I have an activex component being created with the threading model "both" on delphi. It works perfectly, until I execute a stress test which create 50 or more threads and starts creating the activex on each thread. In this scenario after some time of perfect execution, an Access Violation error occurs on the creation of the component, inside AxCmps.TActivexComponentControl.Create, without even reaching my component initialization code. The specific point where the exception occurs is on TWinControl.Create.
Does anyone know if this is a bug, or if I am doing wrong by having multiple threads create an instance of a component with "both" threading model?
Edit: the component isnt visual (means it is an invisible active x)
Edit2: If I wrap the create and free of the component with a critical section, then the problem doesnt occur
Thread code:
Coinitialize(nil);
try
for _j := 1 to LOOPS do
begin
try
CS.Enter;
_comp := MyComp.Create(nil);
CS.Leave;
try
CallMethods; //not synchronized
finally
CS.Enter;
_comp.Free;
CS.Leave;
end;
except
on E: Exception do
LogErrors(E);
end;
end;
finally
Couninitialize;
end;
After changing the implementation of my component from TActiveXComponent to TAutoObject and changing the corresponding factory, the access violation stopped occurring in my tests. Instead of using the automatically generated wrapper class TMyComponent.Create, I called CoMyComponent.Create. The only problem is, I cannot hook events through the interface.
Related
I have a Delphi 10 project using the latest version of EurekaLog. I'm currently using EurekaLog to help me debug problems in my production clients.
I noticed that EurekaLog wasn't registering errors that happened within threads. After I started reading up on it, I found that I need to change from TThread to TThreadEx, and add the following code at the start of my Execute overriden method.
SetEurekaLogStateInThread(ThreadID, true);
Despite this, when an error happens, it does not generate an event in the EL file.
If I add ExceptionManager.StandardEurekaError('TThrdSincArquivos.Execute => ' + ex.Message); on the try..except, it does log. But the stack trace is displayed as if the error occurred on the line where I call StandardEurekaLog(), not on the line where the error actually occurred. This defeats the purpose of the whole thing.
Another problem is that it displays a dialog box, which I don't want, since the error occurred inside a background thread. I just want it logged. I should get a dialog only with errors on the main thread.
How can I achieve theses results within the thread?
Actually log the error with the correct stack.
When on the main thread, display the dialog, but within a thread, just log with no dialog.
EDIT
Below is my EurekaLog Muti-threading configuration
Here is my thread declaration:
unit ThrdSincArquivos;
interface
uses
System.Classes, System.SysUtils, System.Generics.Collections, REST.Client, REST.Types,
System.JSON, Data.DB, Datasnap.DBClient, FireDAC.Comp.Client, FireDAC.Stan.Param, System.SyncObjs, EBase, EExceptionManager, EClasses;
type
TThrdSincArquivos = class(TThreadEx)
private
My thread's Create
constructor TThrdSincArquivos.Create(pPrimeiraExec: boolean; tipoSincParam: TTipoSinc);
begin
inherited Create(true);
NameThreadForDebugging('TThrdSincArquivos');
primeiraExec := pPrimeiraExec;
tipoSinc := tipoSincParam;
executadoThreadSinc := false;
FreeOnTerminate := true
end;
The start of my Execute
procedure TThrdSincArquivos.Execute;
var
contador: Integer;
begin
inherited;
try
and the end of the Execute
except
on ex: Exception do
begin
oLog.GravarLog(ex, 'TThrdSincArquivos.Execute => FIM');
end;
end;
end;
It refuses to log any exception to the Elf file. I tried to add a raise after my own log routine, but it still didn't help. It should log, but it isn't, unless I explicitly call the StandardEurekaError, but I get the stack wrong, and I get the dialog.
When you are using TThread class - it saves thread exception to .FatalException property, which you are supposed to handle in some way. Either from thread event, or from other (caller) thread. EurekaLog does not break this behaviour. E.g. your previosly written code will not change its behaviour when you enable EurekaLog. That way your properly written code would work correctly both with and without EurekaLog.
How your code is currently handling thread exceptions? Are you doing something like ShowMessage or custom logging? This obviosly would not work with EurekaLog, it does not know that you are processing exceptions with ShowMessage or your own custom logging code. You probably want something like Application.ShowException or re-raise in caller thread.
