[OpenAFS] Using a file lock to avoid race conditions?

[Jeffrey Altman]

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On 3/15/2011 12:14 PM, Edgecombe, Jason wrote:

> I=E2=80=99m thinking of using a file lock (i.e. flock) in AFS to determ=
ine who
> fetches the email, but I need to know about the failure scenarios. Does=

> the lock persist if the machine freezes or dies? Will an orphaned lock
> expire, and if so, how long does it take to expire?

Locks in AFS are issued with a five minute lifetime and must be renewed
by a client.

Write-locks are exclusive to a single client.  If the client dies or
otherwise becomes disconnected from the file server that issued the
lock, the lock will expire 5 minutes after it was issued.

Read-locks are shared and can be issued to multiple clients.  A
read-lock is renewed whenever any client requests a renewal.  If a
client fails or becomes disconnected from the file server, its lock
count will persist until five minutes after the last renewal request is
issued.

Obviously, the existence of an outstanding read-lock prevents the
granting of a write-lock.

Jeffrey Altman


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