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Re: Does static initialization of a local variable always happens synchronized ?

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Am 11.09.2021 um 11:06 schrieb Bonita Montero:
> Look at this code:
> 
> #include <iostream>
> 
> using namespace std;
> 
> #if defined(_MSC_VER)
>      #define NOINLINE __declspec(noinline)
> #elif defined(__GNUC__) || defined(__clang__)
>      #define NOINLINE __attribute((noinline))
> #endif
> 
> struct S
> {
>      S();
> };
> 
> NOINLINE
> S::S()
> {
>      cout << "S::S()" << endl;
> }
> 
> NOINLINE
> S &fn()
> {
>      static
>      S s;
>      return s;
> }
> 
> int main()
> {
>      fn();
>      fn();
> }
> 
> 
> I call fn twice, but of course s is initialized only once at the first
> call of fn. What I asked myself if this happens synchronized, i.e. if
> multiple threads try to initialize s, it's only initiailized only once
> in a locked context.
> With MSVC this happens as expected: before the initialization of s, fn
> calls _Init_thread_header and afterwards it calls _Init_thread_footer.
> These functions each call EnterCriticalSection or LeaveCriticalSection
> on a global mutex. But is this behaviour guaranteed for C++ in general ?

And MSVC of course uses double-checked locking here !

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Does static initialization of a local variable always happens synchronized ? Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-11 11:06 +0200
  Re: Does static initialization of a local variable always happens synchronized ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-09-11 13:47 +0200
    Re: Does static initialization of a local variable always happens synchronized ? Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-11 16:17 +0200
      Re: Does static initialization of a local variable always happens synchronized ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-09-11 17:09 +0200
        Re: Does static initialization of a local variable always happens synchronized ? Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-11 17:18 +0200
        Re: Does static initialization of a local variable always happens synchronized ? David Brown <david.brown@hesbynett.no> - 2021-09-11 20:03 +0200
  Re: Does static initialization of a local variable always happens synchronized ? Paavo Helde <myfirstname@osa.pri.ee> - 2021-09-11 15:13 +0300
  Re: Does static initialization of a local variable always happens synchronized ? Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-11 16:02 +0200
  Re: Does static initialization of a local variable always happens synchronized ? Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-11 21:19 +0200
    Re: Does static initialization of a local variable always happens synchronized ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-09-11 22:05 +0200
      Re: Does static initialization of a local variable always happens synchronized ? Bonita Montero <Bonita.Montero@gmail.com> - 2021-09-12 08:24 +0200

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