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digitalmars.D.learn - question about the garbage collector

reply doob <doobnet gmail.com> writes:
I have a small question. I've just started to use D and I've been looking at
this example:

http://www.digitalmars.com/d/windows.html

I see in the example that it initializes the garbage collector using this
function:
gc_init();

My question is then: is this just for D stuff or is it also for the C stuff?
Mar 04 2007
parent reply Sean Kelly <sean f4.ca> writes:
doob wrote:

 I have a small question. I've just started to use D and I've been looking at
this example:
 
 http://www.digitalmars.com/d/windows.html
 
 I see in the example that it initializes the garbage collector using this
function:
 gc_init();
 
 My question is then: is this just for D stuff or is it also for the C stuff?


You only need to do this if you're creating a D dynamic library, because 
in that case the default startup process is not executed and the GC is 
therefore not initialized.


Sean
Mar 04 2007
parent reply "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
"Sean Kelly" <sean f4.ca> wrote in message 
news:esesnv$di1$1 digitalmars.com...


 You only need to do this if you're creating a D dynamic library, because 
 in that case the default startup process is not executed and the GC is 
 therefore not initialized.


You can also do it for regular Windows programs (i.e. in your WinMain), but 
in that case you can also just use the standard D "int/void main()" and use 
some Windows API functions to get the values which are usually passed as 
parameters to WinMain.  This way you don't have to do the D initialization 
crap; D will handle that for you.
Mar 04 2007
parent reply doob <doobnet gmail.com> writes:
Jarrett Billingsley Wrote:


 "Sean Kelly" <sean f4.ca> wrote in message 
 news:esesnv$di1$1 digitalmars.com...
 

 You only need to do this if you're creating a D dynamic library, because 
 in that case the default startup process is not executed and the GC is 
 therefore not initialized.


 
 You can also do it for regular Windows programs (i.e. in your WinMain), but 
 in that case you can also just use the standard D "int/void main()" and use 
 some Windows API functions to get the values which are usually passed as 
 parameters to WinMain.  This way you don't have to do the D initialization 
 crap; D will handle that for you. 
 
 


So you're saying that if I want to create a regular windows program I don't
need to initialize the garbage collector because it will do that by default and
it will handle the C stuff also?
Mar 04 2007
next sibling parent Sean Kelly <sean f4.ca> writes:
doob wrote:

 Jarrett Billingsley Wrote:
 

 "Sean Kelly" <sean f4.ca> wrote in message 
 news:esesnv$di1$1 digitalmars.com...


 You only need to do this if you're creating a D dynamic library, because 
 in that case the default startup process is not executed and the GC is 
 therefore not initialized.


 You can also do it for regular Windows programs (i.e. in your WinMain), but 
 in that case you can also just use the standard D "int/void main()" and use 
 some Windows API functions to get the values which are usually passed as 
 parameters to WinMain.  This way you don't have to do the D initialization 
 crap; D will handle that for you. 


 
 So you're saying that if I want to create a regular windows program I don't
need to initialize the garbage collector because it will do that by default and
it will handle the C stuff also? 


If you want to write a normal D program for Windows then you don't need 
to do anything special.  What do you mean by C stuff?
Mar 04 2007
prev sibling parent reply Daniel Keep <daniel.keep.lists gmail.com> writes:
doob wrote:

 Jarrett Billingsley Wrote:
 

 "Sean Kelly" <sean f4.ca> wrote in message 
 news:esesnv$di1$1 digitalmars.com...


 You only need to do this if you're creating a D dynamic library, because 
 in that case the default startup process is not executed and the GC is 
 therefore not initialized.


 You can also do it for regular Windows programs (i.e. in your WinMain), but 
 in that case you can also just use the standard D "int/void main()" and use 
 some Windows API functions to get the values which are usually passed as 
 parameters to WinMain.  This way you don't have to do the D initialization 
 crap; D will handle that for you. 


 
 So you're saying that if I want to create a regular windows program I don't
need to initialize the garbage collector because it will do that by default and
it will handle the C stuff also? 


D's garbage collector only applies to things that are allocated via the
'new' keyword in D code*.  C typically uses malloc, which the D garbage
collector can't even see, much less mess with.  If you use malloc and
free from D code, then what you allocate using malloc won't be garbage
collected, either.

