使用 C 中的互斥锁使用 2 个线程打印奇数和偶数

Question

程序中的两个线程交替打印偶数和奇数，直到 100。我试过这个，它奏效了。有没有办法访问main内部共享数据的值，当值达到100时终止2个线程

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

pthread_t tid[2];
unsigned int shared_data = 0;
pthread_mutex_t mutex;
unsigned int rc;
//prototypes for callback functions

void* PrintEvenNos(void*);
void* PrintOddNos(void*);

void main(void)
{
    pthread_create(&tid[0],0,&PrintEvenNos,0)
    pthread_create(&tid[1],0,&PrintOddNos,0);
    sleep(3);

    pthread_join(tid[0],NULL);
    pthread_join(tid[1],NULL);
}

void* PrintEvenNos(void *ptr)
{
    pthread_mutex_lock(&mutex);
    do
    {
       if(shared_data%2 == 0)
       {
         printf("Even:%d\n",shared_data);
         shared_data++;
       } else {
          rc=pthread_mutex_unlock(&mutex);//if number is odd, do not print, release mutex
       }
    } while(shared_data <= 100);
}

void* PrintOddNos(void* ptr1)
{
    rc = pthread_mutex_lock(&mutex);
    do
    {
       if(shared_data%2 != 0)
       {
          printf("odd:%d\n",shared_data);
          shared_data++;
       } else {
          rc = pthread_mutex_unlock(&mutex);//if number is even, do not print, release mutex
       }
    } while(shared_data <= 100);
}

Answer 1

Use condition variable to synchronize both threads and a mutex to protect count

#include "stdio.h"
#include "stdlib.h"
#include "pthread.h"

pthread_mutex_t count_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t condition_var = PTHREAD_COND_INITIALIZER;
void *functionCount1();
void *functionCount2();
int count = 0;
#define COUNT_DONE 200

void main()
{
 pthread_t thread1, thread2;
 pthread_create( &thread1, NULL, &functionCount1, NULL);
 pthread_create( &thread2, NULL, &functionCount2, NULL);
 pthread_join( thread1, NULL);
 pthread_join( thread2, NULL);
 exit(0);
}

// Print odd numbers
void *functionCount1()
{
  for(;;) {
   // Lock mutex and then wait for signal to relase mutex
   pthread_mutex_lock( &count_mutex );
   if ( count % 2 != 0 ) {
     pthread_cond_wait( &condition_var, &count_mutex );
   }
   count++;
   printf("Counter value functionCount1: %d\n",count);
   pthread_cond_signal( &condition_var );
   if ( count >= COUNT_DONE ) {
     pthread_mutex_unlock( &count_mutex );
     return(NULL);
   }
   pthread_mutex_unlock( &count_mutex );
 }
}

// print even numbers
void *functionCount2()
{
  for(;;) {
  // Lock mutex and then wait for signal to relase mutex
  pthread_mutex_lock( &count_mutex );
  if ( count % 2 == 0 ) {
    pthread_cond_wait( &condition_var, &count_mutex );
  }
  count++;
  printf("Counter value functionCount2: %d\n",count);
  pthread_cond_signal( &condition_var );
  if( count >= COUNT_DONE ) {
    pthread_mutex_unlock( &count_mutex );
    return(NULL);
  }
  pthread_mutex_unlock( &count_mutex );
 }
}