/*
?*?設置記錄鎖子函數lock_set.c
?*
?*?記錄鎖分為讀取鎖和寫入鎖，其中讀取鎖又稱為共享鎖，可以使多個
?*?進程都能夠在文件的同一部分建立讀取鎖。而寫入鎖又稱為互斥鎖，
?*?在任何時刻只能有一個進程在文件的某個部分建立寫入鎖。當然，在
?*?文件的同一部分不能同時建立讀取鎖和寫入鎖。
?*
?*?fcntl的lock結構如下所示：
?*?struct?flock?{
?*?short?l_type;
?*?off_t?l_start;
?*?short?l_whence;
?*?off_t?l_len;
?*?pid_t?l_pid;
?*?}
?*
?*?技巧：為加鎖整個文件，通常的方法是將l_start說明為0，l_whence
?*?說明為SEEK_SET，l_len說明為0。
?*/
#include?
#include?
#include?

#include?
#include?
#include?


void?print_lock（struct?flock?lock）
{
????????printf（“?-----------------------------\n“）;

????????if?（lock.l_type?==?F_RDLCK）?{
????????????????printf（“\tl_type:?F_RDLCK\n“）;
????????}
????????else?if?（lock.l_type?==?F_WRLCK）?{
????????????????printf（“\tl_type:?F_WRLCK\n“）;
????????}
????????else?if?（lock.l_type?==?F_UNLCK）?{
????????????????printf（“\tl_type:?F_UNLCK\n“）;
????????}

????????printf（“\tl_start:?%d\n“?（int）lock.l_start）;

????????if?（lock.l_whence?==?SEEK_SET）?{
????????????????printf（“\tl_whence:?SEEK_SET\n“）;
????????}
????????else?if?（lock.l_whence?==?SEEK_CUR）?{
????????????????printf（“\tl_whence:?SEEK_CUR\n“）;
????????}
????????else?if?（lock.l_whence?==?SEEK_END）?{
????????????????printf（“\tl_whence:?SEEK_END\n“）;
????????}

????????printf（“\tl_len:?%d\n“?（int）lock.l_len）;

????????printf（“?-----------------------------\n“）;
}

void?lock_set（int?fd?int?type）
{
????????struct?flock?lock;

????????/*賦值lock結構體，加鎖整個文件*/
????????lock.l_whence?=?SEEK_SET;
????????lock.l_start?=?0;
????????lock.l_len?=?0;

????????while?（1）?{
????????????????lock.l_type?=?type;

????????????????/*
?????????????????*?根據不同的type來給文件加鎖或解鎖，
?????????????????*?如果成功，則返回0，失敗則返回1。
?????????????????*?舉例：如果一個文件原來已經建立了互斥鎖，那么再調用fcntl
?????????????????*?建立鎖就會失敗，返回-1。
?????????????????*/
????????????????if?（（fcntl（fd?F_SETLK?&lock））?==?0）?{
????????????????????????/*如果是共享鎖*/
????????????????????????if?（lock.l_type?==?F_RDLCK）?{
????????????????????????????????printf（“read?only?set?by?%d\n“?getpid（））;
????????????????????????}
????????????????????????/*如果是互斥鎖*/
????????????????????????else?if?（lock.l_type?==?F_WRLCK）?{
????????????????????????????????printf（“write?lock?set?by?%d\n“?getpid（））;
??