Jeff King <peff@xxxxxxxx> writes:
> It's not easy for arbitrary code to find out whether it is
> running in an async process or not. A top-level function
> which is fed to start_async() can know (you just pass down
> an argument saying "you are async"). But that function may
> call other global functions, and we would not want to have
> to pass the information all the way through the call stack.
>
> Nor can we simply set a global variable, as those may be
> shared between async threads and the main thread (if the
> platform supports pthreads). We need pthread tricks _or_ a
> global variable, depending on how start_async is
> implemented.
>
> The callers don't have enough information to do this right,
> so let's provide a simple query function that does.
> Fortunately we can reuse the existing infrastructure to make
> the pthread case simple (and even simplify die_async() by
> using our new function).
>
> Signed-off-by: Jeff King <peff@xxxxxxxx>
> ---
What is not immediately obvious from the above description is why a
code may want to care if it is in_async() in the first place.
If there weren't the die_async() update, the readers might have been
left utterly baffled (or they can somehow see this is related to
2/2) but it is a bit hard to arrange in "git log" as going to child
is harder.
The patch looks good. Thanks.
> run-command.c | 16 +++++++++++++++-
> run-command.h | 1 +
> 2 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/run-command.c b/run-command.c
> index 3277cf7..c8029f2 100644
> --- a/run-command.c
> +++ b/run-command.c
> @@ -595,7 +595,7 @@ static NORETURN void die_async(const char *err, va_list params)
> {
> vreportf("fatal: ", err, params);
>
> - if (!pthread_equal(main_thread, pthread_self())) {
> + if (in_async()) {
> struct async *async = pthread_getspecific(async_key);
> if (async->proc_in >= 0)
> close(async->proc_in);
> @@ -614,6 +614,13 @@ static int async_die_is_recursing(void)
> return ret != NULL;
> }
>
> +int in_async(void)
> +{
> + if (!main_thread_set)
> + return 0; /* no asyncs started yet */
> + return !pthread_equal(main_thread, pthread_self());
> +}
> +
> #else
>
> static struct {
> @@ -653,6 +660,12 @@ int git_atexit(void (*handler)(void))
> }
> #define atexit git_atexit
>
> +static int process_is_async;
> +int in_async(void)
> +{
> + return process_is_async;
> +}
> +
> #endif
>
> int start_async(struct async *async)
> @@ -712,6 +725,7 @@ int start_async(struct async *async)
> if (need_out)
> close(fdout[0]);
> git_atexit_clear();
> + process_is_async = 1;
> exit(!!async->proc(proc_in, proc_out, async->data));
> }
>
> diff --git a/run-command.h b/run-command.h
> index 5b4425a..629fab7 100644
> --- a/run-command.h
> +++ b/run-command.h
> @@ -118,5 +118,6 @@ struct async {
>
> int start_async(struct async *async);
> int finish_async(struct async *async);
> +int in_async(void);
>
> #endif
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