在最近使用Delphi开发的项目中,出现了内存泄露的问题,经排查是由于使用New申请的结构体内存用Dispose释放不完全造成的。网上会搜到如下的解释。
delphi设计的 dispose 释放内存时,只是标记这部分内存可以再用来被 new 等函数分配,并不是把从系统申请到的内存归还给操作系统,只在程序结束时,才全部释放给操作系统。
其实,上面的解释是不正确的。用New申请的结构体内存,在使用Dispose释放时,会将结构体所占用的内存立即释放掉。但如果结构体中使用了Delphi动态内存管理的数据类型(如字符串String,动态数组等),如果Dispose使用不正确(下文会做详细说明),会造成这些Delphi动态管理的内存不能释放,最终导致了内存泄露。为了验证该问题编写了下面的代码。
unit untMain;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, PsAPI, StdCtrls, TLHelp32;
type
PMyRec = ^TMyRec;
TMyRec = record
IntMember: Integer;
FloatMember: Double;
StrMember: string;
end;
PStrRec = ^StrRec;
StrRec = packed record
refCnt: Longint;
length: Longint;
end;
TMyList = class(TList)
private
FAdvanced: boolean;
protected
procedure Notify(Ptr: Pointer; Action: TListNotification); override;
end;
TForm1 = class(TForm)
btn1: TButton;
btn2: TButton;
btn3: TButton;
btn4: TButton;
btn5: TButton;
mmoLog: TMemo;
btn7: TButton;
procedure btn2Click(Sender: TObject);
procedure btn3Click(Sender: TObject);
procedure FormCreate(Sender: TObject);
procedure btn4Click(Sender: TObject);
procedure btn1Click(Sender: TObject);
procedure btn7Click(Sender: TObject);
procedure btn5Click(Sender: TObject);
private
{ Private declarations }
FLst: TMyList;
procedure AddLog(Content: string);
public
{ Public declarations }
end;
var
Form1: TForm1;
GVarS1, GVarS2: string;
implementation
function GetProcessMemUse(PID: Cardinal): Cardinal;
var pmc: PPROCESS_MEMORY_COUNTERS; //uses psApi
ProcHandle: HWND;
iSize: DWORD;
begin
Result := 0;
iSize := SizeOf(_PROCESS_MEMORY_COUNTERS);
GetMem(pmc, iSize);
try
pmc^.cb := iSize;
ProcHandle := OpenProcess(PROCESS_QUERY_INFORMATION or PROCESS_VM_READ, False, PID);
if GetProcessMemoryInfo(ProcHandle, pmc, iSize) then
Result := pmc^.WorkingSetSize;
finally
FreeMem(pmc);
end;
end;
function GetCurrentMemUse: Cardinal;
begin
Result := GetProcessMemUse(GetCurrentProcessId);
end;
{$R *.dfm}
procedure TForm1.btn2Click(Sender: TObject);
var idx: Integer;
dMS1, dMS2: Double;
pRec: PMyRec;
begin
dMS1 := GetCurrentMemUse / 1024;
AddLog(Format('开始申请100000个结构体内存(不分配字符串),当前进程占用内存%.2fKB,结构体所占内存为%.2fKB !', [dMS1, SizeOf(