diff --git a/collects/compiler/zo-marshal.rkt b/collects/compiler/zo-marshal.rkt
index ff27685f18..e8206838de 100644
--- a/collects/compiler/zo-marshal.rkt
+++ b/collects/compiler/zo-marshal.rkt
@@ -16,7 +16,6 @@
   
   Less sharing occurs than in the C implementation, creating much larger files
 
-  protect-quote caused some things to be sent to write. But there are some things (like paths) that can be read and passed to protect-quote that cannot be 'read' in after 'write', so we turned it off
 |#
 
 (define current-wrapped-ht (make-parameter #f))
@@ -681,11 +680,11 @@
      (out-module form out)]
     [(struct def-values (ids rhs))
      (out-syntax DEFINE_VALUES_EXPD
-                 (list->vector (cons rhs ids))
+                 (list->vector (cons (protect-quote rhs) ids))
                  out)]
     [(struct def-syntaxes (ids rhs prefix max-let-depth))
      (out-syntax DEFINE_SYNTAX_EXPD
-                 (list->vector (list* rhs
+                 (list->vector (list* (protect-quote rhs)
                                       prefix
                                       max-let-depth
                                       *dummy*
@@ -693,7 +692,7 @@
                  out)]
     [(struct def-for-syntax (ids rhs prefix max-let-depth))
      (out-syntax DEFINE_FOR_SYNTAX_EXPD
-                 (list->vector (list* rhs
+                 (list->vector (list* (protect-quote rhs)
                                       prefix
                                       max-let-depth
                                       *dummy*
@@ -1091,11 +1090,12 @@
 
 (define-struct quoted (v) #:prefab)
 
+; protect-quote caused some things to be sent to write. But there are some things (like paths) that can be read and passed to protect-quote that cannot be 'read' in after 'write', so we turned it off
 (define (protect-quote v)
-  v
-  #;(if (or (list? v) (vector? v) (box? v) (hash? v))
-        (make-quoted v)
-        v))
+  #;v
+  (if (or (list? v) (vector? v) (box? v) (hash? v))
+      (make-quoted v)
+      v))
 
