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多线程例题练手
发布日期：2022-04-11 08:52:52 浏览次数：12 分类：技术文章

本文共 25458 字，大约阅读时间需要 84 分钟。

使用pthreads进行实时编程

需要模板代码critical.c和multithread.c。

/* * critical.c * * Demonstrate use of mutual exclusion using mutexes * * Upper case output indicates critical output * lower case output indicates non-critical output * * compile with gcc critical.c -o critical -lrt -lpthread * */#define _GNU_SOURCE#define _REENTRANT      /* macro to ensure system calls are reentrant */#include 
   
        /* header file for pthreads */#include 
    
          /* header file for POSIX conformance */#include 
     
             /* header file for POSIX time management */#include 
      
             /* header file for POSIX scheduling */#include 
       
              /* header file for standard input/outputlibrary */pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER; /*define mutex */void *threadA(void *);   /* predefine threadA routine */void *threadB(void *);   /* predefine threadB routine */pthread_t threadA_id,threadB_id,main_id; /* thread identifiers */pthread_attr_t attrA,attrB;        /* thread attribute structures */struct sched_param param;          /* scheduling structure for thread attributes */int policy=SCHED_FIFO;int priority_min,priority_max;     /* for range of priority levels *//* main routine */int main(){
     int status;                        /* check that system calls return ok */  /* Set processor affinity */   cpu_set_t mask; CPU_ZERO(&mask); CPU_SET(0,&mask); /* use only 1 CPU core */  unsigned int len = sizeof(mask);  status = sched_setaffinity(0, len, &mask);  if (status < 0) perror("sched_setaffinity");  status = sched_getaffinity(0, len, &mask);  if (status < 0) perror("sched_getaffinity");  /* Find priority limits */  priority_max = sched_get_priority_max(policy);  priority_min = sched_get_priority_min(policy);    /* Set priority and policy of main thread */  main_id = pthread_self();  param.sched_priority=priority_min;  status = pthread_setschedparam(main_id, policy, &param);  if (status != 0) perror("pthread_setschedparam"); /* error check */  /* Create threadA */    param.sched_priority = priority_min;  pthread_attr_init(&attrA);  status = pthread_attr_setschedpolicy(&attrA,policy);  if (status != 0) perror("pthread_attr_setschedpolicy"); /* error check */  status = pthread_attr_setschedparam(&attrA,&param);  if (status != 0) perror("pthread_attr_setschedparam"); /* error check */  status = pthread_create(&threadA_id, &attrA, threadA, NULL);  if (status != 0) perror("pthread_create"); /* error check */  status = pthread_setschedparam(threadA_id,policy,&param);  if (status != 0) perror("pthread_setschedparam");  /* Create threadB */    param.sched_priority = priority_min;  pthread_attr_init(&attrB);  status = pthread_attr_setschedpolicy(&attrB,policy);  