Simplify `expectedFinalRegisterValue` computation (#131274)

In repository analysis we keep an `AtomicLong` counting the number of
successfully-completed increments on the contended register, but we only
check this value if all the increments succeed. We know how many
increments we enqueue up-front so there's no need to count them as they
complete. This commit removes the unnecessary counter.

x-pack/plugin/snapshot-repo-test-kit/src/main/java/org/elasticsearch/repositories/blobstore/testkit/analyze/RepositoryAnalyzeAction.java

@@ -77,7 +77,6 @@ import java.util.Random;
 import java.util.Set;
 import java.util.concurrent.Semaphore;
 import java.util.concurrent.atomic.AtomicBoolean;
-import java.util.concurrent.atomic.AtomicLong;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 import java.util.function.LongSupplier;
@@ -380,7 +379,6 @@ public class RepositoryAnalyzeAction extends HandledTransportAction<RepositoryAn
         // choose the blob path nondeterministically to avoid clashes, assuming that the actual path doesn't matter for reproduction
         private final String blobPath = "temp-analysis-" + UUIDs.randomBase64UUID();
 
-        private final AtomicLong expectedRegisterValue = new AtomicLong();
         private final Queue<Consumer<Releasable>> queue = ConcurrentCollections.newQueue();
         private final AtomicReference<Exception> failure = new AtomicReference<>();
         private final Semaphore innerFailures = new Semaphore(5); // limit the number of suppressed failures
@@ -486,16 +484,17 @@ public class RepositoryAnalyzeAction extends HandledTransportAction<RepositoryAn
             if (minClusterTransportVersion.onOrAfter(TransportVersions.V_8_8_0)) {
                 final String contendedRegisterName = CONTENDED_REGISTER_NAME_PREFIX + UUIDs.randomBase64UUID(random);
                 final AtomicBoolean contendedRegisterAnalysisComplete = new AtomicBoolean();
+                final int registerOperations = Math.max(nodes.size(), request.getRegisterOperationCount());
                 try (
                     var registerRefs = new RefCountingRunnable(
                         finalRegisterValueVerifier(
                             contendedRegisterName,
+                            registerOperations,
                             random,
                             Releasables.wrap(requestRefs.acquire(), () -> contendedRegisterAnalysisComplete.set(true))
                         )
                     )
                 ) {
-                    final int registerOperations = Math.max(nodes.size(), request.getRegisterOperationCount());
                     for (int i = 0; i < registerOperations; i++) {
                         final ContendedRegisterAnalyzeAction.Request registerAnalyzeRequest = new ContendedRegisterAnalyzeAction.Request(
                             request.getRepositoryName(),
@@ -631,9 +630,7 @@ public class RepositoryAnalyzeAction extends HandledTransportAction<RepositoryAn
                     TransportRequestOptions.EMPTY,
                     new ActionListenerResponseHandler<>(ActionListener.releaseAfter(new ActionListener<>() {
                         @Override
-                        public void onResponse(ActionResponse.Empty response) {
-                            expectedRegisterValue.incrementAndGet();
-                        }
+                        public void onResponse(ActionResponse.Empty response) {}
 
                         @Override
                         public void onFailure(Exception exp) {
@@ -647,7 +644,7 @@ public class RepositoryAnalyzeAction extends HandledTransportAction<RepositoryAn
             }
         }
 
-        private Runnable finalRegisterValueVerifier(String registerName, Random random, Releasable ref) {
+        private Runnable finalRegisterValueVerifier(String registerName, int expectedFinalRegisterValue, Random random, Releasable ref) {
             return new Runnable() {
 
                 final CheckedConsumer<ActionListener<OptionalBytesReference>, Exception> finalValueReader = switch (random.nextInt(3)) {
@@ -706,12 +703,9 @@ public class RepositoryAnalyzeAction extends HandledTransportAction<RepositoryAn
                     }
                 };
 
-                long expectedFinalRegisterValue = Long.MIN_VALUE;
-
                 @Override
                 public void run() {
                     if (isRunning()) {
-                        expectedFinalRegisterValue = expectedRegisterValue.get();
                         transportService.getThreadPool()
                             .executor(ThreadPool.Names.SNAPSHOT)
                             .execute(ActionRunnable.wrap(ActionListener.releaseAfter(new ActionListener<>() {