Add locking API

3 files changed, 91 insertions, 0 deletions

diff --git a/vespajlib/src/main/java/com/yahoo/concurrent/Lock.java b/vespajlib/src/main/java/com/yahoo/concurrent/Lock.java
new file mode 100644
index 00000000000..39ccab7034e
--- /dev/null
+++ b/vespajlib/src/main/java/com/yahoo/concurrent/Lock.java
@@ -0,0 +1,23 @@
+package com.yahoo.vespa.hosted.controller.concurrent;
+
+import java.util.concurrent.locks.ReentrantLock;
+
+/** 
+ * An acquired lock which is released on close
+ * 
+ * @author bratseth
+ */
+public final class Lock implements AutoCloseable {
+
+    private final ReentrantLock wrappedLock;
+
+    Lock(ReentrantLock wrappedLock) {
+        this.wrappedLock = wrappedLock;
+    }
+
+    /** Releases this lock */
+    public void close() {
+        wrappedLock.unlock();
+    }
+
+}
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..a08e61c5e8f
--- /dev/null
+++ b/vespajlib/src/main/java/com/yahoo/concurrent/Locks.java
@@ -0,0 +1,54 @@
+package com.yahoo.vespa.hosted.controller.concurrent;
+
+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;
+    
+    public Locks(int timeout, TimeUnit timeoutUnit) {
+        timeoutMs = timeoutUnit.toMillis(timeout);
+    }
+
+    /**
+     * Locks key. This will block until the key is acquired.
+     * Users of this <b>must</b> close any lock acquired.
+     * 
+     * @param key the key to lock
+     * @return the acquired lock
+     * @throws TimeoutException if the lock could not be acquired within the timeout
+     */
+    public Lock lock(TYPE key) {
+        try {
+            ReentrantLock lock = locks.computeIfAbsent(key, k -> new ReentrantLock(true));
+            boolean acquired = lock.tryLock(timeoutMs, TimeUnit.MILLISECONDS);
+            if ( ! acquired)
+                throw new TimeoutException("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);
+        }
+    }
+
+}
diff --git a/vespajlib/src/main/java/com/yahoo/concurrent/TimeoutException.java b/vespajlib/src/main/java/com/yahoo/concurrent/TimeoutException.java
new file mode 100644
index 00000000000..cd2cfacf902
--- /dev/null
+++ b/vespajlib/src/main/java/com/yahoo/concurrent/TimeoutException.java
@@ -0,0 +1,14 @@
+package com.yahoo.vespa.hosted.controller.concurrent;
+
+/**
+ * Throws on timeout
+ * 
+ * @author bratseth
+ */
+public class TimeoutException extends RuntimeException {
+    
+    public TimeoutException(String message) {
+        super(message);
+    }
+    
+}