Sdl-2 thread logic

SDL Threads

SDL Multithreading
SDL Thread creation ：SDL_CreateThread
SDL Thread waiting ：SDL_WaitThead
SDL The mutex ：SDL_CreateMutex/SDL_DestroyMutex
SDL Lock mutex ：SDL_LockMutex/SDL_UnlockMutex
SDL Condition variables, ( Semaphore )：SDL_CreateCond/SDL_DestoryCond
SDL Condition variables, ( Semaphore ) wait for / notice ：SDL_CondWait/SDL_CondSingal

#include <stdio.h>
#include<stdlib.h>
#include <unistd.h> // for close

#include"SDL2/SDL.h"
#define FF_QUIT_EVENT (SDL_USEREVENT + 2) //  User defined events 

SDL_mutex *s_lock = NULL;
SDL_cond *s_cond = NULL;
int thread_work(void *arg){
    
    SDL_LockMutex(s_lock);
    printf(" <============thread_work sleep\n");
    sleep(10);
    printf(" <============thread_work wait\n");
    //  Release s_lock resources , And wait for signal. Why release s_lock Is to enable other threads to get s_lock
    SDL_CondWait(s_cond, s_lock); // Another thread (1) send out signal and (2) Release lock after , This function exits 


}


int main()
{
    
      s_lock = SDL_CreateMutex();
      s_cond = SDL_CreateCond();
      SDL_Thread *t = SDL_CreateThread(thread_work,"thread_work",NULL);
      if(!t)
      {
    
          printf(" %s",SDL_GetError);
          return -1;
      }

      for(int i = 0;i< 2;i++)
      {
    
          sleep(2);
          printf("main execute =====>\n");
      }
      printf("main SDL_LockMutex(s_lock) before ====================>\n");
      SDL_LockMutex(s_lock);  //  Get the lock , But the child thread still holds the lock 
      printf("main ready send signal====================>\n");
      printf("main SDL_CondSignal(s_cond) before ====================>\n");
      printf("main SDL_LockMutex(s_lock) before ====================>\n");
      SDL_LockMutex(s_lock);  //  Get the lock , But the child thread still holds the lock 
      printf("main ready send signal====================>\n");
      printf("main SDL_CondSignal(s_cond) before ====================>\n");
      SDL_CondSignal(s_cond); //  Sending signal , Wakes up the waiting thread 
      printf("main SDL_CondSignal(s_cond) after ====================>\n");
      sleep(10);
      SDL_UnlockMutex(s_lock);//  Release the lock , Let other threads get the lock 
      printf("main SDL_UnlockMutex(s_lock) after ====================>\n");

      SDL_WaitThread(t, NULL);
      SDL_DestroyMutex(s_lock);
      SDL_DestroyCond(s_cond);

      return 0;
  }

Output results

Result analysis
First main Function to create a child thread t And enter the corresponding function “thread_work”

The child thread gets the lock SDL_LockMutex(s_lock);

Then sleep 10 second

The main thread runs 4 Seconds later Get the lock But the lock is always occupied

Wake up after waiting for the signal You must get two conditions at the same time 1 Get the lock 2 Get the semaphore
Pictured