Delphi实现Singleton模式

单例模式用于限制进程中只有一个某个类的对象，本例的Singleton是一个线程实例，在每一个时钟到达时检测是否到达某个时刻（本例的时刻存于Ini文件中），如果到达则产生一个线程，但是如果在这个线程完成其任务前又到达一个时钟，则有可能会产生多个线程执行任务，以致出现混乱，所以考虑使用Singleton模式解决这个问题（当然还有其他解决方案，但本例使用的是Singleton）。
核心代码如下：
//timer单元
procedure TService1.Timer_mainTimer(Sender: TObject);
var
mystringlist:TStringList;
SearchRec: TSearchRec;
nowtime :string;
begin
try
DateTimeToString(nowtime,'hh:nn',now);
if LeftStr(nowtime,4)=LeftStr(GetMSG('GAME','下发时间',theexename+'.ini'),4) then
begin
//创建发送线程
Global_Instance:=TSendThread.getInstance;
//////////////
end;
except
on e: Exception do
begin
mystringlist:=TStringList.Create;
if FileExists(ExtractFilePath(Paramstr(0))+'Err.txt') then
mystringlist.LoadFromFile(ExtractFilePath(Paramstr(0))+'Err.txt');
mystringlist.Add('('+DateTimeToStr(Now)+')[创建线程出错:]'+E.Message);
mystringlist.SaveToFile(ExtractFilePath(Paramstr(0))+'Err.txt');
mystringlist.Free;
if FindFirst(ExtractFilePath(Paramstr(0))+'Err.txt', faAnyFile, SearchRec)=0 then
begin
if SearchRec.Size>5000000 then
begin
RenameFile(ExtractFilePath(Paramstr(0))+'Err.txt',ansireplacestr(ExtractFilePath(Paramstr(0))+'Err.txt','.txt',FormatDateTime('yyyy-MM-dd hh-mm-ss',now)+'.txt'));
end;
end;
end;
end;
end;
//线程单元
unit Unit_Send ;

interface
uses
SysUtils, Classes,StrUtils,main;
type
TSendThread = class(TThread)
public
constructor Create(CreateSuspended: Boolean);
destructor Destroy; override;
class function getInstance:TSendThread;
procedure joke;

protected
procedure Execute; override;
end;

var
Global_Instance:TSendThread;

implementation

uses DB;

class function TSendThread.getInstance:TSendThread;
begin
if Global_Instance=nil then
begin
Global_Instance:=TSendThread.Create(false);
end;
Result:=Global_Instance;
end;
constructor TSendThread.Create(CreateSuspended: Boolean);
begin
if Global_Instance=nil then
begin
inherited Create(CreateSuspended);
FreeOnTerminate:=true ;
end
else
raise Exception.CreateFmt('Can not create more than one TSendThread instance!',[SysErrorMessage(0)]);
end;
destructor TSendThread.Destroy;
begin
inherited Destroy;
end;
procedure TSendThread.joke;
begin
end;
procedure TSendThread.Execute;
var
theuser:TUserInfo;
tmpSql:string;
begin
//执行任务
//处理定时下发 '+GameInfo.mainusertable+'
tmpSql:='select * from '+mainusertable+' where destroy=0 order by id';
Service1.ADOQuery_send.Connection:=conn_Server;
SQLQuery(Service1.ADOQuery_send,tmpSql);
while (not Service1.ADOQuery_send.Eof) and (not Terminated) do
begin
theuser.SeqID:='0';
theuser.UID:='';
theuser.Spc:=GetMSG('PARAMETER','Spcode',theexename+'.ini');
theuser.RecordID:='0';
theuser.Mob:=Service1.ADOQuery_send.FieldByname('mobile').AsString;
AutoJoke(theuser);
Service1.ADOQuery_send.Next;
end;
Sleep(600001);
Global_Instance:=nil;
Terminate;
//任务完成
end;
end.