[GitHub] [beam] bvolpato commented on a diff in pull request #28122: fix: fix a race condition in BigtableService cache

["bvolpato (via GitHub)" <gi...@apache.org>]

bvolpato commented on code in PR #28122:
URL: https://github.com/apache/beam/pull/28122#discussion_r1303312575


##########
sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/bigtable/BigtableServiceFactory.java:
##########
@@ -75,15 +76,15 @@ static BigtableServiceEntry create(ConfigId configId, BigtableService service) {
 
     @Override
     public void close() {
-      int refCount =
-          refCounts.getOrDefault(getConfigId().id(), new AtomicInteger(0)).decrementAndGet();
-      if (refCount < 0) {
-        LOG.error(
-            "close() Ref count is < 0, configId=" + getConfigId().id() + " refCount=" + refCount);
-      }
-      LOG.debug("close() for config id " + getConfigId().id() + ", ref count is " + refCount);
-      if (refCount == 0) {
-        synchronized (lock) {
+      synchronized (lock) {
+        int refCount =
+            refCounts.getOrDefault(getConfigId().id(), new AtomicInteger(0)).decrementAndGet();
+        if (refCount < 0) {
+          LOG.error(
+              "close() Ref count is < 0, configId=" + getConfigId().id() + " refCount=" + refCount);
+        }
+        LOG.debug("close() for config id " + getConfigId().id() + ", ref count is " + refCount);
+        if (refCount == 0) {

Review Comment:
    decrementAndCount is thread safe, so I wonder what's the actual underlying issue here.
   
   I also understand why < 0 is logging an error, but shouldn't we `.remove()` in that case too? Instead of doing `== 0` in the next if



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