r3wp [groups: 83 posts: 189283]
  • Home
  • Script library
  • AltME Archive
  • Mailing list
  • Articles Index
  • Site search
 

World: r3wp

[Core] Discuss core issues

Izkata
31-Mar-2009
[13392x4]
Tom: it's not the replace that's doing it...
>> "^IKSE"
== "^-KSE"
>> "^MERV"
== "^MERV"
>> "^JKSE"
== "^/KSE"
>> "^IKSE"
== "^-KSE"
but I have no actual answer
Well, ^I is a control-i.. and in vim, that inserts a tab.  ^- is 
the tab character in Rebol
I must go to class now
TomBon
31-Mar-2009
[13396]
thx for the info izkata.
Geomol
31-Mar-2009
[13397x2]
Paul, I would probably do:

o: context [q: "blahblah" f: does [insert q "more blah" q]]


And my that have full control over q. It depends on the application, 
I guess.
my -> by
[unknown: 5]
31-Mar-2009
[13399]
I'll stick with ALSO.  ;-)
Geomol
31-Mar-2009
[13400x5]
Izkata, about the timeout. It seems here, that when the open/binary 
returns, the data is immediately available, so the timeout has no 
effect. I'm on OS X, maybe it's different under windows?
Anyway, I can now see, how you use ALSO with ports. By using a function 
approach, you choose to copy the data out to some further external 
computation. And it's up to the user of the function to free the 
data, when finished. I would take an object approach and store the 
data in the object. Then external computation can work on the data 
in the object. I feel, it's confusing using ALSO, but maybe it's 
just me.
An object approach could look like this:

Ports: context [
	Port: none
	Data: none

	Pread: func [URL] [
		either error? try [Port: open/binary URL] [
			print ["Can't open:" URL]
			false
		][
			Data: copy Port
			close Port
			true
		]
	]
]
Using it would then be:

if Ports/Pread http://www.rebol.com[
	... do something with Ports/Data ...
]
Where I see a potential problem with ALSO, is if you in a function 
load a local var with a huge amount of data, say 1GB. And then to 
release that data ends your function with:
also copy local-data local-data: none


At that moment between the two arguments to ALSO, you have 2 GB of 
data allocated. The first 1 GB is freed, when the garbage collector 
comes to it.
[unknown: 5]
31-Mar-2009
[13405]
So is this your assurance to us that we will never see ALSO in your 
code?
Geomol
31-Mar-2009
[13406]
No no, I never say never. ehh ;-)
Izkata
31-Mar-2009
[13407]
Geomol: [Izkata, about the timeout. It seems here, that when the 
open/binary returns, the data is immediately available, so the timeout 
has no effect. I'm on OS X, maybe it's different under windows?]

I'm on Ubuntu  ;)  but yeah, now that I think about it, that's true. 
 Originally it was written differently, and the error appeared to 
be on the copy.  I added it when mininova was timing out on certain 
requests due to high load - it seemed to make a difference then, 
but I don't know if it was coincidence or not.
Graham
31-Mar-2009
[13408]
mininova ? torrenting?
Izkata
31-Mar-2009
[13409x2]
Yeah, the internal function that RSS plugins on Azureus use broke 
at some point, so I'm doing it this way now.  Much nicer, as I can 
collect more information, etc
If you're thinking I'm making a torrrent client in Rebol, not yet 
 ;)
Graham
31-Mar-2009
[13411]
I suspect R2 is not up to it ...
Izkata
31-Mar-2009
[13412x2]
Probably not, but it would be interesting to try
Then again, R2 has surprised me with my current project
Graham
31-Mar-2009
[13414]
networking is not a strong point
Anton
31-Mar-2009
[13415x2]
Geomol, your last "potential problem with ALSO" is not exclusive 
to ALSO. It's a potential problem anywhere COPY is abused by a programmer 
not knowing what's going on.

The way to return the large amount of data and to release the local 
from it is of course like this:

	also local-data local-data: none
load-mp3-data: func [file /local contents][
	contents: read/binary file
	; <- modify contents here
	also contents contents: none
]

data: load-mp3-data %song.mp3
Graham
31-Mar-2009
[13417]
so this frees contents??
Steeve
31-Mar-2009
[13418]
just to say there is no need  anymore to unset the local vars in 
R3
Anton
31-Mar-2009
[13419x4]
In the load-mp3-data function above, a large binary series is loaded 
and contents set to refer to it. The ALSO line returns the binary 
series and unsets CONTENTS so that it no longer refers to the binary 
series. The usage code below the function definition takes the return 
value (the binary series) and sets DATA to it.

So effectively the variable referencing the binary series has been 
switched with another one.
(Steeve, yep.)
Graham, no, it just "unhooks" the local word CONTENTS from the binary 
series data.
Which is a good thing to do, because now the function does not maintain 
a reference to the large binary series after it has been called.
Steeve
31-Mar-2009
[13423]
If the contents var is not unset and then the load-mp3 function is 
not anymre called.

Then, the garbage collector can't free the serie because it stays 
handled by the local var contents.
Graham
31-Mar-2009
[13424x2]
Hmm.  So, one should deference local vars if they pointing to large 
data sets?
dereference
Steeve
31-Mar-2009
[13426]
yes, In R2 we should
Anton
31-Mar-2009
[13427]
Steeve, yes, that's right.
Graham
31-Mar-2009
[13428]
didn't know that ...
Anton
31-Mar-2009
[13429]
Yes, in R2, functions don't bother to unset their local words on 
function exit. This was done for speed reasons. Most functions don't 
need to unset their locals.
Graham
31-Mar-2009
[13430]
I wonder if that would help with the problem I had before when I 
was doing OCR on image data .. and kept getting crashes
Anton
31-Mar-2009
[13431]
Where you running out of memory?
Graham
31-Mar-2009
[13432]
no
Anton
31-Mar-2009
[13433]
*Were you..
Graham
31-Mar-2009
[13434]
If I turned off recycle, the problem disappeared, but then memory 
eventually would run out
Anton
31-Mar-2009
[13435]
That was more likely some external library call problem.
Graham
31-Mar-2009
[13436x3]
not using external libraries
I was posting the data to a web server
web service
Anton
31-Mar-2009
[13439]
That was a memory leak, not really caused by the "local vars not 
unset on R2 function exit" behaviour. (But perhaps contributed, by 
misunderstanding, to the leak bug.)
[unknown: 5]
31-Mar-2009
[13440]
Yes, Graham we need to clear those locals by setting them to none.
BrianH
31-Mar-2009
[13441]
I use ASLO in R2-Forward for that reason - that was the original 
reason ALSO was suggested. You don't need ALSO for that in R3 since 
the locals unset themselves in the new function context model, but 
it is useful for closing ports and changing directories back.