Merge pull request #3507 from vespa-engine/revert-3464-freva/node-admin-shutdown

Revert "Freva/node admin shutdown"

1 files changed, 63 insertions, 0 deletions

diff --git a/vespajlib/src/main/java/com/yahoo/concurrent/Locks.java b/vespajlib/src/main/java/com/yahoo/concurrent/Locks.java
new file mode 100644
index 00000000000..ab167392329
--- /dev/null
+++ b/vespajlib/src/main/java/com/yahoo/concurrent/Locks.java
@@ -0,0 +1,63 @@
+// Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.concurrent;
+
+import com.google.common.util.concurrent.UncheckedTimeoutException;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.ReentrantLock;
+
+/**
+ * Holds a map of locks indexed on keys of a given type.
+ * This is suitable in cases where exclusive access should be granted to any one of a set of keyed objects and
+ * there is a finite collection of keyed objects.
+ * 
+ * The returned locks are reentrant (i.e the owning thread may call lock multiple times) and auto-closable.
+ * 
+ * Typical use is
+ * <code>
+ *     try (Lock lock = locks.lock(id)) {
+ *         exclusive use of the object with key id
+ *     }
+ * </code>
+ * 
+ * @author bratseth
+ */
+public class Locks<TYPE> {
+
+    private final Map<TYPE, ReentrantLock> locks = new ConcurrentHashMap<>();
+    
+    private final long timeoutMs;
+    
+    /** Create locks with a default timeout */
+    public Locks(long timeout, TimeUnit timeoutUnit) {
+        timeoutMs = timeoutUnit.toMillis(timeout);
+    }
+
+    /** Locks key. This will block until the key is acquired or the default timeout is reached. */
+    public Lock lock(TYPE key) {
+        return lock(key, timeoutMs, TimeUnit.MILLISECONDS);
+    }
+
+    /**
+     * Locks key. This will block until the key is acquired or the timeout is reached.
+     * Users of this <b>must</b> close any lock acquired.
+     *
+     * @param key the key to lock
+     * @return the acquired lock
+     * @throws UncheckedTimeoutException if the lock could not be acquired within the timeout
+     */
+    public Lock lock(TYPE key, long timeout, TimeUnit timeoutUnit) {
+        try {
+            ReentrantLock lock = locks.computeIfAbsent(key, k -> new ReentrantLock(true));
+            boolean acquired = lock.tryLock(timeout, timeoutUnit);
+            if ( ! acquired)
+                throw new UncheckedTimeoutException("Timed out waiting for the lock to " + key);
+            return new Lock(lock);
+        } catch (InterruptedException e) {
+            throw new RuntimeException("Interrupted while waiting for lock of " + key);
+        }
+    }
+
+}