[Haskell-cafe] Garbage collection and finalizer thread priority

Gracjan Polak gracjan at acchsh.com
Tue Jun 14 05:29:09 EDT 2005

Simon Marlow wrote:
> On 13 June 2005 11:30, Gracjan Polak wrote:
>>My space problems continued... :)

Follow up :)

>>I have some ForeignPtr's, with finalizers (finalizerFree only). And I
>>have lazyly produced list of those (yes, there is some unsafePerformIO
>>magic behind, but I think I got this right). The problem is I get
>>out-of-memory condition because elements get produced faster than
>>those consumed are garbage collected.
>>list = ...
>>mapM_ writeOut list
>>writeOut :: Ptr Word8
>>writeOut dat = do
>>     hPutBuh handle dat 1024
>>     -- Control.Concurrent.threadDelay 1000

This sould be:

writeOut :: Ptr Word8
writeOut dat = do
      hPutBuh handle dat 1024
      Control.Concurrent.threadDelay 1000

My small experimets show, that gc is not triggered?!?! What are the 
conditions to trigger gc? As I read the docs, is some % of heap. Is 
mallocForeinPtrBytes counted into that %?

Anyway I ended up triggering GC by hand and giving it time to run 
finalizers. Frankly speaking this is nonsolution:(

Related question:

Documentation says:
     [Default: unlimited] Set the maximum heap size to size bytes. The 
heap normally grows and shrinks according to the memory requirements of 
the program...

GHC 6.4 says:
Heap exhausted;
Current maximum heap size is 268435456 bytes (256 Mb);
use `+RTS -M<size>' to increase it.

What am I missing?

PS: I might be mistaken in any of above statements. I'll be thankful for 
any light... :)


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