加锁、解锁及测试代码 lock.c
#include <stdio.h>
#include <stdlib.h>
#include <sys/file.h>
#include <errno.h>
#include <string.h>
#define TRUE 1
#define FALSE 0
/**
* @brief 尝试获取文件锁
* @details 获取文件锁时不会阻塞进程, 获取不到锁时，立即返回不会等待
* @param fd 文件描述符
* @return 是否成功获取文件锁
* @retval TRUE 获取锁成功
* @retval FALSE 获取锁失败
* @attention 这里只是建议性锁，每个使用上锁文件的进程都要检查是否有锁存在，
* 内核不对读写操作做内部检查和强制保护
* @see ngx_trylock_fd
* @ref [http://agentzh.org/misc/code/nginx/os/unix/ngx_files.c.html#L416]
*/
int trylock_fd(int fd)
{
struct flock fl;
memset(&fl, 0, sizeof(struct flock));
fl.l_type = F_WRLCK;
fl.l_whence = SEEK_SET;
if (fcntl(fd, F_SETLK, &fl) == -1) {
return FALSE;
} else {
return TRUE;
}
}
/**
* @brief 获取锁或等待
* @details 获取文件锁时会阻塞进程, 获取不到锁时，一直等到获取成功
* @param fd 文件描述符
* @return 是否成功获取文件锁
* @retval TRUE 获取锁成功
* @retval FALSE 获取锁失败
* @attention 这里只是建议性锁，每个使用上锁文件的进程都要检查是否有锁存在，
* 内核不对读写操作做内部检查和强制保护
* @see ngx_lock_fd
* @ref [http://agentzh.org/misc/code/nginx/os/unix/ngx_files.c.html#L433]
*/
int waitlock_fd(int fd)
{
struct flock fl;
memset(&fl, 0, sizeof(struct flock));
fl.l_type = F_WRLCK;
fl.l_whence = SEEK_SET;
if (fcntl(fd, F_SETLKW, &fl) == -1) {
return FALSE;
} else {
return TRUE;
}
}
/**
* @brief 释放文件锁
* @param fd 文件描述符
* @return 是否成功释放文件锁
* @retval TRUE 释放锁成功
* @retval FALSE 释放锁失败
* @see ngx_unlock_fd
* @ref [http://agentzh.org/misc/code/nginx/os/unix/ngx_files.c.html#L450]
*/
int unlock_fd(int fd)
{
struct flock fl;
memset(&fl, 0, sizeof(struct flock));
fl.l_type = F_UNLCK;
fl.l_whence = SEEK_SET;
if (fcntl(fd, F_SETLK, &fl) == -1) {
return FALSE;
} else {
return TRUE;
}
}
/**
* @brief 检查是否设置了文件锁
* @details 检查文件锁状况，并输出相关信息
* @param fd 文件描述符
*/
void checklock_fd(int fd)
{
struct flock fl;
memset(&fl, 0, sizeof(struct flock));
fl.l_whence = SEEK_SET;
if (fcntl(fd, F_GETLK, &fl) == -1) {
printf("failed to check file lock. detail: %s(%d)\n",
strerror(errno), errno);
return;
} else {
switch (fl.l_type) {
case F_UNLCK:
printf("no file lock\n");
break;
case F_RDLCK:
printf("read lock already set by %d\n", fl.l_pid);
break;
case F_WRLCK:
printf("write lock already set by %d\n", fl.l_pid);
break;
}
return;
}
}
/**
* @brief 主函数
* @details 测试获取锁、检查锁、释放锁的函数
* @param argc 命令参数个数
* @param argv 命令参数指针数组
* @return 程序执行成功与否
* @retval 0 程序执行成功
* @retval 1 程序执行失败
*/
int main(int argc, char *argv[])
{
int fd;
char *file;
pid_t pid;
if (argc == 2) {
file = argv[1];
} else {
file = "file.lock";
}
pid = getpid();
fd = open(file, O_RDWR|O_CREAT, 0666);
if (fd < 0) {
fprintf(stderr, "failed to open \"%s\", detail: %s(%d)\n",
file, strerror(errno), errno);
exit(1);
}
if(trylock_fd(fd)) {
printf("file has been locked by %d. press any key to unlock\n", pid);
} else {
printf("waiting for lock\n");
checklock_fd(fd);
waitlock_fd(fd);
printf("file has been locked by %d. press any key to unlock\n", pid);
}
getchar();
unlock_fd(fd);
printf("file has been unlocked by %d.\n", pid);
close(fd);
exit(0);
}
编译
# gcc lock.c -o lock
测试验证
窗口1
# ./lock
file has been locked by 3286. press any key to unlock
<-- 1) 按任意键，释放锁
file has been unlocked by 3286.
窗口2
# ./lock
waiting for lock
write lock already set by 3286
<-- 等待锁释放，1)按下任意键后继续
file has been locked by 3287. press any key to unlock
<-- 2) 按任意键，释放锁
file has been unlocked by 3287.