 
 (define-struct svector (vec))
diff --git a/collects/tests/compiler/zo-exs.rkt b/collects/tests/compiler/zo-exs.rkt
index b8ab07e067..75aea4d252 100644
--- a/collects/tests/compiler/zo-exs.rkt
+++ b/collects/tests/compiler/zo-exs.rkt
@@ -19,4 +19,17 @@
                                (make-reader-graph ht)))))]
    (hash-test make-hash-placeholder)
    (hash-test make-hasheq-placeholder)
-   (hash-test make-hasheqv-placeholder)))
+   (hash-test make-hasheqv-placeholder))
+ 
+ 
+ (roundtrip 
+  (compilation-top 0 
+                   (prefix 0 empty empty)
+                   (current-directory)))
+ 
+ (roundtrip 
+  (compilation-top 0 
+                   (prefix 0 empty empty)
+                   (list (current-directory)))))
+
+
diff --git a/collects/tests/compiler/zo-test-util.rkt b/collects/tests/compiler/zo-test-util.rkt
new file mode 100644
index 0000000000..cf5c40bd34
--- /dev/null
+++ b/collects/tests/compiler/zo-test-util.rkt
@@ -0,0 +1,12 @@
+#lang racket
+
+(struct result (phase) #:prefab)
+(struct failure result (serious? msg) #:prefab)
+(struct success result () #:prefab)
+
+(provide/contract
+ [struct result ([phase symbol?])]
+ [struct failure ([phase symbol?]
+                  [serious? boolean?]
+                  [msg string?])]
+ [struct success ([phase symbol?])])
\ No newline at end of file
diff --git a/collects/tests/compiler/zo-test-worker.rkt b/collects/tests/compiler/zo-test-worker.rkt
new file mode 100644
index 0000000000..0a698fe246
--- /dev/null
+++ b/collects/tests/compiler/zo-test-worker.rkt
@@ -0,0 +1,270 @@
+#lang racket/base
+(require racket/cmdline
+         compiler/zo-parse
+         compiler/zo-marshal
+         compiler/decompile
+         racket/port
+         racket/bool
+         racket/list
+         racket/match
+         "zo-test-util.rkt")
+
+(define (bytes-gulp f)
+  (with-input-from-file f 
+    (λ () (port->bytes (current-input-port)))))
+
+(define (read-compiled-bytes bs)
+  (define ib (open-input-bytes bs))
+  (dynamic-wind void
+                (lambda ()
+                  (parameterize ([read-accept-compiled #t])
+                    (read ib)))
+                (lambda ()
+                  (close-input-port ib))))
+
+(define (zo-parse/bytes bs)
+  (define ib (open-input-bytes bs))
+  (dynamic-wind void
+                (lambda ()
+                  (zo-parse ib))
+                (lambda ()
+                  (close-input-port ib))))
+
+(define (bytes-not-equal?-error b1 b2)
+  (unless (bytes=? b1 b2)
+    (error 'bytes-not-equal?-error "Not equal")))
+
+(define (replace-file file bytes)
+  (with-output-to-file file
+    (λ () (write-bytes bytes))
+    #:exists 'truncate))
+
+(define (equal?/why-not v1 v2)
+  (define v1->v2 (make-hasheq))
+  (define (interned-symbol=? s1 s2)
+    (symbol=? (hash-ref! v1->v2 s1 s2) s2))
+  (define (yield p m v1 v2)
+    (error 'equal?/why-not "~a in ~a: ~S ~S"
+           m (reverse p) v1 v2))
+  (define (inner p v1 v2)
+    (unless (eq? v1 v2)
+      (match v1
+        [(cons car1 cdr1)
+         (match v2
+           [(cons car2 cdr2)
+            (inner (list* 'car p) car1 car2)
+            (inner (list* 'cdr p) cdr1 cdr2)]
+           [_
+            (yield p "Not a cons on right" v1 v2)])]
+        [(? vector?)
+         (match v2
+           [(? vector?)
+            (define v1l (vector-length v1))
+            (define v2l (vector-length v2))
+            (if (= v1l v2l)
+                (for ([i (in-range v1l)])
+                  (inner (list* `(vector-ref ,i) p)
+                         (vector-ref v1 i)
+                         (vector-ref v2 i)))
+                (yield p "Vector lengths not equal" v1 v2))]
+           [_
+            (yield p "Not a vector on right" v1 v2)])]
+        [(? struct?)
+         (match v2
+           [(? struct?)
+            (define vv1 (struct->vector v1))
+            (define vv2 (struct->vector v2))
+            (inner (list* `(struct->vector ,(vector-ref vv1 0)) p)
+                   vv1 vv2)]
+           [_
+            (yield p "Not a struct on right" v1 v2)])]
+        [(? hash?)
+         (match v2
+           [(? hash?)
+            (let ([p (list* 'in-hash p)])
+              (for ([(k1 hv1) (in-hash v1)])
+                (define hv2 
+                  (hash-ref v2 k1
+                            (lambda ()
+                              (yield p (format "~S not in hash on right" k1) v1 v2))))
+                (inner (list* `(hash-ref ,k1) p)
+                       hv1 hv2)))]
+           [_
+            (yield p "Not a hash on right" v1 v2)])]
+        [(? module-path-index?)
+         (match v2
+           [(? module-path-index?)
+            (define-values (mp1 bmpi1) (module-path-index-split v1))
+            (define-values (mp2 bmpi2) (module-path-index-split v2))
+            (inner (list* 'module-path-index-split_0 p) mp1 mp2)
+            (inner (list* 'module-path-index-split_1 p) bmpi1 bmpi2)]
+           [_
+            (yield p "Not a module path index on right" v1 v2)])]
+        [(? string?)
+         (match v2
+           [(? string?)
+            (unless (string=? v1 v2)
+              (yield p "Unequal strings" v1 v2))]
+           [_
+            (yield p "Not a string on right" v1 v2)])]
+        [(? bytes?)
+         (match v2
+           [(? bytes?)
+            (unless (bytes=? v1 v2)
+              (yield p "Unequal bytes" v1 v2))]
+           [_
+            (yield p "Not a bytes on right" v1 v2)])]
+        [(? path?)
+         (match v2
+           [(? path?)
+            (unless (equal? v1 v2)
+              (yield p "Unequal paths" v1 v2))]
+           [_
+            (yield p "Not a path on right" v1 v2)])]
+        [(? number?)
+         (match v2
+           [(? number?)
+            (unless (equal? v1 v2)
+              (yield p "Unequal numbers" v1 v2))]
+           [_
+            (yield p "Not a number on right" v1 v2)])]
+        [(? regexp?)
+         (match v2
+           [(? regexp?)
+            (unless (string=? (object-name v1) (object-name v2))
+              (yield p "Unequal regexp" v1 v2))]
+           [_
+            (yield p "Not a regexp on right" v1 v2)])]
+        [(? byte-regexp?)
+         (match v2
+           [(? byte-regexp?)
+            (unless (bytes=? (object-name v1) (object-name v2))
+              (yield p "Unequal byte-regexp" v1 v2))]
+           [_
+            (yield p "Not a byte-regexp on right" v1 v2)])]
+        [(? box?)
+         (match v2
+           [(? box?)
+            (inner (list* 'unbox) (unbox v1) (unbox v2))]
+           [_
+            (yield p "Not a box on right" v1 v2)])]
+        [(? symbol?)
+         (match v2
+           [(? symbol?)
+            (unless (symbol=? v1 v2)
+              (cond
+                [(and (symbol-interned? v1) (not (symbol-interned? v1)))
+                 (yield p "Not interned symbol on right" v1 v2)]
+                [(and (symbol-unreadable? v1) (not (symbol-unreadable? v1)))
+                 (yield p "Not unreadable symbol on right" v1 v2)]
+                [(and (symbol-uninterned? v1) (not (symbol-uninterned? v1)))
+                 (yield p "Not uninterned symbol on right" v1 v2)]
+                [(and (symbol-uninterned? v1) (symbol-uninterned? v2))
+                 (unless (interned-symbol=? v1 v2)
+                   (yield p "Uninterned symbols don't align" v1 v2))]
+                [else
+                 (yield p "Other symbol-related problem" v1 v2)]))]
+           [_
+            (yield p "Not a symbol on right" v1 v2)])]
+        [(? empty?)
+         (yield p "Not empty on right" v1 v2)]
+        [_
+         (yield p "Cannot inspect values deeper" v1 v2)])))
+  (inner empty v1 v2))  
+
+(define (symbol-uninterned? s)
+  (not (or (symbol-interned? s) (symbol-unreadable? s))))
+
+(define (run-with-limit file k thnk)
+  (define file-custodian (make-custodian))
+  (define ch (make-channel))
+  (custodian-limit-memory file-custodian k)
+  (define worker-thread
+    (parameterize ([current-custodian file-custodian])
+      (thread
+       (lambda ()
+         (define r (thnk))
+         (channel-put ch r)
+         (channel-get ch)))))
+  (begin0
+    (sync
+     (handle-evt ch
+                 (lambda (v)
+                   (when (exn? v) (raise v))
+                   v))
+     (handle-evt worker-thread
+                 (lambda _
+                   (record! (failure 'memory #f "Over memory limit")))))
+    (custodian-shutdown-all file-custodian)))
+
+(define-syntax run/stages*
+  (syntax-rules ()
+    [(_ file) 
+     (record! (success 'everything))]
+    [(_ file [step1 serious? e] . rst)
+     (let/ec esc
+       (let ([step1 (with-handlers ([exn:fail? 
+                                     (lambda (x)
+                                       (record! (failure 'step1 serious? 
+                                                         (exn-message x)))
+                                       (if serious?
+                                           (esc #f)
+                                           #f))])
+                      e)])
+         (record! (success 'step1))
+         (run/stages* file . rst)))]))
+
+(define-syntax-rule (define-stages (run! file)
+                      [stage serious? e] ...)
+  (define (run! file)
+    (run/stages* file [stage serious? e] ...)))
+
+(define-stages (run! file)
+  [read-orig 
+   #t
+   (bytes-gulp file)]
+  [parse-orig 
+   #t
+   (zo-parse/bytes read-orig)]
+  [marshal-parsed 
+   #t
+   (zo-marshal parse-orig)]
+  [parse-marshalled 
+   #t
+   (zo-parse/bytes marshal-parsed)]
+  [compare-parsed-to-parsed-marshalled 
+   #f
+   (equal?/why-not parse-orig parse-marshalled)]
+  [marshal-marshalled 
+   #t
+   (zo-marshal parse-marshalled)]
+  [compare-marshalled-to-marshalled-marshalled 
+   #f
+   (bytes-not-equal?-error marshal-parsed marshal-marshalled)]
+  #;[replace-with-marshalled 
+     #t
+     (replace-file file marshal-marshalled)]
+  [decompile-parsed 
+   #t
+   (decompile parse-orig)]
+  [c-parse-marshalled
+   #t
+   (read-compiled-bytes marshal-parsed)]
+  [compare-orig-to-marshalled 
+   #f
+   (bytes-not-equal?-error read-orig marshal-parsed)])
+
+(define RESULTS empty)
+(define (record! v)
+  (set! RESULTS (list* v RESULTS)))
+(define (run-test file)
+  (run-with-limit 
+   file
+   (* 1024 1024 128)
+   (lambda ()
+     (run! file)))
+  (write (reverse RESULTS)))
+
+(command-line #:program "zo-test-worker" 
+              #:args (file)
+              (run-test file))
\ No newline at end of file
diff --git a/collects/tests/compiler/zo-test.rkt b/collects/tests/compiler/zo-test.rkt
index 81e86bd365..31ee8825d8 100755
--- a/collects/tests/compiler/zo-test.rkt
+++ b/collects/tests/compiler/zo-test.rkt
@@ -3,204 +3,15 @@
 exec racket -t "$0" -- -s -t 60 -v -R $*
 |#
 
