Autosaving stacks corrupted on network drives

[Ralph DiMola]

True, The stack is not open after it's read into memory. I can see why/why
not this is done from a LC point of view. If the stack is being read in from
a web server it's not possible to lock it. If the file is local/network then
the stack could remain open and locked for write. Other processes could then
open/read it but not save it. This looks like it's been around for a long
time. Could locking stack(s) break existing projects? I vote to lock for
write any open stacks.

Ralph DiMola
IT Director
Evergreen Information Services
rdimola at evergreeninfo.net


-----Original Message-----
From: use-livecode [mailto:use-livecode-bounces at lists.runrev.com] On Behalf
Of Bob Sneidar via use-livecode
Sent: Wednesday, October 25, 2017 1:13 PM
To: How to use LiveCode
Cc: Bob Sneidar
Subject: Re: Autosaving stacks corrupted on network drives

Okay I think I see what is going on here. A Livecode stack, though it
appears to be open in the IDE, is NOT open from the OS point of view. To
test this, create a new livecode stack, save it, then attempt to delete it
in the OS while it's still open in the IDE. If my theory is correct, you
should have no problem doing so. 

I did this and sure enough, I was able to put the file in the trash, AND
THEN EMPTY IT! But when I saved again in the IDE, it recreated the file. 

Bob S


> On Oct 25, 2017, at 09:26 , Mike Kerner via use-livecode
<use-livecode at lists.runrev.com> wrote:
> 
> Now if what you're suggesting is that the server OS should manage the 
> access process so that you cannot have two simultaneous accesses, I 
> would agree, but my experience has been that it doesn't always work that
way.
> 
> On Wed, Oct 25, 2017 at 12:19 PM, Mike Kerner 
> <MikeKerner at roadrunner.com>
> wrote:
> 
>> I'm saying that it is possible to access the same file from the same 
>> share from multiple machines and leave the file in an indeterminate 
>> or corrupted state, afterwards, especially if both machines accessing 
>> the share are trying to save changes to said file.  The purpose of 
>> the semaphore would be to stop the simultaneous access of the file from
multiple machines.
>> 
>> 
>> On Wed, Oct 25, 2017 at 11:54 AM, Bob Sneidar via use-livecode < 
>> use-livecode at lists.runrev.com> wrote:
>> 
>>> I thought the OS takes care of that. Are we saying that when saving 
>>> to a network share this process of creating the semaphore file does not
happen?
>>> 
>>> Bob S
>>> 
>>> 
>>>> On Oct 24, 2017, at 16:01 , Mike Kerner via use-livecode <
>>> use-livecode at lists.runrev.com> wrote:
>>>> 
>>>> Possible solutions:
>>>> 1) Do what LibreOffice does.  Create an invisible semaphore file 
>>>> that
>>> the
>>>> stack checks for on open.  If it exists, the open is rejected and 
>>>> the
>>> stack
>>>> immediately closes.  This will keep secondary and simultaneous 
>>>> users
>>> from
>>>> getting their grubby paws into the stack before the save/sync is
>>> complete.
>>>> As part of this solution, I would suggest any quit/closeStack event 
>>>> has
>>> a
>>>> built in delay to confirm that the sync/save has completed before
>>> removing
>>>> the semaphore.  This is still tricky as you are at the mercy of the 
>>>> sync/save tool, however, if you're clever, you can use the 
>>>> service's
>>> api to
>>>> check, separately, if the sync/save is complete before you let LC 
>>>> finish closing down.
>>>> 2) Split the data out into a separate data file or better into a
>>> database
>>>> (because most databases use transactions, with greatly minimizes 
>>>> the probability of corruption).
>>> 
>>> 
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>> 
>> 
>> 
>> --
>> On the first day, God created the heavens and the Earth On the second 
>> day, God created the oceans.
>> On the third day, God put the animals on hold for a few hours,
>>   and did a little diving.
>> And God said, "This is good."
>> 
> 
> 
> 
> --
> On the first day, God created the heavens and the Earth On the second 
> day, God created the oceans.
> On the third day, God put the animals on hold for a few hours,
>   and did a little diving.
> And God said, "This is good."
> _______________________________________________
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> use-livecode at lists.runrev.com
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