University of Plymouth - Stages 1, 2 and 3 / Mbed OS Task600-ThreadRaces

main.cpp@0:c49a2dd99fc3, 2019-09-20 (annotated)

Committer:
noutram
Date:
Fri Sep 20 14:06:30 2019 +0000
Revision:
0:c49a2dd99fc3
2019

Who changed what in which revision?

UserRevisionLine numberNew contents of line
noutram 0:c49a2dd99fc3 1 #include "mbed.h"
noutram 0:c49a2dd99fc3 2 void countUp();
noutram 0:c49a2dd99fc3 3 void countDown();
noutram 0:c49a2dd99fc3 4
noutram 0:c49a2dd99fc3 5 #define N 1000000
noutram 0:c49a2dd99fc3 6 #define RELEASED 0
noutram 0:c49a2dd99fc3 7 #define PRESSED 1
noutram 0:c49a2dd99fc3 8
noutram 0:c49a2dd99fc3 9 //Hardware
noutram 0:c49a2dd99fc3 10 DigitalOut red_led(PE_15); //CountUp is in its critical section
noutram 0:c49a2dd99fc3 11 DigitalOut yellow_led(PB_10); //CountDown is in its critical section
noutram 0:c49a2dd99fc3 12 DigitalOut green_led(PB_11); //counter != 0
noutram 0:c49a2dd99fc3 13 DigitalIn button(USER_BUTTON);
noutram 0:c49a2dd99fc3 14
noutram 0:c49a2dd99fc3 15 //Additional Threads
noutram 0:c49a2dd99fc3 16 Thread t1;
noutram 0:c49a2dd99fc3 17 Thread t2;
noutram 0:c49a2dd99fc3 18
noutram 0:c49a2dd99fc3 19 //Shared mutable state
noutram 0:c49a2dd99fc3 20 volatile long long counter = 0; //Volatile means it must be stored in memory
noutram 0:c49a2dd99fc3 21
noutram 0:c49a2dd99fc3 22 //Increment the shared variable
noutram 0:c49a2dd99fc3 23 void countUp()
noutram 0:c49a2dd99fc3 24 {
noutram 0:c49a2dd99fc3 25 //RED MEANS THE COUNT UP FUNCTION IS IN ITS CRITICAL SECTION
noutram 0:c49a2dd99fc3 26 red_led = 1;
noutram 0:c49a2dd99fc3 27 for (unsigned int n=0; n<N; n++) {
noutram 0:c49a2dd99fc3 28 counter++;
noutram 0:c49a2dd99fc3 29 counter++;
noutram 0:c49a2dd99fc3 30 counter++;
noutram 0:c49a2dd99fc3 31 counter++;
noutram 0:c49a2dd99fc3 32 counter++;
noutram 0:c49a2dd99fc3 33 counter++;
noutram 0:c49a2dd99fc3 34 counter++;
noutram 0:c49a2dd99fc3 35 counter++;
noutram 0:c49a2dd99fc3 36 counter++;
noutram 0:c49a2dd99fc3 37 counter++;
noutram 0:c49a2dd99fc3 38 }
noutram 0:c49a2dd99fc3 39 red_led = 0;
noutram 0:c49a2dd99fc3 40
noutram 0:c49a2dd99fc3 41 }
noutram 0:c49a2dd99fc3 42
noutram 0:c49a2dd99fc3 43 //Decrement the shared variable
noutram 0:c49a2dd99fc3 44 void countDown()
noutram 0:c49a2dd99fc3 45 {
noutram 0:c49a2dd99fc3 46 //YELLOW MEANS THE COUNT DOWN FUNCTION IS IN ITS CRITICAL SECTION
noutram 0:c49a2dd99fc3 47 yellow_led = 1;
noutram 0:c49a2dd99fc3 48 for (unsigned int n=0; n<N; n++) {
noutram 0:c49a2dd99fc3 49 counter--;
noutram 0:c49a2dd99fc3 50 counter--;
noutram 0:c49a2dd99fc3 51 counter--;
noutram 0:c49a2dd99fc3 52 counter--;
noutram 0:c49a2dd99fc3 53 counter--;
noutram 0:c49a2dd99fc3 54 counter--;
noutram 0:c49a2dd99fc3 55 counter--;
noutram 0:c49a2dd99fc3 56 counter--;
noutram 0:c49a2dd99fc3 57 counter--;
noutram 0:c49a2dd99fc3 58 counter--;
noutram 0:c49a2dd99fc3 59 }
noutram 0:c49a2dd99fc3 60 yellow_led = 0;
noutram 0:c49a2dd99fc3 61
noutram 0:c49a2dd99fc3 62 }
noutram 0:c49a2dd99fc3 63 int main() {
noutram 0:c49a2dd99fc3 64
noutram 0:c49a2dd99fc3 65 green_led = 1;
noutram 0:c49a2dd99fc3 66
noutram 0:c49a2dd99fc3 67 //Start competing threads
noutram 0:c49a2dd99fc3 68 t1.start(countUp);
noutram 0:c49a2dd99fc3 69 t2.start(countDown);
noutram 0:c49a2dd99fc3 70
noutram 0:c49a2dd99fc3 71 //These threads DO exit, so let's wait for BOTH to finish
noutram 0:c49a2dd99fc3 72 t1.join(); //Wait for thread t1 to finish
noutram 0:c49a2dd99fc3 73 t2.join(); //Wait for thread t2 to finish
noutram 0:c49a2dd99fc3 74
noutram 0:c49a2dd99fc3 75 //Did the counter end up at zero?
noutram 0:c49a2dd99fc3 76 if (counter == 0) {
noutram 0:c49a2dd99fc3 77 green_led = 0;
noutram 0:c49a2dd99fc3 78 }
noutram 0:c49a2dd99fc3 79
noutram 0:c49a2dd99fc3 80 //Now spin-lock for ever
noutram 0:c49a2dd99fc3 81 while(1) {
noutram 0:c49a2dd99fc3 82 asm("nop");
noutram 0:c49a2dd99fc3 83 };
noutram 0:c49a2dd99fc3 84 }
noutram 0:c49a2dd99fc3 85