Describe the bug
It is possible to encounter a NullPointerException due to a thread interleaving where one thread reads from shared variable connectReadThread after setting a new object (Line 375), but another thread sets connectReadThread to null (Line 526). I can observe such an execution that results in the exception from running an existing test org.java_websocket.issues.Issue256Test with some added delay, resulting in the following stack trace.
Debug log
runReconnectSocketClose5 Time elapsed: 0.02 sec <<< ERROR!
java.lang.NullPointerException
at org.java_websocket.client.WebSocketClient.connect(WebSocketClient.java:375)
at org.java_websocket.client.WebSocketClient.connectBlocking(WebSocketClient.java:386)
at org.java_websocket.client.WebSocketClient.reconnectBlocking(WebSocketClient.java:328)
at org.java_websocket.issues.Issue256Test.runTestScenarioReconnect(Issue256Test.java:136)
at org.java_websocket.issues.Issue256Test.runReconnectSocketClose(Issue256Test.java:156)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:298)
at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:292)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.lang.Thread.run(Thread.java:829)
Results :
Failed tests: runReconnectSocketClose3: Found 1 zombie thread(s)
runReconnectSocketClose4: Found 1 zombie thread(s)
Tests in error:
runReconnectSocketClose5
Tests run: 20, Failures: 2, Errors: 1, Skipped: 0
To Reproduce
Steps to reproduce the behavior:
- Add Thread.sleep(1000) before Line 526
- Run mvn test -Dtest=org.java_websocket.issues.Issue256Test -Dcheckstyle.skip
Expected behavior
- Null Pointer Exception and test failure should not occur
Additional context
When I investigated the WebSocketClient class, I find connectReadThread is a shared variable that is used on Line 375 and Line 526. By injecting a delay before Line 526 of WebSocketClient.java, I could get a different thread interleaving where the variable is set to null on Line 526 before the variable is used on Line 375. As a result, the execution throws a NullPointerException.
Environment(please complete the following information):
I ran the test on an Ubuntu 20.04 LTS machine using OpenJDK 1.8.0_312.
Describe the bug
It is possible to encounter a NullPointerException due to a thread interleaving where one thread reads from shared variable connectReadThread after setting a new object (Line 375), but another thread sets connectReadThread to null (Line 526). I can observe such an execution that results in the exception from running an existing test org.java_websocket.issues.Issue256Test with some added delay, resulting in the following stack trace.
Debug log
runReconnectSocketClose5 Time elapsed: 0.02 sec <<< ERROR!
java.lang.NullPointerException
at org.java_websocket.client.WebSocketClient.connect(WebSocketClient.java:375)
at org.java_websocket.client.WebSocketClient.connectBlocking(WebSocketClient.java:386)
at org.java_websocket.client.WebSocketClient.reconnectBlocking(WebSocketClient.java:328)
at org.java_websocket.issues.Issue256Test.runTestScenarioReconnect(Issue256Test.java:136)
at org.java_websocket.issues.Issue256Test.runReconnectSocketClose(Issue256Test.java:156)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:298)
at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:292)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.lang.Thread.run(Thread.java:829)
Results :
Failed tests: runReconnectSocketClose3: Found 1 zombie thread(s)
runReconnectSocketClose4: Found 1 zombie thread(s)
Tests in error:
runReconnectSocketClose5
Tests run: 20, Failures: 2, Errors: 1, Skipped: 0
To Reproduce
Steps to reproduce the behavior:
Expected behavior
Additional context
When I investigated the WebSocketClient class, I find connectReadThread is a shared variable that is used on Line 375 and Line 526. By injecting a delay before Line 526 of WebSocketClient.java, I could get a different thread interleaving where the variable is set to null on Line 526 before the variable is used on Line 375. As a result, the execution throws a NullPointerException.
Environment(please complete the following information):
I ran the test on an Ubuntu 20.04 LTS machine using OpenJDK 1.8.0_312.