[REBOL] Re: A collection of garbage
From: carl:rebol at: 8-Jul-2003 20:06
The logic is fairly complicated, but it's also quite fast.
For example, you might be using 50MB of memory, but not
even notice when the GC happens.
There are many REBOL programs that run for months (years?)
at a time without restarting, so we know the GC is stable.
(There are a few exceptions, in operations like TRY on OPEN
failures, etc.)
If you're curious about your code's memory, just put your
code into a loop and print memory stats every so often.
(Use a newer version of REBOL for better accuracy on stats.)
loop 10000 [
your code
print ["Mem:" stats]
]
You'll see the mem usage top out after a while (unless you
are doing things like continuously appending to series, such
as when keeping a log).
The two basic memory methods in REBOL are:
* Small allocations (values, blocks, etc.) are managed by
REBOL for speed reasons. They are efficiently recycled.
* Large allocations (files, images, sounds, big blocks, etc.)
are allocated thru the native OS, because we figure it knows
better the characteristics of its VM paging model and can
optimize the allocation.
So, here's what programmers need to remember:
* If you're just using normal REBOL values and small series,
just sit back and relax.
* If you allocate large memory objects (strings, images,
blocks, etc.), you may want to un-reference them when you
are done with them. For example:
file: read %large-file.txt
do some-stuff-on-file
file: none ; allow file buffer to GC eventually
This is not required, but it will help reduce memory usage.
IMPORTANT: in the example above, if the file variable is a
local variable to a function, DO NOT ASSUME that it will be
un-referenced automatically. By default, the first frame
(first level of call) of local variables for a function remain
referenced. For example, if you have a function:
foo: has [file] [
file: read %large-file.txt
print length? file
]
The file memory will not be released until the local variable
is set to a different value (by a second call to foo, which
will then hold the file memory until the next call, etc.)
To change that, unreference the file series when done:
foo: has [file] [
file: read %large-file.txt
print length? file
file: none
]
-Carl
