diff --git a/esphome/core/defines.h b/esphome/core/defines.h index 7ddb3436cd..4e3145444d 100644 --- a/esphome/core/defines.h +++ b/esphome/core/defines.h @@ -229,6 +229,16 @@ #define USE_SOCKET_SELECT_SUPPORT #endif +// Helper macro for platforms that lack atomic scheduler support +#if defined(USE_ESP8266) || defined(USE_RP2040) +#define ESPHOME_SINGLE_CORE +#endif + +// Helper macro for platforms with atomic scheduler support +#if !defined(ESPHOME_SINGLE_CORE) && !defined(USE_LIBRETINY) +#define ESPHOME_ATOMIC_SCHEDULER +#endif + // Disabled feature flags // #define USE_BSEC // Requires a library with proprietary license // #define USE_BSEC2 // Requires a library with proprietary license diff --git a/esphome/core/scheduler.cpp b/esphome/core/scheduler.cpp index 7a0c08e1f0..21c45c2f97 100644 --- a/esphome/core/scheduler.cpp +++ b/esphome/core/scheduler.cpp @@ -54,7 +54,7 @@ static void validate_static_string(const char *name) { ESP_LOGW(TAG, "WARNING: Scheduler name '%s' at %p might be on heap (static ref at %p)", name, name, static_str); } } -#endif +#endif /* ESPHOME_DEBUG_SCHEDULER */ // A note on locking: the `lock_` lock protects the `items_` and `to_add_` containers. It must be taken when writing to // them (i.e. when adding/removing items, but not when changing items). As items are only deleted from the loop task, @@ -82,9 +82,9 @@ void HOT Scheduler::set_timer_common_(Component *component, SchedulerItem::Type item->callback = std::move(func); item->remove = false; -#if !defined(USE_ESP8266) && !defined(USE_RP2040) +#ifndef ESPHOME_SINGLE_CORE // Special handling for defer() (delay = 0, type = TIMEOUT) - // ESP8266 and RP2040 are excluded because they don't need thread-safe defer handling + // Single-core platforms don't need thread-safe defer handling if (delay == 0 && type == SchedulerItem::TIMEOUT) { // Put in defer queue for guaranteed FIFO execution LockGuard guard{this->lock_}; @@ -92,7 +92,7 @@ void HOT Scheduler::set_timer_common_(Component *component, SchedulerItem::Type this->defer_queue_.push_back(std::move(item)); return; } -#endif +#endif /* not ESPHOME_SINGLE_CORE */ // Get fresh timestamp for new timer/interval - ensures accurate scheduling const auto now = this->millis_64_(millis()); // Fresh millis() call @@ -123,7 +123,7 @@ void HOT Scheduler::set_timer_common_(Component *component, SchedulerItem::Type ESP_LOGD(TAG, "set_%s(name='%s/%s', %s=%" PRIu32 ", offset=%" PRIu32 ")", type_str, item->get_source(), name_cstr ? name_cstr : "(null)", type_str, delay, static_cast(item->next_execution_ - now)); } -#endif +#endif /* ESPHOME_DEBUG_SCHEDULER */ LockGuard guard{this->lock_}; // If name is provided, do atomic cancel-and-add @@ -231,7 +231,7 @@ optional HOT Scheduler::next_schedule_in(uint32_t now) { return item->next_execution_ - now_64; } void HOT Scheduler::call(uint32_t now) { -#if !defined(USE_ESP8266) && !defined(USE_RP2040) +#ifndef ESPHOME_SINGLE_CORE // Process defer queue first to guarantee FIFO execution order for deferred items. // Previously, defer() used the heap which gave undefined order for equal timestamps, // causing race conditions on multi-core systems (ESP32, BK7200). @@ -239,8 +239,7 @@ void HOT Scheduler::call(uint32_t now) { // - Deferred items (delay=0) go directly to defer_queue_ in set_timer_common_ // - Items execute in exact order they were deferred (FIFO guarantee) // - No deferred items exist in to_add_, so processing order doesn't affect correctness - // ESP8266 and RP2040 don't use this queue - they fall