Mbed OS 5 EventLoop和Thread

Question

Newbird到EventLoop和Thread。需要帮忙。我的fall_hanlder和rise_hanlder正在同一个线程上运行，但我的outside_isr（）正在事件线程上运行。为了确保事件线程只运行一次且仅在调用fall_handler时，我该怎么办？

AnalogIn ain(PA_0); //Pin A0 //

EventQueue queue;
Thread thread, thread1;
Timer timer;
int count = 0;

void outside_isr() {

    count = count + 1;

    pc.printf("%.3f seconds\n", timer.read());
    pc.printf("%d pulse\n", count);
}

void rise_handler() {
    timer.reset(); 
    timer.start();
}

void fall_handler() {

    timer.stop();
    queue.call(outside_isr);
}

void signal() {

    bool flag = false; 

    while(1) {
        if (ain > 0.93f) {
            if (flag == false) {
                flag = true;
                rise_handler();    
            }
        }
        if (ain < 0.93f) {
            if (flag == true) {
                flag = false;
                fall_handler();     
            }    
        }
    }
}

int main () {

    thread1.start(callback(signal));
    thread.start(callback(&queue, &EventQueue::dispatch_forever));

    while(1) {}

}