Merge "Make FileUtils#createDir threadsafe"

core/java/android/os/FileUtils.java

@@ -1235,9 +1235,9 @@ public final class FileUtils {
     }
 
     /**
-     * Creates a directory with name {@code name} under an existing directory {@code baseDir}.
-     * Returns a {@code File} object representing the directory on success, {@code null} on
-     * failure.
+     * Creates a directory with name {@code name} under an existing directory {@code baseDir} if it
+     * doesn't exist already. Returns a {@code File} object representing the directory if it exists
+     * and {@code null} if not.
      *
      * @hide
      */
@@ -1247,13 +1247,23 @@ public final class FileUtils {
         return createDir(dir) ? dir : null;
     }
 
-    /** @hide */
+    /**
+     * Ensure the given directory exists, creating it if needed. This method is threadsafe.
+     *
+     * @return false if the directory doesn't exist and couldn't be created
+     *
+     * @hide
+     */
     public static boolean createDir(File dir) {
+        if (dir.mkdir()) {
+            return true;
+        }
+
         if (dir.exists()) {
             return dir.isDirectory();
         }
 
-        return dir.mkdir();
+        return false;
     }
 
     /**