[REBOL] Re: Killer Application
From: atruter:hih:au at: 19-Aug-2002 10:19
<snip>
Rebol [
Name: 'Number
Title: "Title"
File: %Number.r
Author: "Andrew Martin"
eMail: [Al--Bri--xtra--co--nz]
Date: 17/Aug/2002
]
Number: has [File Number] [
File: %Number.txt
if not exists? File [
save File 0
]
Number: load File
Number: Number + 1
save File Number
Number
]
</snip>
To prevent more than one session obtaining the same number (assuming the
file is stored on shared media) some form of locking may be required. The
following code could serve as the basis for such:
<code>
lock-index: function [path] [lock?] [
lock?: false
repeat cnt 5 [
either none? attempt [rename join path %index.dat %lock.dat] [
wait 1
print reform ["Waited:" cnt]
][
lock?: true
break
]
]
if not lock? [print reform ["Could not lock" join path %index.dat]]
]
; ... code that reads / writes path/lock.dat
unlock-index: func [path] [
if none? attempt [rename join path %lock.dat %index.dat] [
print reform ["Could not unlock" join path %lock.dat]
]
]
</code>
Regards,
Ashley
