[CURATOR-66] PathChildrenCache leaks a thread on close().

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Duplicate
• Affects Version/s: 2.2.0-incubating
• Component/s: Recipes
• Assignee: Unassigned
• Reporter: Shawn Smith
• Created: 17/Oct/13 18:36
• Updated: 17/Oct/13 19:37
• Resolved: 17/Oct/13 19:37

Description

The PathChildrenCache does not shutdown its ExecutorService in close(). As a result, using any of the PathChildrenCache constructors that create a single threaded executor (which is all of them but the one that takes an ExecutorService explicitly) will leak a thread when PathChildrenCache.close() is called.

Here's a program that reproduces the error. Currently it prints "# Total PathChildrenCache threads: 100" to indicate that 100 threads were leaked.

import org.apache.curator.ensemble.fixed.FixedEnsembleProvider;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.cache.PathChildrenCache;
import org.apache.curator.retry.RetryOneTime;

import java.util.Map;

public class ThreadLeakTest {
    public static final int NUM_ITERATIONS = 100;

    public static void main(String[] args) throws Exception {
        CuratorFramework curator = CuratorFrameworkFactory.builder()
                .ensembleProvider(new FixedEnsembleProvider("localhost:2181"))
                .retryPolicy(new RetryOneTime(100))
                .build();
        curator.start();

        for (int i = 0; i < NUM_ITERATIONS; i++) {
            PathChildrenCache cache = new PathChildrenCache(curator, "/", true);
            cache.start(PathChildrenCache.StartMode.BUILD_INITIAL_CACHE);
            Thread.sleep(10);
            cache.close();
        }

        curator.close();

        // Wait for things to settle
        Thread.sleep(1000);

        int threadCount = 0;
        Map<Thread,StackTraceElement[]> allThreads = Thread.getAllStackTraces();
        for (Thread thread : allThreads.keySet()) {
            if (thread.getName().startsWith("PathChildrenCache")) {
                System.out.printf("Thread still alive: %s%n", thread.getName());
                threadCount++;
            }
        }
        System.out.printf("# Total PathChildrenCache threads: %d%n", threadCount);
    }
}

Workaround: use the PathChildrenCache constructor that takes an ExecutorService and call shutdown() yourself. Note that closing the CuratorFramework ZK connection does not clean up the leaked threads.

Issue Links

• duplicates: CURATOR-27 PathChildrenCache creates but doesn't shut down Executors