Heap problems: double allocations

[mark smit]

Hello Everybody,


I have been playing around with the heap functions and have seen
something that doesn't make sense. I have included an example of
the code below.

Heres the problem, HeapCreate should preallocate a block of memory
from which HeapAlloc can request a portion. When I create my own
heap the task manager reports that X amount has been allocated(OK).
but when I call HeapAlloc to request memory from my own heap the
tasm manager reports that even more memory get allocated.

HeapCreate(5000000 bytes) Task manager shows increase of ~5000000 bytes
HeapAlloc(myheap,2000000) Task manager shows increase of ~2000000 bytes

As I understand it this shouldn't happen until I request more memory
than what I reserved with HeapCreate.

#compile exe
#register none


%HEAP_NO_SERIALIZE                           = &h00000001
%HEAP_GROWABLE                               = &h00000002
%HEAP_GENERATE_EXCEPTIONS                    = &h00000004
%HEAP_ZERO_MEMORY                            = &h00000008


declare function HeapFree lib "KERNEL32.DLL" alias "HeapFree" (byval long,byval long,any) as long
declare function HeapAlloc lib "KERNEL32.DLL" alias "HeapAlloc" (byval long,byval long,byval long) as long
declare function HeapCreate lib "KERNEL32.DLL" alias "HeapCreate" (byval long,byval long,byval long) as long
declare function HeapDestroy lib "KERNEL32.DLL" alias "HeapDestroy" (byval long) as long


function pbmain as long
    local Heap as long
    local Memory as long
    
    
    rem create 20mb heap
    Heap = HeapCreate(%HEAP_ZERO_MEMORY,20000000,0)
    msgbox str$(Heap)
    
    
    rem Task manager memory usage increases by 20mb
    
    
    rem allocate 5mb from our heap
    Memory = HeapAlloc(Heap,0,5000000)
    msgbox str$(Heap)
    
    
    rem For some reason task manager increases again?
    rem I dont think this should happen because I have
    rem already set allocated the space in the heap


    rem free memory block
    HeapFree Heap,0,byval Memory
    msgbox "done"
    
    rem ddestroy heap
    HeapDestroy Heap
end function

Any help on this would be greatly appreciated!

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Cheers

[Jeffrey R. Radue]

Hi Mark,

The MS documentation does not have the %HEAP_ZERO_MEMORY value
associated with HeapCreate. This is a parameter for the HeapAlloc
function. You only have two choices for HeapCreate:

%HEAP_GENERATE_EXCEPTIONS, or
%HEAP_NO_SERIALIZE

I'm not sure this is your problem, but its worth correcting.

Jeff

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[Jeffrey R. Radue]

Mark, here are some additional comments:

1. I notice you are not specifying any equate for the HeapAlloc function
Again, I,m not sure how Windows will behave, however MS does not
describe a NULL parameter as an option.

2. If you are using Win 95/98 (ME?)

Windows 95/98: The heap managers are designed for memory blocks smaller than four megabytes.
If you expect your memory blocks to be larger than one or two megabytes,
you can avoid significant performance degradation by using the VirtualAlloc or VirtualAllocEx function instead.

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