From d00e20ccdf0b2c9e1e82424f60f3814908ac7fbf Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Thu, 3 Jul 2025 19:53:14 -0500
Subject: [PATCH] Reduce web_server loop overhead on ESP32 by avoiding
 unnecessary semaphore operations (#9308)

---
 esphome/components/web_server/web_server.cpp | 7 ++++++-
 esphome/components/web_server/web_server.h   | 2 ++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/esphome/components/web_server/web_server.cpp b/esphome/components/web_server/web_server.cpp
index 1242db57ff..f576507c0f 100644
--- a/esphome/components/web_server/web_server.cpp
+++ b/esphome/components/web_server/web_server.cpp
@@ -299,7 +299,8 @@ void WebServer::setup() {
 }
 void WebServer::loop() {
 #ifdef USE_ESP32
-  if (xSemaphoreTake(this->to_schedule_lock_, 0L)) {
+  // Check atomic flag first to avoid taking semaphore when queue is empty
+  if (this->to_schedule_has_items_.load(std::memory_order_relaxed) && xSemaphoreTake(this->to_schedule_lock_, 0L)) {
     std::function<void()> fn;
     if (!to_schedule_.empty()) {
       // scheduler execute things out of order which may lead to incorrect state
@@ -307,6 +308,9 @@ void WebServer::loop() {
       // let's execute it directly from the loop
       fn = std::move(to_schedule_.front());
       to_schedule_.pop_front();
+      if (to_schedule_.empty()) {
+        this->to_schedule_has_items_.store(false, std::memory_order_relaxed);
+      }
     }
     xSemaphoreGive(this->to_schedule_lock_);
     if (fn) {
@@ -2061,6 +2065,7 @@ void WebServer::schedule_(std::function<void()> &&f) {
 #ifdef USE_ESP32
   xSemaphoreTake(this->to_schedule_lock_, portMAX_DELAY);
   to_schedule_.push_back(std::move(f));
+  this->to_schedule_has_items_.store(true, std::memory_order_relaxed);
   xSemaphoreGive(this->to_schedule_lock_);
 #else
   this->defer(std::move(f));
diff --git a/esphome/components/web_server/web_server.h b/esphome/components/web_server/web_server.h
index 5f175b6bdd..c654d83bbd 100644
--- a/esphome/components/web_server/web_server.h
+++ b/esphome/components/web_server/web_server.h
@@ -18,6 +18,7 @@
 #include <freertos/FreeRTOS.h>
 #include <freertos/semphr.h>
 #include <deque>
+#include <atomic>
 #endif
 
 #if USE_WEBSERVER_VERSION >= 2
@@ -524,6 +525,7 @@ class WebServer : public Controller, public Component, public AsyncWebHandler {
 #ifdef USE_ESP32
   std::deque<std::function<void()>> to_schedule_;
   SemaphoreHandle_t to_schedule_lock_;
+  std::atomic<bool> to_schedule_has_items_{false};
 #endif
 };