How to implement a watchdog timer in Delphi? - delphi

Question

I would like to implement a simple watchdog timer in Delphi XE 7 with two use cases:
• Watchdog ensures that a operation doesn't execute longer than x seconds
• Watchdog ensures that when errors occur then message exception will be stored in log file
Could you please suggest me any solution?

Answer 1

Here is my solution. I'm not sure that is a proper, but its works. I crated a new thread:
type
// will store all running processes
TProcessRecord = record
Handle: THandle;
DateTimeBegin, DateTimeTerminate: TDateTime;
end;
TWatchDogTimerThread = class(TThread)
private
FItems: TList<TProcessRecord>;
FItemsCS: TCriticalSection;
class var FInstance: TWatchDogTimerThread;
function IsProcessRunning(const AItem: TProcessRecord): Boolean;
function IsProcessTimedOut(const AItem: TProcessRecord): Boolean;
procedure InternalKillProcess(const AItem: TProcessRecord);
protected
constructor Create;
procedure Execute; override;
public
class function Instance: TWatchDogTimerThread;
destructor Destroy; override;
procedure AddItem(AProcess: THandle; ADateStart: TDateTime; ATimeOutMS: Cardinal);
end;
const
csPocessThreadLatencyTimeMs = 500;
And here is an implementation part:
procedure TWatchDogTimerThread.Execute;
var
i: Integer;
begin
while not Terminated do
begin
Sleep(csPocessThreadLatencyTimeMs);
FItemsCS.Enter;
try
i := 0;
while i < FItems.Count do
begin
if not IsProcessRunning(FItems[i]) then
begin
FItems.Delete(i);
end
else if IsProcessTimedOut(FItems[i]) then
begin
InternalKillProcess(FItems[i]);
FItems.Delete(i);
end
else
Inc(i);
end;
finally
FItemsCS.Leave;
end;
end;
end;
procedure TWatchDogTimerThread.AddItem(AProcess: THandle; ADateStart: TDateTime; ATimeOutMS: Cardinal);
var
LItem: TProcessRecord;
begin
LItem.Handle := AProcess;
LItem.DateTimeBegin := ADateStart;
LItem.DateTimeTerminate := IncMilliSecond(ADateStart, ATimeOutMS);
FItemsCS.Enter;
try
FItems.Add(LItem);
finally
FItemsCS.Leave;
end;
end;
constructor TWatchDogTimerThread.Create;
begin
inherited Create(False);
FItems := TList<TProcessRecord>.Create;
FItemsCS := TCriticalSection.Create;
end;
destructor TWatchDogTimerThread.Destroy;
begin
FreeAndNil(FItemsCS);
FItems.Free;
FInstance := nil;
inherited;
end;
class function TWatchDogTimerThread.Instance: TWatchDogTimerThread;
begin
if not Assigned(FInstance) then
FInstance := Create;
Result := FInstance;
end;
procedure TWatchDogTimerThread.InternalKillProcess(const AItem: TProcessRecord);
begin
if AItem.Handle <> 0 then
TerminateProcess(AItem.Handle, 0);
end;
function TWatchDogTimerThread.IsProcessRunning(const AItem: TProcessRecord): Boolean;
var
LPID: DWORD;
begin
LPID := 0;
if AItem.Handle <> 0 then
GetWindowThreadProcessId(AItem.Handle, #LPID);
Result := LPID <> 0;
end;
function TWatchDogTimerThread.IsProcessTimedOut(const AItem: TProcessRecord): Boolean;
begin
Result := (AItem.DateTimeTerminate < Now);// and IsProcessRunning(AItem);
end;
end.