* Windows: Use NUMBER_OF_PROCESSORS environment variable.

* lisp/emacs-lisp/comp.el (comp-effective-async-max-jobs): Use
NUMBER_OF_PROCESSORS environment variable if system is Windows NT,
"nproc" if it is in PATH or a default of 1.

1 files changed, 8 insertions, 3 deletions

diff --git a/lisp/emacs-lisp/comp.el b/lisp/emacs-lisp/comp.el
index e5d3be6eed0..6c152136fb5 100644
--- a/lisp/emacs-lisp/comp.el
+++ b/lisp/emacs-lisp/comp.el
@@ -2302,9 +2302,14 @@ processes from `comp-async-compilations'"
   (if (zerop comp-async-jobs-number)
       (or comp-num-cpus
           (setf comp-num-cpus
-                ;; Half of the CPUs or at least one.
-                ;; FIXME portable?
-                (max 1 (/ (string-to-number (shell-command-to-string "nproc"))
+                ;; FIXME: we already have a function to determine
+                ;; the number of processors, see get_native_system_info in w32.c.
+                ;; The result needs to be exported to Lisp.
+                (max 1 (/ (cond ((eq 'windows-nt system-type)
+                                 (string-to-number (getenv "NUMBER_OF_PROCESSORS")))
+                                ((executable-find "nproc")
+                                 (string-to-number (shell-command-to-string "nproc")))
+                                (t 1))
                           2))))
     comp-async-jobs-number))