Is HDB locking safe?

[Rahul Dhesi]

>I guess creating a second lock file to be held while deleting the first
>would work.

Our in-house software does file locking, to create a lock file L,
like this:

     exlock(L);
     create  L;
     exunlock(L);

     /* critical section here */

     exlock(L);
     delete L;
     exunlock(L);

The definition of exlock(L) is:

     create a lock file called L|lock, looping with sleep(5) several
     times if necessary;  if creation fails, report a very serious
     error and exit process.

The definition of exunlock(L) is:

     delete L|lock;  if nonexistent or can't be deleted, report
     a very serious error and exit process.

Barring a system or process crash during the very brief interval
that L|lock exists, the above scheme is very robust.
--
Rahul Dhesi <dhesi%cirrusl at oliveb.ATC.olivetti.com>
UUCP:  oliveb!cirrusl!dhesi