Xiaogang Shi created CURATOR-640:
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Summary: IllegalThreadStateException thrown when access
PathChildrenCache in different thread groups
Key: CURATOR-640
URL: https://issues.apache.org/jira/browse/CURATOR-640
Project: Apache Curator
Issue Type: Bug
Components: Recipes
Affects Versions: 5.2.1
Reporter: Xiaogang Shi
When we create PathChildrenCache instances without specifying thead factory,
the {{defaultThreadFactory}} will be used to create threads. The
{{defaultThreadFactory}} is typically backed by
{{java.util.concurrent.DefaultThreadFactory}} which will add newly created
threads into the thread group where it is instantiated. That is, the
{{defaultThreadFactory}} will always add newly created threads into the first
thread group that loads the {{PathChildrenCache}} class.
In cases where {{PathChildrenCache}} is accessed in different thread groups, if
the first thread group that load the {{PathChildrenCache}} is destroy, then all
attempts to start the {{PathChildrenCache}} will fail.
The problem can be reproduced using the following code:
{code:java}
ThreadGroup threadGroup1 = new ThreadGroup("testGroup1");
Thread thread1 = new Thread(threadGroup1, () -> {
PathChildrenCache cache1 =
new PathChildrenCache(client, "/test1", true);
try {
cache1.start();
Thread.sleep(1000);
} catch (Throwable t) {
t.printStackTrace();
} finally {
try {
cache1.close();
} catch (IOException e) {
e.printStackTrace();
}
}
});
thread1.start();
thread1.join();
// After the thread group is destroyed, all PathChildrenCache instances
// will fail to start due to inability to add new threads into the first thread
group
threadGroup1.destroy();
ThreadGroup threadGroup2 = new ThreadGroup("testGroup2");
Thread thread2 = new Thread(threadGroup2, () -> {
PathChildrenCache cache2 =
new PathChildrenCache(client, "/test1", true);
try {
cache2.start();
Thread.sleep(1000);
} catch (Throwable t) {
t.printStackTrace();
} finally {
try {
cache2.close();
} catch (IOException e) {
e.printStackTrace();
}
}
});
thread2.start();
thread2.join();
{code}
When starting {{cache2}}, the following exception is thrown:
{code}
java.lang.IllegalThreadStateException
at java.base/java.lang.ThreadGroup.addUnstarted(ThreadGroup.java:892)
at java.base/java.lang.Thread.<init>(Thread.java:434)
at java.base/java.lang.Thread.<init>(Thread.java:708)
at
java.base/java.util.concurrent.Executors$DefaultThreadFactory.newThread(Executors.java:660)
at
org.apache.curator.shaded.com.google.common.util.concurrent.ThreadFactoryBuilder$1.newThread(ThreadFactoryBuilder.java:163)
at
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.<init>(ThreadPoolExecutor.java:630)
at
java.base/java.util.concurrent.ThreadPoolExecutor.addWorker(ThreadPoolExecutor.java:920)
at
java.base/java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1353)
at
java.base/java.util.concurrent.Executors$DelegatedExecutorService.execute(Executors.java:721)
at
org.apache.curator.utils.CloseableExecutorService.submit(CloseableExecutorService.java:191)
at
org.apache.curator.framework.recipes.cache.PathChildrenCache.submitToExecutor(PathChildrenCache.java:841)
at
org.apache.curator.framework.recipes.cache.PathChildrenCache.offerOperation(PathChildrenCache.java:792)
at
org.apache.curator.framework.recipes.cache.PathChildrenCache.start(PathChildrenCache.java:300)
at
org.apache.curator.framework.recipes.cache.PathChildrenCache.start(PathChildrenCache.java:239)
{code}
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