if (status != 0) perror("pthread_attr_setschedpolicy"); /* error check */  status = pthread_attr_setschedparam(&attrB,&param);  if (status != 0) perror("pthread_attr_setschedparam"); /* error check */  status = pthread_create(&threadB_id, &attrB, threadB, NULL);  if (status != 0) perror("pthread_create"); /* error check */  status = pthread_setschedparam(threadB_id,policy,&param);  if (status != 0) perror("pthread_setschedparam");  /* Join threads - force main to wait for the thread to terminate */    status = pthread_join(threadA_id, NULL);  if (status != 0) perror("pthread_join(threadA_id, NULL)"); /* error check */  status = pthread_join(threadB_id, NULL);  if (status != 0) perror("pthread_join(threadB_id, NULL)"); /* error check */    status = pthread_mutex_destroy(&mtx); /* delete mutex */  if (status != 0) perror("pthread_mutex_destroy"); /* error check */    printf("\n");  return(0);  }  /* end of main */void *threadA(void *arg){
     int j;  int status;                        /* check that system calls return ok */      for(j=1;j<=5;j++){
   	printf("a");                     /* non -critical */  }    /* lock to enter critical region */  /* status = pthread_mutex_lock(&mtx);	 if (status != 0) perror("pthread_mutex_lock");*/ /* error check */    for(j=1;j<=5;j++){
   	printf("A");                    /* critical */  }    /* increment priority of threadB above threadA */    param.sched_priority++;   status = pthread_setschedparam(threadB_id,policy,&param);  if (status != 0) perror("pthread_setschedparam"); /* error check */    for(j=1;j<=5;j++){
   	printf("A");                     /* critical */  }    /* unlock critical region */  /* status = pthread_mutex_unlock(&mtx); 	 if (status != 0) perror("pthread_mutex_unlock");*/ /* error check */    for(j=1;j<=5;j++){
   	printf("a");                     /* non -critical */  }    return (NULL);}void *threadB(void *arg){
     int j;  int status;                        /* check that system calls return ok */    for(j=1;j<=5;j++){
   	printf("b");                     /* non -critical */  }    /* lock to enter critical region */  /* status = pthread_mutex_lock(&mtx);  	 if (status != 0) perror("pthread_mutex_lock");*/ /* error check */      for(j=1;j<=5;j++){
   	printf("B");                     /* critical */  }    /* increment priority of threadA to above threadB*/    param.sched_priority++;   status = pthread_setschedparam(threadA_id,policy,&param);  if (status != 0) perror("pthread_setschedparam"); /* error check */    for(j=1;j<=5;j++){
   	printf("B");                    /* critical */  }  /* unlock critical region */  /* status = pthread_mutex_unlock(&mtx);  	 if (status != 0) perror("pthread_mutex_unlock");*/ /* error check */    for(j=1;j<=5;j++){
   	printf("b");                     /* non -critical */  }    return (NULL);}
       
