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TienHuyIoTmathieucarbou
TienHuyIoT
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mathieucarbou
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Fix SSE
- Avoid self-deadlock by using recursive mutex. - Create a new example for the pull request #156
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-13
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3 files changed

+159
-13
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‎examples/ServerSentEvents_PR156/ServerSentEvents_PR156.ino

Lines changed: 141 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,141 @@
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// SPDX-License-Identifier: LGPL-3.0-or-later
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// Copyright 2016-2025 Hristo Gochkov, Mathieu Carbou, Emil Muratov
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//
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// SSE example
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//
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#include <Arduino.h>
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#ifdef ESP32
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#include <AsyncTCP.h>
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#include <WiFi.h>
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#elif defined(ESP8266)
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#include <ESP8266WiFi.h>
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#include <ESPAsyncTCP.h>
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#elif defined(TARGET_RP2040) || defined(TARGET_RP2350) || defined(PICO_RP2040) || defined(PICO_RP2350)
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#include <RPAsyncTCP.h>
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#include <WiFi.h>
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#endif
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#include <ESPAsyncWebServer.h>
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static const char *htmlContent PROGMEM = R"(
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<!DOCTYPE html>
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<html>
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<head>
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<title>Server-Sent Events</title>
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<script>
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if (!!window.EventSource) {
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var source = new EventSource('/events');
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source.onopen = function(e) {
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console.log("Events Connected");
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};
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source.onerror = function(e) {
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if (e.target.readyState != EventSource.OPEN) {
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console.log("Events Disconnected");
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}
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// Uncomment below to prevent the client from proactively establishing a new connection.
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// source.close();
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};
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source.onmessage = function(e) {
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console.log("Message: " + e.data);
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};
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source.addEventListener('heartbeat', function(e) {
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console.log("Heartbeat", e.data);
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}, false);
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}
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</script>
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</head>
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<body>
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<h1>Open your browser console!</h1>
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</body>
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</html>
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)";
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static const size_t htmlContentLength = strlen_P(htmlContent);
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static AsyncWebServer server(80);
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static AsyncEventSource events("/events");
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static volatile size_t connectionCount = 0;
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static volatile uint32_t timestampConnected = 0;
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static constexpr uint32_t timeoutClose = 15000;
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void setup() {
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Serial.begin(115200);
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#ifndef CONFIG_IDF_TARGET_ESP32H2
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WiFi.mode(WIFI_AP);
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WiFi.softAP("esp-captive");
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#endif
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// curl -v http://192.168.4.1/
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server.on("/", HTTP_GET, [](AsyncWebServerRequest *request) {
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// need to cast to uint8_t*
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// if you do not, the const char* will be copied in a temporary String buffer
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request->send(200, "text/html", (uint8_t *)htmlContent, htmlContentLength);
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});
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events.onConnect([](AsyncEventSourceClient *client) {
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/**
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* @brief: Purpose for a test case: count() function
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* Task watchdog shall be triggered due to a self-deadlock by mutex handling of the AsyncEventSource.
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*
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* E (61642) task_wdt: Task watchdog got triggered. The following tasks did not reset the watchdog in time:
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* E (61642) task_wdt: - async_tcp (CPU 0/1)
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*
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* Resolve: using recursive_mutex insteads of mutex.
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*/
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connectionCount = events.count();
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timestampConnected = millis();
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Serial.printf("SSE Client connected! ID: %" PRIu32 "\n", client->lastId());
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client->send("hello!", NULL, millis(), 1000);
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Serial.printf("Number of connected clients: %u\n", connectionCount);
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});
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events.onDisconnect([](AsyncEventSourceClient *client) {
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connectionCount = events.count();
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Serial.printf("SSE Client disconnected! ID: %" PRIu32 "\n", client->lastId());
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Serial.printf("Number of connected clients: %u\n", connectionCount);
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});
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server.addHandler(&events);
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server.begin();
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}
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static constexpr uint32_t deltaSSE = 3000;
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static uint32_t lastSSE = 0;
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static uint32_t lastHeap = 0;
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void loop() {
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uint32_t now = millis();
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if (connectionCount > 0) {
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if (now - lastSSE >= deltaSSE) {
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events.send(String("ping-") + now, "heartbeat", now);
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lastSSE = millis();
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}
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/**
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* @brief: Purpose for a test case: close() function
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* Task watchdog shall be triggered due to a self-deadlock by mutex handling of the AsyncEventSource.
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*
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* E (61642) task_wdt: Task watchdog got triggered. The following tasks did not reset the watchdog in time:
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* E (61642) task_wdt: - async_tcp (CPU 0/1)
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*
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* Resolve: using recursive_mutex insteads of mutex.
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*/
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if (now - timestampConnected >= timeoutClose) {
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Serial.printf("SSE Clients close\n");
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events.close();
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}
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}
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#ifdef ESP32
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if (now - lastHeap >= 2000) {
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Serial.printf("Free heap: %" PRIu32 "\n", ESP.getFreeHeap());
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lastHeap = now;
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}
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#endif
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}

