fix(io_context): decouple concurrency_hint == 1 from lockless mode (#…#316
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fix(io_context): decouple concurrency_hint == 1 from lockless mode (#…#316mvandeberg wants to merge 1 commit into
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An automated preview of the documentation is available at https://316.corosio.prtest3.cppalliance.org/index.html If more commits are pushed to the pull request, the docs will rebuild at the same URL. 2026-07-10 22:53:56 UTC |
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…ppalliance#310) A concurrency_hint of 1 silently enabled full single-threaded lockless mode: scheduler mutex/condvar, per-descriptor locks, IOCP dispatch mutex, and io_uring ring/dispatch mutexes were all disabled, plus io_uring got SINGLE_ISSUER/DEFER_TASKRUN. This made cross-thread post() undefined behavior, contrary to asio (where a plain integer hint never disables locking) and to what migrating users expect. A hint now only tunes performance and never changes the safety contract: - Remove the three hint == 1 -> single_threaded coupling sites (backend-tag template ctor, io_context(unsigned) ctor, and normalize_options, which is deleted along with the now-dead configure_single_threaded_() member). - Rename the public opt-in io_context_options::single_threaded -> single_threaded_lockless, which remains the sole way to enable lockless mode (still gating the io_uring SINGLE_ISSUER flags). The explicit, descriptive name replaces an innocuous flag that read like a mere performance tweak. - Default ctor clamp max(2u, hardware_concurrency()) -> max(1u, ...): the "2" floor existed only to dodge the removed trap; floor at 1 still guards a 0 return. Tests: the resolver/stream_file single-threaded restriction tests switch to explicit opts.single_threaded_lockless; new testHintOneIsThreadSafe proves cross-thread post() into a hint == 1 context is TSan-clean across all backends (verified: fails under TSan with the coupling restored). Docs and benchmarks: header Doxygen (option, Thread Safety, default ctor), the io-context and configuration guide pages, and all perf/bench/corosio sources updated for the new option name. Fixes cppalliance#310
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…310)
A concurrency_hint of 1 silently enabled full single-threaded lockless mode: scheduler mutex/condvar, per-descriptor locks, IOCP dispatch mutex, and io_uring ring/dispatch mutexes were all disabled, plus io_uring got SINGLE_ISSUER/DEFER_TASKRUN. This made cross-thread post() undefined behavior, contrary to asio (where a plain integer hint never disables locking) and to what migrating users expect.
A hint now only tunes performance and never changes the safety contract:
Tests: the resolver/stream_file single-threaded restriction tests switch to explicit opts.single_threaded_unsafe; new testHintOneIsThreadSafe proves cross-thread post() into a hint == 1 context is TSan-clean across all backends (verified: fails under TSan with the coupling restored).
Docs: header Doxygen (option, Thread Safety, default ctor) plus the io-context and configuration guide pages updated.
Fixes #310