How to create a Child process depending on it's Parent? - delphi

Question

My application (main.exe) is executing a Child process (child.exe) using ShellExecuteEx.
But when I close or kill (via Process-Explorer) main.exe the child process remains active.
How to gracefully handle that, when main.exe terminates child.exe terminates also?

Answer 1

You need to use jobs. Main executable should create a job object, then you'll need to set JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE flag to your job object.
uses
JobsApi;
//...
var
jLimit: TJobObjectExtendedLimitInformation;
hJob := CreateJobObject(nil, PChar('JobName');
if hJob <> 0 then
begin
jLimit.BasicLimitInformation.LimitFlags := JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE;
SetInformationJobObject(hJob, JobObjectExtendedLimitInformation, #jLimit,
SizeOf(TJobObjectExtendedLimitInformation));
end;
Then you need to execute another process with CreateProcess function where dwCreationFlags must be set to CREATE_BREAKAWAY_FROM_JOB. If this function succeeds call AssignProcessToJobObject.
function ExecuteProcess(const EXE : String; const AParams: string = ''; AJob: Boolean = True): THandle;
var
SI : TStartupInfo;
PI : TProcessInformation;
AFlag: Cardinal;
begin
Result := INVALID_HANDLE_VALUE;
FillChar(SI,SizeOf(SI),0);
SI.cb := SizeOf(SI);
if AJob then
AFlag := CREATE_BREAKAWAY_FROM_JOB
else
AFlag := 0;
if CreateProcess(
nil,
PChar(EXE + ' ' + AParams),
nil,
nil,
False,
AFlag,
nil,
nil,
SI,
PI
) then
begin
{ close thread handle }
CloseHandle(PI.hThread);
Result := PI.hProcess;
end;
end;
//...
hApp := ExecuteProcess('PathToExecutable');
if hApp <> INVALID_HANDLE_VALUE then
begin
AssignProcessToJobObject(hJob, hApp);
end;
When all of this done all the child processes will be automatically terminated even if the main executable has been killed. You can get the JobsApi unit here. Note: I've not tested it with Delphi 7.
EDIT: Here you can download working demo project.

Answer 2

Try using Job Objects , check these functions CreateJobObject and AssignProcessToJobObject.
A job object allows groups of processes to be managed as a unit. Job
objects are namable, securable, shareable objects that control
attributes of the processes associated with them. Operations performed
on a job object affect all processes associated with the job object.
Examples include enforcing limits such as working set size and process
priority or terminating all processes associated with a job.

Answer 3

I think, it's very cool code. It's working for me, but I add some changes to be able user to set show window flags for child processes like SW_SHOW/SW_HIDE.
...
function ExecuteProcess(const EXE : String; const AParams: string = '';
const nCmdShow: Integer = SW_SHOW; AJob: Boolean = True): THandle;
var
SI : TStartupInfo;
PI : TProcessInformation;
AFlag: Cardinal;
begin
Result := INVALID_HANDLE_VALUE;
FillChar(SI,SizeOf(SI),0);
SI.cb := SizeOf(SI);
SI.dwFlags := STARTF_USESHOWWINDOW or STARTF_USESTDHANDLES;
SI.wShowWindow := nCmdShow;
if AJob then
AFlag := CREATE_BREAKAWAY_FROM_JOB
else
AFlag := 0;
...