Sarthak-Pandey commented on PR #20702:
URL: https://github.com/apache/nuttx/pull/20702#issuecomment-6605953077
Hi @casaroli,
Thank you for the thorough and insightful review! I have addressed all of
your feedback and pushed an updated commit to the branch:
### 1. Code Fixes (`net/local/local_recvmsg.c`)
- **Non-blocking lock contention (`lc_recvlock` + `MSG_DONTWAIT`):**
When `flags & MSG_DONTWAIT` (or `_SS_ISNONBLOCK(conn->lc_conn.s_flags)`)
is set, we now acquire `lc_recvlock` using
`nxmutex_trylock(&conn->lc_recvlock)`. If the lock is held by a concurrent
thread, it returns `-EAGAIN` immediately without blocking.
- **Next `iov` boundary blocking:**
Before reading into subsequent `iov` buffers (`total_recv > 0 && !(flags &
MSG_WAITALL)`), we check available FIFO bytes using
`file_ioctl(&conn->lc_infile, FIONREAD, &data_len)`. If `data_len == 0`, the
loop breaks immediately and returns `total_recv` rather than blocking inside
`local_fifo_read()`.
- **Preserve error code when `from != NULL`:**
Added guard `if (total_recv == 0 && ret < 0) goto errout_with_lock;`
before calling `local_getaddr()`. This ensures that errors (such as `-EAGAIN`
on empty non-blocking sockets) are not overwritten to `0` by `local_getaddr()`.
### 2. Commit Message
- Restored the `Assisted-by: Gemini:gemini-3.8-flash` tag right above
`Signed-off-by` per `CONTRIBUTING.md` Section 1.5.
### 3. PR Description & Documentation Alignment
- **Local DGRAM clarification:** Explicitly noted in the summary and impact
sections that `local SOCK_DGRAM` remains unchanged and continues to return
`-ENOTSUP` for `msg_iovlen > 1` (scatter-gather is supported for Local stream
sockets).
- **Summary clean-up:** Removed Item 3 from "Why change is necessary" which
referred to an earlier PR iteration's race rather than master.
- **Concurrent Reader Test Log:** Added a 4th test run log in the PR
description demonstrating two concurrent reader threads on an `AF_LOCAL` stream
socket:
1. Thread 1 holds `lc_recvlock` waiting for stream data.
2. Thread 2 attempts `recvmsg(MSG_DONTWAIT)` and returns `-EAGAIN`
immediately without blocking on the lock.
3. Inbound stream data is read atomically by Thread 1 across all 4
`iovec`s without interleaving.
All modified files pass `tools/nxstyle` cleanly with 0 errors and 0
warnings. Please take another look!
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