If you can not use default RTL/VCL processing (which is hooked by EurekaLog) for some reason - then you need to tell EurekaLog that you want to handle this particular exception. For example, from docs: you can use (for example) HandleException(E); from EBase unit:
Thread.WaitFor;
if Assigned(Thread.FatalException) then
begin
// Your old code is here
// Do your own thing: show message, log, etc.
// Tell EurekaLog to do its thing:
HandleException(Thread.FatalException);
end;
You would probably want to set exception filter or use events to disable dialogs for thread exceptions, because presumably you have already processed exception yourself (e.g. already showed message).
There is A LOT more ways to handle exception in threads, and EurekaLog's docs illustrate each thread case (like BeginThread, TThread, thread pools, etc.) with several possible options. It is just not reasonable to pack all this information into a single answer.
If, for some reason, you do not have code that processes .FatalException property of TThread - then you can use TThreadEx class and its .AutoHandleException property to handle exceptions automatically when thread exits, as described here:
type
TMyThread = class(TThreadEx)
protected
procedure Execute; override;
end;
procedure TMyThread.Execute;
begin
// ... your code ...
end;
procedure TForm1.Button1Click(Sender: TObject);
var
Thread: TMyThread;
begin
Thread := TMyThread.Create(True, 'My thread');
Thread.AutoHandleException := True; // <- added
Thread.FreeOnTerminate := True;
Thread.Start;
Thread := nil; // never access thread var with FreeOnTerminate after Start
end;
However, be aware that you code will not work properly (e.g. will ignore exceptions) if you decide to disable EurekaLog in the future. Because if you remove EurekaLog from your project - then your project will have no code to handle thread exceptions!
P.S.
I need to change from TThread to TThreadEx, and add the following
code at the start of my Execute overriden method.
SetEurekaLogStateInThread(ThreadID, true);
That is slightly incorrect: you can do either one or another, but not both. And there are other ways to tell EurekaLog that it should hook exceptions in this thread.
Basically, exception life has two stages: raise and handle. EurekaLog hooks both stages when they are implemented in default RTL/VCL code. You need to explicitly indicate which threads you want to hook, because you probably want to ignore system / 3rd party threads, which you have no control over. And it so happens that default processing for TThread does not exist in RTL/VCL. That is why there is nothing to hook.
I have a problem about adding string to Tmemo using TThread.ShowMessage can Show this string.The Application doesn't give any error about adding string to Tmemo but It doesn't be added to TMemo.So here is my code:
procedure TThreadGet.Execute;
var
Filed:TStringList;
begin
Filed:=TStringList.Create;
Filed.LoadFromFile(Username1+'.dat');
Messaged:=Touser+':'+Filed.Text;
Form2.Memo1.Lines.Add(Messaged);//Doesn't give error.But Doesn't Add String.
Showmessage(Messaged);//Shows String Right.
end;
Filed.Free;
Terminate;
end;
All access to VCL components must be performed in the main UI thread. For instance you may use TThread.Synchronize or TThread.Queue to arrange this.
The main reason for this is that Win32 windows have thread affinity. They also are only safe to access from the thread that created them. This property gives a very strong push to single thread UI and the VCL design goes this way.
Multi-threaded UI is possible in Win32 although it is much more tricky to do correctly. The VCL does not support that at all.
I do some reporting on a form with reportbuilder.
On the main form I select some items on a grid and then a generate the reports of the items.
I want to do this in a Tthread but i get an error 'List index out of bounds'.
Here is the call stack:
Classes.TList.Get(1244868)
Classes.TList.Get(???)
Forms.TScreen.GetCustomForms(???)
Forms.TApplication.DoActionIdle
Forms.TApplication.Idle(???)
Forms.TApplication.HandleMessage
Forms.TApplication.Run
Seems some form is either not being added to the Screen.Forms
collection in a timely manner or one is being freed from it during the
loop in DoActionIdle.
Any ideas on how to circumvent this problem?
I work on windows XP and delphi 2010.
I Also I've the problem with a test procedure on my application
TForm3 is just a form with no code.