‎src/AsyncEventSource.cpp

Lines changed: 16 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -193,7 +193,7 @@ AsyncEventSourceClient::AsyncEventSourceClient(AsyncWebServerRequest *request, A
193193

194194
AsyncEventSourceClient::~AsyncEventSourceClient() {
195195
#ifdef ESP32
196-
std::lock_guard<std::mutex> lock(_lockmq);
196+
std::lock_guard<std::recursive_mutex> lock(_lockmq);
197197
#endif
198198
_messageQueue.clear();
199199
close();
@@ -211,7 +211,7 @@ bool AsyncEventSourceClient::_queueMessage(const char *message, size_t len) {
211211

212212
#ifdef ESP32
213213
// length() is not thread-safe, thus acquiring the lock before this call..
214-
std::lock_guard<std::mutex> lock(_lockmq);
214+
std::lock_guard<std::recursive_mutex> lock(_lockmq);
215215
#endif
216216

217217
_messageQueue.emplace_back(message, len);
@@ -241,7 +241,7 @@ bool AsyncEventSourceClient::_queueMessage(AsyncEvent_SharedData_t &&msg) {
241241

242242
#ifdef ESP32
243243
// length() is not thread-safe, thus acquiring the lock before this call..
244-
std::lock_guard<std::mutex> lock(_lockmq);
244+
std::lock_guard<std::recursive_mutex> lock(_lockmq);
245245
#endif
246246

247247
_messageQueue.emplace_back(std::move(msg));
@@ -261,7 +261,7 @@ bool AsyncEventSourceClient::_queueMessage(AsyncEvent_SharedData_t &&msg) {
261261
void AsyncEventSourceClient::_onAck(size_t len __attribute__((unused)), uint32_t time __attribute__((unused))) {
262262
#ifdef ESP32
263263
// Same here, acquiring the lock early
264-
std::lock_guard<std::mutex> lock(_lockmq);
264+
std::lock_guard<std::recursive_mutex> lock(_lockmq);
265265
#endif
266266

