1 files changed, 67 insertions, 0 deletions
diff --git a/service-monitor/src/main/java/com/yahoo/vespa/service/model/ServiceModelCache.java b/service-monitor/src/main/java/com/yahoo/vespa/service/model/ServiceModelCache.java
new file mode 100644
index 00000000000..7a6f37b2c94
--- /dev/null
+++ b/service-monitor/src/main/java/com/yahoo/vespa/service/model/ServiceModelCache.java
@@ -0,0 +1,67 @@
+// Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+package com.yahoo.vespa.service.model;
+
+import com.yahoo.jdisc.Timer;
+import com.yahoo.vespa.service.monitor.ServiceModel;
+
+import java.util.function.Supplier;
+
+/**
+ * Adds caching of a supplier of ServiceModel.
+ *
+ * @author hakonhall
+ */
+public class ServiceModelCache implements Supplier<ServiceModel> {
+    public static final long EXPIRY_MILLIS = 10000;
+
+    private final Supplier<ServiceModel> expensiveSupplier;
+    private final Timer timer;
+
+    private volatile ServiceModel snapshot;
+    private boolean updatePossiblyInProgress = false;
+
+    private final Object updateMonitor = new Object();
+    private long snapshotMillis;
+
+    public ServiceModelCache(Supplier<ServiceModel> expensiveSupplier, Timer timer) {
+        this.expensiveSupplier = expensiveSupplier;
+        this.timer = timer;
+    }
+
+    @Override
+    public ServiceModel get() {
+        if (snapshot == null) {
+            synchronized (updateMonitor) {
+                if (snapshot == null) {
+                    takeSnapshot();
+                }
+            }
+        } else if (expired()) {
+            synchronized (updateMonitor) {
+                if (updatePossiblyInProgress) {
+                    return snapshot;
+                }
+
+                updatePossiblyInProgress = true;
+            }
+
+            takeSnapshot();
+
+            synchronized (updateMonitor) {
+                updatePossiblyInProgress = false;
+            }
+        }
+
+        return snapshot;
+    }
+
+    private void takeSnapshot() {
+        snapshot = expensiveSupplier.get();
+        snapshotMillis = timer.currentTimeMillis();
+    }
+
+    private boolean expired() {
+        return timer.currentTimeMillis() - snapshotMillis >= EXPIRY_MILLIS;
+    }
+}