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{
This file is part of the Free Pascal run time library.
Copyright (c) 2021 by the Free Pascal development team.
OS heap manager for small targets
See the file COPYING.FPC, included in this distribution,
for details about the copyright.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
**********************************************************************}
{
The OS heap manager is a small heap manager for smaller targets with an
operating system. It's similar in comcept to the "cmem" memory manager
for systems with libc support, but it aims systems that have a direct
heap management API (Sinclair QL, AmigaOS, MacOS Classic, some
embedded systems, etc), but not necessarily libc. It's also designed
to be included in the System unit directly, unlike cmem.
The main advantage is that it's much smaller than the regular heap
manager, and it's a thinner layer towards the OS as well, therefore it
can be slightly faster on resource constrained systems.
The disadvantage is that it may not be well suited for bigger Pascal
programs that rely heavily on consistent heap performance, as the
properties of the OS heap manager like alignment and size constraints,
and allocation time are also directly exposed towards the Pascal code.
Additionally, querying the heap status is not supported.
Its main difference to tinyheap is that it can release the allocated
memory back to the system, therefore it suits systems that can run more
than one software in parallel better.
OSHeap needs SysOSAlloc and SysOSFree implemented in the system-specific
code, and nothing else.
}
function SysGetMem(Size: ptruint): pointer;
begin
Inc(size,sizeof(size));
result := SysOSAlloc(size);
if assigned(result) then
begin
pptruint(result)[0] := size;
Inc(result,sizeof(size));
end;
end;
function SysFreeMem(p: Pointer): ptruint;
begin
if assigned(p) then
begin
Dec(p,sizeof(ptruint));
SysOSFree(p,pptruint(p)[0]);
end;
result := 0;
end;
function SysFreeMemSize(p: Pointer; Size: Ptruint): ptruint;
begin
result := SysFreeMem(p);
end;
function SysMemSize(p: pointer): ptruint;
begin
Dec(p,sizeof(ptruint));
result:=pptruint(p)[0]-sizeof(ptruint);
end;
function SysTryResizeMem(var p: pointer; size: ptruint) : boolean;
begin
result := false;
end;
function SysAllocMem(size: ptruint): pointer;
begin
result := SysGetMem(size);
if not assigned(result) then
FillChar(result^,SysMemSize(result),0);
end;
function SysReAllocMem(var p: pointer; size: ptruint):pointer;
var
oldsize: ptruint;
begin
result := nil;
if assigned(p) then
begin
oldsize := SysMemSize(p);
if size <> oldsize then
begin
if size > 0 then
begin
result := SysGetMem(size);
if assigned(result) then
begin
if size < oldsize then
oldsize := size;
Move(p^,result^,oldsize);
end;
end;
SysFreeMem(p);
end
else
result := p;
end
else
result := SysGetMem(size);
p := result;
end;
function SysGetFPCHeapStatus : TFPCHeapStatus;
begin
FillChar(result,sizeof(result),0);
end;
function SysGetHeapStatus : THeapStatus;
begin
FillChar(result,sizeof(result),0);
end;
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