TDebugThread = class(TThread)
protected
procedure Execute; override;
public
constructor Create();
end;
constructor TDebugThread.Create;
begin
FreeOnTerminate := True;
inherited Create(False);
end;
procedure TDebugThread.Execute;
var
oReport: DeBugReport.TForm3;
begin
inherited;
oReport:= DeBugReport.TForm3.Create(Nil);
try
sleep(1000);
finally
oReport.Free;
end;
end;
....
procedure RunThread();
begin
TDebugThread.Create();
end;
Recapitulation:
I have a list of some Intervention on a form. Each detail and resumation of the intervention can I print on 2/5 reports. Therefore I use reports components (reportbuilder) on another form (not visible). The new feature was to multiselect some interventions on the list and set the reports in a folder in pdf format. That's was simple just on each intervention call the reportform and some parameters to change and save into pdf.
But this take to long. The user must wait until the procedure was ended. No problem I set the procedure in a thread. But there I get the error 'List index out of bounds'. ArgggArggg, I was suspected that the reportform (created, to his job and then destroyed) the problem was but hoped that there was another solution. I was thinking to change the TForm into TDataModule. Can I set all the components of the form into the datamodule. I use the TDbGrid to see some values in design. But in the Tdatamodule I can't set a TDBGrid. Ok, I can live without the TDbGrid. So I transformed the TForm into TDataModule.
But the TDataModule is not the answer. There I get the error 'Graphics.OutOfResource' from a TBitmap. I think that the TBitmap is calling from the TppReport. Now I'm done. I'm changing my code all more than 2 days with no result. I leave the TThread for this time.
Let's take a look at TApplication.DoActionIdle:
procedure TApplication.DoActionIdle;
var
I: Integer;
begin
for I := 0 to Screen.CustomFormCount - 1 do
with Screen.CustomForms[I] do
if HandleAllocated and IsWindowVisible(Handle) and
IsWindowEnabled(Handle) then
UpdateActions;
end;
Let's assume that Screen.CustomFormCount and is implemented correctly and always returns the number of items indexed by Screen.CustomForms. In which case the conclusion is that the body of the loop is deleting a form. That is Screen.CustomFormCount is changing during the execution of the loop.
The only way that can happen is if one of the form's action update handlers results in a form being deleted. So, I can't tell you any more than that, but this analysis should lead you to the root cause of the problem.
And the second part of your question is quite simple. You cannot use VCL components outside the main GUI thread.
In fact it is plausible that destroying the VCL form in your thread is what is leading to Screen.CustomFormCount changing during the execution in the GUI thread of TApplication.DoActionIdle.
I have some inherited code for opening IE and I have some troubles, here is what I have:
IEUnit.pas (no form) has routines for LoadIE and OpenIE
OpenIE is called from separate thread and it looks like this
procedure OpenIE(URL: OleVariant; FieldValues: string = '');
var ie : IWebBrowser2; // <-- This should become "global" variable for the IEUnit
begin
ie := CreateOleObject('InternetExplorer.Application') as IWebBrowser2;
ie.Navigate2(URL, Flags, TargetFrameName, PostData, Headers);
ShowWindow(ie.HWND, SW_SHOWMAXIMIZED);
ie.Visible := true;
...
end;
I would like to have "global" ie variable in the unit and to write LoadIE routine like this :
LoadIE should be called from FormCreate (main thread)
It should just create "global" ie object
ie := CreateOleObject('InternetExplorer.Application') as IWebBrowser2;
so the OpenIE function doesn't need to create it, just to use it (purpose is to speed things up)
So problem is how to access same OLE object from 2 different threads, one creates the object, the other one uses it.
When I write code that doesn't take care of threads I get an error
exception class EOleSysError with message 'The application called an interface that was marshalled for a different thread'
How should I do it, to take care of threads (I'm not experienced with threads, some reading and video links are welcome).
Thanks in advance
MTA model COM servers can only be used from within their associated apartment. Here's the explanation of the error with the following advice:
The correct way of transferring an interface pointer (either a direct
pointer or a proxy pointer) from one apartment to another is via COM's
marshaling mechanism. The source apartment can call
CoMarshalInterThreadInterfaceInStream() to marshal the interface
pointer to a shared (global) stream. The destination apartment can
unmarshal this interface pointer by calling
CoGetInterfaceAndReleaseStream().