As for initialising it, I think this is what they're saying:

+) If you write your own WinMain function, you need to handle
initialising and shutting down the D runtime stuff like the GC, unit
tests, module ctors, etc.

+) If your program begins with a main function, on the other hand, you
don't need to worry about doing the setup manually, since D will have
handled it for you.  You just need to figure out a way to get the
information that's usually passed to WinMain in some other manner.

Hope this helps.

	-- Daniel

* Of course, this doesn't apply if you happen to override a particular
class' new and delete methods, but you hopefully won't be doing *that*
unless you already know how the GC works :P

-- 
Unlike Knuth, I have neither proven or tried the above; it may not even
make sense.

v2sw5+8Yhw5ln4+5pr6OFPma8u6+7Lw4Tm6+7l6+7D
i28a2Xs3MSr2e4/6+7t4TNSMb6HTOp5en5g6RAHCP  http://hackerkey.com/
Mar 04 2007
parent reply "Saaa" <empty needmail.com> writes:
And dynamic arrays, right?

(rant below)

I had some really strange problems with the gc.
In my main loop I had to read in .png files quite alot (using SDL_Image) and 
place them on a SDL_Surface.
I had this problem of sometimes iso the png a black screen would appear.
(always the same place(changing the actual picture didn't change a thing))

I traced the problem down to this:
array.length=1800000;

Without this line (the array wasn't even in use) there were no black 
screens.
My best solution still > first line in main > disable(); > no problems and a 
big array :D

I'll report my bug when I'm sure it is (making the program minimal somehow 
:)
Somehow setting the array length enables the gc and somehow the gc redirects 
the pointer, I think... more info later :)



 D's garbage collector only applies to things that are allocated via the
 'new' keyword in D code*.  C typically uses malloc, which the D garbage
 collector can't even see, much less mess with.  If you use malloc and
 free from D code, then what you allocate using malloc won't be garbage
 collected, either.

 As for initialising it, I think this is what they're saying:

 +) If you write your own WinMain function, you need to handle
 initialising and shutting down the D runtime stuff like the GC, unit
 tests, module ctors, etc.

 +) If your program begins with a main function, on the other hand, you
 don't need to worry about doing the setup manually, since D will have
 handled it for you.  You just need to figure out a way to get the
 information that's usually passed to WinMain in some other manner.

 Hope this helps.

 -- Daniel

 * Of course, this doesn't apply if you happen to override a particular
 class' new and delete methods, but you hopefully won't be doing *that*
 unless you already know how the GC works :P

 -- 
 Unlike Knuth, I have neither proven or tried the above; it may not even
 make sense.

 v2sw5+8Yhw5ln4+5pr6OFPma8u6+7Lw4Tm6+7l6+7D
 i28a2Xs3MSr2e4/6+7t4TNSMb6HTOp5en5g6RAHCP  http://hackerkey.com/
Mar 04 2007
parent Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:
Saaa wrote:

 D's garbage collector only applies to things that are allocated via the
 'new' keyword in D code*.  C typically uses malloc, which the D garbage
 collector can't even see, much less mess with.  If you use malloc and
 free from D code, then what you allocate using malloc won't be garbage
 collected, either.


 
 And dynamic arrays, right?


Yes, he forgot to mention using operators '~' or '~=' on (dynamic) 
arrays, and setting their .length to a larger value.


 (rant below)
 
 I had some really strange problems with the gc.
 In my main loop I had to read in .png files quite alot (using SDL_Image) and 
 place them on a SDL_Surface.
 I had this problem of sometimes iso the png a black screen would appear.
 (always the same place(changing the actual picture didn't change a thing))
 
 I traced the problem down to this:
 array.length=1800000;
 
 Without this line (the array wasn't even in use) there were no black 
 screens.


You need to be careful when passing references to GC-allocated data to 
non-D libraries (like SDL). (setting an array length to a larger value 
makes it GC-allocated even if it wasn't previously)
If references are (only) stored where the GC can't see them (e.g. in 
malloc()ed memory), the data will be deleted on the next GC run. This 
may be what's happening here...


 My best solution still > first line in main > disable(); > no problems and a 
 big array :D
 
 I'll report my bug when I'm sure it is (making the program minimal somehow 
 :)
 Somehow setting the array length enables the gc and somehow the gc redirects 
 the pointer, I think... more info later :)


The current GC doesn't move objects. It just deletes them if it can't 
find any references to them.
Mar 05 2007