guard esp8266

esphome/core/scheduler.cpp

@@ -83,6 +83,7 @@ void HOT Scheduler::set_timer_common_(Component *component, SchedulerItem::Type
 
 #ifndef USE_ESP8266
   // Special handling for defer() (delay = 0, type = TIMEOUT)
+  // ESP8266 is excluded because it doesn't need thread-safe defer handling
   if (delay == 0 && type == SchedulerItem::TIMEOUT) {
     // Put in defer queue for guaranteed FIFO execution
     LockGuard guard{this->lock_};
@@ -227,6 +228,8 @@ void HOT Scheduler::call() {
   // - 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 doesn't use this queue - it falls back to the heap-based approach since
+  // it's single-core and doesn't have thread safety concerns.
   while (!this->defer_queue_.empty()) {
     // IMPORTANT: The double-check pattern is REQUIRED for thread safety:
     // 1. First check: !defer_queue_.empty() without lock (may become stale)
@@ -437,6 +440,7 @@ bool HOT Scheduler::cancel_item_common_(Component *component, bool is_static_str
 
   // Check all containers for matching items
 #ifndef USE_ESP8266
+  // Only check defer_queue_ on platforms that have it
   for (auto &item : this->defer_queue_) {
     if (this->matches_item_(item, component, name_cstr, type)) {
       item->remove = true;

esphome/core/scheduler.h

@@ -167,6 +167,11 @@ class Scheduler {
   std::vector<std::unique_ptr<SchedulerItem>> items_;
   std::vector<std::unique_ptr<SchedulerItem>> to_add_;
 #ifndef USE_ESP8266
+  // ESP8266 doesn't need the defer queue because:
+  // 1. It's single-core with no preemptive multitasking
+  // 2. All code runs in a single thread context
+  // 3. defer() calls can't have race conditions without true concurrency
+  // 4. Saves 40 bytes of RAM on memory-constrained ESP8266 devices
   std::deque<std::unique_ptr<SchedulerItem>> defer_queue_;  // FIFO queue for defer() calls
 #endif
   uint32_t last_millis_{0};