[fpc-devel] threads vs widestringmanager / crash

[Martin]

Ok, I don't know too much about the whole initialization....
But on the off chance of triggering some ideas, I throw in a couple of 
my thoughts....

On 19/12/2022 07:42, Sven Barth wrote:
> Am 07.07.2018 um 15:04 schrieb Martin:
>> 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?
>
> This is likely to be the cause, cause the EXEC_TLS_CALLBACK is 
> executed by Windows for every thread that is started for an 
> application. And if the debugger triggers the start of a thread...

Maybe, maybe not always? But, yes at least in the case that I documented 
in 2018: 
https://lists.freepascal.org/pipermail/fpc-devel/2018-July/039374.html

Yet in the system unit:

initialization
.....
   if not Assigned(CurrentTM.BeginThread) then
   begin
     InitHeap;
     InitSystemThreads;
   end;
   SysInitExceptions;
   initunicodestringmanager;
   InitWin32Widestrings;

So the WS-Mgr is only assigned after InitSystemThreads => which sets up  
RelocateThreadVar => which can call InitThread.

So order may need to be changed there (if that is possible).
Of course, the case where EXEC_TLS_CALLBACK calls InitThread remains.

A lot of the WS-Mgr init is assigning pointers to the correct procedure.
So if InitThread sees that this has not been done yet, InitThread could 
call those.
Even if 2 threads (main and the early thread) both assign values to the 
pointer, they assign the same value, and so that should not do harm.
Of course the thread init must not change the value, once it was set by 
the main thread, in case usercode assigned a diff value (so maybe in 
ThreadInit, use Interlocked....)

This may mean to break "InitWin32Widestrings" into 2 parts, because it 
also prepares some tables.
But those are not needed for "GetStandardCodePageProc"

So if the setting of the codepage related proc pointers are moved to a 
separate init-method, then that can be called (if needed) by InitThread.

--------------
Or maybe if EXEC_TLS_CALLBACK calls InitThread, it can do the (partial) 
init of WidestringMgr before? (if the order in the initialization 
section can be changed to do the same?)

--------------
I am not sure if this code needs to worry about any of the other WS-Mgr 
functions.
Any thread that early is not started by Pascal code (neither user, nor 
rtl). It will be a thread working some kernel proc. And that shouldn't 
access the WS-Mgr?