1 files changed, 53 insertions, 0 deletions
diff --git a/vespajlib/src/main/java/com/yahoo/yolean/concurrent/ConcurrentResourcePool.java b/vespajlib/src/main/java/com/yahoo/yolean/concurrent/ConcurrentResourcePool.java
new file mode 100644
index 00000000000..0e91a44bf5d
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+++ b/vespajlib/src/main/java/com/yahoo/yolean/concurrent/ConcurrentResourcePool.java
@@ -0,0 +1,53 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.yolean.concurrent;
+
+import java.util.Iterator;
+import java.util.Queue;
+import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.function.Supplier;
+
+/**
+ * A pool of a resource. This create new instances of the resource on request until enough are created
+ * to deliver a unique one to all threads needing one concurrently and then reuse those instances
+ * in subsequent requests.
+ *
+ * @author baldersheim
+ */
+public class ConcurrentResourcePool<T> implements Iterable<T> {
+
+    private final Queue<T> pool = new ConcurrentLinkedQueue<>();
+    private final Supplier<T> factory;
+
+
+    public ConcurrentResourcePool(Supplier<T> factory) {
+        this.factory = factory;
+    }
+
+    public void preallocate(int instances) {
+        for (int i = 0; i < instances; i++) {
+            pool.offer(factory.get());
+        }
+    }
+
+    /**
+     * Allocates an instance of the resource to the requestor.
+     * The resource will be allocated exclusively to the requestor until it calls free(instance).
+     *
+     * @return a reused or newly created instance of the resource
+     */
+    public final T alloc() {
+        T e = pool.poll();
+        return e != null ? e : factory.get();
+    }
+
+    /** Frees an instance previously acquired bty alloc */
+    public final void free(T e) {
+        pool.offer(e);
+    }
+
+    @Override
+    public Iterator<T> iterator() {
+        return pool.iterator();
+    }
+
+}