Delphi多线程文件编写需要帮助

Question

我正在编写一个 Delphi dll，它计算并将结果写入 CSV 文件。调用程序是多线程的，所以一个问题是同时多次写入文件导致调用程序崩溃。我尝试使用临界区锁定文件写入，但仍然发生崩溃。如果我将程序配置为只使用一个线程，问题就会消失。以下是我的代码：

    library Question;

    uses
      SysUtils,
      Classes,
      Math,
      SyncObjs;

    {$R *.res}

    Var

        Outputfile: textfile;

        CriticalSection: TCriticalSection;

        CalNumb: integer = 0;

        PrintString: String;

    Threadvar

    Cal1, Cal2, Cal1Last: double;

    Function Calculator (input1, input2, input3, input4: double; 
    Factor: double; LastCal: Boolean; Print: integer): double stdcall;

    Const
        Divisor = 4;
    Var
        Temp: double;
    Begin

    Cal1Last:= Cal1;
    Cal1:= (input1+ input2+input3+ input4)/Divisor;
    Cal2:= (Cal1+Factor*Cal1Last)/2;
    Temp:= Cal2 - Cal1Last;

          If LastCal and (Print = 1) then
                begin

                  CriticalSection:= TCriticalSection.Create;
                  Try
                    Try
                      Inc(CalNumb);
                      Assign(Outputfile, 'C:\Calculator\Result.csv');
                      If FileExists('C:\Calculator\Result.csv') then 
                      Append(Outputfile) else rewrite (Outputfile);

                      If CalNumb = 1 then
                      begin
                        PrintString:= 'CalNumb' + ',' + 'Cal1' + ',' + 
                        'Cal1Last' + ',' + 'Cal2' + ',';

                        Writeln(Outputfile, PrintString);
                      end;


                      Writeln(Outputfile,
                      CalNumb, ',', Cal1:5:2, ',', Cal1Last:5:2, ',', Cal2:5:2, ',');


                    Finally
                      Close(Outputfile);
                    End;

                  Finally
                    CriticalSection.Free;
                  End;

                end;

    If Cal1 <> 0 then Calculator:= Temp/Cal1 else Calculator:= 0;

    End;

    Exports
           Calculator;

    begin
    end.

我的代码有错误吗？多线程计算和外部文件写入对于这个项目是必不可少的。你有什么建议和cmets？我是初学者，所以如果你可以在这里发布你的代码，这对我来说将是一个很大的帮助。非常感谢您！ ///////////////////////////////////////// //////////////////////////////////////////////// p>

Graymatter，感谢您的建议。在我做出您建议的更改后，应用程序在写入文件之前崩溃。以前版本的dll可以在崩溃前将某些行数据写入文件中。如果我可能做出错误的更改，我会在下面发布更改的部分。其他部分代码不变。

          If LastCal and (Print = 1) then
                begin

                  CriticalSection.Acquire;
                  Try
                    Try
                      Inc(CalNumb);
                      Assign(Outputfile, 'C:\Calculator\Result.csv');
                      If FileExists('C:\Calculator\Result.csv') then 
                      Append(Outputfile) else rewrite (Outputfile);

                      If CalNumb = 1 then
                      begin
                        PrintString:= 'CalNumb' + ',' + 'Cal1' + ',' + 
                        'Cal1Last' + ',' + 'Cal2' + ',';

                        Writeln(Outputfile, PrintString);
                      end;


                      Writeln(Outputfile,
                      CalNumb, ',', Cal1:5:2, ',', Cal1Last:5:2, ',', Cal2:5:2, ',');


                    Finally
                      Close(Outputfile);
                    End;

                  Finally
                    CriticalSection.Release;
                  End;

                end;

    If Cal1 <> 0 then Calculator:= Temp/Cal1 else Calculator:= 0;

    End;

    Exports
           Calculator;

    begin
    end.


    initialization
      CriticalSection := TCriticalSection.Create;
    finalization
      CriticalSection.Free;
    end;

Answer 1

创建临界区对象不会进行任何锁定。您需要调用Acquire 获取锁，调用Release 释放锁。

请参阅在线帮助中的Using Critical Sections。

问题是在加载 DLL 时需要创建临界区，因此您需要执行以下操作：

begin
  ...
  CriticalSection.Acquire;
  try
    ...
    // The code that needs to be locked goes inside here.
    // In your case it would be the code that opens the file
    // and appends the data.
    ...
  finally
    CriticalSection.Release;
  end;
  ...
end;

您必须将代码移动到一个单独的单元中，以便您可以包含 initialization 和 finalization 块。这些块将分别在第一次加载和卸载 DLL 时执行。

您的新单位将如下所示：

unit UnitForDLL;

interface

function Calculator(input1, input2, input3, input4: double; 
  Factor: double; LastCal: Boolean; Print: integer): double; stdcall;

implementation

uses
  SyncObjs, SysUtils;

var
  ...
  CriticalSection: TCriticalSection;
  ...

function Calculator(input1, input2, input3, input4: double; 
  Factor: double; LastCal: Boolean; Print: integer): double; stdcall;
begin
  ...
  CriticalSection.Acquire;
  try
    ...
    // The code that needs to be locked goes inside here.
    // In your case it would be the code that opens the file
    // and appends the data.
    ...
  finally
    CriticalSection.Release;
  end;
  ...
end;

initialization
  CriticalSection := TCriticalSection.Create;
finalization
  CriticalSection.Free;
end.

一旦你这样做了，你的项目本身就会变得更简单：

library Question;

uses
  SysUtils,
  Classes,
  UnitForDLL;

{$R *.res}

exports
       Calculator;

begin
end.