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[scheduler] Use __atomic_load_n only on reader fast-path

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Walk back the __atomic_store_n on the writer paths — the mutators
already hold lock_, so plain counter_++/=/+=/-- is sufficient to
serialise against other writers. The reader fast-path still uses
__atomic_load_n(&counter, __ATOMIC_RELAXED) to express concurrent-
read intent in the C++ memory model and keep the compiler from
caching/eliding the read. On ARMv5TE it compiles to a plain LDR —
same codegen as before.
This commit is contained in:
J. Nick Koston
2026-04-23 06:07:51 -05:00
parent 22ed9b3c1e
commit 202bcf5b10
1 changed files with 9 additions and 16 deletions
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esphome/core/scheduler.h
+9 -16
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@@ -550,16 +550,15 @@ class Scheduler {
}
// Increment to_add_count_ (no-op on single-threaded platforms).
// On NO_ATOMICS the caller must hold lock_ to serialise the load-modify-store
// against other writers; the __atomic_store_n makes the write visible to
// concurrent readers in the C++ memory model.
// On NO_ATOMICS the caller must hold lock_ to serialise RMW against
// other writers; reader fast-path uses __atomic_load_n.
void to_add_count_increment_locked_() {
#ifdef ESPHOME_THREAD_SINGLE
// No counter needed — to_add_empty_() checks the vector directly
#elif defined(ESPHOME_THREAD_MULTI_ATOMICS)
this->to_add_count_.fetch_add(1, std::memory_order_relaxed);
#else
__atomic_store_n(&this->to_add_count_, __atomic_load_n(&this->to_add_count_, __ATOMIC_RELAXED) + 1, __ATOMIC_RELAXED);
this->to_add_count_++;
#endif
}
@@ -570,7 +569,7 @@ class Scheduler {
#elif defined(ESPHOME_THREAD_MULTI_ATOMICS)
this->to_add_count_.store(0, std::memory_order_relaxed);
#else
__atomic_store_n(&this->to_add_count_, 0, __ATOMIC_RELAXED);
this->to_add_count_ = 0;
#endif
}
@@ -602,7 +601,7 @@ class Scheduler {
#ifdef ESPHOME_THREAD_MULTI_ATOMICS
this->defer_count_.fetch_add(1, std::memory_order_relaxed);
#else
__atomic_store_n(&this->defer_count_, __atomic_load_n(&this->defer_count_, __ATOMIC_RELAXED) + 1, __ATOMIC_RELAXED);
this->defer_count_++;
#endif
}
@@ -610,7 +609,7 @@ class Scheduler {
#ifdef ESPHOME_THREAD_MULTI_ATOMICS
this->defer_count_.store(0, std::memory_order_relaxed);
#else
__atomic_store_n(&this->defer_count_, 0, __ATOMIC_RELAXED);
this->defer_count_ = 0;
#endif
}
@@ -639,30 +638,24 @@ class Scheduler {
void to_remove_add_locked_(uint32_t count) {
#ifdef ESPHOME_THREAD_MULTI_ATOMICS
this->to_remove_.fetch_add(count, std::memory_order_relaxed);
#elif defined(ESPHOME_THREAD_MULTI_NO_ATOMICS)
__atomic_store_n(&this->to_remove_, __atomic_load_n(&this->to_remove_, __ATOMIC_RELAXED) + count, __ATOMIC_RELAXED);
#else
this->to_remove_ += count;
this->to_remove_ += count;
#endif
}
void to_remove_decrement_locked_() {
#ifdef ESPHOME_THREAD_MULTI_ATOMICS
this->to_remove_.fetch_sub(1, std::memory_order_relaxed);
#elif defined(ESPHOME_THREAD_MULTI_NO_ATOMICS)
__atomic_store_n(&this->to_remove_, __atomic_load_n(&this->to_remove_, __ATOMIC_RELAXED) - 1, __ATOMIC_RELAXED);
#else
this->to_remove_--;
this->to_remove_--;
#endif
}
void to_remove_clear_locked_() {
#ifdef ESPHOME_THREAD_MULTI_ATOMICS
this->to_remove_.store(0, std::memory_order_relaxed);
#elif defined(ESPHOME_THREAD_MULTI_NO_ATOMICS)
__atomic_store_n(&this->to_remove_, 0, __ATOMIC_RELAXED);
#else
this->to_remove_ = 0;
this->to_remove_ = 0;
#endif
}