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hio_write/hio_close are documented thread-safe, but they read io->ready/closed unlocked while the loop thread rewrites neighbouring bits of the same bitfield word, and hio_write stamps last_write_hrtime from the loop's cur_hrtime. Make those fields atomic, and make loop->status atomic, stored before hloop_stop's wakeup so the woken loop sees STOP. Found with ThreadSanitizer.
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🟡 Changes recommended
Shutdown can access an auto-freed loop, and fallback atomic types leave shared accesses insufficiently synchronized.
2 open findings
What changed in this PR
This PR addresses ThreadSanitizer-reported races in libhv’s event loop and cross-thread IO operations.
Changes:
- Converts shared status, IO flags, and timestamps to atomic types.
- Publishes thread identifiers before RUNNING and sets STOP before wakeup.
- Adds atomic exchange support across backends.
| File | Description |
|---|---|
| event/hloop.c | Reorders startup publication and shutdown signaling. |
| event/hevent.h | Changes shared fields to atomic types. |
| base/hatomic.h | Adds atomic aliases and exchange operations. |
🧠 Review effort: Balanced
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| uint64_t start_hrtime; // us | ||
| uint64_t end_hrtime; | ||
| uint64_t cur_hrtime; | ||
| atomic_ullong cur_hrtime; // read by hio_write from other threads |
| if (loop == NULL) return -1; | ||
| if (loop->status == HLOOP_STATUS_STOP) return -2; | ||
| // set the status before waking the loop, or it can wake, see RUNNING and block again | ||
| if (hatomic_exchange(&loop->status, HLOOP_STATUS_STOP) == HLOOP_STATUS_STOP) return -2; |
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Fixes data races reported by ThreadSanitizer when
hio_write/hio_closeare called from a non-loop thread (both are documented as thread-safe).Changes
hio_s:ready,connected,closedare nowatomic_boolinstead of bitfield bits. They are read without a lock from other threads, while the loop thread rewrites neighbouring bits in the same word.hio_s:last_read_hrtime/last_write_hrtimeandhloop_s::cur_hrtimeare nowatomic_ullong, sincehio_writestampslast_write_hrtimefromcur_hrtimeon the caller's thread.hloop_s::statusis nowatomic_int.hloop_runstoresRUNNINGafter settingpid/tid, sohloop_stopsees a validtid.hloop_stopsetsSTOP(via newhatomic_exchange) before the wakeup. Before, the loop could wake, still seeRUNNING, and block again.base/hatomic.h: addATOMIC_EXCHANGE/hatomic_exchangefor C11, C++, GCC__sync, Win32 and a non-atomic fallback.sizeof(struct hio_s)grows from 424 to 432 on linux-x64.