When NO_PTHREADS is still used in this file, we have two separate code
paths for thread and no thread support. The latter will always have
num_threads remain zero while the former uses num_threads zero as
"default number of threads".
With recent changes blur the line between thread and no-thread
support, this num_threads handling becomes a bit strange so let's
redefine it like this:
- num_threads == 0 means default number of threads and should become
positive after all configuration and option parsing is done if
multithread is supported.
- num_threads <= 1 runs no threads. It does not matter if the platform
supports threading or not.
- num_threads > 1 will run multiple threads and is invalid if
HAVE_THREADS is false. pthread API is only used in this case.
PS. a new warning is also added when num_threads is forced back to one
because a thread-incompatible option is specified.
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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