      
     
    
   
/* * multithread.c * * Demonstrate use of a multi threading and scheduling using pthreads * * compile with gcc multithread.c -o multithread -lrt -lpthread * */#define _GNU_SOURCE#define _REENTRANT      /* macro to ensure system calls are reentrant */#include 
   
        /* header file for pthreads */#include 
    
          /* header file for POSIX conformance */#include 
     
             /* header file for POSIX time management */#include 
      
             /* header file for POSIX scheduling */#include 
       
              /* header file for standard input/outputlibrary */void *threadA(void *);   /* predefine threadA routine */void *threadB(void *);   /* predefine threadB routine */void *threadC(void *);   /* predefine threadC routine */pthread_t threadA_id,threadB_id,threadC_id,main_id; /* thread identifiers */pthread_attr_t attrA,attrB,attrC;  /* thread attribute structures */struct sched_param param;          /* scheduling structure for thread attributes */int policy=SCHED_FIFO;int priority_min,priority_max;     /* for range of priority levels *//* main routine */int main(){
     int status;                        /* check that system calls return ok */  /* Set processor affinity */   cpu_set_t mask; CPU_ZERO(&mask); CPU_SET(0,&mask); /* use only 1 CPU core */  unsigned int len = sizeof(mask);  status = sched_setaffinity(0, len, &mask);  if (status < 0) perror("sched_setaffinity");  status = sched_getaffinity(0, len, &mask);  if (status < 0) perror("sched_getaffinity");  /* Find priority limits */  priority_max = sched_get_priority_max(policy);  priority_min = sched_get_priority_min(policy);    /* Set priority and policy of main thread */  main_id = pthread_self();  param.sched_priority=priority_min;  status = pthread_setschedparam(main_id, policy, &param);  if (status != 0) perror("pthread_setschedparam"); /* error check */  /* Create threadA */    param.sched_priority = priority_min;  pthread_attr_init(&attrA);  status = pthread_attr_setschedpolicy(&attrA,policy);  if (status != 0) perror("pthread_attr_setschedpolicy"); /* error check */  status = pthread_attr_setschedparam(&attrA,&param);  if (status != 0) perror("pthread_attr_setschedparam"); /* error check */  status = pthread_create(&threadA_id, &attrA, threadA, NULL);  if (status != 0) perror("pthread_create"); /* error check */  status = pthread_setschedparam(threadA_id,policy,&param);  if (status != 0) perror("pthread_setschedparam");  /* Create threadB */    param.sched_priority = priority_min;  pthread_attr_init(&attrB);  status = pthread_attr_setschedpolicy(&attrB,policy);  if (status != 0) perror("pthread_attr_setschedpolicy"); /* error check */  status = pthread_attr_setschedparam(&attrB,&param);  if (status != 0) perror("pthread_attr_setschedparam"); /* error check */  status = pthread_create(&threadB_id, &attrB, threadB, NULL);  if (status != 0) perror("pthread_create"); /* error check */  status = pthread_setschedparam(threadB_id,policy,&param);  if (status != 0) perror("pthread_setschedparam");    /* Create threadC */    param.sched_priority = priority_min;  pthread_attr_init(&attrC);  status = pthread_attr_setschedpolicy(&attrC,policy);  if (status != 0) perror("pthread_attr_setschedpolicy"); /* error check */  status = pthread_attr_setschedparam(&attrC,&param);  if (status != 0) perror("pthread_attr_setschedparam"); /* error check */  status = pthread_create(&threadC_id, &attrC, threadC, NULL);  if (status != 0) perror("pthread_create"); /* error check */  status = pthread_setschedparam(threadC_id,policy,&param);  if (status != 0) perror("pthread_setschedparam");  /* Join threads - force main to wait for the thread to terminate */    status = pthread_join(threadA_id, NULL);  if (status != 0) perror("pthread_join(threadA_id, NULL)"); /* error check */  status = pthread_join(threadB_id, NULL);  if (status != 0) perror("pthread_join(threadB_id, NULL)"); /* error check */  status = pthread_join(threadC_id, NULL);  if (status != 0) perror("pthread_join(threadC_id, NULL)"); /* error check */    printf("\n");  return(0);  }  /* end of main */void *threadA(void *arg){
     int j;    for(j=1;j<=10;j++){
   	printf("a");  }    return (NULL);}void *threadB(void *arg){
     int j;    for(j=1;j<=10;j++){
   	printf("b");  }  return (NULL);}void *threadC(void *arg){
     int j;    for(j=1;j<=10;j++){
   	printf("c");  }  return (NULL);}

可以使用以下命令编译源代码:

GCC filename.c -o filename -lrt -lpthread
其中filename是源代码文件的名称。生成的可执行文件应该使用sudo来运行，
即，使用以下命令:
sudo ./文件名
检查上面提供的源代码是否适用，并完成下面的练习。检查multithread.c程序的代码，确保您理解了它的功能。

  1. 运行代码并报告输出。要运行这个程序，您需要使用sudo(即，使用
    命令:sudo ./multithread)。简要解释这个程序做什么，以及调度是如何引起观察到的行为的。
    在这里插入图片描述
  • 程序包括三个线程A, B, C，但只使用一个CPU核心。线程的调度策略为FIFO(先到先出)，优先级范围在min和max之间，status用来检查系统调用是否正常返回。
    线程A、B、C按顺序创建。一个线程是for循环，输出10a, B输出10b, C输出10c。按照FIFO调度策略，输出为:aaaaaaaaaabbbbbbbbbbcccccccc。
  1. 修改threadA函数，在打印出一半的字母后，会调用以下两条指令:
param.sched_priority = priority_min+2;pthread_setschedparam(threadB id,policy,&param);

