legionxiong opened a new pull request, #3406:
URL: https://github.com/apache/brpc/pull/3406
Make the handshake state atomic and publish RDMA_OFF before FALLBACK_TCP.
This prevents TCP event handling from observing a partially published fallback
state. Use a relaxed load for the completion-path check because it does not
consume related data.
### What problem does this PR solve?
Issue Number: #3405
Problem Summary:
`RdmaEndpoint::_state` is concurrently accessed by the RDMA handshake,
TCP event handling, and completion handling paths, but it is not atomic.
This causes a C++ data race.
In addition, `RdmaConnect::StartConnect()` publishes `FALLBACK_TCP`
before setting `RdmaTransport::_rdma_state` to `RDMA_OFF`. A concurrent
TCP event may therefore observe a partially published fallback state and
start TCP message processing while the transport still appears to use
RDMA.
### What is changed and the side effects?
Changed:
- Change `RdmaEndpoint::_state` to `butil::atomic<State>`.
- Set `RdmaTransport::_rdma_state` to `RDMA_OFF` before publishing
`RdmaEndpoint::_state` as `FALLBACK_TCP`.
- Use a relaxed atomic load for the `_state` check in
`RdmaEndpoint::HandleCompletion()`, because the check does not consume
data published by the state transition.
Side effects:
- Performance effects:
The handshake and TCP fallback paths use the default sequentially
consistent ordering. These paths are not hot after the handshake
completes. The completion hot path uses a relaxed load, so it does not
introduce unnecessary ordering overhead.
- Breaking backward compatibility:
None. This change does not modify any public API, wire protocol, or
externally visible behavior.
---
### Check List:
- Please make sure your changes are compilable.
- When providing us with a new feature, it is best to add related tests.
- Please follow [Contributor Covenant Code of
Conduct](https://github.com/apache/brpc/blob/master/CODE_OF_CONDUCT.md).
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