As you know, because it was the subject of your previous question, you need all calls to the COM object to be made from the same thread. The obvious choice is the main GUI thread. So, create the IWebBrowser2 in your main form's OnCreate event handler. And then use TThread.Synchronize or TThread.Queue whenever you need to show the browser. The code that you pass to Synchronize or Queue will be executed on the main GUI thread.
Assuming you are using a modern version of Delphi with support for anonymous methods you'd write it like this:
procedure TMyThread.ShowBrowser(const URL: string);
var
Proc: TThreadProcedure;
begin
Proc := procedure
begin
MainForm.Browser.Navigate2(URL, ...);
ShowWindow(MainForm.Browser.HWND, SW_SHOWMAXIMIZED);
MainForm.Browser.Visible := true;
end;
Queue(Proc);
end;
Non-free-threaded COM objects can only be used by/on/in the same thread as the one it's created for/on/in/with. In your case, to speed things up, I would use a plain global treadvar value of type IWebBrowser2, or a property in your class overriding TThread.
use CriticalSection to wrap all calls to the OleObject. also use Synchronize to call from the "other" thread to the main UI thread (this is why you get the exception).
i use this code in a thread (through Indy Onexecute event) . is there any problem ?
function TFrmMain.ShellExecute_AndWait(FileName, Params: string): bool;
var
exInfo: TShellExecuteInfo;
Ph: DWORD;
begin
FillChar(exInfo, SizeOf(exInfo), 0);
with exInfo do
begin
cbSize := SizeOf(exInfo);
fMask := SEE_MASK_NOCLOSEPROCESS or SEE_MASK_FLAG_DDEWAIT;
Wnd := GetActiveWindow();
exInfo.lpVerb := 'open';
exInfo.lpParameters := PChar(Params);
lpFile := PChar(FileName);
nShow := SW_NORMAL;
end;
if ShellExecuteEx(#exInfo) then
Ph := exInfo.hProcess
else
begin
Result := true;
exit;
end;
while WaitForSingleObject(exInfo.hProcess, 50) <> WAIT_OBJECT_0 do
begin
end;
CloseHandle(Ph);
Result := true;
end;
MSDN has this advice:
Because ShellExecuteEx can delegate execution to Shell extensions (data sources, context menu handlers, verb implementations) that are activated using Component Object Model (COM), COM should be initialized before ShellExecuteEx is called. Some Shell extensions require the COM single-threaded apartment (STA) type. In that case, COM should be initialized as shown here:
CoInitializeEx(NULL, COINIT_APARTMENTTHREADED | COINIT_DISABLE_OLE1DDE)
There are instances where ShellExecuteEx does not use one of these types of Shell extension and those instances would not require COM to be initialized at all. Nonetheless, it is good practice to always initalize COM before using this function.
(In Delphi, you'd of course replace the first parameter with nil and use or for the bitwise operation.)
Raymond Chen recently wrote about the consequences of getting this wrong. The specific example was that the function might fail with the Error_Access_Denied error code.
That's the only potential multithreading issue I see in your code. Below are further things that occurred to me when I read your code, although they have nothing to do with multithreading (and not even much to do with Indy).
You have a peculiar way of waiting for the program to stop running. You repeatedly wait for 50 milliseconds at a time, but if the process isn't finished yet, you do nothing but wait again. Describe your intention more accurately by specifying Infinite for the timeout.
The function always returns True. If there's no useful return value, then you should just make it a procedure so there's no return value at all. Don't confuse the caller with useless information. If you're going to keep it as a function, then use the Delphi native type Boolean instead of the Windows compatibility type Bool for the return type.
I'm a little wary about the idea of a server executing user-interactive programs upon receipt of network messages.
Notice when MSDN says you might not get a process handle. There are cases when ShellExecuteEx can service your request without creating a new process, so you'll have nothing to wait on.
The user might end up using the program awhile, and your server will be stuck waiting all that time. I wonder whether it really needs to wait at all. Is the client going to be waiting for a response from the server, too?