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From: alexis@panix.UUCP (Alexis Rosen)
Newsgroups: comp.databases
Subject: Re: rlock() in SCO foxbase+.
Keywords: foxbase, rlock
Message-ID: <10499@panix.UUCP>
Date: 25 Sep 90 06:45:17 GMT
References: <553@safn2.UUCP>
Organization: PANIX - Public Access Unix Systems of NY
Lines: 53


I know it can be confusing, but I'd suggest that you RTFM, two times. briefly:

The *PROGRAM* (which is to say, the pid in unix) owns locks. However, you can't
use rlock to append. It's a really stupid way to do things, but the only way
to append in multi-user is:
1) Obvious but slow- Flock() the file, and if you get the lock, append and
   release.
2) Fast and ugly- just do append blank. If you can't make the record, it'll
   generate an error. Catch the error in your error-handling routine (you do
   have one, right?)  This becomes enourmously easier if you encapsulate the
   Append routine. Here's mine, for Fox/Mac, which should work identically:

* DelayAppnd(secs)
* Try up to 'secs' seconds to append a blank record.
* Relies on the error-handling routine to set appenderr to .F. if the
* append fails.  Returns .T. if append succeeded, .F. if not
 
Param secs		&& number of seconds to wait
Priv appenderr		&& semaphore flipped by Error-handler if append fails
Priv t			&& ending time
Priv junk
 
t = Val(Sys(2))+secs
Do While (Val(Sys(2)) <= t)
	appenderr = .F.		&& no error condition yet this pass in loop
	Append Blank		&& give it a shot
	If appenderr		&& if append failed, the error-handler set this
		junk = Inkey(1)	&& wait a second so we don't thrash the DBMS
	Else
		appenderr = !Rlock()	&& We don't get a lock on a record
					&& just by creating it
		Exit
	Endif
Enddo		&& loop for 'secs' seconds or until we achieve a lock
Return !appenderr

-----
Remeber to look for the specific error number for a "failed to append" in
B
your error-trapping routine.

Also, don't forget to release any lock you create. Generally speaking you
shouldn't hold on to locks for more than a fraction of a second- no reason.

Unlike dBase IV and FoxPro, you can only have ONE lock at a time- I think.
There's some small possibility that the unix version is different.


Hope this helps,
---
Alexis Rosen
cmcl2!panix!alexis