#63291 CellFormat global cache isn't thread-safe

move date format synchronization down to where the problem instance is held. 

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1856647 13f79535-47bb-0310-9956-ffa450edef68

.settings/com.vaadin.designer.prefs

+applicationTheme=Project structure is not supported.
+eclipse.preferences.version=1

src/java/org/apache/poi/ss/format/CellDateFormatter.java

     }
 
     /** {@inheritDoc} */
-    public void formatValue(StringBuffer toAppendTo, Object value) {
+    public synchronized void formatValue(StringBuffer toAppendTo, Object value) {
         if (value == null)
             value = 0.0;
         if (value instanceof Number) {

src/java/org/apache/poi/ss/format/CellFormatter.java

 
     /**
      * Format a value according the format string.
+     * <p/>
+     * NOTE: this method must be thread safe!  In particular, if it uses a 
+     * Format instance that is not thread safe, i.e. DateFormat, this method
+     * must be synchronized, either on the method, if the format is a final 
+     * property, or on the format instance itself.
      *
      * @param toAppendTo The buffer to append to.
      * @param value      The value to format.
 
     /**
      * Format a value according to the type, in the most basic way.
+     * <p/>
+     * NOTE: this method must be thread safe!  In particular, if it uses a 
+     * Format instance that is not thread safe, i.e. DateFormat, this method
+     * must be synchronized, either on the method, if the format is a final 
+     * property, or on the format instance itself.
      *
      * @param toAppendTo The buffer to append to.
      * @param value      The value to format.

src/java/org/apache/poi/ss/usermodel/DataFormatter.java

         return getFormat(cell.getNumericCellValue(), formatIndex, formatStr);
     }
 
-    private synchronized Format getFormat(double cellValue, int formatIndex, String formatStrIn) {
+    private Format getFormat(double cellValue, int formatIndex, String formatStrIn) {
         localeChangedObservable.checkForLocaleChange();
 
         // Might be better to separate out the n p and z formats, falling back to p when n and z are not set.

src/testcases/org/apache/poi/ss/usermodel/TestDataFormatter.java

 
     @Test
     public void testConcurrentCellFormat() throws Exception {
-        DataFormatter formatter = new DataFormatter();
-        doFormatTestSequential(formatter);
-        doFormatTestConcurrent(formatter);
+        DataFormatter formatter1 = new DataFormatter();
+        DataFormatter formatter2 = new DataFormatter();
+        doFormatTestSequential(formatter1);
+        doFormatTestConcurrent(formatter1, formatter2);
     }
 
     private void doFormatTestSequential(DataFormatter formatter) {
         }
     }
 
-    private void doFormatTestConcurrent(DataFormatter formatter) throws Exception {
+    private void doFormatTestConcurrent(DataFormatter formatter1, DataFormatter formatter2) throws Exception {
         ArrayList<CompletableFuture<Boolean>> futures = new ArrayList<>();
         for (int i = 0; i < 1_000; i++) {
             final int iteration = i;
             CompletableFuture<Boolean> future = CompletableFuture.supplyAsync(
                     () -> {
-                        boolean r1 = doFormatTest(formatter, 43551.50990171296, "3/27/19 12:14:15 PM", iteration);
-                        boolean r2 = doFormatTest(formatter, 36104.424780092595, "11/5/98 10:11:41 AM", iteration);
+                        boolean r1 = doFormatTest(formatter1, 43551.50990171296, "3/27/19 12:14:15 PM", iteration);
+                        boolean r2 = doFormatTest(formatter1, 36104.424780092595, "11/5/98 10:11:41 AM", iteration);
+                        return r1 && r2;
+                    });
+            futures.add(future);
+            future = CompletableFuture.supplyAsync(
+                    () -> {
+                        boolean r1 = doFormatTest(formatter2, 43551.50990171296, "3/27/19 12:14:15 PM", iteration);
+                        boolean r2 = doFormatTest(formatter2, 36104.424780092595, "11/5/98 10:11:41 AM", iteration);
                         return r1 && r2;
                     });
             futures.add(future);