How to share flags in spresense?

[gyps]

Sorry for the frequent postings.
I recently implemented a multi-threaded program using shared flags without mutex and it did not work.
And when I created a simple multi-threaded program using shared flags to try it out, the shared flags were not shared and I was able to run it on my computer, indicating that it is a spresense specific problem.
Is it a problem with the way spresense handles memory that the flags are not shared?
If anyone can tell me, I would appreciate your advice.

↓Here are the results of the run with SPRESENSE.

| Start first thread |
First thread : share_var = 1 
| Start secound thread |
Secound thread : share_var = 2
Secound thread : finished

(stopped...)

↓Here is the execution result with WSL2 (gcc compiler).

| Start first thread |
First thread : share_var = 1 
| Start secound thread |
Secound thread : share_var = 2
Secound thread : finished
First thread : share_var = 3 
First thread : finished

↓This is the program that was executed.

#include <stdio.h>
#include <time.h>
#include <pthread.h>

int flag_1 = 0;
int flag_2 = 0;
int share_var = 0;


static void *first_thread(){
  printf("| Start first thread |\n");

  share_var += 1;
  printf("First thread : share_var = 1 \n");
  flag_1=1;
  
  while(flag_2==0);
  flag_2=0;
  
  share_var += 1;
  printf("First thread : share_var = 3 \n");
  printf("First thread : finished\n");
  return NULL;
}


static void *secound_thread(){
  printf("| Start secound thread |\n");
  
  while(flag_1==0);
  flag_1=0;
  share_var += 1;
  printf("Secound thread : share_var = 2\n");
  flag_2=1;
  printf("Secound thread : finished\n");
  return NULL;
}


// Main function //
int main(void){
  
  int ret;
  pthread_t thread1, thread2;

　ret = pthread_create(&thread1, NULL, first_thread, NULL);
  if (ret != 0){
    printf("ERROR: Failed to create new thread1.\n");
  }
　ret = pthread_create(&thread2, NULL, secound_thread, NULL);
  if (ret != 0){
    printf("ERROR: Failed to create new thread2.\n");
  }

  ret = pthread_join(thread1, NULL);
  if (ret != 0){
    printf("ERROR: Failed to join first thread. \n");
  }
  ret = pthread_join(thread2, NULL);
  if (ret != 0){
    printf("ERROR: Failed to join secound thread. \n");
  }
　return 0;
}

[jens6151 0 1 1]

This works.

volatile int flag_1 = 0;
volatile int flag_2 = 0;
volatile int share_var = 0;

Maybe you had different compiler flags. Arduino optimizes for size as a default.

To my knowledge volatile prevents the compiler from optimizing out as the compiler does not see that you modify the variable from another thread and thinks it is useless and removes it.

[gyps]

@jens6151-0-1-1 Thanks for your suggestion, It worked with that program.