[fpc-devel] threads vs widestringmanager / crash

[Martin]

Ok, I guess the "TThread.Queue"  is wrong.
Because that may create an instance, but there would not actually be a 
2nd thread as observed. (Question 1 is still interesting)

Yet there is no other TThread.Create call made.

So (guessing) the original issue may be due to the debugger. The 
debugger interrupts the target early on. And that does create a thread 
in the target.
If such an external thread happens, would fcp execute the code in question?

Could/Should there be a nil check at the location of the crash?


On 07/07/2018 14:40, Martin wrote:
> "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" ?

> 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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