[gwt-contrib] Remove cache file if nothing was written to it. (issue1396804)

[scottb]

Reviewers: zundel,

Message:
In the case where you re-run a compile/startup without changing any
code, we produce an empty cache file each time.  This change removes the
file on exit if we never wrote anything to it.


Please review this at http://gwt-code-reviews.appspot.com/1396804/

Affected files:
  M dev/core/src/com/google/gwt/dev/javac/PersistentUnitCache.java


Index: dev/core/src/com/google/gwt/dev/javac/PersistentUnitCache.java
diff --git a/dev/core/src/com/google/gwt/dev/javac/PersistentUnitCache.java  
b/dev/core/src/com/google/gwt/dev/javac/PersistentUnitCache.java
index  
8d2a926cbf4b10e91aea12edda8d847db09a1082..dcff5e299139e87395ce5073a3074560bb28dbe4  
100644
--- a/dev/core/src/com/google/gwt/dev/javac/PersistentUnitCache.java
+++ b/dev/core/src/com/google/gwt/dev/javac/PersistentUnitCache.java
@@ -184,7 +184,8 @@ class PersistentUnitCache extends MemoryUnitCache {
         logger.log(TreeLogger.ERROR, "Error creating cache " +  
currentCacheFile
             + ". Disabling cache.", ex);
       }
-      int unitsWritten = 0;
+      int recentUnitsWritten = 0;
+      int totalUnitsWritten = 0;
       try {
         while (true) {
           UnitWriteMessage msg = null;
@@ -202,9 +203,9 @@ class PersistentUnitCache extends MemoryUnitCache {
           try {
             if (msg != null) {
               if (msg == UnitWriteMessage.DELETE_OLD_CACHE_FILES) {
-                logger.log(TreeLogger.TRACE, "Wrote " + unitsWritten
+                logger.log(TreeLogger.TRACE, "Wrote " + recentUnitsWritten
                     + " units to persistent cache.");
-                unitsWritten = 0;
+                recentUnitsWritten = 0;
                 deleteOldCacheFiles(logger, currentCacheFile);
               } else if (msg == UnitWriteMessage.SHUTDOWN_THREAD) {
                 stream.flush();
@@ -214,7 +215,8 @@ class PersistentUnitCache extends MemoryUnitCache {
                 CompilationUnit unit = msg.unitCacheEntry.getUnit();
                 assert unit != null;
                 stream.writeObject(unit);
-                unitsWritten++;
+                recentUnitsWritten++;
+                totalUnitsWritten++;
               }
             }

@@ -234,6 +236,10 @@ class PersistentUnitCache extends MemoryUnitCache {
         // Paranoia - close all streams
         Utility.close(bstream);
         Utility.close(fstream);
+        if (totalUnitsWritten == 0) {
+          // Remove useless empty output.
+          currentCacheFile.delete();
+        }
         shutDownLatch.countDown();
         logger.log(TreeLogger.TRACE, "Shutting down PersistentUnitCache  
thread");
       }


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