读书笔记：第9章 记录上锁 (1)
《UNIX网络编程：卷2》P155-P156：图9-2
不上锁的加1测试
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/*
* lockmain.c
* 图9-2 文件上锁例子的main函数
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#define FILE_MODE (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)
#define MAXLINE 1024
#define SEQFILE "seqno"
void my_lock(int fd);
void my_unlock(int fd);
int main(int argc, char *argv[])
{
int fd;
long i, seqno;
pid_t pid;
ssize_t n;
char line[MAXLINE + 1];
pid = getpid(); // 获取进程ID
// 打开文件
if ((fd = open(SEQFILE, O_RDWR, FILE_MODE)) < 0) {
fprintf(stderr, "open %s error: %s\n", SEQFILE, strerror(errno));
exit(1);
}
for (i = 0; i < 20; i++) {
my_lock(fd); // 锁定文件
lseek(fd, 0L, SEEK_SET); //定位到文件开始位置
if ((n = read(fd, line, MAXLINE)) < 0) { // 读取一行
fprintf(stderr, "read error: %s\n", strerror(errno));
exit(1);
}
line[n] = '\0';
n = sscanf(line, "%ld\n", &seqno); // 将字符转换成数字
printf("%s: pid = %d, seq# = %ld\n", argv[0], pid, seqno);
seqno++; // 加1
snprintf(line, sizeof(line), "%ld\n", seqno); // 将数字写回缓冲区
lseek(fd, 0L, SEEK_SET); // 定位到文件开始处
if (write(fd, line, strlen(line)) < 0) { // 将缓冲区内容写回文件
fprintf(stderr, "write error: %s\n", strerror(errno));
exit(1);
}
my_unlock(fd); // 解锁文件
}
exit(0);
}
/*
* locknone.c
* P155 图9-1 不上锁的函数
*/
void my_lock(int fd)
{
return; // 不做任何事情，直接返回
}
void my_unlock(int fd)
{
return; // 不做任何事情，直接返回
}
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创建文件seqno，并写入1。运行程序：
$ ./locknone & ./locknone & [1] 2805 [2] 2806 $ ./locknone: pid = 2806, seq# = 1 ./locknone: pid = 2806, seq# = 2 ./locknone: pid = 2806, seq# = 3 ./locknone: pid = 2806, seq# = 4 ./locknone: pid = 2806, seq# = 5 ./locknone: pid = 2806, seq# = 6 ./locknone: pid = 2806, seq# = 7 ./locknone: pid = 2806, seq# = 8 ./locknone: pid = 2806, seq# = 9 ./locknone: pid = 2806, seq# = 10 ./locknone: pid = 2806, seq# = 11 ./locknone: pid = 2806, seq# = 12 ./locknone: pid = 2806, seq# = 13 ./locknone: pid = 2806, seq# = 14 ./locknone: pid = 2806, seq# = 15 ./locknone: pid = 2806, seq# = 16 ./locknone: pid = 2805, seq# = 15 开始出错了 ./locknone: pid = 2806, seq# = 17 ./locknone: pid = 2806, seq# = 18 ./locknone: pid = 2806, seq# = 19 ./locknone: pid = 2805, seq# = 19 ./locknone: pid = 2806, seq# = 20 ./locknone: pid = 2805, seq# = 20 ./locknone: pid = 2805, seq# = 21 ./locknone: pid = 2805, seq# = 22 ./locknone: pid = 2805, seq# = 23 ./locknone: pid = 2805, seq# = 24 ./locknone: pid = 2805, seq# = 25 ./locknone: pid = 2805, seq# = 26 ./locknone: pid = 2805, seq# = 27 ./locknone: pid = 2805, seq# = 28 ./locknone: pid = 2805, seq# = 29 ./locknone: pid = 2805, seq# = 30 ./locknone: pid = 2805, seq# = 31 ./locknone: pid = 2805, seq# = 32 ./locknone: pid = 2805, seq# = 33 ./locknone: pid = 2805, seq# = 34 ./locknone: pid = 2805, seq# = 35 ./locknone: pid = 2805, seq# = 36 ./locknone: pid = 2805, seq# = 37 [1]- 完成 ./locknone [2]+ 完成 ./locknone