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.
Related
I'm wondering if it's possible to create UI elements , even a complete form, in a background thread ( "without using it of course" ) , and once it's done, make it available in main thread to be shown.
It's relatively easy now to separate time consuming data operations in background threads and synchronize the results with your main thread but what if creating the UI itself IS the time consuming operation ?
If possible, you could maybe have a fast startup screen and then start a background thread to create a set of forms. Whenever one is ready, it enables a menu item in the main thread so that it can be used.
I tried simple code, but it freezes immediatly. Is it possible ?
Execute in main program :
...
// declare var in main form
public
{ Public declarations }
lForm : TForm ;
...
// Execute e.g. with button click in main form
TThread.CreateAnonymousThread( procedure begin
// this stops application from running when the form is show
// in the synchronize part
lForm := TForm1.Create(Self);
TThread.Synchronize(nil,
procedure begin
// This does not stops the application but freezes the gui of course
//lForm := TForm1.Create(Self);
lForm.Parent := Self ;
lForm.Show ;
end );
end ).Start ;`
procedure TForm1.FormCreate(Sender: TObject);
begin
sleep(2000);
end;
...
If it's not possible, how could you do this in the main thread while still 'simulating' that your main thread is responsive ? ( by calling something like application.processmessages regularly or so ? )
I'm using Delphi Rio 10.3, fmx framework.
I'm wondering if it's possible to create UI elements , even a complete
form, in a background thread ( "without using it of course" ) , and
once it's done, make it available in main thread to be shown.
NO.
Creating and accessing UI controls from background thread is not thread safe.
While you can create some proof of concept code that seemingly works, such code is inherently broken. It may fail randomly.
So , in summary, UI controls can only be used safely in the thread they are created in, and you can't change this behaviour after their creation time ( and make them 'belonging' to another thread as if they were created there in the first place ).
It might be though that conceptually, creating forms, that do not interact with another can work looking at
How to make a form in a DLL embedded inside my application?
I'm assuming that also here, the form is indeed created in different thread , probably even in a different process, right ?
I found that the following does not freeze instantly, but if that's pure luck for now or wisdom, I'm unsure..
Instead if making the form visible in the synchronize part of the background thread, I do it 'really' in the main thread...
( I could understand that as long as you don't give any parent to UI controls, they are 'safe'. How would the main thread know about their existence ? )
I might test this a bit further afterall.
procedure TTabbedForm.Button1Click(Sender: TObject);
begin
TThread.CreateAnonymousThread( procedure begin
lForm := TForm1.Create(Self);
TThread.Synchronize(nil,
procedure begin
//lForm.Parent := Self ;
//lForm.Show ;
Button2.Enabled := True ;
end );
end ).Start ;
end;
procedure TTabbedForm.Button2Click(Sender: TObject);
begin
if Assigned(lForm) then begin
lForm.Parent := Self ;
lForm.Show ;
end;
end;
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 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.
What I basically want is to start AsyncCall and proceed with my code loading. I have Interface section that consumes lots of time (600+ms) and I want to load this code in independent thread.
I've tried to use AsyncCall to make something like this:
procedure Load;
begin
...
end;
initialization
AsyncCall(#Load, []); // or LocalAsyncCall(#Load)
However, this Load procedure actually starts in Main thread and not in the new created thread. How can I force the Load procedure to be loaded in any thread other than MainThread?
I can create TThread and Execute this but I want to force AsyncCall or LocalAsyncCall or anything from AsyncCall library to make to work.
Thanks for your help.
Have you tried something like this?:
procedure Load;
begin
if GetCurrentThreadId <> MainThreadID then
Beep;
end;
var a: IAsyncCall;
initialization
a := AsyncCall(#Load, []);
a.ForceDifferentThread;
ForceDifferentThread() tells AsyncCalls that the assigned function must
not be executed in the current thread.
The problem is that your code is not retaining the IAsyncCall interface that is returned by the AsyncCall function.