back to the heap-based approach - // (ESP8266: single-core, RP2040: empty mutex implementation). + // Single-core platforms don't use this queue and fall back to the heap-based approach. // // Note: Items cancelled via cancel_item_locked_() are marked with remove=true but still // processed here. They are removed from the queue normally via pop_front() but skipped @@ -262,7 +261,7 @@ void HOT Scheduler::call(uint32_t now) { this->execute_item_(item.get(), now); } } -#endif +#endif /* not ESPHOME_SINGLE_CORE */ // Convert the fresh timestamp from main loop to 64-bit for scheduler operations const auto now_64 = this->millis_64_(now); // 'now' from parameter - fresh from Application::loop() @@ -274,13 +273,15 @@ void HOT Scheduler::call(uint32_t now) { if (now_64 - last_print > 2000) { last_print = now_64; std::vector> old_items; -#if !defined(USE_ESP8266) && !defined(USE_RP2040) && !defined(USE_LIBRETINY) - ESP_LOGD(TAG, "Items: count=%zu, now=%" PRIu64 " (%u, %" PRIu32 ")", this->items_.size(), now_64, - this->millis_major_, this->last_millis_.load(std::memory_order_relaxed)); -#else - ESP_LOGD(TAG, "Items: count=%zu, now=%" PRIu64 " (%u, %" PRIu32 ")", this->items_.size(), now_64, +#ifdef ESPHOME_ATOMIC_SCHEDULER + const auto last_dbg = this->last_millis_.load(std::memory_order_relaxed); + const auto major_dbg = this->millis_major_.load(std::memory_order_relaxed); + ESP_LOGD(TAG, "Items: count=%zu, now=%" PRIu64 " (%" PRIu16 ", %" PRIu32 ")", this->items_.size(), now_64, + major_dbg, last_dbg); +#else /* not ESPHOME_ATOMIC_SCHEDULER */ + ESP_LOGD(TAG, "Items: count=%zu, now=%" PRIu64 " (%" PRIu16 ", %" PRIu32 ")", this->items_.size(), now_64, this->millis_major_, this->last_millis_); -#endif +#endif /* else ESPHOME_ATOMIC_SCHEDULER */ while (!this->empty_()) { std::unique_ptr item; { @@ -305,7 +306,7 @@ void HOT Scheduler::call(uint32_t now) { std::make_heap(this->items_.begin(), this->items_.end(), SchedulerItem::cmp); } } -#endif // ESPHOME_DEBUG_SCHEDULER +#endif /* ESPHOME_DEBUG_SCHEDULER */ // If we have too many items to remove if (this->to_remove_ > MAX_LOGICALLY_DELETED_ITEMS) { @@ -352,7 +353,7 @@ void HOT Scheduler::call(uint32_t now) { ESP_LOGV(TAG, "Running %s '%s/%s' with interval=%" PRIu32 " next_execution=%" PRIu64 " (now=%" PRIu64 ")", item->get_type_str(), item->get_source(), item_name ? item_name : "(null)", item->interval, item->next_execution_, now_64); -#endif +#endif /* ESPHOME_DEBUG_SCHEDULER */ // Warning: During callback(), a lot of stuff can happen, including: // - timeouts/intervals get added, potentially invalidating vector pointers @@ -460,7 +461,7 @@ bool HOT Scheduler::cancel_item_locked_(Component *component, const char *name_c size_t total_cancelled = 0; // Check all containers for matching items -#if !defined(USE_ESP8266) && !defined(USE_RP2040) +#ifndef ESPHOME_SINGLE_CORE // Only check defer queue for timeouts (intervals never go there) if (type == SchedulerItem::TIMEOUT) { for (auto &item : this->defer_queue_) { @@ -470,7 +471,7 @@ bool HOT Scheduler::cancel_item_locked_(Component *component, const char *name_c } } } -#endif +#endif /* not ESPHOME_SINGLE_CORE */ // Cancel items in the main heap for (auto &item : this->items_) { @@ -496,7 +497,7 @@ bool HOT Scheduler::cancel_item_locked_(Component *component, const char *name_c uint64_t Scheduler::millis_64_(uint32_t now) { // THREAD SAFETY NOTE: // This function can be called from multiple threads simultaneously on ESP32/LibreTiny. - // On single-threaded platforms (ESP8266, RP2040), atomics are not needed. + // On single-core platforms, atomics are not needed. // // IMPORTANT: Always pass fresh millis() values to this function. The implementation // handles out-of-order timestamps between threads, but minimizing time differences @@ -508,99 +509,128 @@ uint64_t Scheduler::millis_64_(uint32_t now) { // This prevents race conditions at the rollover boundary without requiring // 64-bit atomics or locking on every call. +#ifdef ESPHOME_ATOMIC_SCHEDULER + for (;;) { + uint16_t major = this->millis_major_.load(std::memory_order_acquire); +#else /* not ESPHOME_ATOMIC_SCHEDULER */ + uint16_t major = this->millis_major_; +#endif /* else ESPHOME_ATOMIC_SCHEDULER */ + #ifdef USE_LIBRETINY - // LibreTiny: Multi-threaded but lacks atomic operation support - // TODO: If LibreTiny ever adds atomic support, remove this entire block and - // let it fall through to the atomic-based implementation below - // We need to use a lock when near the rollover boundary to prevent races - uint32_t last = this->last_millis_; + // LibreTiny: Multi-threaded but lacks atomic operation support + // TODO: If LibreTiny ever adds atomic support, remove this entire block and + // let it fall through to the atomic-based implementation below + // We need to use a lock when near the rollover boundary to prevent races + uint32_t last = this->last_millis_; - // Define a safe window around the rollover point (10 seconds) - // This covers any reasonable scheduler delays or thread preemption - static const uint32_t ROLLOVER_WINDOW = 10000; // 10 seconds in milliseconds + // Define a safe window around the rollover point (10 seconds) + // This covers any reasonable scheduler delays or thread preemption + static const uint32_t ROLLOVER_WINDOW = 10000; // 10 seconds in milliseconds - // Check if we're near the rollover boundary (close to std::numeric_limits::max() or just past 0) - bool near_rollover = (last > (std::numeric_limits::max() - ROLLOVER_WINDOW)) || (now < ROLLOVER_WINDOW); + // Check if we're near the rollover boundary (close to std::numeric_limits::max() or just past 0) + bool near_rollover = (last > (std::numeric_limits::max() - ROLLOVER_WINDOW)) || (now < ROLLOVER_WINDOW); - if (near_rollover || (now < last && (last - now) > HALF_MAX_UINT32)) { - // Near rollover or detected a rollover - need lock for safety - LockGuard guard{this->lock_}; - // Re-read with lock held - last = this->last_millis_; + if (near_rollover || (now < last && (last - now) > HALF_MAX_UINT32)) { + // Near rollover or detected a rollover - need lock for safety + LockGuard guard{this->lock_}; + // Re-read with lock held + last = this->last_millis_; - if (now < last && (last - now) > HALF_MAX_UINT32) { - // True rollover detected (happens every ~49.7 days) - this->millis_major_++; + if (now < last && (last - now) > HALF_MAX_UINT32) { + // True rollover detected (happens every ~49.7 days) + this->millis_major_++; + major++; #ifdef ESPHOME_DEBUG_SCHEDULER - ESP_LOGD(TAG, "Detected true 32-bit rollover at %" PRIu32 "ms (was %" PRIu32 ")", now, last); -#endif + ESP_LOGD(TAG, "Detected true 32-bit rollover at %" PRIu32 "ms (was %" PRIu32 ")", now, last); +#endif /* ESPHOME_DEBUG_SCHEDULER */ + } + // Update last_millis_ while holding lock + this->last_millis_ = now; + } else if (now > last) { + // Normal case: Not near rollover and time moved forward + // Update without lock. While this may cause minor races (microseconds of + // backwards time movement), they're acceptable because: + // 