Crete CachedSupplier

2 files changed, 91 insertions, 0 deletions

diff --git a/vespajlib/src/main/java/com/yahoo/lang/CachedSupplier.java b/vespajlib/src/main/java/com/yahoo/lang/CachedSupplier.java
new file mode 100644
index 00000000000..07ce1250855
--- /dev/null
+++ b/vespajlib/src/main/java/com/yahoo/lang/CachedSupplier.java
@@ -0,0 +1,52 @@
+// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.lang;
+
+import java.time.Clock;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.function.Supplier;
+
+/**
+ * Supplier that caches the value for a given duration with ability to invalidate at demand.
+ * Is thread safe.
+ *
+ * @author freva
+ */
+public class CachedSupplier<T> implements Supplier<T> {
+
+    private final Supplier<T> delegate;
+    private final Duration period;
+    private final Clock clock;
+
+    private Instant nextRefresh;
+    private volatile T value;
+
+    public CachedSupplier(Supplier<T> delegate, Duration period) {
+        this(delegate, period, Clock.systemUTC());
+    }
+
+    CachedSupplier(Supplier<T> delegate, Duration period, Clock clock) {
+        this.delegate = delegate;
+        this.period = period;
+        this.clock = clock;
+        this.nextRefresh = Instant.MIN;
+    }
+
+    @Override
+    public T get() {
+        synchronized (this) {
+            if (clock.instant().isAfter(nextRefresh))
+                refresh();
+        }
+
+        return value;
+    }
+
+    public void refresh() {
+        synchronized (this) {
+            this.value = delegate.get();
+            this.nextRefresh = clock.instant().plus(period);
+        }
+    }
+
+}
diff --git a/vespajlib/src/test/java/com/yahoo/lang/CachedSupplierTest.java b/vespajlib/src/test/java/com/yahoo/lang/CachedSupplierTest.java
new file mode 100644
index 00000000000..b0dc1262ebc
--- /dev/null
+++ b/vespajlib/src/test/java/com/yahoo/lang/CachedSupplierTest.java
@@ -0,0 +1,39 @@
+// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.lang;
+
+import com.yahoo.test.ManualClock;
+import org.junit.Test;
+
+import java.time.Duration;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * @author freva
+ */
+public class CachedSupplierTest {
+
+    @Test
+    public void test() {
+        ManualClock clock = new ManualClock();
+        MutableInteger integer = new MutableInteger(0);
+        CachedSupplier<Integer> supplier = new CachedSupplier<>(() -> integer.add(1), Duration.ofMinutes(1), clock);
+
+        assertEquals(1, supplier.get().intValue());
+        assertEquals(1, supplier.get().intValue());
+
+        clock.advance(Duration.ofSeconds(30));
+        assertEquals(1, supplier.get().intValue());
+
+        clock.advance(Duration.ofSeconds(31));
+        assertEquals(2, supplier.get().intValue());
+        assertEquals(2, supplier.get().intValue());
+
+        supplier.refresh();
+        assertEquals(3, supplier.get().intValue());
+        assertEquals(3, supplier.get().intValue());
+
+        clock.advance(Duration.ofSeconds(61));
+        assertEquals(4, supplier.get().intValue());
+    }
+}