From 5dfe8e2421af5d9eaae31d779d1636180799ddef Mon Sep 17 00:00:00 2001
From: Jon Marius Venstad <venstad@gmail.com>
Date: Thu, 16 Jan 2020 14:52:06 +0100
Subject: Hold a JVM-wide reentrant lock to grab mutex — helps ZK stale reads?
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---
 zkfacade/src/main/java/com/yahoo/vespa/curator/Lock.java | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/zkfacade/src/main/java/com/yahoo/vespa/curator/Lock.java b/zkfacade/src/main/java/com/yahoo/vespa/curator/Lock.java
index 30af89d0ea8..404c8be3326 100644
--- a/zkfacade/src/main/java/com/yahoo/vespa/curator/Lock.java
+++ b/zkfacade/src/main/java/com/yahoo/vespa/curator/Lock.java
@@ -7,6 +7,7 @@ import org.apache.curator.framework.recipes.locks.InterProcessLock;
 
 import java.time.Duration;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.ReentrantLock;
 
 /**
  * A cluster-wide re-entrant mutex which is released on (the last symmetric) close
@@ -15,11 +16,13 @@ import java.util.concurrent.TimeUnit;
  */
 public class Lock implements Mutex {
 
+    private final ReentrantLock lock;
     private final InterProcessLock mutex;
     private final String lockPath;
 
     public Lock(String lockPath, Curator curator) {
         this.lockPath = lockPath;
+        this.lock = new ReentrantLock(true);
         mutex = curator.createMutex(lockPath);
     }
 
@@ -27,21 +30,26 @@ public class Lock implements Mutex {
     public void acquire(Duration timeout) throws UncheckedTimeoutException {
         boolean acquired;
         try {
+            lock.tryLock(timeout.toMillis(), TimeUnit.MILLISECONDS);
             acquired = mutex.acquire(timeout.toMillis(), TimeUnit.MILLISECONDS);
         }
         catch (Exception e) {
+            if (lock.isHeldByCurrentThread()) lock.unlock();
             throw new RuntimeException("Exception acquiring lock '" + lockPath + "'", e);
         }
 
-        if (! acquired)
+        if ( ! acquired) {
+            if (lock.isHeldByCurrentThread()) lock.unlock();
             throw new UncheckedTimeoutException("Timed out after waiting " + timeout +
                                                 " to acquire lock '" + lockPath + "'");
+        }
     }
 
     @Override
     public void close() {
         try {
             mutex.release();
+            lock.unlock();
         }
         catch (Exception e) {
             throw new RuntimeException("Exception releasing lock '" + lockPath + "'");
-- 
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