Delphi service app crashes at a random time - delphi

Question

I have a Delphi Service app. Indy TCP server and many clients (up to 50), ADO connection to Firebird and simply network exchange. App randomly crashes (may be workin 7 days, may be 1 hour) with next event (for example):
Имя сбойного приложения: rollcontrol.exe, версия: 1.1.20.2, метка времени: 0x60acd5f2
Имя сбойного модуля: ntdll.dll, версия: 6.3.9600.19678, метка времени: 0x5e82c0f7
Код исключения: 0xc0000005
Смещение ошибки: 0x00058def
Идентификатор сбойного процесса: 0x4178
or:
Имя сбойного приложения: rollcontrol.exe, версия: 1.1.1.9, метка времени: 0x607b239c
Имя сбойного модуля: msvcrt.dll, версия: 7.0.9600.16384, метка времени: 0x52158ff5
Код исключения: 0xc0000005
Смещение ошибки: 0x00009e80
All jobs in app makes in anonimius threads or in tcp/ip connections threads. All code in each thread executed in try except statments. There no memory leaks or growing threads count. The main code of service thread very simple:
procedure TRollControl_Svc.ServiceExecute(Sender: TService);
begin
while not Terminated do
try
ServiceThread.ProcessRequests(False);
ServiceThread.Sleep(100);
except
on e : exception do LogException('ServiceExecute', E);
end;
end;
How I can handled this exception and prevent app crash? How it possible to crash service thread with two simple lines of code?
Thanks
UPDATE: Example of connections to DB:
function TRollControl_Svc.GetNodeIdByIP(ip: string): integer;
Var
SQLConnection : TADOConnection;
SQLQuery : TADOQuery;
Thread : TThread;
fResult : integer;
begin
fResult := 0;
try
Thread := nil;
Thread := TThread.CreateAnonymousThread(
procedure
begin
try
SQLConnection := nil;
SQLQuery := nil;
CoInitialize(nil);
SQLConnection := TADOConnection.Create(nil);
SQLConnection.ConnectionString := 'Provider=MSDASQL.1;Password=' + Psw + ';Persist Security Info=True;User ID=' + Usr + ';Data Source=' + Srv ;
SQLConnection.LoginPrompt := false;
SQLQuery := TADOQuery.Create(nil);
SQLQuery.Connection := SQLConnection;
SQLQuery.LockType := ltReadOnly;
try SQLConnection.Open; except SQLConnection.Open; end;
SQLConnection.BeginTrans;
SQLQuery.Close;
SQLQuery.SQL.Text := 'select nodes.* from nodes where nodes.ip = :ip';
SQLQuery.Parameters.ParamByName('ip').Value := ip;
try SQLQuery.Open; except SQLQuery.Open; end;
if SQLQuery.IsEmpty then exit;
fResult := SQLQuery.FieldByName('ID').AsInteger;
if SQLConnection.InTransaction then
SQLConnection.CommitTrans;
finally
TryFree(SQLQuery);
TryFree(SQLConnection);
CoUninitialize;
end;
end
);
Thread.FreeOnTerminate := false;
Thread.Start;
Thread.WaitFor;
finally
TryFree(Thread);
end;
result := fResult;
end;

Answer 1

Error Handling
This isn't an answer as to what is causing your problem, but I thought it probably wouldn't be clear in a comment.
In languages that support structured exception handling the language gives the programmer an opportunity to fail gracefully when things don't work. That's not how you are using it. From your example anonymous thread you have:
try SQLConnection.Open; except SQLConnection.Open; end;
So you are told that the connection can't be made and instead of responding to that situation you go ahead and attempt to connect again. There are lots of reasons why a connection may not work, some of those are transient so the attempt may work a little later but if you simply try doing it again without any pause it seems reasonable to expect it to fail again.
It's obviously important to catch errors, but you have to have appropriate failure paths.
I have no way of knowing if this is related to what's actually going wrong.

