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Skip to_add_count_ field on single-threaded platforms

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On ESPHOME_THREAD_SINGLE there are no concurrent writers, so
to_add_empty_() checks to_add_.empty() directly. The counter
field and its increment/clear operations are compiled out.
This commit is contained in:
J. Nick Koston
2026-03-17 02:09:39 -10:00
parent 1ed30414c9
commit 9c9464f29f
1 changed files with 18 additions and 14 deletions
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esphome/core/scheduler.h
+18 -14
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@@ -529,49 +529,53 @@ class Scheduler {
std::vector<SchedulerItem *> items_;
std::vector<SchedulerItem *> to_add_;
#ifndef ESPHOME_THREAD_SINGLE
// Fast-path counter for process_to_add() to skip taking the lock when there is
// nothing to add. Uses std::atomic on platforms that support it, plain uint32_t
// otherwise. On non-atomic platforms, callers must hold the scheduler lock when
// mutating this counter.
// mutating this counter. Not needed on single-threaded platforms where we can
// check to_add_.empty() directly.
#ifdef ESPHOME_THREAD_MULTI_ATOMICS
std::atomic<uint32_t> to_add_count_{0};
#else
uint32_t to_add_count_{0};
#endif
#endif /* ESPHOME_THREAD_SINGLE */
// Fast-path helper for process_to_add() to decide if it can try the lock-free path.
// - On ESPHOME_THREAD_MULTI_ATOMICS: performs a lock-free check via to_add_count_.
// - On ESPHOME_THREAD_SINGLE: direct container check is safe (no concurrent writers).
// - On ESPHOME_THREAD_MULTI_ATOMICS: performs a lock-free check via to_add_count_.
// - On ESPHOME_THREAD_MULTI_NO_ATOMICS: always returns false to force the caller
// down the locked path; this is NOT a lock-free emptiness check on that platform.
bool to_add_empty_() const {
#ifdef ESPHOME_THREAD_MULTI_ATOMICS
return this->to_add_count_.load(std::memory_order_relaxed) == 0;
#elif defined(ESPHOME_THREAD_SINGLE)
// Single-threaded: no concurrent writers, direct check is safe
#ifdef ESPHOME_THREAD_SINGLE
return this->to_add_.empty();
#elif defined(ESPHOME_THREAD_MULTI_ATOMICS)
return this->to_add_count_.load(std::memory_order_relaxed) == 0;
#else
// Multi-threaded without atomics: must take lock; always indicate "not empty"
// so the caller does not attempt a lock-free path.
return false;
#endif
}
// Increment to_add_count_ (caller must hold lock on non-atomic platforms)
// Increment to_add_count_ (no-op on single-threaded platforms)
void to_add_count_increment_() {
#ifdef ESPHOME_THREAD_MULTI_ATOMICS
#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
this->to_add_count_++;
this->to_add_count_++;
#endif
}
// Reset to_add_count_ (caller must hold lock)
// Reset to_add_count_ (no-op on single-threaded platforms)
void to_add_count_clear_() {
#ifdef ESPHOME_THREAD_MULTI_ATOMICS
#ifdef ESPHOME_THREAD_SINGLE
// No counter needed — to_add_empty_() checks the vector directly
#elif defined(ESPHOME_THREAD_MULTI_ATOMICS)
this->to_add_count_.store(0, std::memory_order_relaxed);
#else
this->to_add_count_ = 0;
this->to_add_count_ = 0;
#endif
}