JE currently avoids your deadlock problem by not having deadlock
detection. I'd like to keep it that way if possible.
Querying the status of a lock should be easy, as long as you don't
expect JE to tell you which task(s) have the lock(s).
Henry Rich
On 4/27/2022 12:13 PM, Raul Miller wrote:
On Wed, Apr 27, 2022 at 11:40 AM Henry Rich <[email protected]> wrote:
1. Wouldn't it be better, in most cases, to copy the names in v
atomically and then run u on the copy? That would keep the names tied
up for much less time.
Yes, for analytic reporting, where we're doing intensive computation
work on the values from those names.
No, for editing contexts and algorithms implementing analogous
feedback mechanisms.
Generally speaking, it's on the programmer to decide what needs to be
atomic. For good performance, the programmer needs to make well
informed choices here.
2. Wouldn't a simple readlock/writelock on a name give the same result?
It would be easier to implement. A routine that wants to use a shared
name would establish a readlock on it before copying or using the value;
a routine that wants to write to the name would establish a writelock.
If there are multiple names, all users should agree on an order and lock
the same name.
I am thinking that would give the same benefits as your suggestion, more
simply.
Mostly.
What the programmer should want here is (shorthand): "u under locks"
(in other words unlock needs to be the dual of lock, and this needs to
work reliably without creating deadlocks).
A problem here is that unlocking in the same order that locking
occurred can (in the general case) trigger deadlock detection
mechanisms. A "lock single name" mechanism, used naively, tends to
create situations which are indistinguishable (inside the interpreter)
from deadlock conditions.
Read/write locks can be implemented with very little overhead. I would
say that if you want to be able to list the locks you would need to
implement a verb to add that layer of functionality.
Listing does not need to be super fast, but it's needed for debugging.
It should be sufficient to be able to ask the interpreter if a name is
locked.
Thanks,
--
This email has been checked for viruses by AVG.
https://www.avg.com
----------------------------------------------------------------------
For information about J forums see http://www.jsoftware.com/forums.htm
