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Groups > comp.lang.c++ > #81160

Does static initialization of a local variable always happens synchronized ?

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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 ?

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Thread

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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