CreateDCW is crashing for Printer on worker thread

Shyam Butani 135

Hi,

I want to print something using printer. For that I need to get the HDC of the printer like below:

HDC hdc = CreateDCW (NULL, L"Printer Name", NULL, NULL);

This is crashing with below error:

Exception thrown at 0x00007FFAE3B85B0C (KernelBase.dll) in TWTallySCPNative.exe: WinRT originate error - 0x80040155 : 'Failed to find proxy registration for IID: {79EAC9E4-BAF9-11CE-8C82-00AA004BA90B}.'.

But If I do winrt::init_apartment (apartment_type::single_threaded) before this, It works fine.

Can you please explain the reason behind this.

Printer name is valid (verified). This code is being executing on worker thread, can that be a problem?

Thanks.

RLWA32 41,831 Reputation points

2024-05-16T08:59:34.7433333+00:00

Can you share a sample that reproduces the issue?

3 answers

Jeanine Zhang-MSFT 9,346 Reputation points Microsoft Vendor

2024-05-15T09:16:19.13+00:00

Hello,

Welcome to Microsoft Q&A!

According to the Doc: CreateDCW function

Note that the handle to the DC can only be used by a single thread at any one time.

Refer to the Doc: Get started with C++/WinRT

The call to winrt::init_apartment initializes the thread in the Windows Runtime; by default, in a multithreaded apartment.

As far as I'm concerned, you need to call winrt::init_apartment to initializes the thread to single-threaded apartments in the Windows Runtime.

Thank you.

Jeanine

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Shyam Butani 135 Reputation points

2024-05-15T09:23:11.69+00:00

Here, the HDC is being used in the a single thread only. Worker thread will get the HDC, do it's work and the will release it. So thread should not be a problem, correct me if I'm wrong.

And anyway, why we need to initialize COM (using winrt::inti_apartment) for Win32 API?

David Lowndes 2,455 Reputation points MVP

2024-05-15T11:36:25.69+00:00

The comment in the documentation of CreateDC says it can only be used by 1 thread at a time, not that it can't be used in multiple threads - i.e. if you do try and use it in multiple threads, you need to do synchronisation - as noted by Raymond Chen here.

RLWA32 41,831 Reputation points

2024-05-15T13:02:31.6133333+00:00

My own test on Win10 22H2 in a minimal console application to create a printer DC in a background thread succeeded when

a) COM was not initialized in the process or

b) the worker thread was in the MTA or

c) the main thread was MTA and the worker thread was STA.

And the docs for CreateDC don't mention COM at all.

kwikc 131 Reputation points

2024-05-15T14:12:12.22+00:00

Maybe the default call to winrt::init_apartment() setting up multithreaded apartment modifies an internal something involved in CreateDCW(). This should be a piece of evidence that winrt and win32 are highly inter-operative within the Windows subsystem.

Jeanine Zhang-MSFT 9,346 Reputation points Microsoft Vendor

2024-05-16T07:54:15.16+00:00

It is easier to support apartment threading in single-threaded apartments because COM provides synchronization on a per-call basis. Supporting free-threading is more difficult because the object must implement synchronization.

https://stackoverflow.com/a/127240

If the COM object don't handle its own synchronization then the STA model can be used.

If the COM object can handle its own synchronization then the MTA model can be used.

If you do not handle synchronization, you should initialize COM to STA model.

Shyam Butani 135 Reputation points

2024-05-17T07:18:41.3233333+00:00

I'm not able to reproduce the issue in another project. I'm not sure if any project properties that we've set might causing the issue.

If I do init_apartment before CreateDC, CreateDC works but then StartDoc crashes.

Shyam Butani 135 Reputation points

2024-05-17T09:31:36.67+00:00

It works if I use CoInitialize. Can you please explain how it makes the difference? Thanks.

RLWA32 41,831 Reputation points

2024-05-17T09:56:51.3933333+00:00

It works if I use CoInitialize. Can you please explain how it makes the difference? Thanks.

Since I don't have any insight into your project or its code I can't give you a definitive explanation.

However, since your worker thread appears to be calling Win32 GDI functions it made sense to me that the Win32 function to initialize COM made sense if the worker thread did not otherwise use C++/WinRT.

I converted my earlier comment to an Answer that can be accepted to close the issue.

Shyam Butani 135 Reputation points

2024-05-17T10:23:43.6166667+00:00

Worker thread is not calling Win32 GDI api, but it is using WinRT artifacts like hstring and unordered map. Can that be an issue?

RLWA32 41,831 Reputation points

2024-05-17T10:33:13.7166667+00:00

Worker thread is not calling Win32 GDI api,

CreateDCW is a Win32 GDI function and the Win32 printing API uses GDI objects.

I don't believe that the COM issue is related to printing.

Since C++/WinRT is COM based the usage of its data structures might have something to do with the need to initialize COM but I can't give you a definitive explanation.

Shyam Butani 135 Reputation points

2024-05-20T09:42:56.88+00:00

I've able to reproduce the issue. I've attached the project here. When we execute line 25 (project attached), I'm getting below error.

Exception thrown at 0x00007FFD7CE953AC (KernelBase.dll) in DesktopWin32App1.exe: WinRT originate error - 0x80040155 : 'Failed to find proxy registration for IID: {79EAC9E4-BAF9-11CE-8C82-00AA004BA90B}.'. Exception thrown at 0x00007FFD7CE953AC (KernelBase.dll) in DesktopWin32App1.exe: 0x80040155: Interface not registered. Exception thrown at 0x00007FFD7CE953AC (KernelBase.dll) in DesktopWin32App1.exe: 0x80040155: Interface not registered.

Sample project: https://drive.google.com/file/d/1TGChFX7Jm9T74CjynT4WrAovn5TSA27G/view?usp=drivesdk

And the thing is, even if I get this error, print works.

@RLWA32 @Jeanine Zhang-MSFT

David Lowndes 2,455 Reputation points MVP

2024-05-20T10:44:18.8266667+00:00

I can reproduce those exception outputs in the debugger, but they're not ones causing any issues with your program, so just ignore them.

RLWA32 41,831 Reputation points

2024-05-20T11:47:47.1333333+00:00

It is not uncommon for some windows components to report non-fatal errors that can be seen in a debugger but that do not otherwise impact program execution. In my experience these errors are often only reported when the components determine that a debugger is attached to the process. If debug output is displayed using a program like Sysinternals DebugView these error messages do not appear. Finally, the noted error messages did not manifest when running the sample code in an x64 debug build under a fully updated Win10 22H2 VM.
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RLWA32 41,831 Reputation points

2024-05-17T07:34:51.66+00:00

I'm not able to reproduce the issue in another project. I'm not sure if any project properties that we've set might causing the issue. If I do init_apartment before CreateDC, CreateDC works but then StartDoc crashes.

Apparently, the problem is in that specific project, not in the Windows API.

Perhaps the need to initialize COM is unrelated to the Windows API printing functions. Have you tried using CoInitialize(Ex) instead of winrt::init_apartment?
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Shyam Butani 135 Reputation points

2024-05-22T06:28:38.9266667+00:00

Okay, so we can ignore this exception.

Thing is, the project I'm working on has a mechanism to catch unhandled exception and then crash. Had to make changes there to ignore this type of exception(s).

Thanks everyone for help.
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CreateDCW is crashing for Printer on worker thread

3 answers