[java] Fix concurrency issue in Selenium Manager

java/src/org/openqa/selenium/manager/SeleniumManager.java

@@ -16,6 +16,9 @@
 // under the License.
 package org.openqa.selenium.manager;
 
+import static java.nio.file.StandardCopyOption.REPLACE_EXISTING;
+import static java.util.Objects.requireNonNull;
+import static java.util.UUID.randomUUID;
 import static org.openqa.selenium.Platform.LINUX;
 import static org.openqa.selenium.Platform.MAC;
 import static org.openqa.selenium.Platform.UNIX;
@@ -213,11 +216,10 @@ private synchronized Path getBinary() {
         }
 
         binary = getBinaryInCache(SELENIUM_MANAGER + extension);
-        if (!binary.toFile().exists()) {
-          String binaryPathInJar = String.format("%s/%s%s", folder, SELENIUM_MANAGER, extension);
-          try (InputStream inputStream = this.getClass().getResourceAsStream(binaryPathInJar)) {
+        if (!Files.exists(binary)) {
+          try (InputStream inputStream = findBinaryInClasspath(folder, extension)) {
             Files.createDirectories(binary.getParent());
-            Files.copy(inputStream, binary);
+            saveToFileSafely(inputStream, binary);
           }
         }
       } catch (Exception e) {
@@ -233,6 +235,29 @@ private synchronized Path getBinary() {
     return binary;
   }
 
+  /**
+   * Protect from concurrency issue when executed by 2+ processes simultaneously. Every process sees
+   * the file created by another process only when the file is fully completed.
+   */
+  private void saveToFileSafely(InputStream inputStream, Path target) throws IOException {
+    Path temporaryFile = target.resolveSibling(target.getFileName() + "." + randomUUID() + ".tmp");
+    Files.copy(inputStream, temporaryFile);
+    try {
+      if (!Files.exists(target)) {
+        Files.move(temporaryFile, target, REPLACE_EXISTING);
+      }
+    } finally {
+      Files.deleteIfExists(temporaryFile);
+    }
+  }
+
+  private InputStream findBinaryInClasspath(String folder, String extension) {
+    String binaryPathInJar = String.format("%s/%s%s", folder, SELENIUM_MANAGER, extension);
+    return requireNonNull(
+        getClass().getResourceAsStream(binaryPathInJar),
+        () -> "Resource not found in classpath: " + binaryPathInJar);
+  }
+
   /**
    * Executes Selenium Manager to get the locations of the requested assets
    *