我想将以下消息“无限美好!”打印为无限大。 ,从头开始,我有3个线程来完成这项工作,第一个是“什么一个,第二个是“精彩”,第三个是“世界”,(我在./a.out 3中作为参数给出),问题出在下面的代码是这样显示的消息:What a wonderful what a wonderful
World
丢失了。我认为条件变量有些不好,有什么建议吗?
int p;
void *disp(void *arg);
pthread_mutex_t muta,mutb,mutc;
pthread_cond_t condition_cond= PTHREAD_COND_INITIALIZER;
void *disp(void *arg)
{
int id=*(int*)arg;
free(arg);
arg=0;
pthread_mutex_lock(&muta);
while (id==0)
{
pthread_cond_wait (&condition_cond,&muta);
}
printf("What a");
pthread_mutex_unlock(&muta);
pthread_mutex_lock(&mutb);
while (id==1)
{
pthread_cond_wait (&condition_cond,&mutb);
}
printf(" Wonderful");
pthread_mutex_unlock(&mutb);
pthread_mutex_lock(&mutc);
while(id==2)
{
pthread_cond_wait (&condition_cond,&mutc);
}
printf(" World!\n");
pthread_mutex_unlock(&mutc);
return NULL;
}
编辑:基于dbush的答案更新了代码:
#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
#include <semaphore.h>
#include <unistd.h>
int p;
void *disp(void *arg);
pthread_mutex_t mut=PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond1= PTHREAD_COND_INITIALIZER;
pthread_cond_t cond2= PTHREAD_COND_INITIALIZER;
pthread_cond_t cond3= PTHREAD_COND_INITIALIZER;
void *disp(void *arg)
{
int id=*(int*)arg;
free(arg);
arg=0;
pthread_mutex_lock(&mut);
while(1)
{
if (id==0)
{
pthread_cond_wait (&cond1,&mut);
printf("What a ");
pthread_cond_signal (&cond2);
}
else if(id==1)
{
pthread_cond_wait (&cond2,&mut);
printf(" wonderful ");
pthread_cond_signal (&cond3);
}
else if(id==2)
{
pthread_cond_wait (&cond3,&mut);
printf(" world!\n ");
pthread_cond_signal (&cond1);
}
}
return NULL;
}
int main (int argc,char *argv[])
{
int i;
pthread_t *tid;
if(argc!=2)
{
printf("Provide number of threads.\n");
exit(1);
}
p=atoi(argv[1]);
tid=(pthread_t *) malloc (p*sizeof(pthread_t));
if (tid==NULL)
{
printf("Could not allocate memory.\n");
exit(1);
}
for (i=0;i<p;++i)
{
int *a;
a=malloc(sizeof(int)); //pointer to pass
*a=i;
pthread_create(&tid[i],NULL,disp,a);
}
pthread_cond_signal(&cond1);
for (i=0;i<p;++i)
pthread_join(tid[i],NULL);
return 0;
}
答案 0 :(得分:0)
互斥量和条件变量的用法已颠倒了。您需要一个互斥锁来控制所有三个线程,以及三个条件变量(每个线程一个)。
每个线程完成其工作后,应使用目标线程的条件变量来发信号通知下一个线程。另外,main函数需要向第一个线程发出信号以开始操作。您希望它休眠一小段时间,以便所有线程都有时间启动。
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
void *disp(void *arg);
pthread_mutex_t mux = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond1= PTHREAD_COND_INITIALIZER;
pthread_cond_t cond2= PTHREAD_COND_INITIALIZER;
pthread_cond_t cond3= PTHREAD_COND_INITIALIZER;
void *disp(void *arg)
{
int id=*(int*)arg;
free(arg);
arg=0;
pthread_mutex_lock(&mux);
while (1) {
if (id==0) {
pthread_cond_wait (&cond1,&mux);
printf("What a");
pthread_cond_signal(&cond2);
} else if (id == 1) {
pthread_cond_wait (&cond2,&mux);
printf(" Wonderful");
pthread_cond_signal(&cond3);
} else if (id == 2) {
pthread_cond_wait (&cond3,&mux);
printf(" World!\n");
pthread_cond_signal(&cond1);
}
}
return NULL;
}
int main()
{
pthread_t t1, t2, t3;
int *id = malloc(sizeof(int));
*id=0;
pthread_create(&t1, NULL, disp, id);
id = malloc(sizeof(int));
*id=1;
pthread_create(&t2, NULL, disp, id);
id = malloc(sizeof(int));
*id=2;
pthread_create(&t3, NULL, disp, id);
sleep(1);
pthread_cond_signal(&cond1);
pthread_join(t1, NULL);
pthread_join(t2, NULL);
pthread_join(t3, NULL);
return 0;
}