1 files changed, 30 insertions, 0 deletions
diff --git a/src/main/java/org/junit/internal/requests/MemoizingRequest.java b/src/main/java/org/junit/internal/requests/MemoizingRequest.java
new file mode 100644
index 0000000..191c230
--- /dev/null
+++ b/src/main/java/org/junit/internal/requests/MemoizingRequest.java
@@ -0,0 +1,30 @@
+package org.junit.internal.requests;
+
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+import org.junit.runner.Request;
+import org.junit.runner.Runner;
+
+abstract class MemoizingRequest extends Request {
+    private final Lock runnerLock = new ReentrantLock();
+    private volatile Runner runner;
+
+    @Override
+    public final Runner getRunner() {
+        if (runner == null) {
+            runnerLock.lock();
+            try {
+                if (runner == null) {
+                    runner = createRunner();
+                }
+            } finally {
+                runnerLock.unlock();
+            }
+        }
+        return runner;
+    }
+
+    /** Creates the {@link Runner} to return from {@link #getRunner()}. Called at most once. */
+    protected abstract Runner createRunner();
+}