Answer 2

I found the reason. The problem was in the ADO source codes (Data.Win.ADODB.pas):
procedure RefreshFromOleDB;
var
I: Integer;
ParamCount: ULONG_PTR;
ParamInfo: PDBParamInfoArray;
NamesBuffer: POleStr;
Name: WideString;
Parameter: _Parameter;
Direction: ParameterDirectionEnum;
OLEDBCommand: ICommand;
OLEDBParameters: ICommandWithParameters;
CommandPrepare: ICommandPrepare;
begin
OLEDBCommand := (Command.CommandObject as ADOCommandConstruction).OLEDBCommand as ICommand;
OLEDBCommand.QueryInterface(ICommandWithParameters, OLEDBParameters);
OLEDBParameters.SetParameterInfo(0, nil, nil); // ----- Error here
if Assigned(OLEDBParameters) then
begin
ParamInfo := nil;
NamesBuffer := nil;
try
OLEDBCommand.QueryInterface(ICommandPrepare, CommandPrepare);
if Assigned(CommandPrepare) then CommandPrepare.Prepare(0);
if OLEDBParameters.GetParameterInfo(ParamCount, PDBPARAMINFO(ParamInfo), #NamesBuffer) = S_OK then
for I := 0 to ParamCount - 1 do//
begin
{ When no default name, fabricate one like ADO does }
if ParamInfo[I].pwszName = nil then
Name := 'Param' + IntToStr(I+1) else { Do not localize }
Name := ParamInfo[I].pwszName;
{ ADO maps DBTYPE_BYTES to adVarBinary }
if ParamInfo[I].wType = DBTYPE_BYTES then ParamInfo[I].wType := adVarBinary;
{ ADO maps DBTYPE_STR to adVarChar }
if ParamInfo[I].wType = DBTYPE_STR then ParamInfo[I].wType := adVarChar;
{ ADO maps DBTYPE_WSTR to adVarWChar }
if ParamInfo[I].wType = DBTYPE_WSTR then ParamInfo[I].wType := adVarWChar;
Direction := ParamInfo[I].dwFlags and $F;
{ Verify that the Direction is initialized }
if Direction = adParamUnknown then Direction := adParamInput;
Parameter := Command.CommandObject.CreateParameter(Name, ParamInfo[I].wType, Direction, ParamInfo[I].ulParamSize, EmptyParam);
Parameter.Precision := ParamInfo[I].bPrecision;
Parameter.NumericScale := ParamInfo[I].bScale;
//if ParamInfo[I].dwFlags and $FFFFFFF0 <= adParamSigned + adParamNullable + adParamLong then
Parameter.Attributes := ParamInfo[I].dwFlags and $FFFFFFF0; { Mask out Input/Output flags }
AddParameter.FParameter := Parameter;
end;
finally
if Assigned(CommandPrepare) then CommandPrepare.Unprepare;
if (ParamInfo <> nil) then GlobalMalloc.Free(ParamInfo);
if (NamesBuffer <> nil) then GlobalMalloc.Free(NamesBuffer);
end;
end;
end;
Line
OLEDBParameters.SetParameterInfo(0, nil, nil)
executed before
if Assigned(OLEDBParameters)
I moved this line after checking on nil and all working fine

Answer 3

I managed to isolate the problem. Errors occur periodically when working with ADO. If I try to use TADOQuery objects again, the application more susceptible to crashes. What I've done:
System.NeverSleepOnMMThreadContention: = false;
Significantly reduces errors when working with ADO
All uses of TADOQuery are single use.
For example it was:
for ii := 0 to SettingsXML.Root.NamedItem['sql_clear_base'].NamedItem['XML'].Count - 1 do
begin
try
SQLQuery.Close;
SQLQuery.SQL.Text := SettingsXML.Root.NamedItem['sql_clear_base'].NamedItem['XML'][ii].AsString;
SQLQuery.ExecSQL;
except
on e : exception do LogException('ClearBase', '', E);
end;
end;
Became:
for ii := 0 to SettingsXML.Root.NamedItem['sql_clear_base'].NamedItem['XML'].Count - 1 do
begin
SQLQuery := nil;
try
SQLQuery := TADOQuery.Create(nil);
SQLQuery.Connection := SQLConnection;
try
SQLQuery.Close;
SQLQuery.SQL.Text := SettingsXML.Root.NamedItem['sql_clear_base'].NamedItem['XML'][ii].AsString;
SQLQuery.ExecSQL;
except
on e : exception do LogException('ClearBase', '', E);
end;
finally
TryFree(SQLQuery);
end;
end;
I make self-control:
main procces started as windows service (process A)
process A starts a copy of itself as B
one per minutes A check if B alive and restart if not
one per minutes B check if A alive and restart if not
check - simple TCP packet and answer
For example:
TThread.CreateAnonymousThread(
procedure
var tcpClient : TidTCPClient;
begin
tcpClient := nil;
LastKeepAlive := Date + Time;
while ServerMode do
begin
try
if not Assigned(tcpClient) then
begin
tcpClient := TIdTCPClient.Create(nil);
tcpClient.Host := '127.0.0.1';
tcpClient.Port := RollControl_Svc.TCPServer.Bindings[0].Port;
tcpClient.Connect;
tcpClient.IOHandler.ReadTimeout := 1000;
end;
tcpClient.IOHandler.Write(START_PACKET + #0 + END_PACKET);
tcpClient.IOHandler.ReadString(3);
LastKeepAlive := Date + Time;
except
TryFree(tcpClient);
end;
sleep(15 * 1000);
end;
end).Start;
TThread.CreateAnonymousThread(
procedure
Var Res: TRequestResult;
begin
while ServerMode do
begin
if Date + Time - LastKeepAlive > OneMinute then
begin
Res.Clear('', '');
Res.Nodes_ID := -1;
Res.Data_In := 'KeepAlive';
Res.Data_Out := 'Exception: ExitProcess(1)';
try
Log(Res, true);
finally
ExitProcess(1);
end;
end;
sleep(1000);
end;
end).Start;
P.S. Local tests never crashed applications. The program simply proceed a million requests (connect, request, disconnect), there are no memory leaks or failures. On several clients servers are crashed. In the future I want to port to Lazarus to use ODBC directly insteed ADO