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https://issues.apache.org/jira/browse/ACCUMULO-2027?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13860835#comment-13860835
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Keith Turner commented on ACCUMULO-2027:
----------------------------------------
bq. There's no corresponding creation of resources in ZooKeeperInstance so it
seems odd that when it dies, it has to bring down resources that weren't
clearly opened by it.
It is odd, but that the reason ZooKeeperInstance.close() was created. It was
created to clean up those resources.
bq. Would those be separate issues, more specific to ZooCache and
ThriftTransport pool?
I don't think so. My reasoning is that ZooKeeperInstance.close() is not always
solving the problem it was intended to solve because of race conditions.
> ZooKeeperInstance.close() not freeing resources in multithreaded env
> --------------------------------------------------------------------
>
> Key: ACCUMULO-2027
> URL: https://issues.apache.org/jira/browse/ACCUMULO-2027
> Project: Accumulo
> Issue Type: Bug
> Reporter: Keith Turner
> Assignee: William Slacum
> Priority: Critical
> Fix For: 1.4.5, 1.5.1, 1.6.0
>
>
> While looking at the changes related to ZooKeeperInstance.close() in the
> 1.4.5-SNAPSHOT branch I noticed there were race conditions where resources
> were not properly released. One type of race condition is where a thread is
> between a closed check in ZooKeeperInstance and calling a ZooCache method
> when ZooKeeperInstance.close() is called. The following is an example
> situation
> # Thread 1 uses ZooKeeperInstance1 to get a zoocache.
> # Thread 2 calls close() on ZooKeeperInstnce1 which calls close() on zoocache
> # Thread 1 uses the zoocache it has reference to, causing a new zookeeper
> connection to be created.
> Below is an example program that will trigger this behavior. For me this
> little example program reliably shows a connected zookeeper after all of the
> threads die. If I use 0 threads it will show a closed zookeeper connection
> at the end.
> {code:java}
> static class WriteTask implements Runnable {
> private BatchWriter writer;
> private Random rand;
> WriteTask(Connector conn) throws TableNotFoundException {
> rand = new Random();
> writer = conn.createBatchWriter("foo5", 10000000, 30000, 1);
> }
> @Override
> public void run() {
> try {
> while (true) {
> Mutation m1 = new Mutation(String.format("%06d",
> rand.nextInt(1000000)));
> m1.put(String.format("%06d", rand.nextInt(100)),
> String.format("%06d", rand.nextInt(100)), String.format("%06d",
> rand.nextInt(1000000)));
> writer.addMutation(m1);
> writer.flush();
> }
> } catch (Exception e) {
> System.out.println(e.getMessage());
> }
> }
> }
> static class ReadTask implements Runnable {
> private Scanner scanner;
> ReadTask(Connector conn) throws TableNotFoundException {
> scanner = conn.createScanner("foo5", new Authorizations());
> }
> @Override
> public void run() {
> try {
> while (true) {
> for (Entry<Key,Value> entry : scanner) {
> }
> }
> } catch (Exception e) {
> System.out.println(e.getMessage());
> }
> }
> }
> @Test(timeout = 30000)
> public void test2() throws Exception {
> ZooKeeperInstance zki = new ZooKeeperInstance(accumulo.getInstanceName(),
> accumulo.getZooKeepers());
> Connector conn = zki.getConnector("root", "superSecret");
> conn.tableOperations().create("foo5");
> ArrayList<Thread> threads = new ArrayList<Thread>();
> int numThreads = 10;
> for (int i = 0; i < numThreads; i++) {
> Thread t = new Thread(new WriteTask(conn));
> t.start();
> threads.add(t);
> }
> for (int i = 0; i < numThreads; i++) {
> Thread t = new Thread(new ReadTask(conn));
> t.start();
> threads.add(t);
> }
> // let threads get spun up
> Thread.sleep(1000);
> ZooSession.printSessions();
> zki.close();
> // wait for the threads to die
> for (Thread thread : threads) {
> thread.join();
> }
> ZooSession.printSessions();
> }
> {code}
> Below are some changes I made to ZooSession for debugging purposes.