267267
// adjust in-flight len
@@ -290,7 +290,7 @@ void AsyncEventSourceClient::_onPoll() {
290290
if (_messageQueue.size()) {
291291
#ifdef ESP32
292292
// Same here, acquiring the lock early
293-
std::lock_guard<std::mutex> lock(_lockmq);
293+
std::lock_guard<std::recursive_mutex> lock(_lockmq);
294294
#endif
295295
_runQueue();
296296
}
@@ -367,7 +367,7 @@ void AsyncEventSource::_addClient(AsyncEventSourceClient *client) {
367367
return;
368368
}
369369
#ifdef ESP32
370-
std::lock_guard<std::mutex> lock(_client_queue_lock);
370+
std::lock_guard<std::recursive_mutex> lock(_client_queue_lock);
371371
#endif
372372
_clients.emplace_back(client);
373373
if (_connectcb) {
@@ -382,7 +382,7 @@ void AsyncEventSource::_handleDisconnect(AsyncEventSourceClient *client) {
382382
_disconnectcb(client);
383383
}
384384
#ifdef ESP32
385-
std::lock_guard<std::mutex> lock(_client_queue_lock);
385+
std::lock_guard<std::recursive_mutex> lock(_client_queue_lock);
386386
#endif
387387
for (auto i = _clients.begin(); i != _clients.end(); ++i) {
388388
if (i->get() == client) {
@@ -398,10 +398,15 @@ void AsyncEventSource::close() {
398398
// iterator should remain valid even when AsyncEventSource::_handleDisconnect()
399399
// is called very early
400400
#ifdef ESP32
401-
std::lock_guard<std::mutex> lock(_client_queue_lock);
401+
std::lock_guard<std::recursive_mutex> lock(_client_queue_lock);
402402
#endif
403403
for (const auto &c : _clients) {
404404
if (c->connected()) {
405+
/**
406+
* @brief: Fix self-deadlock by using recursive_mutex instead.
407+
* Due to c->close() shall call the callback function _onDisconnect()
408+
* The calling flow _onDisconnect() --> _handleDisconnect() --> deadlock
409+
*/
405410
c->close();
406411
}
407412
}
@@ -412,7 +417,7 @@ size_t AsyncEventSource::avgPacketsWaiting() const {
412417
size_t aql = 0;
413418
uint32_t nConnectedClients = 0;
414419
#ifdef ESP32
415-
std::lock_guard<std::mutex> lock(_client_queue_lock);
420+
std::lock_guard<std::recursive_mutex> lock(_client_queue_lock);
416421
#endif
417422
if (!_clients.size()) {
418423
return 0;
@@ -430,7 +435,7 @@ size_t AsyncEventSource::avgPacketsWaiting() const {
430435
AsyncEventSource::SendStatus AsyncEventSource::send(const char *message, const char *event, uint32_t id, uint32_t reconnect) {
431436
AsyncEvent_SharedData_t shared_msg = std::make_shared<String>(generateEventMessage(message, event, id, reconnect));
432437
#ifdef ESP32
433-
std::lock_guard<std::mutex> lock(_client_queue_lock);
438+
std::lock_guard<std::recursive_mutex> lock(_client_queue_lock);
434439
#endif
435440
size_t hits = 0;
436441
size_t miss = 0;
@@ -446,7 +451,7 @@ AsyncEventSource::SendStatus AsyncEventSource::send(const char *message, const c
446451

447452
size_t AsyncEventSource::count() const {
448453
#ifdef ESP32
449-
std::lock_guard<std::mutex> lock(_client_queue_lock);
454+
std::lock_guard<std::recursive_mutex> lock(_client_queue_lock);
450455
#endif
451456
size_t n_clients{0};
452457
for (const auto &i : _clients) {

‎src/AsyncEventSource.h

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -129,7 +129,7 @@ class AsyncEventSourceClient {
129129
size_t _max_inflight{SSE_MAX_INFLIGH}; // max num of unacknowledged bytes that could be written to socket buffer
130130
std::list<AsyncEventSourceMessage> _messageQueue;
131131
#ifdef ESP32
132-
mutable std::mutex _lockmq;
132+
mutable std::recursive_mutex _lockmq;
133133
#endif
134134
bool _queueMessage(const char *message, size_t len);
135135
bool _queueMessage(AsyncEvent_SharedData_t &&msg);
@@ -230,7 +230,7 @@ class AsyncEventSource : public AsyncWebHandler {
230230
#ifdef ESP32
231231
// Same as for individual messages, protect mutations of _clients list
232232
// since simultaneous access from different tasks is possible
233-
mutable std::mutex _client_queue_lock;
233+
mutable std::recursive_mutex _client_queue_lock;
234234
#endif
235235
ArEventHandlerFunction _connectcb = nullptr;
236236
ArEventHandlerFunction _disconnectcb = nullptr;

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