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explain why its safe

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This commit is contained in:
J. Nick Koston
2025-09-03 16:34:47 -05:00
parent d505f5ecaa
commit ca0029e002
1 changed files with 13 additions and 6 deletions
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19
esphome/core/scheduler.h
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@@ -94,13 +94,15 @@ class Scheduler {
char *dynamic_name; // For allocated strings char *dynamic_name; // For allocated strings
} name_; } name_;
uint32_t interval; uint32_t interval;
// Split 64-bit time to handle millis() rollover. The scheduler combines the 32-bit millis() // Split time to handle millis() rollover. The scheduler combines the 32-bit millis()
// with a 16-bit rollover counter to create a 64-bit time that won't roll over for // with a 16-bit rollover counter to create a 48-bit time space (stored as 64-bit
// billions of years. This ensures correct scheduling even when devices run for months. // for compatibility). With 49.7 days per 32-bit rollover, the 16-bit counter
// Split into two fields for better memory alignment on 32-bit systems. // supports 49.7 days × 65536 = ~8900 years. This ensures correct scheduling
uint32_t next_execution_low_; // Lower 32 bits of next execution time // even when devices run for months. Split into two fields for better memory
// alignment on 32-bit systems.
uint32_t next_execution_low_; // Lower 32 bits of execution time (millis value)
std::function<void()> callback; std::function<void()> callback;
uint16_t next_execution_high_; // Upper 16 bits of next execution time uint16_t next_execution_high_; // Upper 16 bits (millis_major counter)
#ifdef ESPHOME_THREAD_MULTI_ATOMICS #ifdef ESPHOME_THREAD_MULTI_ATOMICS
// Multi-threaded with atomics: use atomic for lock-free access // Multi-threaded with atomics: use atomic for lock-free access
@@ -186,12 +188,17 @@ class Scheduler {
static bool cmp(const std::unique_ptr<SchedulerItem> &a, const std::unique_ptr<SchedulerItem> &b); static bool cmp(const std::unique_ptr<SchedulerItem> &a, const std::unique_ptr<SchedulerItem> &b);
// Helper methods to work with split execution time (constexpr for optimization) // Helper methods to work with split execution time (constexpr for optimization)
// Note: We use 48 bits total (32 + 16), stored in a 64-bit value for API compatibility.
// The upper 16 bits of the 64-bit value are always zero, which is fine since
// millis_major_ is also 16 bits and they must match.
constexpr uint64_t get_next_execution() const { constexpr uint64_t get_next_execution() const {
return (static_cast<uint64_t>(next_execution_high_) << 32) | next_execution_low_; return (static_cast<uint64_t>(next_execution_high_) << 32) | next_execution_low_;
} }
constexpr void set_next_execution(uint64_t value) { constexpr void set_next_execution(uint64_t value) {
next_execution_low_ = static_cast<uint32_t>(value); next_execution_low_ = static_cast<uint32_t>(value);
// Cast to uint16_t intentionally truncates to lower 16 bits of the upper 32 bits.
// This is correct because millis_major_ that creates these values is also 16 bits.
next_execution_high_ = static_cast<uint16_t>(value >> 32); next_execution_high_ = static_cast<uint16_t>(value >> 32);
} }
constexpr const char *get_type_str() const { return (type == TIMEOUT) ? "timeout" : "interval"; } constexpr const char *get_type_str() const { return (type == TIMEOUT) ? "timeout" : "interval"; }