Use fibers when processing new revisions

Just have one fiber at the moment, but this will enable using fibers for
parallelism in the future.

Fibers seemed to cause problems with the logging setup, which was a bit odd in
the first place. So move logging to the parent process which is better anyway.

scripts/guix-data-service-process-job.in

@@ -25,6 +25,8 @@
 (use-modules (srfi srfi-1)
              (srfi srfi-37)
              (ice-9 match)
+             (ice-9 suspendable-ports)
+             (fibers)
              (guix-data-service database)
              (guix-data-service data-deletion)
              (guix-data-service model package-derivation-by-guix-revision-range)
@@ -38,12 +40,21 @@
 ;; Make stack traces more useful
 (setenv "COLUMNS" "256")
 
+(install-suspendable-ports!)
+
 (define %options
   (list (option '("skip-system-tests") #f #f
                 (lambda (opt name _ result)
-                  (alist-cons 'skip-system-tests #t result)))))
+                  (alist-cons 'skip-system-tests #t result)))
+        (option '("parallelism") #t #f
+                (lambda (opt name arg result)
+                  (alist-cons 'parallelism
+                              (string->number arg)
+                              (alist-delete 'parallelism
+                                            result))))))
 
-(define %default-options '())
+(define %default-options
+  '((parallelism . 1)))
 
 (define (parse-options args)
   (args-fold
@@ -62,6 +73,11 @@
 (let ((opts (parse-options (cdr (program-arguments)))))
   (match (assq-ref opts 'arguments)
     ((job)
-     (process-load-new-guix-revision-job
-      job
-      #:skip-system-tests? (assq-ref opts 'skip-system-tests)))))
+     (run-fibers
+      (lambda ()
+        (process-load-new-guix-revision-job
+         job
+         #:skip-system-tests? (assq-ref opts 'skip-system-tests)))
+      #:hz 0
+      #:parallelism (assq-ref opts 'parallelism)
+      #:drain? #t))))