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[scheduler] Use std::atomic<uint8_t> instead of std::atomic<bool> for remove flag

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GCC on Xtensa (ESP32) generates an indirect function call for
std::atomic<bool>::load() instead of inlining it. This adds unnecessary
call overhead on the scheduler hot path where the remove flag is checked
multiple times per loop iteration.

std::atomic<uint8_t>::load() inlines correctly on all platforms,
producing a simple load instruction with memory barrier. This eliminates
5 indirect calls and saves 30 bytes of flash on the scheduler hot path.
This commit is contained in:
J. Nick Koston
2026-03-08 08:40:54 -10:00
parent 3f143d9f19
commit 706fdc66fb
1 changed files with 7 additions and 5 deletions
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esphome/core/scheduler.h
+7 -5
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@@ -178,9 +178,11 @@ class Scheduler {
uint16_t next_execution_high_; // Upper 16 bits (millis_major counter)
#ifdef ESPHOME_THREAD_MULTI_ATOMICS
// Multi-threaded with atomics: use atomic for lock-free access
// Place atomic<bool> separately since it can't be packed with bit fields
std::atomic<bool> remove{false};
// Multi-threaded with atomics: use atomic uint8_t for lock-free access.
// std::atomic<bool> is not used because GCC on Xtensa generates an indirect
// function call for std::atomic<bool>::load() instead of inlining it.
// std::atomic<uint8_t> inlines correctly on all platforms.
std::atomic<uint8_t> remove{0};
// Bit-packed fields (4 bits used, 4 bits padding in 1 byte)
enum Type : uint8_t { TIMEOUT, INTERVAL } type : 1;
@@ -204,7 +206,7 @@ class Scheduler {
next_execution_low_(0),
next_execution_high_(0),
#ifdef ESPHOME_THREAD_MULTI_ATOMICS
// remove is initialized in the member declaration as std::atomic<bool>{false}
// remove is initialized in the member declaration
type(TIMEOUT),
name_type_(NameType::STATIC_STRING),
is_retry(false) {
@@ -508,7 +510,7 @@ class Scheduler {
// Multi-threaded with atomics: use atomic store with appropriate ordering
// Release ordering when setting to true ensures cancellation is visible to other threads
// Relaxed ordering when setting to false is sufficient for initialization
item->remove.store(removed, removed ? std::memory_order_release : std::memory_order_relaxed);
item->remove.store(removed ? 1 : 0, removed ? std::memory_order_release : std::memory_order_relaxed);
#else
// Single-threaded (ESPHOME_THREAD_SINGLE) or
// multi-threaded without atomics (ESPHOME_THREAD_MULTI_NO_ATOMICS): direct write