Jamie McCracken wrote:
Marco van de Voort wrote:
The best solution I can think for this is to reference count non-component classes. This should be safe for TObjects but obviously not for Tcomponent descendants (cf circular reference problem) so a protected variable could be added to TObject to specify whether to ref count it or not (with TComponent turning it off).
This is impossible. 90% of the language wouldn't work anymore as it does now, and besides, it would be dog slow. Could be that it gets slower than Boehm GC even.
Thats very pessimistic!
Why wouldn't existing code work with this? If you call free on an object it would ignore the ref count and free it - so it wont alter how existing code works so it certainly should not break anything. You can always create a new dialect that has this if you're worried about existing code (I take it most of the existing code is using FPC mode dialect).
Is'nt the overhead for reference counting negligible compared to having try..finally blocks which the programmer would have to add anyway if we didn't refcount them?
(there also pointers for cases where you dont need try..finally)
Ref. counting creates an huge amount of implicit try .. finally blocks which have a heavy impact on speed.
Consider
function f1(myobject : tobject) : tobject; begin end;
function f2(myobject : iunknown) : iunknown; begin end;
var o : tobject; i : iunknown;
begin f1(o); f2(i); end.
lets have a look at the ouput (IUnknown is ref. counted):
# [2] begin
.globl P$PROGRAM_F1$TOBJECT$$TOBJECT
P$PROGRAM_F1$TOBJECT$$TOBJECT:
# Temps allocated between ebp+0 and ebp+0
pushl %ebp
movl %esp,%ebp
# Var myobject located in register
# Var $result located in register
movl %eax,%edx
# [3] result:=myobject;
movl %edx,%ecx
# [4] end;
movl %ecx,%eax
leave
ret.section .text
.balign 4
.balign 4
# [7] begin
.globl P$PROGRAM_F2$IUNKNOWN$$IUNKNOWN
P$PROGRAM_F2$IUNKNOWN$$IUNKNOWN:
# Temps allocated between ebp-48 and ebp-4
pushl %ebp
movl %esp,%ebp
subl $48,%esp
movl %ebx,-48(%ebp)
# Var myobject located in register
# Var $result located at ebp-4
movl %eax,%ebx
movl $0,-4(%ebp)
leal -16(%ebp),%eax
movl %eax,%ecx
leal -40(%ebp),%eax
movl %eax,%edx
movl $1,%eax
call FPC_PUSHEXCEPTADDR
call FPC_SETJMP
pushl %eax
testl %eax,%eax
jne .L15
# [8] result:=myobject;
movl %ebx,%edx
leal -4(%ebp),%eax
call fpc_intf_assign
.L15:
call FPC_POPADDRSTACK
popl %eax
testl %eax,%eax
je .L16
# [9] end;
movl $INIT__SYSTEM_IUNKNOWN,%edx
leal -4(%ebp),%eax
call fpc_finalize
call FPC_RERAISE
.L16:
movl -4(%ebp),%eax
movl -48(%ebp),%ebx
leave
ret[...]
# [16] f1(o);
movl %esi,%eax
call P$PROGRAM_F1$TOBJECT$$TOBJECT
# [17] f2(i);
leal -44(%ebp),%edx
movl %edx,%eax
call FPC_INTF_DECR_REF
movl %ebx,%eax
call P$PROGRAM_F2$IUNKNOWN$$IUNKNOWN
movl %eax,-44(%ebp)
leal -44(%ebp),%edx
movl %edx,%eax
call FPC_INTF_DECR_REF
movl $0,-44(%ebp)So if you look at this, you know why classes aren't ref. counted. And there is no chance to avoid the code generated for the interface.
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