Code speed (and back to the memory leaks...)

[Steven Schveighoffer]

On Wed, 14 Apr 2010 17:19:53 -0400, Joseph Wakeling  
<joseph.wakeling at webdrake.net> wrote:


> /////////////////////////////////////////////////////////////////////////
> version(Tango) {
>     import tango.stdc.stdio: printf;
> } else {
>     import std.stdio: printf;
> }
>
> void main()
> {
>     double[] x;
>
>     for(uint i=0;i<100;++i) {
>         x.length = 0;
>
>         for(uint j=0;j<5_000;++j) {
>             for(uint k=0;k<1_000;++k) {
>                 x ~= j*k;
>             }
>         }
>
>         printf("At iteration %u, x has %u elements.\n",i,x.length);
>     }
> }
> /////////////////////////////////////////////////////////////////////////
>
> I noticed that when compiled with LDC the memory usage stays constant,
> but in DMD the memory use blows up.  Is this a D1/D2 difference (with D2
> having the more advanced features that require preservation of memory)
> or is it a bug in one or the other of the compilers ... ?

It is because D2 is more advanced in preserving memory.  In D1, setting  
length to zero is equivalent to also assuming it can append safely.

One thing I forgot about, there is currently a design flaw in D2 array  
appending which will keep around a certain number of arrays even after all  
references have been removed (i.e. the arrays should be collectable, but  
they are not collected by the GC).  I have a clear path on how to fix  
that, but I haven't done it yet.

See this bugzilla report:  
http://d.puremagic.com/issues/show_bug.cgi?id=3929

This might also help explain why the memory blows up.

-Steve