一道多线程编程题初解
本帖最后由 cjdao 于 2013-05-30 17:23 编辑请各位指点指点
/*
* 作者: cjdao@163.com
* 日期：2013-05-29
* 描述：
* 有四个线程1、2、3、4。线程1的功能就是输出A，线程2的功能就是输出B，以此类推.........
* 现在有四个文件file1, file2,file3, file4。初始都为空。现要让四个文件呈如下格式：
* file1：A B C D A B....
* file2：B C D A B C....
* file3：C D A B C D....
* file4：D A B C D A....
*/
#include <stdio.h>
#include <pthread.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
pthread_t threads;
char writer_char = {'A','B', 'C', 'D'};
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
struct file_res{
pthread_t *writer; /*当前文件可以被哪个线程写入*/
int fd; /*文件描述符*/
}file_res =
{
{.writer=&threads},/*file1初始化可以被线程1写入'A'*/
{.writer=&threads},/*file2初始化可以被线程1写入'B'*/
{.writer=&threads},/*file3初始化可以被线程1写入'C'*/
{.writer=&threads},/*file4初始化可以被线程1写入'D'*/
};
void *writer_routine(void *arg)
{
int index = (int)arg;
int file_index ;
int can_write_file_cnt = 0;
int i = 0;
int next_index=0;
printf("thread %d is running, and will write '%c' to files\n", index, writer_char);
while(1)
{
if (0!=pthread_mutex_lock(&mutex))
exit(-1);
for( ;; ) {
/*下面的for语句查询本线程可以写的文件id*/
for(i=0; i<(sizeof(file_res)/sizeof(file_res)); i++) {
if (&threads==file_res.writer) {
file_index = i;
next_index = index+1;
if (next_index>3)next_index=0;
file_res.writer = &threads;
}
}
/*找到本线程可以写的文件id,则退出for( ;; ), 执行写操作*/
if (can_write_file_cnt != 0)
break;
/*没有可以写的文件, 等待其他线程唤醒*/
pthread_cond_wait(&cond,&mutex);
}
/*针对本线程可以写的文件,执行写操作*/
for(i=0; i<can_write_file_cnt; i++) {
write(file_res].fd, &writer_char, sizeof(writer_char));
}
can_write_file_cnt = 0;
/*唤醒下一批线程*/
pthread_cond_broadcast(&cond);
if (0!=pthread_mutex_unlock(&mutex))
exit(-1);
}
}
int main(int argc, char* argv[])
{
int i;
for(i=0; i<4; i++)
{
char file_name[] = "filex";
sprintf(file_name, "file%d", i+1);
if ((file_res.fd = open(file_name, O_RDWR|O_CREAT|O_TRUNC, 0666))<0)
{
printf("open %s error.\n", file_name);
exit(-1);
}
}
for (i=0; i<(sizeof(threads)/sizeof(pthread_t)); i++)
{
if(pthread_create(&threads, NULL, writer_routine, (void *)i))
{
printf("create writer thread error\n");
exit(-1);
}
}
pthread_exit(NULL);
}
初解??????
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