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Do I need to call Coinitialize in the main/VCL thread in Delphi before using ShellExecuteEx?

For a thread, yes but for the VCL thread ?

David Heffernan
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user382591
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3 Answers3

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No need to call CoInitialize for Windows Forms Applications. This is done for you in the main thread. More specific TApplication.Create in Forms.Pas:

...
if not IsLibrary then
 FNeedToUninitialize := Succeeded(OleInitialize(nil));
...
whosrdaddy
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  • Isn't the initialization done in an InitProc during Application.Initialize? – David Heffernan Nov 16 '13 at 10:58
  • @DavidHeffernan: This is the only COM related initialization I could find in the source startup code(Delphi XE here). – whosrdaddy Nov 16 '13 at 12:02
  • I bet you'll find a call to CoInitializeEx in an initial proc. – David Heffernan Nov 16 '13 at 12:03
  • @DavidHeffernan: I did a Grep on the source code, if you found something else, feel free to add it. Anyway `OleInitialize` calls `CoInitializeEx` internally. – whosrdaddy Nov 16 '13 at 12:06
  • I've added some more details in an answer of my own. I just want to do that for extra information. I take nothing away from your answer. The initialization that you highlight is the one that counts. +1 – David Heffernan Nov 16 '13 at 13:29
3

If in doubt, do it. In either case, CoInitialize() will return a hr : HRESULT which you should check, because you need to CoUninitialize() on SUCCEEDED(hr), but not when FAILED(hr). A failed result usually indicates that it already has been called.

Cited from your MSDN ref:

Nonetheless, it is good practice to always initalize COM before using this function.

JensG
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  • The question specifically asks to remove the doubt. – David Heffernan Nov 16 '13 at 10:41
  • ... which can be done easily by checking the HRESULT. – JensG Nov 16 '13 at 10:43
  • Which would be the wrong way to do it. Trial and error is never better than easily discoverable and demonstrable facts. – David Heffernan Nov 16 '13 at 10:55
  • @JensG, MSDN writes: "To close the COM library gracefully on a thread, each successful call to `CoInitialize` or `CoInitializeEx`, including any call that returns `S_FALSE`, must be balanced by a corresponding call to `CoUninitialize`", so that `CoUninitialize` must be called for both `S_OK` and `S_FALSE` results of `CoInitialize[Ex]` – ALZ Feb 28 '14 at 09:53
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    @ALZ: Exactly, that's why we have macros/functions like `SUCCEEDED()`and `FAILED()` which you should use. And `S_FALSE` is an success code, thus `SUCCEEDED(S_FALSE)` evaluates to true. – JensG Feb 28 '14 at 10:53
  • @JensG, Thanks! I didn't know that "`SUCCEEDED(S_FALSE)` evaluates to true." Live a century - learn a century! :) – ALZ Feb 28 '14 at 11:13
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In the RTL/VCL source, COM is initialized in the following ways:

  1. By a call to OleInitialize made from Forms.TApplication.Create. So this call will be made for all VCL forms applications, but not, for example, for service applications.
  2. By a call to CoInitialize or CoInitializeEx in ComObj.InitComObj. This is registered as an InitProc in the initialization section of the ComObj unit. In turn, the call to Application.Initialize in your project .dpr file's code will invoke ComObj.InitComObj.
  3. In many and various other locations around the RTL/VCL. Including, but not limited to, Datasnap, ComServ, Soap, System.Win.Sensors, Winapi.DirectShow9. Some of these areas of code are more recent than Delphi 7.

Now, of these various COM initializations, the ones that count are 1 and 2. In any standard VCL forms application, both of these will run at startup in the main thread. Item 1 runs first and so gets to initialize COM first. That's the initialization that counts. Item 2 runs after and returns S_FALSE meaning that COM was already initialized.

So, to your question:

Do I need to call Coinitialize in the main/VCL thread?

No you do not. You can be sure that COM has already been initialized in a VCL application's main thread.

David Heffernan
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