Semaphore

The Semaphore class, provided by the underlining MbedOS, is used to manage thread access to a pool of shared resources of a certain type. For more information about Semaphore, please visit MbedOS.

Assembly

Arduino.h

Summary

Constructors

Semaphore

rtos::Semaphore::Semaphore(int32_t count = 0)   

Parameters

Type	Name	Description
int32_t	count	number of available resources; maximum index value is (count-1).

Methods

release

osStatus rtos::Semaphore::release(void) 

Release a Semaphore resource that was obtained with Semaphore::wait.

Return value

Status code that indicates the execution status of the function: osOK the token has been correctly released. osErrorResource the maximum token count has been reached. osErrorParameter internal error.

wait

int32_t rtos::Semaphore::wait( uint32_t millisec = osWaitForever)

Wait until a Semaphore resource becomes available.

Type	Name	Description
uint32	millisec	timeout value or 0 in case of no time-out.

Return value

Number of available tokens, before taking one; or -1 in case of incorrect parameters.

Sample code

Semaphore two_slots(2);
Thread t1;
Thread t2;

void test_thread(void const *name) {
    while (true) {
        two_slots.wait();
        Serial.printf("%s\n\r", (const char*)name);
        delay(1000);
        two_slots.release();
    }
}


void setup() {
  // put your setup code here, to run once:
    t1.start(callback(test_thread, (void *)"Thread 1"));
    t2.start(callback(test_thread, (void *)"Thread 2"));
}

void loop() {
    two_slots.wait();
    Serial.printf("%s\n\r", "Main thread");
    delay(1000);
    two_slots.release();
}