> {noformat}
> diff --git
> a/src/core/src/main/java/org/apache/accumulo/core/zookeeper/ZooSession.java
> b/src/core/src/main/java/org/apache/accumulo/core/zookeeper/ZooSession.java
> index b3db26f..475a21d 100644
> ---
> a/src/core/src/main/java/org/apache/accumulo/core/zookeeper/ZooSession.java
> +++
> b/src/core/src/main/java/org/apache/accumulo/core/zookeeper/ZooSession.java
> @@ -20,6 +20,8 @@
> import java.net.UnknownHostException;
> import java.util.HashMap;
> import java.util.Map;
> +import java.util.Map.Entry;
> +import java.util.Set;
>
> import org.apache.accumulo.core.util.UtilWaitThread;
> import org.apache.log4j.Logger;
> @@ -29,7 +31,7 @@
> import org.apache.zookeeper.ZooKeeper;
> import org.apache.zookeeper.ZooKeeper.States;
>
> -class ZooSession {
> +public class ZooSession {
>
> private static final Logger log = Logger.getLogger(ZooSession.class);
>
> @@ -121,6 +123,8 @@
>
> ZooSessionInfo zsi = sessions.get(sessionKey);
> if (zsi != null && zsi.zooKeeper.getState() == States.CLOSED) {
> + System.out.println("Removing closed session ");
> + new Exception().printStackTrace();
> if (auth != null && sessions.get(readOnlySessionKey) == zsi)
> sessions.remove(readOnlySessionKey);
> zsi = null;
> @@ -137,4 +141,13 @@
> }
> return zsi.zooKeeper;
> }
> +
> + public static synchronized void printSessions() {
> + Set<Entry<String,ZooSessionInfo>> es = sessions.entrySet();
> +
> + for (Entry<String,ZooSessionInfo> entry : es) {
> + System.out.println(entry.getKey() + " " +
> entry.getValue().zooKeeper.getState());
> + }
> + }
> +
> }
> {noformat}
> With the above changes I will see an exception like the following when one of
> the race conditions occurs.
> {noformat}
> Removing closed session
> java.lang.Exception
> at
> org.apache.accumulo.core.zookeeper.ZooSession.getSession(ZooSession.java:127)
> at
> org.apache.accumulo.core.zookeeper.ZooReader.getSession(ZooReader.java:37)
> at
> org.apache.accumulo.core.zookeeper.ZooReader.getZooKeeper(ZooReader.java:41)
> at
> org.apache.accumulo.core.zookeeper.ZooCache.getZooKeeper(ZooCache.java:56)
> at org.apache.accumulo.core.zookeeper.ZooCache.retry(ZooCache.java:127)
> at org.apache.accumulo.core.zookeeper.ZooCache.get(ZooCache.java:233)
> at org.apache.accumulo.core.zookeeper.ZooCache.get(ZooCache.java:188)
> at
> org.apache.accumulo.core.client.ZooKeeperInstance.getInstanceID(ZooKeeperInstance.java:156)
> at
> org.apache.accumulo.core.client.impl.TabletLocator.getInstance(TabletLocator.java:96)
> at
> org.apache.accumulo.core.client.impl.ThriftScanner.scan(ThriftScanner.java:245)
> at
> org.apache.accumulo.core.client.impl.ScannerIterator$Reader.run(ScannerIterator.java:94)
> at
> org.apache.accumulo.core.client.impl.ScannerIterator.hasNext(ScannerIterator.java:176)
> at
> org.apache.accumulo.minicluster.MiniAccumuloClusterTest$ReadTask.run(MiniAccumuloClusterTest.java:109)
> at java.lang.Thread.run(Thread.java:662)
> {noformat}
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