Fix starting with an empty database

guix-data-service/substitutes.scm

@@ -19,6 +19,7 @@
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-19)
   #:use-module (ice-9 match)
+  #:use-module (ice-9 atomic)
   #:use-module (ice-9 threads)
   #:use-module (fibers)
   #:use-module (fibers channels)
@@ -149,7 +150,7 @@
             (lambda (channel)
               (put-message channel (cons build-server-id build-ids)))))))
 
-(define (start-substitute-query-threads)
+(define (start-substitute-query-threads startup-completed?)
   (define channel
     (make-channel))
 
@@ -162,6 +163,9 @@
          (set-thread-name "request substitute query"))
        (const #t))
 
+     (while (not (atomic-box-ref startup-completed?))
+       (sleep 1))
+
      (while #t
        (with-exception-handler
            (lambda (exn)
@@ -208,6 +212,9 @@
          (set-thread-name "bulk substitute query"))
        (const #t))
 
+     (while (not (atomic-box-ref startup-completed?))
+       (sleep 1))
+
      (while #t
        (with-exception-handler
            (lambda (exn)

guix-data-service/web/server.scm

@@ -260,6 +260,9 @@ port. Also, the port used can be changed by passing the --port option.\n"
 
                   (spawn-fiber
                    (lambda ()
+                     (while (not (check-startup-completed startup-completed))
+                       (sleep 1))
+
                      (with-resource-from-pool (background-connection-pool) conn
                        (backfill-guix-revision-package-derivation-distribution-counts
                         conn)))

scripts/guix-data-service.in

@@ -197,7 +197,7 @@
           (lambda (port)
             (simple-format port "~A\n" (getpid)))))
 
-      (start-substitute-query-threads)
+      (start-substitute-query-threads startup-completed)
 
       (call-with-new-thread
        (lambda ()