[bug-62176] synchronize temp dir creation

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1826655 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/poi/util/DefaultTempFileCreationStrategy.java

@@ -85,11 +85,12 @@ public class DefaultTempFileCreationStrategy implements TempFileCreationStrategy
     /**
      * Attempt to create a directory, including any necessary parent directories.
      * Does nothing if directory already exists.
+     * The method is synchronized to ensure that multiple threads don't try to create the directory at the same time.
      *
      * @param directory  the directory to create
      * @throws IOException if unable to create temporary directory or it is not a directory
      */
-    private void createTempDirectory(File directory) throws IOException {
+    private synchronized void createTempDirectory(File directory) throws IOException {
         // create directory if it doesn't exist
         final boolean dirExists = (directory.exists() || directory.mkdirs());
         
@@ -138,4 +139,4 @@ public class DefaultTempFileCreationStrategy implements TempFileCreationStrategy
         // All done
         return newDirectory;
     }
-}
+}