运行修改后的程序并记录输出。解释这种变化对观察到的行为的影响。

在这里插入图片描述

  • 修改两行代码的作用是增加2的for循环的线程优先级线程的输出一半,和进度执行线程B for循环输出B。在执行线程B,因为线程的优先级高于C,所以继续输出5,然后执行线程C。
  1. 使用nanosleep命令修改原始程序，使threadA在打印一半字母后休眠1毫秒。运行代码并报告输出。解释这种变化对观察到的行为的影响。
    在这里插入图片描述
  • nanosleep()函数将导致当前线程暂停执行，直到参数1指定的时间间隔。或者在指定的时间间隔内将信号传递给当前线程，这将导致当前线程调用信号捕获函数或终止线程。
    因此，当ThreadA打印出一半的字母时，它会休眠一毫秒，这足够threadb和threadc在继续执行ThreadA之前完成执行。
  1. 编译并运行critical程序。报告输出。简要解释这个程序做什么，以及调度是如何引起观察到的行为的。
    在这里插入图片描述
  • critical.c包括线程a和线程b，调度策略为FIFO，其余均为多线程。
    依次执行线程A、B，然后销毁
    首先，线程A执行一个非关键操作，输出5个字母，然后执行一个关键操作，输出5个字母。
    然后，线程B的优先级增加到线程a以上，线程B执行一个非关键操作输出5b个字母，执行一个关键操作输出5b个字母。
    接下来，线程A的优先级增加到线程b以上，线程A的优先级更高，调度回线程A，执行关键操作，输出5个A，解锁关键区域，线程A执行非关键操作，输出A的5个字母，线程A结束。
    CPU调度threadB，输出5b，增加threadA的优先级到更高的threadB，最后输出5b。
  1. 修改critical代码，使互斥对象不再被“注释掉”。运行程序并报告输出。简要解释修改后的程序的执行。
    在这里插入图片描述
  • 由于互斥操作的增加，线程会锁定进入临界区，并在输出5a之前进入临界区。此时，线程B基本上具有更高的优先级，无法进入临界区执行输出B的操作。
    当threadA完成执行关键操作时，threadB将立即进入关键区段并执行输出B的关键操作。

以下是2，3，5题修改后的代码

/* * multithread2.c */#define _GNU_SOURCE#define _REENTRANT      /* macro to ensure system calls are reentrant */#include 
   
