I tested your code and found that indeed version in ucopylist is slightly faster (by about 9.5 / 7 =~ 1.357). Two things:

1. Speedup is only 1.357x, not 3x, like you said. Are you sure that you're getting 3x speedup ? On what OS and with what FPC version are you testing this ? I was doing tests with Linux/i386 with FPC 1.9.4 and 1.9.5 (from CVS 2004-12-20).

2. Still, speedup 1.357x may be significant in some cases so I investigated what's the cause:

After many tests I found that this slight speedup is caused by the fact that in ucopylist you declared string constants SListIndexError, SListCapacityError and SListCountError as normal constants while with original Classes unit these constants are taken from RTLConst unit that defines them as resourcestrings.

Using resourcestrings in RTL is a must, since this allows to translate error messages without modifying unit Classes sources.

However in this case exceptions are not raised, so resourcestrings are not actually used. But it looks that any procedure that uses some resourcestring in implementation is doomed to be slower than the similar procedure that instead uses normal string consts, *even if this procedure doesn't actually access the string at runtime*. It seems that if some procedure uses resourcestring then upon entry it does some lengthy initialization of this resourcestring, even if it will not actually make use of that resourcestring.

I'm attaching a simple demo program that shows this. When compiled like
fpc -OG -O2 -Op2 demo_resourcestring_slow.pas
(to get maximum optimizations) sample output of it is
Time of Foo_Normal: 16
Time of Foo_ResourceString: 106
So time difference is really noticeable. Question goes to FPC developers, maybe such cases with using resourcestrings can be speed up ?


Ales Katona wrote:
I've read a complaint about TList being slow so I decided to give it a test.
Quite frankly the test showed this is truth, but I couldn't find out why.
I found out that if I copy the TList from classes "as-is" into my unit and use this
copy, it is about 3x faster in certain conditions. I have no idea why this is so but
I think there's something wrong...

I posted my test at http://members.chello.sk/ales/testlist.zip
Just download, unzip and compile:
you'll get swap time and access time for the original TList
uncomment {$DEFINE USEMYLIST} to get the times for my copy of TList

The copy there is unchanged.

Ales Katona

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{$mode objfpc}{$H+}

  {BaseUnix, Unix needed only to implement Clock} BaseUnix, Unix,

function Clock: Int64;
var Dummy: tms;
 Clock := FpTimes(Dummy);

  SNormal    = 'blah blah blah blah blah blah blah blah blah blah';
  SResString = 'blah blah blah blah blah blah blah blah blah blah';

{ Foo_Normal and Foo_ResourceString do the same thing,
  but Foo_Normal uses normal string constant while
  Foo_ResourceString uses resourcestring. }

procedure Foo_Normal(i: Integer);
 if i = -1 then raise Exception.Create(SNormal);

procedure Foo_ResourceString(i: Integer);
 if i = -1 then raise Exception.Create(SResString);

{ Note that when I call Foo_Normal and Foo_ResourceString
  i is always >= 0 so Exception is never actually raised.
  So string constants SNormal and SResString are not really used. }

  TestCount = 10000000;
  i: Integer;
  Start: Int64;
 Start := Clock;
 for i := 0 to TestCount do Foo_Normal(i);
 Writeln('Time of Foo_Normal:         ', Clock - Start);

 Start := Clock;
 for i := 0 to TestCount do Foo_ResourceString(i);
 Writeln('Time of Foo_ResourceString: ', Clock - Start);
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