[fpc-devel] threads vs widestringmanager / crash

[Martin]

There actually isnt a thread started.

But during initialization "TThread.Queue" is called (because the code in 
question can be called in threads aswell, and must ensure work is done 
in the main thread)

"TThread.Queue" creates a new external thread. This fails during unit 
initialization for the reason below.

This leads me to the following questionQ

1) out of interest.
If "TThread.Queue" is called in the main thread, then it does not queue 
anyway, but rather run immediately.
In this case, why not avoid creating a thread, and check 
"CurrentThreadVar = nil" ?

2) how to solve my problem. (including other OS, for which I do not know 
if the issue exists)
- Is there a way to test, if current code is in the main thread? (and 
doing so, without creating a TThread instance)?

- If not, then for windows (and fpc 3.0.4) the following *should* do 
(but is really rather a hack)
   {$IFDEF MsWindows}  if WideStringManager.GetStandardCodePageProc = 
nil then

Any better ideas?



On 07/07/2018 14:00, Martin wrote:
> fpc 3.0.4
> Win 10 / 32bit
>
> Lazarus trunk, but that may not be relevant.
> This is the first time I am seeing this, and I am therefore not sure I 
> will be able to reproduce, since it seems a race condition.
>
> This appears to happen during unit initialization.
>
> Something must have started a thread, before widestring manager got 
> initialized.
> In other word, some unit (used in such order that it's initialization 
> runs before unit system initialization) has started a thread.
>
> This thread crashes, if it is fast enough, because in the threads init 
> it will access widestringmanager.
>
> Is this a bug in fpc?
> Or is this wrong of the calling code (eg starting threads during unit 
> initialization).
>
> In the latter case, is it documented?
>
> The trace from the thread:
> #0 ?? at :0
> #1 OPENSTDIO({}, 55217, 168) at ..\inc\text.inc:2670
> #2 SYSINITSTDIO at ..\win\syswin.inc:520
> #3 INITTHREAD(16777216) at ..\inc\thread.inc:59
> #4 EXEC_TLS_CALLBACK(0x400000, 2, 0x0) at ..\win\systlsdir.inc:90
> #5 ntdll!WinSqmSetDWORD64 at :0
> #6 ?? at :0
> #7 ntdll!RtlDeactivateActivationContextUnsafeFast at :0
> #8 ntdll!RtlCaptureStackContext at :0
> #9 ntdll!LdrShutdownThread at :0
> #10 ntdll!LdrInitializeThunk at :0
> #11 ntdll!LdrInitializeThunk at :0
> #12 ntdll!LdrInitializeThunk at :0
> #13 ?? at :0
>
> The main thread sit right before widestring initialization.
> #0 INITUNICODESTRINGMANAGER at ..\inc\ustrings.inc:2311
> #1 SYSTEM_$$_init$ at :674
> #2 fpc_initializeunits at ..\inc\system.inc:886
> #3 main at lazarus.pp:87
>
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