        /* header file for pthreads */#include 
    
          /* header file for POSIX conformance */#include 
     
             /* header file for POSIX time management */#include 
      
             /* header file for POSIX scheduling */#include 
       
              /* header file for standard input/outputlibrary */void *threadA(void *);   /* predefine threadA routine */void *threadB(void *);   /* predefine threadB routine */void *threadC(void *);   /* predefine threadC routine */pthread_t threadA_id,threadB_id,threadC_id,main_id; /* thread identifiers */pthread_attr_t attrA,attrB,attrC;  /* thread attribute structures */struct sched_param param;          /* scheduling structure for thread attributes */int policy=SCHED_FIFO;int priority_min,priority_max;     /* for range of priority levels *//* main routine */int main(){
     int status;                        /* check that system calls return ok */  /* Set processor affinity */   cpu_set_t mask; CPU_ZERO(&mask); CPU_SET(0,&mask); /* use only 1 CPU core */  unsigned int len = sizeof(mask);  status = sched_setaffinity(0, len, &mask);  if (status < 0) perror("sched_setaffinity");  status = sched_getaffinity(0, len, &mask);  if (status < 0) perror("sched_getaffinity");  /* Find priority limits */  priority_max = sched_get_priority_max(policy);  priority_min = sched_get_priority_min(policy);    /* Set priority and policy of main thread */  main_id = pthread_self();  param.sched_priority=priority_min;  status = pthread_setschedparam(main_id, policy, &param);  if (status != 0) perror("pthread_setschedparam"); /* error check */  /* Create threadA */    param.sched_priority = priority_min;  pthread_attr_init(&attrA);  status = pthread_attr_setschedpolicy(&attrA,policy);  if (status != 0) perror("pthread_attr_setschedpolicy"); /* error check */  status = pthread_attr_setschedparam(&attrA,&param);  if (status != 0) perror("pthread_attr_setschedparam"); /* error check */  status = pthread_create(&threadA_id, &attrA, threadA, NULL);  if (status != 0) perror("pthread_create"); /* error check */  status = pthread_setschedparam(threadA_id,policy,&param);  if (status != 0) perror("pthread_setschedparam");  /* Create threadB */    param.sched_priority = priority_min;  pthread_attr_init(&attrB);  status = pthread_attr_setschedpolicy(&attrB,policy);  if (status != 0) perror("pthread_attr_setschedpolicy"); /* error check */  status = pthread_attr_setschedparam(&attrB,&param);  if (status != 0) perror("pthread_attr_setschedparam"); /* error check */  status = pthread_create(&threadB_id, &attrB, threadB, NULL);  if (status != 0) perror("pthread_create"); /* error check */  status = pthread_setschedparam(threadB_id,policy,&param);  if (status != 0) perror("pthread_setschedparam");    /* Create threadC */    param.sched_priority = priority_min;  pthread_attr_init(&attrC);  status = pthread_attr_setschedpolicy(&attrC,policy);  if (status != 0) perror("pthread_attr_setschedpolicy"); /* error check */  status = pthread_attr_setschedparam(&attrC,&param);  if (status != 0) perror("pthread_attr_setschedparam"); /* error check */  status = pthread_create(&threadC_id, &attrC, threadC, NULL);  if (status != 0) perror("pthread_create"); /* error check */  status = pthread_setschedparam(threadC_id,policy,&param);  if (status != 0) perror("pthread_setschedparam");  /* Join threads - force main to wait for the thread to terminate */    status = pthread_join(threadA_id, NULL);  if (status != 0) perror("pthread_join(threadA_id, NULL)"); /* error check */  status = pthread_join(threadB_id, NULL);  if (status != 0) perror("pthread_join(threadB_id, NULL)"); /* error check */  status = pthread_join(threadC_id, NULL);  if (status != 0) perror("pthread_join(threadC_id, NULL)"); /* error check */    printf("\n");  return(0);  }  /* end of main */void *threadA(void *arg){
     int j;    for(j=1;j<=10;j++){
   	printf("a");	if(j==5){
   		param.sched_priority = priority_min+2;		pthread_setschedparam(threadB_id,policy,&param);	}	  }    return (NULL);}void *threadB(void *arg){
     int j;    for(j=1;j<=10;j++){
   	printf("b");  }  return (NULL);}void *threadC(void *arg){
     int j;    for(j=1;j<=10;j++){
   	printf("c");  }  return (NULL);}
       
      
     
    
   
/* * multithread3.c */#define _GNU_SOURCE#define _REENTRANT      /* macro to ensure system calls are reentrant */#include 
   