1. The scheduler operates at millisecond resolution, not microsecond + // 2. We've already prevented the critical rollover race condition + // 3. Any backwards movement is orders of magnitude smaller than scheduler delays + this->last_millis_ = now; } - // Update last_millis_ while holding lock - this->last_millis_ = now; - } else if (now > last) { - // Normal case: Not near rollover and time moved forward - // Update without lock. While this may cause minor races (microseconds of - // backwards time movement), they're acceptable because: - // 1. The scheduler operates at millisecond resolution, not microsecond - // 2. We've already prevented the critical rollover race condition - // 3. Any backwards movement is orders of magnitude smaller than scheduler delays - this->last_millis_ = now; - } - // If now <= last and we're not near rollover, don't update - // This minimizes backwards time movement + // If now <= last and we're not near rollover, don't update + // This minimizes backwards time movement -#elif !defined(USE_ESP8266) && !defined(USE_RP2040) - // Multi-threaded platforms with atomic support (ESP32) - uint32_t last = this->last_millis_.load(std::memory_order_relaxed); +#elif defined(ESPHOME_ATOMIC_SCHEDULER) + /* + * Multi-threaded platforms with atomic support (ESP32) + * Acquire so that if we later decide **not** to take the lock we still + * observe a `millis_major_` value coherent with the loaded `last_millis_`. + * The acquire load ensures any later read of `millis_major_` sees its + * corresponding increment. + */ + uint32_t last = this->last_millis_.load(std::memory_order_acquire); // If we might be near a rollover (large backwards jump), take the lock for the entire operation // This ensures rollover detection and last_millis_ update are atomic together if (now < last && (last - now) > HALF_MAX_UINT32) { // Potential rollover - need lock for atomic rollover detection + update LockGuard guard{this->lock_}; - // Re-read with lock held + // Re-read with lock held; mutex already provides ordering last = this->last_millis_.load(std::memory_order_relaxed); if (now < last && (last - now) > HALF_MAX_UINT32) { // True rollover detected (happens every ~49.7 days) - this->millis_major_++; + this->millis_major_.fetch_add(1, std::memory_order_relaxed); + major++; #ifdef ESPHOME_DEBUG_SCHEDULER ESP_LOGD(TAG, "Detected true 32-bit rollover at %" PRIu32 "ms (was %" PRIu32 ")", now, last); -#endif +#endif /* ESPHOME_DEBUG_SCHEDULER */ } - // Update last_millis_ while holding lock to prevent races - this->last_millis_.store(now, std::memory_order_relaxed); + /* + * Update last_millis_ while holding the lock to prevent races + * Publish the new low-word *after* bumping `millis_major_` (done above) + * so readers never see a mismatched pair. + */ + this->last_millis_.store(now, std::memory_order_release); } else { // Normal case: Try lock-free update, but only allow forward movement within same epoch // This prevents accidentally moving backwards across a rollover boundary while (now > last && (now - last) < HALF_MAX_UINT32) { - if (this->last_millis_.compare_exchange_weak(last, now, std::memory_order_relaxed)) { + if (this->last_millis_.compare_exchange_weak(last, now, + std::memory_order_release, // success + std::memory_order_relaxed)) { // failure break; } + // CAS failure means no data was published; relaxed is fine // last is automatically updated by compare_exchange_weak if it fails } } - -#else - // Single-threaded platforms (ESP8266, RP2040): No atomics