diff --git a/official/update.rkt b/official/update.rkt
index d0847f1..8597ab7 100644
--- a/official/update.rkt
+++ b/official/update.rkt
@@ -3,31 +3,94 @@
          racket/function
          racket/system
          racket/package
+         racket/port
          racket/match
+         racket/async-channel
          pkg/private/stage
          (prefix-in pkg: pkg/lib)
          "common.rkt"
          "notify.rkt"
          "static.rkt")
 
+(define NUM-THREADS 4)
+
 (define (update-all)
   (update-checksums #f (package-list)))
 (define (update-pkgs pkgs)
   (update-checksums #t pkgs))
 
+(define (t:log! . args)
+  (thread-send current-display-thd
+               (format "~a: ~a"
+                       (current-thd-no)
+                       (with-output-to-string (λ () (apply log! args))))))
+
+(define current-thd-no (make-parameter #f))
+(define current-display-thd #f)
+
 (define (update-checksums force? pkgs)
-  (filter (λ (pkg-name)
-            (cond
-              [(package-exists? pkg-name)
-               (update-checksum force? pkg-name)]
-              [else (log! "update-checksums: invariant broken; ~a doesn't exist" pkg-name)
-                    ;; considered not update
-                    #f]))
-          pkgs))
+  (define updated-pkgs '())
+
+  (define collector-thd
+    (thread
+     (λ ()
+       (let loop ()
+         (match (thread-receive)
+           ['terminate (void)]
+           [pkg-name
+            (set! updated-pkgs (cons pkg-name updated-pkgs))
+            (loop)])))))
+
+  (set! current-display-thd
+        (thread
+         (λ ()
+           (let loop ()
+             (match (thread-receive)
+               ['terminate (void)]
+               [s (display s)
+                  (loop)])))))
+
+  (define ch (make-async-channel))
+
+  (define thds
+    (for/list ([i NUM-THREADS])
+      (thread
+       (λ ()
+         (parameterize ([current-thd-no i])
+           (let loop ()
+             (match (async-channel-get ch)
+               ['terminate (void)]
+               [pkg-name
+                (when (update-checksum force? pkg-name)
+                  (thread-send collector-thd pkg-name))
+                (loop)])))))))
+
+  (for ([pkg-name pkgs])
+    (cond
+      [(package-exists? pkg-name)
+       (async-channel-put ch pkg-name)]
+      [else
+       (parameterize ([current-thd-no 'main])
+         (t:log! "update-checksums: invariant broken; ~a doesn't exist" pkg-name))]))
+
+  (for ([thd thds])
+    (async-channel-put ch 'terminate))
+
+  (for ([thd thds])
+    (thread-wait thd))
+
+  (thread-send current-display-thd 'terminate)
+  (thread-wait current-display-thd)
+  (set! current-display-thd #f)
+
+  (thread-send collector-thd 'terminate)
+  (thread-wait collector-thd)
+
+  updated-pkgs)
 
 ;; precondition: pkg-name must exist
 (define (update-checksum force? pkg-name)
-  (log! "update-checksum ~v ~v" force? pkg-name)
+  (t:log! "update-checksum ~v ~v" force? pkg-name)
   (with-handlers
       ([exn:fail?
         (λ (x)
@@ -79,14 +142,14 @@
     (when (or force?
               (>= (- now last) (* 1 60 60))
               (not old-checksum))
-      (log! "\tupdating ~a" pkg-name)
+      (t:log! "\tupdating ~a" pkg-name)
       (define new-checksum
         (package-url->checksum
          (package-ref i 'source)
          #:pkg-name pkg-name))
       (unless (equal? new-checksum old-checksum)
-        (log! "\told: ~v" old-checksum)
-        (log! "\tnew: ~v" new-checksum)
+        (t:log! "\told: ~v" old-checksum)
+        (t:log! "\tnew: ~v" new-checksum)
         (set! changed? #t))
       (package-begin
        (define* i
@@ -105,8 +168,8 @@
                              (hash-ref vi 'source "")
                              #:pkg-name pkg-name))
                           (unless (equal? new-checksum old-checksum)
-                            (log! "\t~a old: ~v" vi old-checksum)
-                            (log! "\t~a new: ~v" vi new-checksum)
+                            (t:log! "\t~a old: ~v" vi old-checksum)
+                            (t:log! "\t~a new: ~v" vi new-checksum)
                             (set! changed? #t))
                           (values v
                                   (hash-set vi 'checksum
@@ -130,12 +193,12 @@
               (hash-set next-i 'last-updated now))]))
        (define* i
          (hash-set i 'checksum-error #f))
-       (log! "\twriting with checksum ~v" (hash-ref i 'checksum))
+       (t:log! "\twriting with checksum ~v" (hash-ref i 'checksum))
        (package-info-set! pkg-name i)))
     changed?))
 
 (define (update-from-content i)
-  (log! "\tgetting package content for ~v" (hash-ref i 'name))
+  (t:log! "\tgetting package content for ~v" (hash-ref i 'name))
   (match-define-values
    (checksum module-paths (list dependencies implies collection))
    (pkg:get-pkg-content