topic Re: Acquire a lock on SAS data set in SAS Programming

Acquire a lock on SAS data set

ASASProgrammer — Mon, 28 Oct 2013 13:48:20 GMT

Hi,

I need change a SAS data set's name while someone is reading the data from the data set.

It does not matter the renaming interrupts the reading.

How can I acquire the a lock and force to rename the data set?

Thanks in advance!

Shi

Re: Acquire a lock on SAS data set

SASKiwi — Mon, 28 Oct 2013 20:00:30 GMT

I don't believe this is possible - not without SAS/Share anyway. SAS uses operating system locking. If a SAS dataset is locked while being read, it means the file is locked by the operating system so you can't "force" a lock and rename it.

What operating system are you using? I believe Unix may be more flexible in this area than Windows. If you were using SAS/Share and the dataset was being accessed via a SAS/Share server then I think this might be possible.

Re: Acquire a lock on SAS data set

ASASProgrammer — Mon, 28 Oct 2013 20:39:12 GMT

Thanks for the information.

It is on Unix box.

It might not be a OS level lock.

I tested with a small text file: Open a file with vi in one session, and I still can rename it with mv in another session.

However, even for small SAS data set, when one session reading the data set, it is not allowed to change the name with proc datasets.

It can be renamed with mv using xcmd, but it is not a "pure" SAS way...

Re: Acquire a lock on SAS data set

FriedEgg — Mon, 28 Oct 2013 22:21:14 GMT

To obtain a lock you can use the lock statement.

data foo;

set sashelp.class;

run;

lock work.foo;

proc datasets lib=work;

change foo=bar;

run;

lock work.foo clear;

I remember an old paper that contained a macro call %trylock, which you may find useful. You cannot lock a SAS file or modify one by force when a lock is held by another process in SAS.

You could try having the session performing the read use cntllev=rec, but I have not tested it.

I found the paper, I think: http://www.lexjansen.com/pharmasug/2005/posters/po33.pdf

Re: Acquire a lock on SAS data set

Peter_C — Mon, 28 Oct 2013 22:52:09 GMT

the problem is that you cannot stop the current user/use of a table to apply the lock.

What would be nice is a RESERVE type of lock.

Macro %TRYLOCK() is an attempt to obtain a lock. However this is os-dependent - if it doesn't support that functionality. I think there is nothing else to hold that RESERVE-request.

Re: Acquire a lock on SAS data set

Patrick — Mon, 28 Oct 2013 23:22:14 GMT

I've tried in the past to make this %trylock() macro work failsafe but with no real success. So can't really recommend to use it.