AsyncCall(#Load, []);
//AsyncCall returns an IAsyncCall interface,
//but this code does not take a reference to it
Because of this, the interface that is returned has its reference count decremented to zero as soon as the initialization section completes. This therefore frees the object that implements the interface which does this:
destructor TAsyncCall.Destroy;
begin
if FCall <> nil then
begin
try
--> FCall.Sync; // throw raised exceptions here
finally
FCall.Free;
end;
end;
inherited Destroy;
end;
The key line is the call to Sync which forces the asynchronous call to be executed to completion. All this happens in the main thread which explains the behaviour that you report.
The solution is that you simply need to keep the IAsyncCall interface alive by storing it in a variable.
var
a: IAsyncCall;
initialization
a := AsyncCall(#Load, []);
In the real code you need to ensure that Load had completed before running any code that is reliant on Load. When your program reached a point where it required Load to have been called it has to call Sync on the IAsyncCall interface.
So you might write it something like this.
unit MyUnit;
interface
procedure EnsureLoaded;
implementation
uses
AsyncCalls;
....
procedure Load;
begin
....
end;
var
LoadAsyncCall: IAsyncCall;
procedure EnsureLoaded;
begin
LoadAsyncCall := nil;//this will effect a call to Sync
end;
initialization
LoadAsyncCall := AsyncCall(#Load, []);
end.
The call EnsureLoaded from other units that required Load to have run. Or, alternatively, call EnsureLoaded from any methods exported by MyUnit that depended on Load having run. The latter option has much better encapsulation.
I have just written my own logging framework (very lightweight, no need for a big logging framework). It consists of an interface ILogger and a number of classes implementing that interface. The one I have a question about is TGUILogger which takes a TStrings as the logging target and synchronizes the logging with the main thread so that the Items member of a listbox can be used as the target.
type
ILogger = Interface (IInterface)
procedure Log (const LogString : String; LogLevel : TLogLevel);
procedure SetLoggingLevel (LogLevel : TLogLevel);
end;
type
TGUILogger = class (TInterfacedObject, ILogger)
public
constructor Create (Target : TStrings);
procedure Log (const LogString : String; LogLevel : TLogLevel);
procedure SetLoggingLevel (LogLevel : TLogLevel);
private
procedure PerformLogging;
end;
procedure TGUILogger.Log (const LogString : String; LogLevel : TLogLevel);
begin
TMonitor.Enter (Self);
try
FLogString := GetDateTimeString + ' ' + LogString;
TThread.Synchronize (TThread.CurrentThread, PerformLogging);
finally
TMonitor.Exit (Self);
end;
end;
procedure TGUILogger.PerformLogging;
begin
FTarget.Add (FLogString);
end;
The logging works, but the application does not close properly. It seems to hang in the Classes unit. The stack trace:
System.Halt0, System.FinalizeUnits, Classes.Finalization, Classes.FreeExternalThreads,
System.TObject.Free, Classes.TThread.Destroy, Classes.TThread.RemoveQueuedEvents
What am I doing wrong here?
EDIT: I just found the following hint in the Delphi help for TThread.StaticSynchronize
Warning: Do not call StaticSynchronize from within the main thread. This can cause
an infinite loop.
This could be exactly my problem since some logging request come from the main thread. How can I solve this?
If you compare the CurrentThreadID with MainThreadID then you can choose to synchronize or not.
Personally, I chose to have the GUI ask the log system for the latest info, rather than have threads pause. Otherwise your logging interferes with the fast operation of the thread which defeats the purpose of having it.
If you don't find any simpler way, you could try doing this:
At program initialization, (from the main thread,) have your logging subsystem call the Windows API function GetCurrentThreadID and store the result in a variable. (EDIT: the MainThreadID variable in the System unit, gets initialized this way automatically for you at startup. Thanks, mghie.) When a logging request comes in after that, call GetCurrentThreadID again, and only synchronize if it's coming from a different thread.
There are other tricks that don't involve the Windows API, but they end up being more complicated, especially if you have a bunch of different custom TThread descendants. The basic principle is the same, though: Verify whether or not you're in the main thread before you decide whether or not to call StaticSynchronize.