return const value to be thread save?

So, I wonder if it is necessary to return constant values to be thread
save in functions and code the fucntion like this:
[example 3:]

int f(){

MACRO_THREADS_ENTER();

if( /* ... */ ){

/* result ok */
goto jmp_ok;
}

MACRO_THREADS_LEAVE();
return 1;

jmp_ok:

MACRO_THREADS_LEAVE();
return 0;
}

normally I use a local variable assigned to different return values
inside the function and return it like this: [snip] If I now add two macros to make the function thread save (assume they
work properly) isn't there still a slight chance that the return
variable is changed by a second thread just before the first thread
leaves the function?

Hi,

normally I use a local variable assigned to different return values inside the function and return it like this:
[example 1:]

int f(){
int my_err_code;
my_err_code=1;

if( /* ... */ ){

/* result ok */
my_err_code=0;
}

return my_err_code;
}
If I now add two macros to make the function thread save
Standard C doesn't support threads as such but similar situations can
arise in signal handling. Problems only occur when 2 "threads" (including
signal handlers) could access the same object in memory. Each invocation
of a function gets its own set of automatic variables so this isn't an
issue, i.e. the code we can see above is already thread safe in any
reasonable implementation of threads.
(assume they
work properly) isn't there still a slight chance that the return
variable is changed by a second thread just before the first thread
leaves the function?