Are there best practices and code snippets available which show how I can handle Ctrl+C in a Delphi console application?
I have found some articles which give some information about possible problems with the debugger, with exception handling, unloading of DLLs, closing of stdin, and finalization for example this CodeGear forums thread.
From Windows API (MSDN):
BOOL WINAPI SetConsoleCtrlHandler(
PHANDLER_ROUTINE HandlerRoutine, // address of handler function
BOOL Add // handler to add or remove
);
A HandlerRoutine function is a function that a console process specifies to handle control signals received by the process. The function can have any name.
BOOL WINAPI HandlerRoutine(
DWORD dwCtrlType // control signal type
);
In the Delphi the handler routine should be like:
function console_handler( dwCtrlType: DWORD ): BOOL; stdcall;
begin
// Avoid terminating with Ctrl+C
if ( CTRL_C_EVENT = dwCtrlType ) then
result := TRUE
else
result := FALSE;
end;
I wrote a little program to show you how to stop properly a background task. Hopefully it is clearer.
Content of ThreadConsoleApplication.dpr file :
program ThreadConsoleApplication;
{$APPTYPE CONSOLE}
uses
SysUtils,
Windows,
Classes;
type
{ **
* Classe TQueueReaderTestApplication
* }
TThreadConsoleApplication = class(TThread)
public
procedure Execute; override;
constructor Create; virtual;
destructor Destroy; override;
class function getInstance: TThreadConsoleApplication;
end;
function TThreadConsoleApplication_consoleCtrlHandler(dwCtrlType: DWORD): BOOL;
stdcall; forward;
{ **
* Classe TQueueReaderTestApplication
* }
constructor TThreadConsoleApplication.Create;
begin
inherited Create(True { CreateSuspended } );
Windows.setConsoleCtrlHandler(@TThreadConsoleApplication_consoleCtrlHandler,
True { add } );
end;
var
threadConsoleApplicationInstance: TThreadConsoleApplication = nil;
destructor TThreadConsoleApplication.Destroy;
begin
threadConsoleApplicationInstance := nil;
inherited;
end;
procedure TThreadConsoleApplication.Execute;
begin
System.Writeln('[TThreadConsoleApplication.Execute] begin');
try
while not Terminated do
begin
System.Writeln('[TThreadConsoleApplication.Execute] running ...');
Windows.Sleep(1000 { dwMilliseconds } );
end;
finally
System.Writeln('[TThreadConsoleApplication.Execute] end');
end;
end;
class function TThreadConsoleApplication.getInstance: TThreadConsoleApplication;
begin
if nil = threadConsoleApplicationInstance then
begin
threadConsoleApplicationInstance := TThreadConsoleApplication.Create;
end;
Result := threadConsoleApplicationInstance;
end;
function TThreadConsoleApplication_consoleCtrlHandler(dwCtrlType: DWORD): BOOL;
begin
Result := False;
if Windows.CTRL_C_EVENT = dwCtrlType then
begin
TThreadConsoleApplication.getInstance.Terminate;
Result := True;
end;
end;
var
thread: TThread;
begin
System.Writeln('[program] begin');
try
thread := nil;
try
thread := TThreadConsoleApplication.getInstance;
thread.Resume;
System.Writeln('[program] press a CTRL+C to stop running');
thread.WaitFor;
finally
thread.Free;
end;
System.Writeln('[program] end');
except
on E: Exception do
begin
System.Writeln(System.ErrOutput, '[program] end with error');
System.Writeln(System.ErrOutput, E.ClassName, ': ', E.Message);
end;
end;
System.Writeln('[program] press a key to quit');
System.Readln;
end.