-#lang scheme
-(require compiler/zo-parse
-         compiler/zo-marshal
-         compiler/decompile
-         setup/dirs)
-
-;; Helpers
-(define (bytes->hex-string bs)
-  (apply string-append
-         (for/list ([b bs])
-           (format "~a~x"
-                   (if (b . <= . 15) "0" "")
-                   b))))
-
-(define (show-bytes-side-by-side orig new)
-  (define max-length
-    (max (bytes-length orig) (bytes-length new)))
-  (define BYTES-PER-LINE 38)
-  (define lines
-    (ceiling (/ max-length BYTES-PER-LINE)))
-  (define (subbytes* b s e)
-    (subbytes b (min s (bytes-length b)) (min e (bytes-length b))))
-  (for ([line (in-range lines)])
-    (define start (* line BYTES-PER-LINE))
-    (define end (* (add1 line) BYTES-PER-LINE))
-    (printf "+ ~a\n" (bytes->hex-string (subbytes* orig start end)))
-    (printf "- ~a\n" (bytes->hex-string (subbytes* new start end)))))
-
-(define (bytes-gulp f)
-  (with-input-from-file f 
-    (λ () (port->bytes (current-input-port)))))
-
-(define (read-compiled-bytes bs)
-  (define ib (open-input-bytes bs))
-  (dynamic-wind void
-                (lambda ()
-                  (parameterize ([read-accept-compiled #t])
-                    (read ib)))
-                (lambda ()
-                  (close-input-port ib))))
-
-(define (zo-parse/bytes bs)
-  (define ib (open-input-bytes bs))
-  (dynamic-wind void
-                (lambda ()
-                  (zo-parse ib))
-                (lambda ()
-                  (close-input-port ib))))
-
-(define (bytes-not-equal?-error b1 b2)
-  (unless (bytes=? b1 b2)
-    (error 'bytes-not-equal?-error "Not equal")))
-
-(define (replace-file file bytes)
-  (with-output-to-file file
-    (λ () (write-bytes bytes))
-    #:exists 'truncate))
+#lang racket
+(require setup/dirs
+         racket/runtime-path
+         racket/future
+         "zo-test-util.rkt")
 
