在TThread派生类中重新创建TThread

Question

I created a new class derived from TThread class, and on the constructor i call "inherited Create(True);", and then call "Resume()" since i have override the Execute() call, now i wanna recall the Execute() (Run the Thread Again) without destroying the class instance, so i have a function inside the new class called "myRestart()", which recalls "inherited Create(True);" and makes me able to call "Resume()" again and thread works again.

my question is, is this a safe practice? will it work also if i have multiple instances of this class? or is there a better way to do it?

thanks

Answer 1

Don't go around doing things like that. If you want procedures/functions in your thread class to run more than once, call them from a while() loop in your Execute override and signal the thread to run the code with a suitable synchro object at the top, a semaphore or event, say:

TmyThread.Execute;
begin
  while true do
  begin
    someEvent.waitFor(INFINITE);
    if terminated then exit;
    doMyProcedure(params);
    doOtherStuff;
  end;
end;

Answer 2

I think you must show your Restart Code? Because as I know if the thread finish it's Execute procedure then It's state in OS will change to DONE and calling resume again only start that thread as just a function in main thread not a real separate thread.

by the way you can use this sample code for your need

unit UWorker;

interface

uses Windows, Classes, Contnrs;

type
  TWorkerThread=class;

  TWorkerJob=class
    procedure ExecuteJob(Worker: TWorkerThread); virtual; abstract;
  end;

  TWorkerThread=class(TThread)
  private
    FFinished: TObjectList;
    FNotFinished: TObjectList;
  protected
    procedure Execute;Override;
  public
    constructor Create(createSuspended: Boolean);override;
    destructor Destroy; override;
  public
    property Finished: TObjectList read FFinished;
    property NotFinished: TObjectList read FNotFinished;
  end;



implementation

{ TWorkerThread }

constructor TWorkerThread.Create(createSuspended: Boolean);
begin
  inherited;
  FFinished := TObjectList.Create;
  FNotFinished := TObjectList.Create;
end;

destructor TWorkerThread.Destroy;
begin
  FFinished.Free;
  FNotFinished.Free;
  inherited;
end;

procedure TWorkerThread.Execute;
var
  CurrentJob: TWorkerJob;
begin
  while not Terminated do
  begin
    if FNotFinished.Count > 0 then
    begin
      CurrentJob := TWorkerJob(FNotFinished.Items[0]);
      FNotFinished.Extract(CurrentJob);

      with CurrentJob do
      begin
        ExecuteJob(Self);
      end;
      FFinished.Add(CurrentJob);
    end else
    begin
      // pass the cpu to next thread or process
      Sleep(5);
    end;
  end;

end;

end.

for use this code just create a worker and then create some instance of jobs and add them to NotFinished list. the Worker will execute all jobs one by one. To restart a job just extract it from Finished list and add it again to the NotFinished.

remember you must inherit your jobs and override the ExecuteJob procedure.