added note about deadlock to all examples

README.md

@@ -71,14 +71,19 @@ void connect() {
 
 void messageReceived(String &topic, String &payload) {
   Serial.println("incoming: " + topic + " - " + payload);
+
+  // Note: Do not use the client in the callback to publish, subscribe or
+  // unsubscribe as it may cause deadlocks when other things arrive while
+  // sending and receiving acknowledgments. Instead, change a global variable,
+  // or push to a queue and handle it in the loop after calling `client.loop()`.
 }
 
 void setup() {
   Serial.begin(115200);
   WiFi.begin(ssid, pass);
 
-  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported by Arduino.
-  // You need to set the IP address directly.
+  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported
+  // by Arduino. You need to set the IP address directly.
   client.begin("broker.shiftr.io", net);
   client.onMessage(messageReceived);
 

examples/AdafruitHuzzahESP8266/AdafruitHuzzahESP8266.ino

@@ -39,14 +39,19 @@ void connect() {
 
 void messageReceived(String &topic, String &payload) {
   Serial.println("incoming: " + topic + " - " + payload);
+
+  // Note: Do not use the client in the callback to publish, subscribe or
+  // unsubscribe as it may cause deadlocks when other things arrive while
+  // sending and receiving acknowledgments. Instead, change a global variable,
+  // or push to a queue and handle it in the loop after calling `client.loop()`.
 }
 
 void setup() {
   Serial.begin(115200);
   WiFi.begin(ssid, pass);
 
-  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported by Arduino.
-  // You need to set the IP address directly.
+  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported
+  // by Arduino. You need to set the IP address directly.
   client.begin("broker.shiftr.io", net);
   client.onMessage(messageReceived);
 

examples/AdafruitHuzzahESP8266Secure/AdafruitHuzzahESP8266Secure.ino

@@ -44,14 +44,19 @@ void connect() {
 
 void messageReceived(String &topic, String &payload) {
   Serial.println("incoming: " + topic + " - " + payload);
+
+  // Note: Do not use the client in the callback to publish, subscribe or
+  // unsubscribe as it may cause deadlocks when other things arrive while
+  // sending and receiving acknowledgments. Instead, change a global variable,
+  // or push to a queue and handle it in the loop after calling `client.loop()`.
 }
 
 void setup() {
   Serial.begin(115200);
   WiFi.begin(ssid, pass);
 
-  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported by Arduino.
-  // You need to set the IP address directly.
+  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported
+  // by Arduino. You need to set the IP address directly.
   //
   // MQTT brokers usually use port 8883 for secure connections.
   client.begin("broker.shiftr.io", 8883, net);

examples/ArduinoEthernetShield/ArduinoEthernetShield.ino

@@ -33,14 +33,19 @@ void connect() {
 
 void messageReceived(String &topic, String &payload) {
   Serial.println("incoming: " + topic + " - " + payload);
+
+  // Note: Do not use the client in the callback to publish, subscribe or
+  // unsubscribe as it may cause deadlocks when other things arrive while
+  // sending and receiving acknowledgments. Instead, change a global variable,
+  // or push to a queue and handle it in the loop after calling `client.loop()`.
 }
 
 void setup() {
   Serial.begin(115200);
   Ethernet.begin(mac, ip);
 
-  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported by Arduino.
-  // You need to set the IP address directly.
+  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported
+  // by Arduino. You need to set the IP address directly.
   client.begin("broker.shiftr.io", net);
   client.onMessage(messageReceived);
 

examples/ArduinoMKRGSM1400/ArduinoMKRGSM1400.ino

@@ -56,13 +56,18 @@ void connect() {
 
 void messageReceived(String &topic, String &payload) {
   Serial.println("incoming: " + topic + " - " + payload);
+
+  // Note: Do not use the client in the callback to publish, subscribe or
+  // unsubscribe as it may cause deadlocks when other things arrive while
+  // sending and receiving acknowledgments. Instead, change a global variable,
+  // or push to a queue and handle it in the loop after calling `client.loop()`.
 }
 
 void setup() {
   Serial.begin(115200);
 
-  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported by Arduino.
-  // You need to set the IP address directly.
+  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported
+  // by Arduino. You need to set the IP address directly.
   client.begin("broker.shiftr.io", net);
   client.onMessage(messageReceived);
 

examples/ArduinoMKRGSM1400Secure/ArduinoMKRGSM1400Secure.ino

@@ -56,13 +56,18 @@ void connect() {
 
 void messageReceived(String &topic, String &payload) {
   Serial.println("incoming: " + topic + " - " + payload);
+
+  // Note: Do not use the client in the callback to publish, subscribe or
+  // unsubscribe as it may cause deadlocks when other things arrive while
+  // sending and receiving acknowledgments. Instead, change a global variable,
+  // or push to a queue and handle it in the loop after calling `client.loop()`.
 }
 
 void setup() {
   Serial.begin(115200);
 
-  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported by Arduino.
-  // You need to set the IP address directly.
+  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported
+  // by Arduino. You need to set the IP address directly.
   //
   // MQTT brokers usually use port 8883 for secure connections.
   client.begin("broker.shiftr.io", 8883, net);

examples/ArduinoWiFi101/ArduinoWiFi101.ino

@@ -41,14 +41,19 @@ void connect() {
 
 void messageReceived(String &topic, String &payload) {
   Serial.println("incoming: " + topic + " - " + payload);
+
+  // Note: Do not use the client in the callback to publish, subscribe or
+  // unsubscribe as it may cause deadlocks when other things arrive while
+  // sending and receiving acknowledgments. Instead, change a global variable,
+  // or push to a queue and handle it in the loop after calling `client.loop()`.
 }
 
 void setup() {
   Serial.begin(115200);
   WiFi.begin(ssid, pass);
 