needed +#else /* not USE_LIBRETINY; not ESPHOME_ATOMIC_SCHEDULER */ + // Single-core platforms: No atomics needed uint32_t last = this->last_millis_; // Check for rollover if (now < last && (last - now) > HALF_MAX_UINT32) { this->millis_major_++; + major++; #ifdef ESPHOME_DEBUG_SCHEDULER ESP_LOGD(TAG, "Detected true 32-bit rollover at %" PRIu32 "ms (was %" PRIu32 ")", now, last); -#endif +#endif /* ESPHOME_DEBUG_SCHEDULER */ } // Only update if time moved forward if (now > last) { this->last_millis_ = now; } -#endif +#endif /* else (USE_LIBRETINY / ESPHOME_ATOMIC_SCHEDULER) */ +#ifdef ESPHOME_ATOMIC_SCHEDULER + uint16_t major_end = this->millis_major_.load(std::memory_order_relaxed); + if (major_end == major) + return now + (static_cast(major) << 32); + } +#else /* not ESPHOME_ATOMIC_SCHEDULER */ // Combine major (high 32 bits) and now (low 32 bits) into 64-bit time - return now + (static_cast(this->millis_major_) << 32); + return now + (static_cast(major) << 32); +#endif /* ESPHOME_ATOMIC_SCHEDULER */ } bool HOT Scheduler::SchedulerItem::cmp(const std::unique_ptr &a, diff --git a/esphome/core/scheduler.h b/esphome/core/scheduler.h index 64df2f2bb0..540db3c16c 100644 --- a/esphome/core/scheduler.h +++ b/esphome/core/scheduler.h @@ -1,10 +1,11 @@ #pragma once +#include "esphome/core/defines.h" #include #include #include #include -#if !defined(USE_ESP8266) && !defined(USE_RP2040) && !defined(USE_LIBRETINY) +#ifdef ESPHOME_ATOMIC_SCHEDULER #include #endif @@ -204,22 +205,37 @@ class Scheduler { Mutex lock_; std::vector> items_; std::vector> to_add_; -#if !defined(USE_ESP8266) && !defined(USE_RP2040) - // ESP8266 and RP2040 don't need the defer queue because: - // ESP8266: Single-core with no preemptive multitasking - // RP2040: Currently has empty mutex implementation in ESPHome - // Both platforms save 40 bytes of RAM by excluding this +#ifndef ESPHOME_SINGLE_CORE + // Single-core platforms don't need the defer queue and save 40 bytes of RAM std::deque> defer_queue_; // FIFO queue for defer() calls -#endif -#if !defined(USE_ESP8266) && !defined(USE_RP2040) && !defined(USE_LIBRETINY) - // Multi-threaded platforms with atomic support: last_millis_ needs atomic for lock-free updates +#endif /* ESPHOME_SINGLE_CORE */ +#ifdef ESPHOME_ATOMIC_SCHEDULER + /* + * Multi-threaded platforms with atomic support: last_millis_ needs atomic for lock-free updates + * + * MEMORY-ORDERING NOTE + * -------------------- + * `last_millis_` and `millis_major_` form a single 64-bit timestamp split in half. + * Writers publish `last_millis_` with memory_order_release and readers use + * memory_order_acquire. This ensures that once a reader sees the new low word, + * it also observes the corresponding increment of `millis_major_`. + */ std::atomic last_millis_{0}; -#else +#else /* not ESPHOME_ATOMIC_SCHEDULER */ // Platforms without atomic support or single-threaded platforms uint32_t last_millis_{0}; -#endif - // millis_major_ is protected by lock when incrementing +#endif /* else ESPHOME_ATOMIC_SCHEDULER */ + /* + * Upper 16 bits of the 64-bit millis counter. Incremented only while holding + * `lock_`; read concurrently. Atomic (relaxed) avoids a formal data race. + * Ordering relative to `last_millis_` is provided by its release store and the + * corresponding acquire loads. + */ +#ifdef ESPHOME_ATOMIC_SCHEDULER + std::atomic millis_major_{0}; +#else /* not ESPHOME_ATOMIC_SCHEDULER */ uint16_t millis_major_{0}; +#endif /* else ESPHOME_ATOMIC_SCHEDULER */ uint32_t to_remove_{0}; };