Re: [PATCH 1/1] mingw: safe-guard a bit more against getenv() problems

> From: Johannes Schindelin <johannes.schindelin@gmx.de>
> 
> Running up to v2.21.0, we fixed two bugs that were made prominent by the
> Windows-specific change to retain copies of only the 30 latest getenv()
> calls' returned strings, invalidating any copies of previous getenv()
> calls' return values.
> 
> While this really shines a light onto bugs of the form where we hold
> onto getenv()'s return values without copying them, it is also a real
> problem for users.
> 
> And even if Jeff King's patches merged via 773e408881 (Merge branch
> 'jk/save-getenv-result', 2019-01-29) provide further work on that front,
> we are far from done. Just one example: on Windows, we unset environment
> variables when spawning new processes, which potentially invalidates
> strings that were previously obtained via getenv(), and therefore we
> have to duplicate environment values that are somehow involved in
> spawning new processes (e.g. GIT_MAN_VIEWER in show_man_page()).
> 
> We do not have a chance to investigate, let address, all of those issues
> in time for v2.21.0, so let's at least help Windows users by increasing
> the number of getenv() calls' return values that are kept valid. The
> number 64 was determined by looking at the average number of getenv()
> calls per process in the entire test suite run on Windows (which is
> around 40) and then adding a bit for good measure. And it is a power of
> two (which would have hit yesterday's theme perfectly).
> 
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>   compat/mingw.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/compat/mingw.c b/compat/mingw.c
> index 4276297595..8141f77189 100644
> --- a/compat/mingw.c
> +++ b/compat/mingw.c
> @@ -1632,7 +1632,7 @@ int mingw_kill(pid_t pid, int sig)
>    */
>   char *mingw_getenv(const char *name)
>   {
> -#define GETENV_MAX_RETAIN 30
> +#define GETENV_MAX_RETAIN 64
>   	static char *values[GETENV_MAX_RETAIN];
>   	static int value_counter;
>   	int len_key, len_value;
>