Slack fails to stop metrics and OkHTTPClient threads when calling *.close()

[raglandba]

The Slack API is starting metrics threads even though I have set stats enabled to false in the MethodsConfig and the SlackConfig.

slackConfig = new SlackConfig();
slackConfig.setStatsEnabled(false);
			
methodsConfig = new MethodsConfig();
methodsConfig.setStatsEnabled(false);

You can see in the log here when shutting down Tomcat that they are running, and not only that, but they are not being closed even though I'm calling close on both the SlackConfig and the Slack instance as such:

slackConfig.close();
slack.getHttpClient().close();
slack.close();

Here is the log output for the Metrics threads:

appears to have started a thread named [slack-api-metrics:5c93780d-worker-161] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.base/jdk.internal.misc.Unsafe.park(Native Method)
java.base/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:269)
java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:1758)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1182)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
java.base/java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1070)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
java.base/java.lang.Thread.run(Thread.java:1583)
05-Mar-2024 16:04:01.360 WARNING [Thread-21] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [Integrity] appears to have started a thread named [slack-api-metrics:5b828b31-worker-162] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.base/jdk.internal.misc.Unsafe.park(Native Method)
java.base/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:269)
java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:1758)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1182)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
java.base/java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1070)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
java.base/java.lang.Thread.run(Thread.java:1583)
05-Mar-2024 16:04:01.360 WARNING [Thread-21] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [Integrity] appears to have started a thread named [slack-api-metrics:1ff1164f-worker-163] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.base/jdk.internal.misc.Unsafe.park(Native Method)
java.base/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:269)
java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:1758)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1182)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
java.base/java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1070)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
java.base/java.lang.Thread.run(Thread.java:1583)
05-Mar-2024 16:04:01.360 WARNING [Thread-21] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [Integrity] appears to have started a thread named [slack-api-metrics:1c277f62-worker-164] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.base/jdk.internal.misc.Unsafe.park(Native Method)
java.base/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:269)
java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:1758)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1182)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
java.base/java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1070)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
java.base/java.lang.Thread.run(Thread.java:1583)
05-Mar-2024 16:04:01.360 WARNING [Thread-21] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [Integrity] appears to have started a thread named [slack-api-metrics:6eb1ec31-worker-165] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.base/jdk.internal.misc.Unsafe.park(Native Method)
java.base/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:269)
java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:1758)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1182)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
java.base/java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1070)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
java.base/java.lang.Thread.run(Thread.java:1583)
05-Mar-2024 16:04:01.360 WARNING [Thread-21] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [Integrity] appears to have started a thread named [slack-api-metrics:1329ca59-worker-166] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.base/jdk.internal.misc.Unsafe.park(Native Method)
java.base/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:269)
java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:1758)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1182)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
java.base/java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1070)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
java.base/java.lang.Thread.run(Thread.java:1583)
05-Mar-2024 16:04:01.360 WARNING [Thread-21] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [Integrity] appears to have started a thread named [slack-api-metrics:13c6d7e5-worker-167] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.base/jdk.internal.misc.Unsafe.park(Native Method)
java.base/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:269)
java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:1758)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1182)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
java.base/java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1070)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
java.base/java.lang.Thread.run(Thread.java:1583)
05-Mar-2024 16:04:01.360 WARNING [Thread-21] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [Integrity] appears to have started a thread named [slack-api-metrics:3c4f6997-worker-168] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.base/jdk.internal.misc.Unsafe.park(Native Method)
java.base/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:269)
java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:1758)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1182)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
java.base/java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1070)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
java.base/java.lang.Thread.run(Thread.java:1583)
05-Mar-2024 16:04:01.360 WARNING [Thread-21] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [Integrity] appears to have started a thread named [slack-api-metrics:48ea8cdf-worker-169] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.base/jdk.internal.misc.Unsafe.park(Native Method)
java.base/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:269)
java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:1758)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1182)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
java.base/java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1070)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
java.base/java.lang.Thread.run(Thread.java:1583)
05-Mar-2024 16:04:01.361 WARNING [Thread-21] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [Integrity] appears to have started a thread named [slack-api-metrics:1a1c6d0-worker-170] but has failed to stop it. This is very likely to create a memory leak. Stacktrace of thread:
java.base/jdk.internal.misc.Unsafe.park(Native Method)
java.base/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:269)
java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:1758)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1182)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
java.base/java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1070)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
java.base/java.lang.Thread.run(Thread.java:1583)
05-Mar-2024 16:04:01.361 WARNING [Thread-21] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [Integrity] appears to have started a thread named [slack-api-metrics:5ebcf262-worker-171] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.base/jdk.internal.misc.Unsafe.park(Native Method)
java.base/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:269)
java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:1758)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1182)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
java.base/java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1070)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
java.base/java.lang.Thread.run(Thread.java:1583)
05-Mar-2024 16:04:01.361 WARNING [Thread-21] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [Integrity] appears to have started a thread named [slack-api-metrics:7e430def-worker-172] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.base/jdk.internal.misc.Unsafe.park(Native Method)
java.base/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:269)
java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:1758)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1182)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
java.base/java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1070)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
java.base/java.lang.Thread.run(Thread.java:1583)
05-Mar-2024 16:04:01.361 WARNING [Thread-21] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [Integrity] appears to have started a thread named [slack-api-metrics:2cb074a6-worker-173] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.base/jdk.internal.misc.Unsafe.park(Native Method)
java.base/java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:269)
java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:1758)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1182)
java.base/java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
java.base/java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1070)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
java.base/java.lang.Thread.run(Thread.java:1583)

The Slack SDK version

com.slack.api:slack-api-client:1.38.2

Java Runtime version

openjdk version "21.0.2" 2024-01-16
OpenJDK Runtime Environment (build 21.0.2+13-suse-4.1-x8664)
OpenJDK 64-Bit Server VM (build 21.0.2+13-suse-4.1-x8664, mixed mode, sharing)

OS info

openSUSE Tumbleweed, CentOS7, CentOS8

Expected result:

That slack closes it's threads like any other application should. This is ridiculous. This bug has been reported in several different versions, and y'all close it claiming it's fixed and it has never been fixed!

Actual result:

The threads don't stop

[seratch]

Hi @raglandba, thanks for writing in. The threads for a new Slack instance you create in your code are closed for sure in the latest version. However, the default singleton is out of the scope in the PR, therefore, there are still "slack-api-metrics" threads and Okhttp ones. This issue is tracked here but we cannot tell when the issue can be improved:

• 5 threads (for the default singleton) can be created even when SlackConfig#statsEnabled is false #987
• Completely disable thread pool initialization for metrics feature #731

If this is critical for your use case and your goal is just to perform a simple web API call such as chat.postMessage, please consider directly using an HTTP client (Okhttp or whatever) for it as a short-term workaround. We are sorry for the inconvience, but it'd be appreciated if you could understand this.

[github-actions]

👋 It looks like this issue has been open for 30 days with no activity. We'll mark this as stale for now, and wait 10 days for an update or for further comment before closing this issue out. If you think this issue needs to be prioritized, please comment to get the thread going again! Maintainers also review issues marked as stale on a regular basis and comment or adjust status if the issue needs to be reprioritized.

[github-actions]

As this issue has been inactive for more than one month, we will be closing it. Thank you to all the participants! If you would like to raise a related issue, please create a new issue which includes your specific details and references this issue number.