uuid_short() 源代码

/*
uuid_short handling.

The short uuid is defined as a longlong that contains the following bytes:

Bytes Comment
1 Server_id & 255
4 Startup time of server in seconds
3 Incrementor

This means that an uuid is guaranteed to be unique
even in a replication environment if the following holds:

- The last byte of the server id is unique
- If you between two shutdown of the server don't get more than
an average of 2^24 = 16M calls to uuid_short() per second.
*/

ulonglong uuid_value;

void uuid_short_init()
{
uuid_value= ((((ulonglong) server_id) << 56) + 
(((ulonglong) server_start_time) << 24));
}


longlong Item_func_uuid_short::val_int()
{
ulonglong val;
mysql_mutex_lock(&LOCK_uuid_generator);
val= uuid_value++;
mysql_mutex_unlock(&LOCK_uuid_generator);
return (longlong) val;
}