fix: Data race on failedPromises in DeterministicRunnerImpl (#1060)

failedPromises (HashSet) is written to via
registerFailedPromise/forgetFailedPromise without holding the lock,
while close() reads it under the lock on another thread. Concurrent
HashMap.put and HashMap.size is a data race.

Replace HashSet with ConcurrentHashMap.newKeySet() so add/remove/copy
are safe without requiring callers to hold the lock.

Signed-off-by: Hünkar Tunç <tunc+UBER@uber.com>
Co-authored-by: Hünkar Tunç <tunc+UBER@uber.com>

Author: hcantunc

src/main/java/com/uber/cadence/internal/sync/DeterministicRunnerImpl.java

@@ -53,6 +53,7 @@
 import java.util.Random;
 import java.util.Set;
 import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Future;
@@ -121,7 +122,7 @@ static void setCurrentThreadInternal(WorkflowThread coroutine) {
    * Used to check for failedPromises that contain an error, but never where accessed. It is to
    * avoid failure swallowing by failedPromises which is very hard to troubleshoot.
    */
-  private Set<Promise> failedPromises = new HashSet<>();
+  private Set<Promise> failedPromises = ConcurrentHashMap.newKeySet();
 
   private boolean exitRequested;
   private Object exitValue;