unit uSingleton;
interface
uses
SysUtils;
type
ESingletonException = class(Exception);
TSingleton = class
private
// 单例类真正使用的构造函数，此处命名为CreateNew
constructor CreateNew;
public
// 用于阻止显式调用，因为即便将其设为私有的，
// 也可以调用构造函数Create，
// 虽然实际上调用的是其父类的构造函数，
// 这样显然不是很理想，
// 所以只好声明并在实现中引发 ESingletonException
constructor Create;
// 类方法，返回对唯一的实例
class function Instance: TSingleton;
end;
implementation
uses SyncObjs;
var
SingletonInstance: TSingleton = nil;
// 用于锁定 TSingleton.Instance 方法，防止多线程访问
SingletonLocker: TCriticalSection = nil;
{ TSingleton }
constructor TSingleton.Create;
begin
raise ESingletonException.Create('单例类，禁止显式调用构造函数');
end;
constructor TSingleton.CreateNew;
begin
// do something
end;
class function TSingleton.Instance: TSingleton;
begin
SingletonLocker.Enter;
try
if not Assigned(SingletonInstance) then
SingletonInstance := TSingleton.CreateNew;
Result := SingletonInstance;
finally
SingletonLocker.Leave;
end;
end;
initialization
SingletonLocker := TCriticalSection.Create;
finalization
SingletonLocker.Free;
end.