Mutex

The Mutex class, provides by the underlining mbed OS, is used to synchronize the execution of threads and protect the access to a shared resource. For more information about Mutex, please visit MbedOS

Assembly

Arduino.h

Summary

Constructors

Mutex

rtos::Mutex::Mutex()  

Methods

lock

osStatus rtos::Mutex::lock(uint32_t millisec = osWaitForever)

Wait until a Mutex becomes available.

Parameters

Type	Name	Description
uint32_t	millisec	timeout value or 0 in case of no time-out.

Return value

Status code that indicates the execution status of the function: osOK the mutex has been obtained. osErrorTimeout the mutex could not be obtained in the given time. osErrorParameter internal error. osErrorResource the mutex could not be obtained when no timeout was specified. osErrorISR this function cannot be called from the interrupt service routine.

trylock

bool rtos::Mutex::trylock(  ) 

Try to lock the mutex, and return immediately.

Return value

true if the mutex was acquired, false otherwise.

unlock

osStatus rtos::Mutex::unlock(void) 

Unlock the mutex that has previously been locked by the same thread.

Return value

Status code that indicates the execution status of the function: osOK the mutex has been released. osErrorParameter internal error. osErrorResource the mutex was not locked or the current thread wasn’t the owner. osErrorISR this function cannot be called from the interrupt service routine.

Sample code

Mutex _mutex;
Thread t1;
Thread t2;

void notify(const char* name, int state) {
    _mutex.lock();
    Serial.printf("%s: %d\n\r", name, state);
    _mutex.unlock();
}

void test_thread(void const *args) {
    while (true) {
        notify((const char*)args, 0); 
        delay(1000);
        notify((const char*)args, 1); 
        delay(1000);
    }
}

void setup() {
    t1.start(callback(test_thread, (void *)"Thread 1"));
    t2.start(callback(test_thread, (void *)"Thread 2"));
}

void loop() {
    // Main thread
    notify((const char*)"Main Thread", 0); 
    delay(1000);
    notify((const char*)"Main Thread", 1); 
    delay(1000);
}