Thread

Thread class hierarchy

The Thread class allows defining, creating and controlling parallel tasks.

Note: The function main is a special thread function that is started at system initialization.

Thread class reference

/// Priority values.
typedef enum {
  osPriorityNone          =  0,         ///< No priority (not initialized).
  osPriorityIdle          =  1,         ///< Reserved for Idle thread.
  osPriorityLow           =  8,         ///< Priority: low
  osPriorityLow1          =  8+1,       ///< Priority: low + 1
  osPriorityLow2          =  8+2,       ///< Priority: low + 2
  osPriorityLow3          =  8+3,       ///< Priority: low + 3
  osPriorityLow4          =  8+4,       ///< Priority: low + 4
  osPriorityLow5          =  8+5,       ///< Priority: low + 5
  osPriorityLow6          =  8+6,       ///< Priority: low + 6
  osPriorityLow7          =  8+7,       ///< Priority: low + 7
  osPriorityBelowNormal   = 16,         ///< Priority: below normal
  osPriorityBelowNormal1  = 16+1,       ///< Priority: below normal + 1
  osPriorityBelowNormal2  = 16+2,       ///< Priority: below normal + 2
  osPriorityBelowNormal3  = 16+3,       ///< Priority: below normal + 3
  osPriorityBelowNormal4  = 16+4,       ///< Priority: below normal + 4
  osPriorityBelowNormal5  = 16+5,       ///< Priority: below normal + 5
  osPriorityBelowNormal6  = 16+6,       ///< Priority: below normal + 6
  osPriorityBelowNormal7  = 16+7,       ///< Priority: below normal + 7
  osPriorityNormal        = 24,         ///< Priority: normal
  osPriorityNormal1       = 24+1,       ///< Priority: normal + 1
  osPriorityNormal2       = 24+2,       ///< Priority: normal + 2
  osPriorityNormal3       = 24+3,       ///< Priority: normal + 3
  osPriorityNormal4       = 24+4,       ///< Priority: normal + 4
  osPriorityNormal5       = 24+5,       ///< Priority: normal + 5
  osPriorityNormal6       = 24+6,       ///< Priority: normal + 6
  osPriorityNormal7       = 24+7,       ///< Priority: normal + 7
  osPriorityAboveNormal   = 32,         ///< Priority: above normal
  osPriorityAboveNormal1  = 32+1,       ///< Priority: above normal + 1
  osPriorityAboveNormal2  = 32+2,       ///< Priority: above normal + 2
  osPriorityAboveNormal3  = 32+3,       ///< Priority: above normal + 3
  osPriorityAboveNormal4  = 32+4,       ///< Priority: above normal + 4
  osPriorityAboveNormal5  = 32+5,       ///< Priority: above normal + 5
  osPriorityAboveNormal6  = 32+6,       ///< Priority: above normal + 6
  osPriorityAboveNormal7  = 32+7,       ///< Priority: above normal + 7
  osPriorityHigh          = 40,         ///< Priority: high
  osPriorityHigh1         = 40+1,       ///< Priority: high + 1
  osPriorityHigh2         = 40+2,       ///< Priority: high + 2
  osPriorityHigh3         = 40+3,       ///< Priority: high + 3
  osPriorityHigh4         = 40+4,       ///< Priority: high + 4
  osPriorityHigh5         = 40+5,       ///< Priority: high + 5
  osPriorityHigh6         = 40+6,       ///< Priority: high + 6
  osPriorityHigh7         = 40+7,       ///< Priority: high + 7
  osPriorityRealtime      = 48,         ///< Priority: realtime
  osPriorityRealtime1     = 48+1,       ///< Priority: realtime + 1
  osPriorityRealtime2     = 48+2,       ///< Priority: realtime + 2
  osPriorityRealtime3     = 48+3,       ///< Priority: realtime + 3
  osPriorityRealtime4     = 48+4,       ///< Priority: realtime + 4
  osPriorityRealtime5     = 48+5,       ///< Priority: realtime + 5
  osPriorityRealtime6     = 48+6,       ///< Priority: realtime + 6
  osPriorityRealtime7     = 48+7,       ///< Priority: realtime + 7
  osPriorityISR           = 56,         ///< Reserved for ISR deferred thread.
  osPriorityError         = -1,         ///< System cannot determine priority or illegal priority.
  osPriorityReserved      = 0x7FFFFFFF  ///< Prevents enum down-size compiler optimization.
} osPriority_t;

Thread example

The code below uses two separate threads to blink two LEDs. The first thread is automatically created and executes the main function; the second thread is created explicitly inside main.

#include "mbed.h"
 
DigitalOut led1(LED1);
DigitalOut led2(LED2);
Thread thread;
 
void led2_thread() {
    while (true) {
        led2 = !led2;
        wait(1);
    }
}
 
int main() {
    thread.start(led2_thread);
    
    while (true) {
        led1 = !led1;
        wait(0.5);
    }
}

Thread example with callbacks

The Callback API provides a convenient way to pass arguments to spawned threads.

#include "mbed.h"

Thread thread;
DigitalOut led1(LED1);
volatile bool running = true;

// Blink function toggles the led in a long running loop
void blink(DigitalOut *led) {
    while (running) {
        *led = !*led;
        wait(1);
    }
}

// Spawns a thread to run blink for 5 seconds
int main() {
    thread.start(callback(blink, &led1));
    wait(5);
    running = false;
    thread.join();
}

Related content

• Application flow control tutorial.
• ThisThread API reference.