[jira] [Created] (CURATOR-640) IllegalThreadStateException thrown when access PathChildrenCache in different thread groups

["Xiaogang Shi (Jira)" <ji...@apache.org>]

Xiaogang Shi created CURATOR-640:
------------------------------------

             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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