.check(AsyncContextImpl.java:534)
        at org.apache.catalina.core.AsyncContextImpl.getResponse(AsyncContextImpl.java:248)
        at org.apache.catalina.core.TestAsyncContextImpl.doTestAsyncISE(TestAsyncContextImpl.java:1937)
        at org.apache.catalina.core.TestAsyncContextImpl.testGetResponseISE(TestAsyncContextImpl.java:1907)
        at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
        at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
        at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
        at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
        at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
        at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
        at org.junit.rules.TestWatcher$1.evaluate(TestWatcher.java:55)
        at org.junit.rules.RunRules.evaluate(RunRules.java:20)
        at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
        at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
        at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
        at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
        at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
        at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
        at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
        at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
        at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
        at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
        at junit.framework.JUnit4TestAdapter.run(JUnit4TestAdapter.java:38)
        at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.run(JUnitTestRunner.java:535)
        at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.launch(JUnitTestRunner.java:1182)
        at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.main(JUnitTestRunner.java:1033)
    T1 is the main thread

    Concurrent write in thread T204 (locks held: {Monitor@424a8381})
 ---->  at org.apache.catalina.core.AsyncContextImpl.recycle(AsyncContextImpl.java:326)
        at org.apache.catalina.connector.Request.recycle(Request.java:533)
        at org.apache.catalina.connector.CoyoteAdapter.asyncDispatch(CoyoteAdapter.java:456)
        at org.apache.coyote.http11.AbstractHttp11Processor.asyncDispatch(AbstractHttp11Processor.java:1709)
        at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:651)
        at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:277)
        - locked Monitor@424a8381 at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:259) 
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    T204 is created by T202
        at java.util.concurrent.ThreadPoolExecutor.addWorker(ThreadPoolExecutor.java:1010)
}}}