linux 多線程面試題

編寫一個程序，開啓3個線程，這3個線程的ID分別爲A、B、C,每個線程將自己的ID在屏幕上打印10遍，要求輸出結果必須按ABC的順序顯示；如：ABCABC…依次遞推。

• 使用pthread_join進行阻塞，等對應的id線程運行結束再往下運行

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

pthread_mutex_t mutex;

void ThreadProc(void* arg)
{
	char *str = (char*)arg;
	printf("%s", str);
}
int main()
{
	pthread_t id;
	int i = 0;
	for (i = 0; i<10; i++)
	{
	    pthread_create(&id, NULL, (void*)ThreadProc, "A");
        pthread_join(id, NULL);	

    	pthread_create(&id, NULL, (void*)ThreadProc, "B");
        pthread_join(id, NULL);	

        pthread_create(&id, NULL, (void*)ThreadProc, "C");
        pthread_join(id, NULL);	

	}
	
	printf("\n");

	return 0;
}

• 使用sem信號量PV互斥操作，來達到輸出

#include <stdlib.h>
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <semaphore.h>

sem_t sem1;
sem_t sem2;

void ThreadProc1(void* arg)
{
    char *str = (char*)arg;

    sem_wait(&sem1);
    
    printf("%s", str);
    sem_post(&sem2);
}
void ThreadProc2(void* arg)
{
    char *str = (char*)arg;
    sem_wait(&sem2);

    printf("%s", str);

}
void ThreadProc3(void* arg)
{
    char *str = (char*)arg;
    sem_post(&sem1);
    printf("%s", str);

}
int main()
{
  sem_init(&sem1, 0, 0);
  sem_init(&sem2, 0, 0);

  pthread_t id1, id2, id3;
  int i = 0;
  for (i = 0; i<10; i++)
  {
      pthread_create(&id1, NULL, (void*)ThreadProc1, "B");
      pthread_create(&id2, NULL, (void*)ThreadProc2, "C");
      pthread_create(&id3, NULL, (void*)ThreadProc3, "A");
      pthread_join(id2, NULL);

  }

  sem_destroy(&sem1);
  sem_destroy(&sem2);
  printf("\n");
  return 0;
}