一、 管道
1. 匿名管道
用于进程间通信, 创建一个管道,一端写,一端读
#include <unistd.h>
int pipe(int fildes[2]);
fides[0]读取,fides[1]写入
成功返回0,失败返回-1
示例代码
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
int main()
{
int fd[2];
int ret = pipe(fd);
if(ret == -1)
{
printf("pipe error: %s\n", strerror(errno));
}
pid_t pid = fork();
if(pid == 0)
{
char buf[128];
printf("before read\n");
sleep(5);
ssize_t chars_read = read(fd[0], buf, sizeof(buf));
printf("end read\n");
printf("chars_read = %ld, data = %s\n", chars_read, buf);
}
else if(pid > 0)
{
char str[] = "hello world";
printf("before write\n");
// sleep(5);
ssize_t chars_write = write(fd[1], str, strlen(str));
chars_write += write(fd[1], str, strlen(str));
printf("end write\n");
printf("chars_write = %ld\n", chars_write);
}
getchar();
return 0;
}
通过在示例中添加额外代码测试,可知:
- 管道读入端会一直阻塞,直到有数据写入才返回;
- 写入端即使没有读入段,依旧能写入,不阻塞。
- 如果多次写入,读取端一次能读取到所有数据
通信速度测试
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <time.h>
int main()
{
int fd[2];
int ret = pipe(fd);
if(ret == -1)
{
printf("pipe error: %s\n", strerror(errno));
}
pid_t pid = fork();
if(pid == 0)
{
timespec t0, t1;
while (true)
{
read(fd[0], &t0, sizeof(timespec));
clock_gettime(CLOCK_REALTIME, &t1);
printf("%lds, %ldns\n", t1.tv_sec - t0.tv_sec, t1.tv_nsec - t0.tv_nsec);
}
}
else if(pid > 0)
{
timespec t0;
while (true)
{
sleep(1);
clock_gettime(CLOCK_REALTIME, &t0);
write(fd[1], &t0, sizeof(timespec));
}
}
getchar();
return 0;
}
输出结果:
0s, 85000ns
0s, 45000ns
0s, 43000ns
0s, 31000ns
0s, 40000ns
0s, 37000ns
0s, 32000ns
0s, 40000ns
...
大约通信一次速度 35us