-  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported by Arduino.
-  // You need to set the IP address directly.
+  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported
+  // by Arduino. You need to set the IP address directly.
   client.begin("broker.shiftr.io", net);
   client.onMessage(messageReceived);
 

examples/ArduinoWiFi101Secure/ArduinoWiFi101Secure.ino

@@ -44,14 +44,19 @@ void connect() {
 
 void messageReceived(String &topic, String &payload) {
   Serial.println("incoming: " + topic + " - " + payload);
+
+  // Note: Do not use the client in the callback to publish, subscribe or
+  // unsubscribe as it may cause deadlocks when other things arrive while
+  // sending and receiving acknowledgments. Instead, change a global variable,
+  // or push to a queue and handle it in the loop after calling `client.loop()`.
 }
 
 void setup() {
   Serial.begin(115200);
   WiFi.begin(ssid, pass);
 
-  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported by Arduino.
-  // You need to set the IP address directly.
+  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported
+  // by Arduino. You need to set the IP address directly.
   //
   // MQTT brokers usually use port 8883 for secure connections.
   client.begin("broker.shiftr.io", 8883, net);

examples/ArduinoWiFiShield/ArduinoWiFiShield.ino

@@ -39,14 +39,19 @@ void connect() {
 
 void messageReceived(String &topic, String &payload) {
   Serial.println("incoming: " + topic + " - " + payload);
+
+  // Note: Do not use the client in the callback to publish, subscribe or
+  // unsubscribe as it may cause deadlocks when other things arrive while
+  // sending and receiving acknowledgments. Instead, change a global variable,
+  // or push to a queue and handle it in the loop after calling `client.loop()`.
 }
 
 void setup() {
   Serial.begin(115200);
   WiFi.begin(ssid, pass);
 
-  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported by Arduino.
-  // You need to set the IP address directly.
+  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported
+  // by Arduino. You need to set the IP address directly.
   client.begin("broker.shiftr.io", net);
   client.onMessage(messageReceived);
 

examples/ArduinoYun/ArduinoYun.ino

@@ -31,14 +31,19 @@ void connect() {
 
 void messageReceived(String &topic, String &payload) {
   Serial.println("incoming: " + topic + " - " + payload);
+
+  // Note: Do not use the client in the callback to publish, subscribe or
+  // unsubscribe as it may cause deadlocks when other things arrive while
+  // sending and receiving acknowledgments. Instead, change a global variable,
+  // or push to a queue and handle it in the loop after calling `client.loop()`.
 }
 
 void setup() {
   Bridge.begin();
   Serial.begin(115200);
 
-  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported by Arduino.
-  // You need to set the IP address directly.
+  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported
+  // by Arduino. You need to set the IP address directly.
   client.begin("broker.shiftr.io", net);
   client.onMessage(messageReceived);
 

examples/ArduinoYunSecure/ArduinoYunSecure.ino

@@ -31,14 +31,19 @@ void connect() {
 
 void messageReceived(String &topic, String &payload) {
   Serial.println("incoming: " + topic + " - " + payload);
+
+  // Note: Do not use the client in the callback to publish, subscribe or
+  // unsubscribe as it may cause deadlocks when other things arrive while
+  // sending and receiving acknowledgments. Instead, change a global variable,
+  // or push to a queue and handle it in the loop after calling `client.loop()`.
 }
 
 void setup() {
   Bridge.begin();
   Serial.begin(115200);
 
-  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported by Arduino.
-  // You need to set the IP address directly.
+  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported
+  // by Arduino. You need to set the IP address directly.
   //
   // MQTT brokers usually use port 8883 for secure connections.
   client.begin("broker.shiftr.io", 8883, net);

examples/ESP32DevelopmentBoard/ESP32DevelopmentBoard.ino

@@ -39,14 +39,19 @@ void connect() {
 
 void messageReceived(String &topic, String &payload) {
   Serial.println("incoming: " + topic + " - " + payload);
+
+  // Note: Do not use the client in the callback to publish, subscribe or
+  // unsubscribe as it may cause deadlocks when other things arrive while
+  // sending and receiving acknowledgments. Instead, change a global variable,
+  // or push to a queue and handle it in the loop after calling `client.loop()`.
 }
 
 void setup() {
   Serial.begin(115200);
   WiFi.begin(ssid, pass);
 
-  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported by Arduino.
-  // You need to set the IP address directly.
+  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported
+  // by Arduino. You need to set the IP address directly.
   client.begin("broker.shiftr.io", net);
   client.onMessage(messageReceived);
 

examples/ESP32DevelopmentBoardSecure/ESP32DevelopmentBoardSecure.ino

@@ -39,14 +39,19 @@ void connect() {
 
 void messageReceived(String &topic, String &payload) {
   Serial.println("incoming: " + topic + " - " + payload);
+
+  // Note: Do not use the client in the callback to publish, subscribe or
+  // unsubscribe as it may cause deadlocks when other things arrive while
+  // sending and receiving acknowledgments. Instead, change a global variable,
+  // or push to a queue and handle it in the loop after calling `client.loop()`.
 }
 
 void setup() {
   Serial.begin(115200);
   WiFi.begin(ssid, pass);
 
-  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported by Arduino.
-  // You need to set the IP address directly.
+  // Note: Local domain names (e.g. "Computer.local" on OSX) are not supported
+  // by Arduino. You need to set the IP address directly.
   //
   // MQTT brokers usually use port 8883 for secure connections.
   client.begin("broker.shiftr.io", 8883, net);