[core] Fix scheduler race condition where cancelled items still execute (#10268)

esphome/core/scheduler.h

@@ -97,22 +97,42 @@ class Scheduler {
 
     std::function<void()> callback;
 
-    // Bit-packed fields to minimize padding
+#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};
+
+    // Bit-packed fields (3 bits used, 5 bits padding in 1 byte)
+    enum Type : uint8_t { TIMEOUT, INTERVAL } type : 1;
+    bool name_is_dynamic : 1;  // True if name was dynamically allocated (needs delete[])
+    bool is_retry : 1;         // True if this is a retry timeout
+                               // 5 bits padding
+#else
+    // Single-threaded or multi-threaded without atomics: can pack all fields together
+    // Bit-packed fields (4 bits used, 4 bits padding in 1 byte)
     enum Type : uint8_t { TIMEOUT, INTERVAL } type : 1;
     bool remove : 1;
     bool name_is_dynamic : 1;  // True if name was dynamically allocated (needs delete[])
     bool is_retry : 1;         // True if this is a retry timeout
-    // 4 bits padding
+                               // 4 bits padding
+#endif
 
     // Constructor
     SchedulerItem()
         : component(nullptr),
           interval(0),
           next_execution_(0),
+#ifdef ESPHOME_THREAD_MULTI_ATOMICS
+          // remove is initialized in the member declaration as std::atomic<bool>{false}
+          type(TIMEOUT),
+          name_is_dynamic(false),
+          is_retry(false) {
+#else
           type(TIMEOUT),
           remove(false),
           name_is_dynamic(false),
           is_retry(false) {
+#endif
       name_.static_name = nullptr;
     }
 
@@ -219,6 +239,37 @@ class Scheduler {
     return item->remove || (item->component != nullptr && item->component->is_failed());
   }
 
+  // Helper to check if item is marked for removal (platform-specific)
+  // Returns true if item should be skipped, handles platform-specific synchronization
+  // For ESPHOME_THREAD_MULTI_NO_ATOMICS platforms, the caller must hold the scheduler lock before calling this
+  // function.
+  bool is_item_removed_(SchedulerItem *item) const {
+#ifdef ESPHOME_THREAD_MULTI_ATOMICS
+    // Multi-threaded with atomics: use atomic load for lock-free access
+    return item->remove.load(std::memory_order_acquire);
+#else
+    // Single-threaded (ESPHOME_THREAD_SINGLE) or
+    // multi-threaded without atomics (ESPHOME_THREAD_MULTI_NO_ATOMICS): direct read
+    // For ESPHOME_THREAD_MULTI_NO_ATOMICS, caller MUST hold lock!
+    return item->remove;
+#endif
+  }
+
+  // Helper to mark item for removal (platform-specific)
+  // For ESPHOME_THREAD_MULTI_NO_ATOMICS platforms, the caller must hold the scheduler lock before calling this
+  // function.
+  void mark_item_removed_(SchedulerItem *item) {
+#ifdef ESPHOME_THREAD_MULTI_ATOMICS
+    // Multi-threaded with atomics: use atomic store
+    item->remove.store(true, std::memory_order_release);
+#else
+    // Single-threaded (ESPHOME_THREAD_SINGLE) or
+    // multi-threaded without atomics (ESPHOME_THREAD_MULTI_NO_ATOMICS): direct write
+    // For ESPHOME_THREAD_MULTI_NO_ATOMICS, caller MUST hold lock!
+    item->remove = true;
+#endif
+  }
+
   // Template helper to check if any item in a container matches our criteria
   template<typename Container>
   bool has_cancelled_timeout_in_container_(const Container &container, Component *component, const char *name_cstr,