（1）使用临界区对象。
临界区对象有两种：TRTLCriticalSection 和 CriticalSection。
 TRTLCriticalSection的用法
var
GlobalVariable:Double;
var
CriticalSection:TRTLCriticalSection;
procedure SetGlobalVariable(Value:Double);
begin
EnterCriticalSection(CriticalSection); //进入临界区
try
GlobalVariable:=Value;
finally
LeaveCriticalSection(CriticalSection); //离开临界区
end;
end;
initialization
InitializeCriticalSection(CriticalSection); //初始化
finalization
DeleteCriticalSection(CriticalSection); //删除
end.
 CriticalSection（重要区段）的用法：
var criticalsection: TCriticalsection;
创建：criticalsection := TCriticalsection.create;
使用：
criticalsection.enter;
try
...
finally
criticalsection.leave;
end;
(2)使用互斥
先在主线程中创建事件对象：
var
hMutex: THandle = 0;
...
hMutex := CreateMutex(nil, False, nil);
在线程的Execute方法中加入以下代码：
if WaitForSingleObject(hMutex, INFINITE) = WAIT_OBJECT_0 then
//Do Something;
...
ReleaseMutex(hMutex);
最后记得要释放互斥对象：
CloseHandle(hMutex);
(3)使用信号量
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,
Dialogs, ExtCtrls, StdCtrls;
type
TForm1 = class(TForm)
Edit1: TEdit;
Button1: TButton;
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
type
TMyThread = class(TThread)
private
protected
procedure Execute; override;
public
constructor Create; virtual;
end;
var
Form1 : TForm1;
HSem : THandle = 0 ;
implementation
{$R *.dfm}
var
tick: Integer = 0;
procedure TMyThread.Execute;
var
WaitReturn : DWord ;
begin
WaitReturn := WaitForSingleObject(HSem,INFINITE) ;
Form1.Edit1.Text := IntToStr(tick);
Inc(tick);
Sleep(10);
ReleaseSemaphore(HSem, 1, Nil)
end;
constructor TMyThread.Create;
begin
inherited Create(False);
FreeOnTerminate := True;
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
HSem := CreateSemaphore(Nil,1,1,Nil) ;
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
CloseHandle(HSem) ;
end;
procedure TForm1.Button1Click(Sender: TObject);
var
index: Integer;
begin
for index := 0 to 10 do
begin
TMyThread.Create;
end;
end;
end.
一般的同步对象使用Mutex对象，是因为Mutex有一个特别之处：当一个持有对象的线程DOWN掉的时候，mutex对象可以自动让其它等待这个对象的线程接受，而其它的内核对象则不具体这个功能。
之所要使用Semaphore则是因为Semaphore可以提供一个活动线程的上限，即lMaximumCount参数，这才是它的真正有用之处。
