[RATIS-2007] Zero-copy buffers are not released

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.1.0
• Component/s: server
• Assignee: Duong
• Reporter: Duong
• Created: 18/Jan/24 02:10
• Updated: 27/Jan/24 20:52
• Resolved: 27/Jan/24 20:50

Description

Found this bug when working on adding assertions to ensure all zero-copy buffers are released in tests (RATIS-1978).

When client connections are terminated, the `whenComplete` promise seems not executed. This leads to unreleased zero-copy buffers. For example, the whenComplete block as below may not be executed when clients time out. 

// In RaftServerImpl
@Override
public CompletableFuture<RaftClientReply> submitClientRequestAsync(
    ReferenceCountedObject<RaftClientRequest> requestRef) {
  final RaftClientRequest request = requestRef.retain();
  ...
  return replyFuture(requestRef).whenComplete((clientReply, exception) -> {
  requestRef.release();
  timerContext.ifPresent(Timekeeper.Context::stop);
  if (exception != null || clientReply.getException() != null) {
    raftServerMetrics.incFailedRequestCount(request.getType());
  }
}); 

Issue Links

• is related to: RATIS-2018 Zero-copy buffers are not released - 2nd chunk
• links to: GitHub Pull Request #1027