From e3d8fe4854a7ef7ff0637688cda9e65feb680122 Mon Sep 17 00:00:00 2001 From: Berke Güzel Date: Thu, 15 Oct 2026 12:37:10 +0300 Subject: Replace the writer spin lock with a blocking mutex term_write_begin spun on an atomic sequence word. A waiter burned CPU, and with no priority inheritance a SCHED_FIFO waiter could starve a preempted holder on the same CPU. The writer section is now a pthread mutex with PTHREAD_PRIO_INHERIT where the platform has it, and an SRWLOCK on Windows. Re-entry on the owning thread still only counts the depth. The platform wrapper (init, lock, unlock, destroy) is in compat.h. term_new initializes the mutex, and term_free destroys it. Meson links the thread library into the core, term_dep, and term_internal_dep. The README, term.h, and the amalgamation note say that POSIX needs -pthread. Tests: the feed and snapshot thread test now checks the final screen and history against a serial reference. A new test checks that term_lock nests and that another thread waits for the last term_unlock. Co-Authored-By: Claude Haiku 5.5 --- src/internal.h | 18 ++++-------------- 1 file changed, 4 insertions(+), 14 deletions(-) (limited to 'src/internal.h') diff --git a/src/internal.h b/src/internal.h index 8c02c91..d67e67e 100644 --- a/src/internal.h +++ b/src/internal.h @@ -108,7 +108,8 @@ struct resize_scratch { struct term { - _Atomic uint64_t seq; + /* The writer section. A waiting thread sleeps on it. */ + term_mutex write_lock; _Atomic uint64_t writer_tid; uint32_t write_depth; int cols; @@ -375,18 +376,7 @@ static inline void term_write_begin(struct term *t) t->write_depth++; return; } - uint64_t s; - for (;;) { - s = atomic_load_explicit(&t->seq, memory_order_relaxed); - if (s & 1) { - term_cpu_relax(); - continue; - } - if (atomic_compare_exchange_weak_explicit(&t->seq, &s, s + 1, - memory_order_acquire, - memory_order_relaxed)) - break; - } + term_mutex_lock(&t->write_lock); atomic_store_explicit(&t->writer_tid, self, memory_order_relaxed); t->write_depth = 1; } @@ -396,7 +386,7 @@ static inline void term_write_end(struct term *t) if (!t) return; if (--t->write_depth == 0) { atomic_store_explicit(&t->writer_tid, 0, memory_order_relaxed); - atomic_fetch_add_explicit(&t->seq, 1, memory_order_release); + term_mutex_unlock(&t->write_lock); } } -- cgit v1.2.3