        /* header file for pthreads */#include 
    
          /* header file for POSIX conformance */#include 
     
             /* header file for POSIX time management */#include 
      
             /* header file for POSIX scheduling */#include 
       
              /* header file for standard input/outputlibrary */void *threadA(void *);   /* predefine threadA routine */void *threadB(void *);   /* predefine threadB routine */void *threadC(void *);   /* predefine threadC routine */pthread_t threadA_id,threadB_id,threadC_id,main_id; /* thread identifiers */pthread_attr_t attrA,attrB,attrC;  /* thread attribute structures */struct sched_param param;          /* scheduling structure for thread attributes */int policy=SCHED_FIFO;int priority_min,priority_max;     /* for range of priority levels *//* main routine */int main(){
     int status;                        /* check that system calls return ok */  /* Set processor affinity */   cpu_set_t mask; CPU_ZERO(&mask); CPU_SET(0,&mask); /* use only 1 CPU core */  unsigned int len = sizeof(mask);  status = sched_setaffinity(0, len, &mask);  if (status < 0) perror("sched_setaffinity");  status = sched_getaffinity(0, len, &mask);  if (status < 0) perror("sched_getaffinity");  /* Find priority limits */  priority_max = sched_get_priority_max(policy);  priority_min = sched_get_priority_min(policy);    /* Set priority and policy of main thread */  main_id = pthread_self();  param.sched_priority=priority_min;  status = pthread_setschedparam(main_id, policy, &param);  if (status != 0) perror("pthread_setschedparam"); /* error check */  /* Create threadA */    param.sched_priority = priority_min;  pthread_attr_init(&attrA);  status = pthread_attr_setschedpolicy(&attrA,policy);  if (status != 0) perror("pthread_attr_setschedpolicy"); /* error check */  status = pthread_attr_setschedparam(&attrA,&param);  if (status != 0) perror("pthread_attr_setschedparam"); /* error check */  status = pthread_create(&threadA_id, &attrA, threadA, NULL);  if (status != 0) perror("pthread_create"); /* error check */  status = pthread_setschedparam(threadA_id,policy,&param);  if (status != 0) perror("pthread_setschedparam");  /* Create threadB */    param.sched_priority = priority_min;  pthread_attr_init(&attrB);  status = pthread_attr_setschedpolicy(&attrB,policy);  if (status != 0) perror("pthread_attr_setschedpolicy"); /* error check */  status = pthread_attr_setschedparam(&attrB,&param);  if (status != 0) perror("pthread_attr_setschedparam"); /* error check */  status = pthread_create(&threadB_id, &attrB, threadB, NULL);  if (status != 0) perror("pthread_create"); /* error check */  status = pthread_setschedparam(threadB_id,policy,&param);  if (status != 0) perror("pthread_setschedparam");    /* Create threadC */    param.sched_priority = priority_min;  pthread_attr_init(&attrC);  status = pthread_attr_setschedpolicy(&attrC,policy);  if (status != 0) perror("pthread_attr_setschedpolicy"); /* error check */  status = pthread_attr_setschedparam(&attrC,&param);  if (status != 0) perror("pthread_attr_setschedparam"); /* error check */  status = pthread_create(&threadC_id, &attrC, threadC, NULL);  if (status != 0) perror("pthread_create"); /* error check */  status = pthread_setschedparam(threadC_id,policy,&param);  if (status != 0) perror("pthread_setschedparam");  /* Join threads - force main to wait for the thread to terminate */    status = pthread_join(threadA_id, NULL);  if (status != 0) perror("pthread_join(threadA_id, NULL)"); /* error check */  status = pthread_join(threadB_id, NULL);  if (status != 0) perror("pthread_join(threadB_id, NULL)"); /* error check */  status = pthread_join(threadC_id, NULL);  if (status != 0) perror("pthread_join(threadC_id, NULL)"); /* error check */    printf("\n");  return(0);  }  /* end of main */void *threadA(void *arg){
     int j;    for(j=1;j<=10;j++){
   	printf("a");	if(j==5){
   	      struct timespec req  =  {
    0 },  rem  =  {
   0};                req.tv_sec  =  0;                req.tv_nsec  =  1000000L;                nanosleep (&req ,  &rem) ;	}	  }    return (NULL);}void *threadB(void *arg){
     int j;    for(j=1;j<=10;j++){
   	printf("b");  }  return (NULL);}void *threadC(void *arg){
     int j;    for(j=1;j<=10;j++){
   	printf("c");  }  return (NULL);}
       
      
     
    
   
/* * critical2.c */#define _GNU_SOURCE#define _REENTRANT      /* macro to ensure system calls are reentrant */#include 
   
