Add helper for combining multiple completable futures

1 files changed, 66 insertions, 0 deletions

diff --git a/vespajlib/src/test/java/com/yahoo/concurrent/CompletableFuturesTest.java b/vespajlib/src/test/java/com/yahoo/concurrent/CompletableFuturesTest.java
new file mode 100644
index 00000000000..cf9c36537d9
--- /dev/null
+++ b/vespajlib/src/test/java/com/yahoo/concurrent/CompletableFuturesTest.java
@@ -0,0 +1,66 @@
+package com.yahoo.concurrent;// Copyright Verizon Media. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
+/**
+ * @author bjorncs
+ */
+class CompletableFuturesTest {
+
+    @Test
+    public void firstof_completes_when_first_futures_has_completed() {
+        CompletableFuture<String> f1 = new CompletableFuture<>();
+        CompletableFuture<String> f2 = new CompletableFuture<>();
+        CompletableFuture<String> f3 = new CompletableFuture<>();
+        CompletableFuture<String> result = CompletableFutures.firstOf(List.of(f1, f2, f3));
+        f1.complete("success");
+        assertTrue(result.isDone());
+        assertFalse(result.isCompletedExceptionally());
+        assertEquals("success", result.join());
+    }
+
+    @Test
+    public void firstof_completes_if_any_futures_completes() {
+        CompletableFuture<String> f1 = new CompletableFuture<>();
+        CompletableFuture<String> f2 = new CompletableFuture<>();
+        CompletableFuture<String> f3 = new CompletableFuture<>();
+        CompletableFuture<String> result = CompletableFutures.firstOf(List.of(f1, f2, f3));
+        f1.completeExceptionally(new Throwable("t1"));
+        f2.completeExceptionally(new Throwable("t2"));
+        f3.complete("success");
+        assertTrue(result.isDone());
+        assertFalse(result.isCompletedExceptionally());
+        assertEquals("success", result.join());
+    }
+
+    @Test
+    public void firstof_completes_exceptionally_when_all_futures_have_complete_exceptionally() {
+        CompletableFuture<String> f1 = new CompletableFuture<>();
+        CompletableFuture<String> f2 = new CompletableFuture<>();
+        CompletableFuture<String> f3 = new CompletableFuture<>();
+        CompletableFuture<String> result = CompletableFutures.firstOf(List.of(f1, f2, f3));
+        f1.completeExceptionally(new Throwable("t1"));
+        f2.completeExceptionally(new Throwable("t2"));
+        f3.completeExceptionally(new Throwable("t3"));
+        assertTrue(result.isDone());
+        assertTrue(result.isCompletedExceptionally());
+        try {
+            result.join();
+            fail("Exception expected");
+        } catch (CompletionException e) {
+            Throwable cause = e.getCause();
+            assertEquals("t1", cause.getMessage());
+            assertEquals(2, cause.getSuppressed().length);
+        }
+    }
+
+}
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