Synchronize MyersDiff and HistogramDiff invocations on local variable

I4516bcc2c synchronized MyersDiff and HistogramDiff invocations but it
used a synchronization object that is not local to the PatchList being
loaded. In other words, even if PatchList can be loaded in parallel,
only one file header diff can be computed at the time across the entire
server.

In stable-2.12, a fresh instance of PatchListLoaded is used every time a
PatchList is loaded so this change is not needed, and must be reverted
when merging stable-2.11 into stable-2.12.

Change-Id: I5acace093b16c9b87cf465c515018433c3f38d6a

1 files changed, 2 insertions, 4 deletions

diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchListLoader.java b/gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchListLoader.java
index 13cb50673b..838b3433de 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchListLoader.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchListLoader.java
@@ -87,7 +87,6 @@ public class PatchListLoader extends CacheLoader<PatchListKey, PatchList> {
   private final ThreeWayMergeStrategy mergeStrategy;
   private final ExecutorService diffExecutor;
   private final long timeoutMillis;
-  private final Object lock;
 
   @Inject
   PatchListLoader(GitRepositoryManager mgr,
@@ -98,7 +97,6 @@ public class PatchListLoader extends CacheLoader<PatchListKey, PatchList> {
     patchListCache = plc;
     mergeStrategy = MergeUtil.getMergeStrategy(cfg);
     diffExecutor = de;
-    lock = new Object();
     timeoutMillis =
         ConfigUtil.getTimeUnit(cfg, "cache", PatchListCacheImpl.FILE_NAME,
             "timeout", TimeUnit.MILLISECONDS.convert(5, TimeUnit.SECONDS),
@@ -206,7 +204,7 @@ public class PatchListLoader extends CacheLoader<PatchListKey, PatchList> {
     Future<FileHeader> result = diffExecutor.submit(new Callable<FileHeader>() {
       @Override
       public FileHeader call() throws IOException {
-        synchronized (lock) {
+        synchronized (diffEntry) {
           return diffFormatter.toFileHeader(diffEntry);
         }
       }
@@ -222,7 +220,7 @@ public class PatchListLoader extends CacheLoader<PatchListKey, PatchList> {
                       + " comparing " + diffEntry.getOldId().name()
                       + ".." + diffEntry.getNewId().name());
       result.cancel(true);
-      synchronized (lock) {
+      synchronized (diffEntry) {
         return toFileHeaderWithoutMyersDiff(diffFormatter, diffEntry);
       }
     } catch (ExecutionException e) {