delphi 字符串函数_C语言字符串函数

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QueueUserWorkItem 函数 Windows 说明如下：

一、异步调用函数:
BOOL QueueUserWorkItem(
PTHREAD_START_ROUTINE pfnCallback,
PVOID pvContext，
ULONG dwFlags);
该函数将“工作项目”放入线程池并且立即返回。工作项目是指一个用pfnCallback参数标识的函数。它被调用并且传递单个参数pvContext.工作项目函数原型如下：
DWORD WINAPI WorkItemFunc(PVOID pvContext);
dwFlags参数：WT_EXECUTEDEFAULT 工作项目放入非I/O组件得线程中
             WT_EXECUTEINIOTHREAD 工作项目放入I/O组件的线程中，这样的线程在I/O请求没有完成之前不会被终止运行                                  ，防止因为线程被终止导致I/O请求丢失。
             WT_EXECUTEINPERSISTENTTHREAD 放入永久线程池，
             WT_EXECUTELONGFUNCTION 工作项目需要长时间的工作，系统会据此安排更多的线程。

线程池不能设置线程个数的上限，否则排队个数超过线程个数上限的时候，会导致所有的线程都被中断。

工作项目函数如果访问了已经被卸载的DLL,会产生违规访问。

delphi 官网给出的调用例子：

unit ThreadPoolUnit;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, ExtCtrls;

type
TForm3 = class(TForm)
    PaintBox1: TPaintBox;
    Button1: TButton;
    ListBox1: TListBox;
    procedure Button1Click(Sender: TObject);
private
    type
      TWorkerColor = class
        FThreadID: Integer;
        FColor: TColor;
        FForm: TForm3;
        procedure PaintLines(Sender: TObject);
        procedure PaintLine;
        constructor Create(AForm: TForm3; AColor: TColor);
      end;
    var
      FIndex: Integer;
public
    {
Public declarations }
end;

TObjectHelper = class helper for TObject

end;

TThreadPool = class
private
    type
      TUserWorkItem = class
        FSender: TObject;
        FWorkerEvent: TNotifyEvent;
      end;
    class procedure QueueWorkItem(Sender: TObject; WorkerEvent: TNotifyEvent; Flags: ULONG); overload; static;
public
    class procedure QueueWorkItem(Sender: TObject; WorkerEvent: TNotifyEvent); overload; static;
    class procedure QueueIOWorkItem(Sender: TObject; WorkerEvent: TNotifyEvent); static;
    class procedure QueueUIWorkItem(Sender: TObject; WorkerEvent: TNotifyEvent); static;
end;

var
Form3: TForm3;
ThreadPool: TThreadPool;

implementation

{
$R *.dfm}

const
WT_EXECUTEDEFAULT       = ULONG($00000000);
WT_EXECUTEINIOTHREAD    = ULONG($00000001);
WT_EXECUTEINUITHREAD    = ULONG($00000002);
WT_EXECUTEINWAITTHREAD = ULONG($00000004);
WT_EXECUTEONLYONCE      = ULONG($00000008);
WT_EXECUTEINTIMERTHREAD = ULONG($00000020);
WT_EXECUTELONGFUNCTION = ULONG($00000010);
WT_EXECUTEINPERSISTENTIOTHREAD = ULONG($00000040);
WT_EXECUTEINPERSISTENTTHREAD = ULONG($00000080);
WT_TRANSFER_IMPERSONATION = ULONG($00000100);

function QueueUserWorkItem (func: TThreadStartRoutine; Context: Pointer; Flags: ULONG): BOOL; stdcall; external kernel32 name ‘QueueUserWorkItem‘;

function InternalThreadFunction(lpThreadParameter: Pointer): Integer; stdcall;
begin
Result := 0;
try
    try
      with TThreadPool.TUserWorkItem(lpThreadParameter) do
        if Assigned(FWorkerEvent) then
          FWorkerEvent(FSender);
    finally
      TThreadPool.TUserWorkItem(lpThreadParameter).Free;
    end;
except

end;
end;

{
TThreadPool }

class procedure TThreadPool.QueueWorkItem(Sender: TObject; WorkerEvent: TNotifyEvent);
begin
QueueWorkItem(Sender, WorkerEvent, WT_EXECUTEDEFAULT);
end;

class procedure TThreadPool.QueueIOWorkItem(Sender: TObject; WorkerEvent: TNotifyEvent);
begin
QueueWorkItem(Sender, WorkerEvent, WT_EXECUTEINIOTHREAD);
end;

class procedure TThreadPool.QueueUIWorkItem(Sender: TObject; WorkerEvent: TNotifyEvent);
begin
QueueWorkItem(Sender, WorkerEvent, WT_EXECUTEINUITHREAD);
end;

class procedure TThreadPool.QueueWorkItem(Sender: TObject; WorkerEvent: TNotifyEvent; Flags: ULONG);
var
WorkItem: TUserWorkItem;
begin
if Assigned(WorkerEvent) then
begin
    IsMultiThread := True;
    WorkItem := TUserWorkItem.Create;
    try
      WorkItem.FWorkerEvent := WorkerEvent;
      WorkItem.FSender := Sender;
      if not QueueUserWorkItem(InternalThreadFunction, WorkItem, Flags) then
        RaiseLastOSError;
    except
      WorkItem.Free;
      raise;
    end;
end;
end;

procedure TForm3.Button1Click(Sender: TObject);
begin
FIndex := PaintBox1.Height;
PaintBox1.Repaint;
ListBox1.Items.Clear;
TWorkerColor.Create(Self, clBlue);
TWorkerColor.Create(Self, clRed);
TWorkerColor.Create(Self, clYellow);
TWorkerColor.Create(Self, clLime);
TWorkerColor.Create(Self, clFuchsia);
TWorkerColor.Create(Self, clTeal);
end;

{
TForm3.TWorkerColor }

constructor TForm3.TWorkerColor.Create(AForm: TForm3; AColor: TColor);
begin
FForm := AForm;
FColor := AColor;
TThreadPool.QueueWorkItem(Self, PaintLines);
end;

procedure TForm3.TWorkerColor.PaintLines(Sender: TObject);
var
I: Integer;
begin
FThreadID := GetCurrentThreadID;
for I := 0 to 9 do
begin
    PaintLine;
    //TThread.Synchronize(nil, PaintLine);
    Sleep(100);
end;
Destroy;
end;

procedure TForm3.TWorkerColor.PaintLine;
begin
FForm.PaintBox1.Canvas.Lock;
try
    FForm.ListBox1.Items.Add(IntToStr(FThreadID));
    with FForm.PaintBox1 do
    begin
      Canvas.Pen.Color := FColor;
      Canvas.Polyline([Point(0, FForm.FIndex), Point(Width, FForm.FIndex)]);
      Dec(FForm.FIndex);
      if FForm.FIndex <= 0 then
        FForm.FIndex := 0;
    end;
finally
    FForm.PaintBox1.Canvas.Unlock;
end;
end;