Re: argv subscript range uses too many memory

[Han Pingtian <hanpt@xxxxxxxxxxxxxxxxxx>]

On Sat, Nov 10, 2012 at 06:57:09AM -0800, Bart Schaefer wrote:
> Further discussion probably should be re-routed to zsh-workers.
> 
> On Nov 10,  6:58pm, Han Pingtian wrote:
> }
> } Looks like when running with 'print -- "$argv[1,3]", the call trace is
> } something like this:
> } 
> } (gdb) bt
> } #0  mmap_heap_alloc (n=0x7fff0852e880) at mem.c:449
> } #1  0x000000000045f5f9 in zhalloc (size=1594456) at mem.c:542
> } #2  0x00000000004a4dfa in arrdup (s=0x313b008) at utils.c:3648
> } #3  0x0000000000471fa9 in getarrvalue (v=0x7fff0852ea20) at params.c:2174
> 
> Ah, yes.  Array slices are implemented by copying the entire array and
> then extracting the desired subset from the copy.  Individual array
> elements are string references and therefore copy only the one element.
> 
> Unfortunately this is pretty deeply ingrained in zsh's parameter
> expansion implementation and likely requires some serious rewriting to
> fix.  It might be easier to come up with a way to garbage-collect more
> frequently.
> 
> In a loop, the heap allocations are not popped until the loop is done,
> IIRC, so you'll end up with a large number of copies of the original
> array in the heap with slice results pointing into different parts of
> each copy.  Maybe there's a narrower scope in which a pushheap/popheap
> could be inserted.
Looks like I have found the reason of this problem. If I revert this commit:

commit 61505654942cb9895a9811fde1dcbb662fd7d66a
Author: Bart Schaefer <barts@xxxxxxxxxxxxxxxxxxxxx>
Date:   Sat May 7 19:32:57 2011 +0000

    29175: optimize freeheap

Then the problem will be fixed. Please have a look. Thanks.