Replace thread-let with thread-utils

lib/syntax.rkt

@@ -4,8 +4,6 @@
 (provide
  ; help make a nested if. if/in will gain the same false form of its containing if/out.
  if/out
- ; let, but the value for each variable is evaluated within a thread
- thread-let
  ; cond, but values can be defined between conditions
  cond/var
  ; wrap sql statements into lambdas so they can be executed during migration
@@ -25,7 +23,6 @@
 
   (provide
    transform-if/out
-   transform-thread-let
    transform/out-cond/var)
 
   (define (transform-if/out stx)
@@ -51,26 +48,6 @@
           [#t node])))
     (datum->syntax stx (cons 'if result)))
 
-  (define (transform-thread-let stx)
-    (define tree (cdr (syntax->datum stx)))
-    (define defs (car tree))
-    (define forms (cdr tree))
-    (when (eq? (length forms) 0)
-      (error (format "thread-let: bad syntax (need some forms to execute after the threads)~n  forms: ~a" forms)))
-    (define counter (build-list (length defs) values))
-    (datum->syntax
-     stx
-     `(let ([chv (build-vector ,(length defs) (λ (_) (make-channel)))])
-        ,@(map (λ (n)
-                 (define def (list-ref defs n))
-                 `(thread (λ () (channel-put (vector-ref chv ,n) (let _ () ,@(cdr def))))))
-               counter)
-        (let ,(map (λ (n)
-                     (define def (list-ref defs n))
-                     `(,(car def) (channel-get (vector-ref chv ,n))))
-                   counter)
-          ,@forms))))
-
   (define (transform/out-cond/var stx)
     (define tree (transform-cond/var (cdr (syntax->datum stx))))
     (datum->syntax
@@ -119,35 +96,6 @@
   (check-equal? (if/out #t (if/in #f 'yes) 'no) 'no)
   (check-equal? (if/out #f (if/in #f 'yes) 'no) 'no))
 
-(define-syntax (thread-let stx)
-  (transform-thread-let stx))
-(module+ test
-  ; check that it is transformed as expected
-  (check-syntax-equal?
-   (transform-thread-let
-    #'(thread-let ([a (hey "this is a")]
-                   [b (hey "this is b")])
-                  (list a b)))
-   #'(let ([chv (build-vector 2 (λ (_) (make-channel)))])
-       (thread (λ () (channel-put (vector-ref chv 0) (let _ () (hey "this is a")))))
-       (thread (λ () (channel-put (vector-ref chv 1) (let _ () (hey "this is b")))))
-       (let ([a (channel-get (vector-ref chv 0))]
-             [b (channel-get (vector-ref chv 1))])
-         (list a b))))
-  ; check that they actually execute concurrently
-  (define ch (make-channel))
-  (check-equal? (thread-let ([a (begin
-                                  (channel-put ch 'a)
-                                  (channel-get ch))]
-                             [b (begin0
-                                    (channel-get ch)
-                                  (channel-put ch 'b))])
-                            (list a b))
-                '(b a))
-  ; check that it assigns the correct value to the correct variable
-  (check-equal? (thread-let ([a (sleep 0) 'a] [b 'b]) (list a b))
-                '(a b)))
-
 (define-syntax (cond/var stx)
   (transform/out-cond/var stx))
 (module+ test

lib/thread-utils.rkt

@@ -0,0 +1,72 @@
+#lang racket/base
+(require (prefix-in easy: net/http-easy)
+         "../src/data.rkt"
+         "xexpr-utils.rkt")
+
+(provide
+ thread-values)
+
+(module+ test
+  (require rackunit))
+
+(define (thread-values . thunks)
+  (parameterize-break #t
+    (define the-exn (box #f))
+    (define original-thread (current-thread))
+    (define (break e)
+      (when (box-cas! the-exn #f e)
+        (break-thread original-thread))
+      (sleep 0))
+    (define-values (threads channels)
+      (for/fold ([ts null]
+                 [chs null]
+                 #:result (values (reverse ts) (reverse chs)))
+                ([th thunks])
+        (define ch (make-channel))
+        (define t
+          (thread (λ ()
+                    (with-handlers ([exn? break])
+                      (channel-put ch (th))))))
+        (values (cons t ts) (cons ch chs))))
+    (apply
+     values
+     (with-handlers ([exn:break? (λ (_)
+                                   (for ([t threads]) (kill-thread t))
+                                   (if (unbox the-exn)
+                                       (raise (unbox the-exn))
+                                       (error 'thread-values "a thread broke, but without reporting its exception")))])
+       (for/list ([ch channels])
+         (channel-get ch))))))
+
+(module+ test
+  ; check that they actually execute concurrently
+  (define ch (make-channel))
+  (check-equal? (let-values ([(a b)
+                              (thread-values
+                               (λ ()
+                                 (begin
+                                   (channel-put ch 'a)
+                                   (channel-get ch)))
+                               (λ ()
+                                 (begin0
+                                     (channel-get ch)
+                                   (channel-put ch 'b))))])
+                  (list a b))
+                '(b a))
+  ; check that it assigns the correct value to the correct variable
+  (check-equal? (let-values ([(a b)
+                              (thread-values
+                               (λ () (sleep 0) 'a)
+                               (λ () 'b))])
+                  (list a b))
+                '(a b))
+  ; check that exceptions are passed to the original thread, and other threads are killed
+  ;; TODO: if the other thread was making an HTTP request, could it be left stuck open by the kill?
+  (check-equal? (let* ([x "!"]
+                       [res
+                        (with-handlers ([exn:fail:user? (λ (e) (exn-message e))])
+                          (thread-values
+                           (λ () (sleep 0) (set! x "?") (println "this side effect should not happen"))
+                           (λ () (raise-user-error "catch me"))))])
+                  (string-append res x))
+                "catch me!"))

lib/tree-updater.rkt

@@ -277,8 +277,8 @@
   ; check that noscript images are removed
   (check-equal? ((query-selector (λ (t a c) (eq? t 'noscript)) transformed)) #f)
   ; benchmark
-  (when (file-exists? "../misc/Frog.html")
-    (with-input-from-file "../misc/Frog.html"
+  (when (file-exists? "../storage/Frog.html")
+    (with-input-from-file "../storage/Frog.html"
       (λ ()
         (define tree (html->xexp (current-input-port)))
         (time (length (update-tree-wiki tree "minecraft")))))))