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Code Issues Releases Wiki Activity

Fix scheduler rollover detection with concurrent task calls (#9624)

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This commit is contained in:
J. Nick Koston
2025-07-17 13:07:36 -10:00
committed by GitHub
parent 7f807e08b1
commit dfa8c8c77f
2 changed files with 88 additions and 9 deletions
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82
esphome/core/scheduler.cpp
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@@ -14,6 +14,8 @@ namespace esphome {
static const char *const TAG = "scheduler";
static const uint32_t MAX_LOGICALLY_DELETED_ITEMS = 10;
// Half the 32-bit range - used to detect rollovers vs normal time progression
static const uint32_t HALF_MAX_UINT32 = 0x80000000UL;
// Uncomment to debug scheduler
// #define ESPHOME_DEBUG_SCHEDULER
@@ -91,7 +93,8 @@ void HOT Scheduler::set_timer_common_(Component *component, SchedulerItem::Type
}
#endif
const auto now = this->millis_64_(millis());
// Get fresh timestamp for new timer/interval - ensures accurate scheduling
const auto now = this->millis_64_(millis()); // Fresh millis() call
// Type-specific setup
if (type == SchedulerItem::INTERVAL) {
@@ -220,7 +223,8 @@ optional<uint32_t> HOT Scheduler::next_schedule_in(uint32_t now) {
if (this->empty_())
return {};
auto &item = this->items_[0];
const auto now_64 = this->millis_64_(now);
// Convert the fresh timestamp from caller (usually Application::loop()) to 64-bit
const auto now_64 = this->millis_64_(now); // 'now' from parameter - fresh from caller
if (item->next_execution_ < now_64)
return 0;
return item->next_execution_ - now_64;
@@ -259,7 +263,8 @@ void HOT Scheduler::call(uint32_t now) {
}
#endif
const auto now_64 = this->millis_64_(now);
// 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()
this->process_to_add();
#ifdef ESPHOME_DEBUG_SCHEDULER
@@ -268,8 +273,13 @@ void HOT Scheduler::call(uint32_t now) {
if (now_64 - last_print > 2000) {
last_print = now_64;
std::vector<std::unique_ptr<SchedulerItem>> old_items;
#if !defined(USE_ESP8266) && !defined(USE_RP2040)
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,
this->millis_major_, this->last_millis_);
#endif
while (!this->empty_()) {
std::unique_ptr<SchedulerItem> item;
{
@@ -483,16 +493,70 @@ bool HOT Scheduler::cancel_item_locked_(Component *component, const char *name_c
}
uint64_t Scheduler::millis_64_(uint32_t now) {
// Check for rollover by comparing with last value
if (now < this->last_millis_) {
// Detected rollover (happens every ~49.7 days)
// 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.
//
// IMPORTANT: Always pass fresh millis() values to this function. The implementation
// handles out-of-order timestamps between threads, but minimizing time differences
// helps maintain accuracy.
//
// The implementation handles the 32-bit rollover (every 49.7 days) by:
// 1. Using a lock when detecting rollover to ensure atomic update
// 2. Restricting normal updates to forward movement within the same epoch
// This prevents race conditions at the rollover boundary without requiring
// 64-bit atomics or locking on every call.
#if !defined(USE_ESP8266) && !defined(USE_RP2040)
// Multi-threaded platforms: Need to handle rollover carefully
uint32_t last = this->last_millis_.load(std::memory_order_relaxed);
// 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
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_++;
#ifdef ESPHOME_DEBUG_SCHEDULER
ESP_LOGD(TAG, "Detected true 32-bit rollover at %" PRIu32 "ms (was %" PRIu32 ")", now, last);
#endif
}
// Update last_millis_ while holding lock to prevent races
this->last_millis_.store(now, std::memory_order_relaxed);
} 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)) {
break;
}
// last is automatically updated by compare_exchange_weak if it fails
}
}
#else
// Single-threaded platforms: No atomics needed
uint32_t last = this->last_millis_;
// Check for rollover
if (now < last && (last - now) > HALF_MAX_UINT32) {
this->millis_major_++;
#ifdef ESPHOME_DEBUG_SCHEDULER
ESP_LOGD(TAG, "Incrementing scheduler major at %" PRIu64 "ms",
now + (static_cast<uint64_t>(this->millis_major_) << 32));
ESP_LOGD(TAG, "Detected true 32-bit rollover at %" PRIu32 "ms (was %" PRIu32 ")", now, last);
#endif
}
this->last_millis_ = now;
// Only update if time moved forward
if (now > last) {
this->last_millis_ = now;
}
#endif
// Combine major (high 32 bits) and now (low 32 bits) into 64-bit time
return now + (static_cast<uint64_t>(this->millis_major_) << 32);
}