Write to temp file and do atomic rename in Java DocumentAPI tests

Should avoid racing with concurrent reads by C++ DocumentAPI tests.

1 files changed, 12 insertions, 1 deletions

diff --git a/documentapi/src/test/java/com/yahoo/documentapi/messagebus/protocol/test/TestFileUtil.java b/documentapi/src/test/java/com/yahoo/documentapi/messagebus/protocol/test/TestFileUtil.java
index 8bc6f56e574..50f8f82b180 100644
--- a/documentapi/src/test/java/com/yahoo/documentapi/messagebus/protocol/test/TestFileUtil.java
+++ b/documentapi/src/test/java/com/yahoo/documentapi/messagebus/protocol/test/TestFileUtil.java
@@ -4,16 +4,27 @@ package com.yahoo.documentapi.messagebus.protocol.test;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.nio.charset.Charset;
+import java.nio.file.FileSystems;
 import java.nio.file.Files;
+import java.nio.file.Path;
 import java.nio.file.Paths;
 
+import static java.nio.file.StandardCopyOption.ATOMIC_MOVE;
+
 public class TestFileUtil {
     protected static final String DATA_PATH = "./test/crosslanguagefiles";
 
     public static void writeToFile(String path, byte[] data) throws IOException {
-        try (FileOutputStream stream = new FileOutputStream(path)) {
+        // Write to a temporary file to avoid racing with cross-language tests reading the
+        // exact same file we're trying to write.
+        String tmpPath = path + ".tmp";
+        try (FileOutputStream stream = new FileOutputStream(tmpPath)) {
             stream.write(data);
+            stream.flush();
         }
+        // We make the assumption that all file systems we run these tests on support some form
+        // of atomic moving rather than "move by content copy".
+        Files.move(FileSystems.getDefault().getPath(tmpPath), FileSystems.getDefault().getPath(path), ATOMIC_MOVE);
     }
 
     /**