        /* header file for pthreads */#include 
    
          /* header file for POSIX conformance */#include 
     
             /* header file for POSIX time management */#include 
      
             /* header file for POSIX scheduling */#include 
       
              /* header file for standard input/outputlibrary */pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER; /*define mutex */void *threadA(void *);   /* predefine threadA routine */void *threadB(void *);   /* predefine threadB routine */pthread_t threadA_id,threadB_id,main_id; /* thread identifiers */pthread_attr_t attrA,attrB;        /* thread attribute structures */struct sched_param param;          /* scheduling structure for thread attributes */int policy=SCHED_FIFO;int priority_min,priority_max;     /* for range of priority levels *//* main routine */int main(){
     int status;                        /* check that system calls return ok */  /* Set processor affinity */   cpu_set_t mask; CPU_ZERO(&mask); CPU_SET(0,&mask); /* use only 1 CPU core */  unsigned int len = sizeof(mask);  status = sched_setaffinity(0, len, &mask);  if (status < 0) perror("sched_setaffinity");  status = sched_getaffinity(0, len, &mask);  if (status < 0) perror("sched_getaffinity");  /* Find priority limits */  priority_max = sched_get_priority_max(policy);  priority_min = sched_get_priority_min(policy);    /* Set priority and policy of main thread */  main_id = pthread_self();  param.sched_priority=priority_min;  status = pthread_setschedparam(main_id, policy, &param);  if (status != 0) perror("pthread_setschedparam"); /* error check */  /* Create threadA */    param.sched_priority = priority_min;  pthread_attr_init(&attrA);  status = pthread_attr_setschedpolicy(&attrA,policy);  if (status != 0) perror("pthread_attr_setschedpolicy"); /* error check */  status = pthread_attr_setschedparam(&attrA,&param);  if (status != 0) perror("pthread_attr_setschedparam"); /* error check */  status = pthread_create(&threadA_id, &attrA, threadA, NULL);  if (status != 0) perror("pthread_create"); /* error check */  status = pthread_setschedparam(threadA_id,policy,&param);  if (status != 0) perror("pthread_setschedparam");  /* Create threadB */    param.sched_priority = priority_min;  pthread_attr_init(&attrB);  status = pthread_attr_setschedpolicy(&attrB,policy);  if (status != 0) perror("pthread_attr_setschedpolicy"); /* error check */  status = pthread_attr_setschedparam(&attrB,&param);  if (status != 0) perror("pthread_attr_setschedparam"); /* error check */  status = pthread_create(&threadB_id, &attrB, threadB, NULL);  if (status != 0) perror("pthread_create"); /* error check */  status = pthread_setschedparam(threadB_id,policy,&param);  if (status != 0) perror("pthread_setschedparam");  /* Join threads - force main to wait for the thread to terminate */    status = pthread_join(threadA_id, NULL);  if (status != 0) perror("pthread_join(threadA_id, NULL)"); /* error check */  status = pthread_join(threadB_id, NULL);  if (status != 0) perror("pthread_join(threadB_id, NULL)"); /* error check */    status = pthread_mutex_destroy(&mtx); /* delete mutex */  if (status != 0) perror("pthread_mutex_destroy"); /* error check */    printf("\n");  return(0);  }  /* end of main */void *threadA(void *arg){
     int j;  int status;                        /* check that system calls return ok */      for(j=1;j<=5;j++){
   	printf("a");                     /* non -critical */  }    /* lock to enter critical region */  status = pthread_mutex_lock(&mtx);  if (status != 0) perror("pthread_mutex_lock"); /* error check */    for(j=1;j<=5;j++){
   	printf("A");                    /* critical */  }    /* increment priority of threadB above threadA */    param.sched_priority++;   status = pthread_setschedparam(threadB_id,policy,&param);  if (status != 0) perror("pthread_setschedparam"); /* error check */    for(j=1;j<=5;j++){
   	printf("A");                     /* critical */  }    /* unlock critical region */  status = pthread_mutex_unlock(&mtx);   if (status != 0) perror("pthread_mutex_unlock"); /* error check */    for(j=1;j<=5;j++){
   	printf("a");                     /* non -critical */  }    return (NULL);}void *threadB(void *arg){
     int j;  int status;                        /* check that system calls return ok */    for(j=1;j<=5;j++){
   	printf("b");                     /* non -critical */  }    /* lock to enter critical region */  status = pthread_mutex_lock(&mtx);    if (status != 0) perror("pthread_mutex_lock"); /* error check */      for(j=1;j<=5;j++){
   	printf("B");                     /* critical */  }    /* increment priority of threadA to above threadB*/    param.sched_priority++;   status = pthread_setschedparam(threadA_id,policy,&param);  if (status != 0) perror("pthread_setschedparam"); /* error check */    for(j=1;j<=5;j++){
   	printf("B");                    /* critical */  }  /* unlock critical region */  status = pthread_mutex_unlock(&mtx);    if (status != 0) perror("pthread_mutex_unlock"); /* error check */    for(j=1;j<=5;j++){
   	printf("b");                     /* non -critical */  }    return (NULL);}

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初次前来，多多关照！
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