3.3.7

libraries/ESP32/examples/FreeRTOS/Mutex/Mutex.ino

@@ -0,0 +1,102 @@
+/* Basic Multi Threading Arduino Example
+   This example code is in the Public Domain (or CC0 licensed, at your option.)
+   Unless required by applicable law or agreed to in writing, this
+   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+   CONDITIONS OF ANY KIND, either express or implied.
+*/
+// Please read file README.md in the folder containing this example.
+
+#define USE_MUTEX
+int shared_variable = 0;
+SemaphoreHandle_t shared_var_mutex = NULL;
+
+// Define a task function
+void Task(void *pvParameters);
+
+// The setup function runs once when you press reset or power on the board.
+void setup() {
+  // Initialize serial communication at 115200 bits per second:
+  Serial.begin(115200);
+
+  Serial.printf(" Task 0          | Task 1\n");
+
+#ifdef USE_MUTEX
+  shared_var_mutex = xSemaphoreCreateMutex();  // Create the mutex
+#endif
+
+  // Set up two tasks to run the same function independently.
+  static int task_number0 = 0;
+  xTaskCreate(
+    Task, "Task 0"  // A name just for humans
+    ,
+    2048  // The stack size
+    ,
+    (void *)&task_number0  // Pass reference to a variable describing the task number
+    //,  5  // High priority
+    ,
+    1  // priority
+    ,
+    NULL  // Task handle is not used here - simply pass NULL
+  );
+
+  static int task_number1 = 1;
+  xTaskCreate(
+    Task, "Task 1", 2048  // Stack size
+    ,
+    (void *)&task_number1  // Pass reference to a variable describing the task number
+    ,
+    1  // Low priority
+    ,
+    NULL  // Task handle is not used here - simply pass NULL
+  );
+
+  // Now the task scheduler, which takes over control of scheduling individual tasks, is automatically started.
+}
+
+void loop() {}
+
+/*--------------------------------------------------*/
+/*---------------------- Tasks ---------------------*/
+/*--------------------------------------------------*/
+
+void Task(void *pvParameters) {  // This is a task.
+  int task_num = *((int *)pvParameters);
+  Serial.printf("%s\n", task_num ? " Starting        |" : "                 | Starting");
+  for (;;) {  // A Task shall never return or exit.
+#ifdef USE_MUTEX
+    if (shared_var_mutex != NULL) {  // Sanity check if the mutex exists
+      // Try to take the mutex and wait indefinitely if needed
+      if (xSemaphoreTake(shared_var_mutex, portMAX_DELAY) == pdTRUE) {
+        // Mutex successfully taken
+#endif
+        int new_value = random(1000);
+
+        char str0[35];  // Maximum possible length of the string
+        snprintf(str0, sizeof(str0), " %d <- %d      |", shared_variable, new_value);
+        char str1[46];  // Maximum possible length of the string
+        snprintf(str1, sizeof(str1), "                 | %d <- %d", shared_variable, new_value);
+        Serial.printf("%s\n", task_num ? str0 : str1);
+
+        shared_variable = new_value;
+        delay(random(100));  // wait random time of max 100 ms - simulating some computation
+
+        snprintf(str0, sizeof(str0), " R: %d          |", shared_variable);
+        snprintf(str1, sizeof(str1), "                 | R: %d", shared_variable);
+        Serial.printf("%s\n", task_num ? str0 : str1);
+        //Serial.printf("Task %d after write: reading %d\n", task_num, shared_variable);
+
+        if (shared_variable != new_value) {
+          Serial.printf("%s\n", task_num ? " Mismatch!       |" : "                 | Mismatch!");
+          //Serial.printf("Task %d: detected race condition - the value changed!\n", task_num);
+        }
+
+#ifdef USE_MUTEX
+        xSemaphoreGive(shared_var_mutex);  // After accessing the shared resource give the mutex and allow other processes to access it
+      } else {
+        // We could not obtain the semaphore and can therefore not access the shared resource safely.
+      }  // mutex take
+    }  // sanity check
+#endif
+    delay(10);  // Allow other task to be scheduled
+  }  // Infinite loop
+}