Experiment 1: Example of leaky bucket, flow control, output cat10 characters per second to standard output
signal + alarm + pause + signal interrupts blocked system calls
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>
#define BUFSIZE 10
static volatile int loop = 0;
static void alrm_handler(int s)
{
alarm(1);//重新定时
loop = 1;
}
int main(int argc,char *argv[])
{
int sfd,dfd=1;
char buf[BUFSIZE];
int len,ret,pos;
if(argc < 2)
{
fprintf(stderr,"Usage:%s <src_file> <dest_file>\n",argv[0]);
exit(1);
}
signal(SIGALRM,alrm_handler);
alarm(1);
do
{
sfd = open(argv[1],O_RDONLY);
if(sfd < 0)
{
if(errno != EINTR)//防止是 信号打断阻塞的系统调用
{
perror("open()");
exit(1);
}
}
}while(sfd < 0);
while(1)
{
//休眠挂起 直到收到信号，重新开始执行while(!loop)循环，实现一秒一输出
// 这里也可以 不用pause()，while()后 执行空，但是这样 CPU 占用率会很高，一秒钟会在这里执行循环上亿次，所以用pause()替换，直接休眠等待信号来唤醒
/*
while(!loop)
;
*/
while(!loop)
pause();
loop = 0;
while((len = read(sfd,buf,BUFSIZE)) < 0)
{
if(errno == EINTR)//防止是 信号打断阻塞的系统调用
continue;
perror("read()");
break;
}
if(len == 0)
break;
//确保写进去 len 个字节
pos = 0;
while(len > 0)
{
ret = write(dfd,buf+pos,len);
if(ret < 0)
{
if(errno == EINTR) //防止是 信号打断阻塞的系统调用
continue;
perror("write()");
exit(1);
}
pos += ret;
len -= ret;
}
}
close(sfd);
}
Disadvantages:
If you are reading a printer-like device, and there is no data on the printer at the time, the program will always loop at the read position
while((len = read(sfd,buf,BUFSIZE)) < 0)
{
if(errno == EINTR)//防止是 信号打断阻塞的系统调用
continue;
即 一直循环于：
读阻塞 ，打断阻塞 判断是假错误(信号打断阻塞的系统调用) 返回重新读 。。。。
读阻塞 ，打断阻塞 判断是假错误(信号打断阻塞的系统调用) 返回重新读 。。。。
读阻塞 ，打断阻塞 判断是假错误(信号打断阻塞的系统调用) 返回重新读 。。。。
Therefore, the defect of the leaky bucket is that if there is no data, it will wait in a loop until there is data. If the amount of data is suddenly large, the data cannot be read quickly, only 10 bytes per second slowly. Read n times
The advantage of the token bucket is that when there is no data to read, it will accumulate its own permissions. This means that if there has been no data for 30 seconds before reading for 30 seconds, then 30 permissions will be saved and wait until there is data. , Use the first 30 permissions quickly and read 30 times in quick succession.
Experiment 2: Token Bucket Example
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>
#define CPS 10
#define BUFSIZE CPS
#define BURST 100
static volatile int token = 0;
static void alrm_handler(int s)
{
alarm(1);
token++;
if(token > BURST)
token = BURST;
}
int main(int argc,char *argv[])
{
int sfd,dfd=1;
char buf[BUFSIZE];
int len,ret,pos;
if(argc < 2)
{
fprintf(stderr,"Usage:%s <src_file> <dest_file>\n",argv[0]);
exit(1);
}
signal(SIGALRM,alrm_handler);
alarm(1);
do
{
sfd = open(argv[1],O_RDONLY);
if(sfd < 0)
{
if(errno != EINTR)//signal
{
perror("open()");
exit(1);
}
}
}while(sfd < 0);
while(1)
{
while(token <= 0)
pause();
token--;
while((len = read(sfd,buf,BUFSIZE)) < 0)
{ if(errno == EINTR)//signal
continue;
perror("read()");
break;
}
if(len == 0)
break;
//确保写进去 len 个字节
pos = 0;
while(len > 0)
{
ret = write(dfd,buf+pos,len);
if(ret < 0)
{
if(errno == EINTR) //signal
continue;
perror("write()");
exit(1);
}
pos += ret;
len -= ret;
}
}
close(sfd);
}