Memory Barriers at pthread using CYGWIN

[Takashi Yano]

Any suggestions?

On Tue, 20 Jun 2023 21:53:00 +0900
Takashi Yano wrote:
> On Sat, 10 Jun 2023 13:08:04 +0900 (JST)
> Takashi Yano wrote:
> > "M?min A." wrote:
> > > //windows cmd line
> > > C:\cygwin64\home\maydin\test>cygcheck ./main.exe
> > > C:\cygwin64\home\maydin\test\main.exe
> > >   C:\cygwin64\bin\cygwin1.dll
> > >     C:\WINDOWS\system32\KERNEL32.dll
> > >       C:\WINDOWS\system32\ntdll.dll
> > >       C:\WINDOWS\system32\KERNELBASE.dll
> > > 
> > > C:\cygwin64\home\maydin\test>ldd ./main.exe
> > >         ntdll.dll => /cygdrive/c/WINDOWS/SYSTEM32/ntdll.dll (0x7ffa92350000)
> > >         KERNEL32.DLL => /cygdrive/c/WINDOWS/System32/KERNEL32.DLL
> > > (0x7ffa90570000)
> > >         KERNELBASE.dll => /cygdrive/c/WINDOWS/System32/KERNELBASE.dll
> > > (0x7ffa8ffb0000)
> > >         cygwin1.dll => /usr/bin/cygwin1.dll (0x7ffa27960000)
> > 
> > Looks OK.
> > 
> > > //When cygwin terminal closed and cmd line command. Join throw fails.
> > > C:\cygwin64\home\maydin\test>main.exe
> > > Failed to join the thread t1.
> > > Failed to join the thread t2.
> > > r1 = 1, r2 = 1
> > > 
> > > //when cygwin terminal opened. The test is passed.
> > > C:\cygwin64\home\maydin\test>main.exe
> > > r1 = 1, r2 = 1
> > > 
> > > 
> > > I think Cygwin terminal should be always open in order to execute a file in
> > > windows. Am I right ?
> > 
> > It should not be. Weird enough.
> > 
> > Could you please provide a strace log file such as:
> > strace -o faild.log ./main.exe
> > ?
> 
> I looked into this problem, and I think this is a problem regarding
> _my_tls initialization order, so far. This seems to happen in LDAP
> environment.
> 
> My assumption is:
> 
> If the program is the first program which load cygwin1.dll, ldap
> connection seems to be made before pthread::init_mainthread().
> In cyg_ldap.cc, cyg_ldap::connect(), cyg_ldap::search() or
> cyg_ldap::next_page() calls cygwait() in which pthread::self()
> is called.
> 
> Then, _my_tls.tid is initialized with null_pthread, therefore,
> _my_tls.tid is not set in pthread::init_mainthread().
> 
> This causes pthread_join() failure at:
> winsup/cygwin/thread.cc: line 2196
>    if (!is_good_object (&joiner))
>      return EINVAL;
> 
> 
> The first idea to fix this issue is remove set_tls_self_pointer()
> call from pthread::self().
> 
> diff --git a/winsup/cygwin/thread.cc b/winsup/cygwin/thread.cc
> index 5c1284a93..a0f2d5546 100644
> --- a/winsup/cygwin/thread.cc
> +++ b/winsup/cygwin/thread.cc
> @@ -392,10 +392,7 @@ pthread::self ()
>  {
>    pthread *thread = _my_tls.tid;
>    if (!thread)
> -    {
> -      thread = pthread_null::get_null_pthread ();
> -      thread->set_tls_self_pointer ();
> -    }
> +    thread = pthread_null::get_null_pthread ();
>    return thread;
>  }
>  
> 
> The secnd approach is to re-initialize _my_tls.tid in
> pthread::init_mainthread() if _my_tls.tid is null_pthread.
> 
> diff --git a/winsup/cygwin/thread.cc b/winsup/cygwin/thread.cc
> index 5c1284a93..f614e01c4 100644
> --- a/winsup/cygwin/thread.cc
> +++ b/winsup/cygwin/thread.cc
> @@ -364,7 +364,7 @@ void
>  pthread::init_mainthread ()
>  {
>    pthread *thread = _my_tls.tid;
> -  if (!thread)
> +  if (!thread || thread == pthread_null::get_null_pthread ())
>      {
>        thread = new pthread ();
>        if (!thread)
> 
> 
> Which is the better approach, do you think?
> Or any other idea?

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>