CoInitialize error working with database inside threads

Question

Using Delphi 7, whenever I try to do any database work inside of a thread I get this error:

"CoInitialize has not been called"

I used a simple code containing an ADOConnection.Open inside the thread.

But the same code works fine if it's used in a form any ideas?

I can't believe the number of people still programming on Delphi 7 (or older) :( PS: just "use" unit "ActiveX", and call CoInitialize (0)! — paulsm4, Jan 13 '13 at 07:30
You know, when get used to something, you can't let it go easily, lol — riad, Jan 13 '13 at 07:46
@paulsm4: Would using a more recent version of Delphi prevent this particular error? — mghie, Jan 13 '13 at 17:21
See also: [When do I need to call CoInitialize() in this scenario?](http://stackoverflow.com/q/9286600/576719). — LU RD, Jan 13 '13 at 18:19

score 14 · Accepted Answer · answered Jan 13 '13 at 10:43

14

@mjn: I'm not allowed to comment your remark in the previous answer, so I created a new answer: calling CoInitialize from the constructor is one of typical error programmers do.

Constructor is executed in a context of another thread, but you need to initialize COM on the current thread (when a thread procedure is running i.e. as part of Execute method) see

answered Jan 13 '13 at 10:43

pf1957

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+1 thanks for answer, as far as commenting seems not be available for you. – bummi Jan 13 '13 at 11:57
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+1 and an Amen! Threads are fragile pieces of art, you need to know what you're doing to do a thread right. – Jerry Dodge Jan 14 '13 at 00:15

score 10 · Answer 2 · edited Jan 14 '13 at 09:50

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procedure TYourThread.execute;
begin
  CoInitialize(nil); 
  FConnection:=TConnection.Create(...);
  try
    ThreadCode ....
  finally
    FConnection.free;
    CoUninitialize;
  end;
end;

edited Jan 14 '13 at 09:50

kludg

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answered Jan 13 '13 at 07:33

bummi

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@paulsm4 AFAIK Coinitialize has to be called in the threadcontext. – bummi Jan 13 '13 at 07:40
it's not about Coinitialize, but about threadcontext: http://embarcadero.newsgroups.archived.at/public.delphi.vcl.components.using/200911/0911093410.html – bummi Jan 13 '13 at 11:53
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@mjn, have you tested `GetCurrentThreadId = MainThreadId` inside a subclassed `TThread.Create`? The `TThread` constructor is always executed in the context of the calling thread. – LU RD Jan 13 '13 at 15:11
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@mjn my comment about threadcontext was written because I don't agree with the comment: "CoInitialize / CoUninitialize could be called in the thread constructor / destructor" – bummi Jan 13 '13 at 15:29
Why do I see many comments about @mjn but see nothing posted them? – Jerry Dodge Jan 14 '13 at 00:17
@JerryDodge: Because mjn deleted the comments after people responded to them. – Ken White Jan 14 '13 at 03:54
Which IMHO is a ugly practice! (deleting the comments and leave the comment thread incomplete!). @mjn: If you're ashamed of what you said, let it stay and let the world know you're not perfect, and learn to think twice before posting a comment the next time. :) – jachguate Jan 14 '13 at 05:15
@mjn, there was a time when the context switch happened immediately after the call `inherited Create(false)`. Before Delphi 6 that was, see [`Recreating a TThread Inside a TThread derived class`](http://stackoverflow.com/q/13561939/576719) and the answer [`Which is the correct way to start a suspended thread in delphi 2007?`](http://stackoverflow.com/a/4206993/576719). If `FreeOnTerminate` is true, the destructor is executed in the thread context. In principal it would have been possible to do CoInitialize/CoUninitialize in the constructor/destructor, but that would anyway be a bad practice. – LU RD Jan 14 '13 at 06:35
@LURD: prior to D6, setting `ACreateSuspended=False` would run `Execute()` immediately, even if the constructor was still running. D6 fixed that. But it was **never** possible in any Delphi version to call `CoInitialize()` in the thread constructor and have it take effect inside of `Execute()`. `CoInitialize()` must always be called inside of `Execute()` itself in all Delphi versions. – Remy Lebeau Jan 14 '13 at 20:11

score 0 · Answer 3 · answered Sep 09 '15 at 05:44

0

Another cause is that Application.Initialize; is missing or commented out in the main application DPR.

answered Sep 09 '15 at 05:44

Allan F

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CoInitialize error working with database inside threads

3 Answers3