 (define ((make-recorder! ht) file phase)
   (hash-update! ht phase (curry list* file) empty))
 
-(define (equal?/why-not v1 v2)
-  (define v1->v2 (make-hasheq))
-  (define (interned-symbol=? s1 s2)
-    (symbol=? (hash-ref! v1->v2 s1 s2) s2))
-  (define (yield p m v1 v2)
-    (error 'equal?/why-not "~a in ~a: ~S ~S"
-           m (reverse p) v1 v2))
-  (define (inner p v1 v2)
-    (unless (eq? v1 v2)
-      (match v1
-        [(cons car1 cdr1)
-         (match v2
-           [(cons car2 cdr2)
-            (inner (list* 'car p) car1 car2)
-            (inner (list* 'cdr p) cdr1 cdr2)]
-           [_
-            (yield p "Not a cons on right" v1 v2)])]
-        [(? vector?)
-         (match v2
-           [(? vector?)
-            (define v1l (vector-length v1))
-            (define v2l (vector-length v2))
-            (if (= v1l v2l)
-                (for ([i (in-range v1l)])
-                  (inner (list* `(vector-ref ,i) p)
-                         (vector-ref v1 i)
-                         (vector-ref v2 i)))
-                (yield p "Vector lengths not equal" v1 v2))]
-           [_
-            (yield p "Not a vector on right" v1 v2)])]
-        [(? struct?)
-         (match v2
-           [(? struct?)
-            (define vv1 (struct->vector v1))
-            (define vv2 (struct->vector v2))
-            (inner (list* `(struct->vector ,(vector-ref vv1 0)) p)
-                   vv1 vv2)]
-           [_
-            (yield p "Not a struct on right" v1 v2)])]
-        [(? hash?)
-         (match v2
-           [(? hash?)
-            (let ([p (list* 'in-hash p)])
-              (for ([(k1 hv1) (in-hash v1)])
-                (define hv2 
-                  (hash-ref v2 k1
-                            (lambda ()
-                              (yield p (format "~S not in hash on right" k1) v1 v2))))
-                (inner (list* `(hash-ref ,k1) p)
-                       hv1 hv2)))]
-           [_
-            (yield p "Not a hash on right" v1 v2)])]
-        [(? module-path-index?)
-         (match v2
-           [(? module-path-index?)
-            (define-values (mp1 bmpi1) (module-path-index-split v1))
-            (define-values (mp2 bmpi2) (module-path-index-split v2))
-            (inner (list* 'module-path-index-split_0 p) mp1 mp2)
-            (inner (list* 'module-path-index-split_1 p) bmpi1 bmpi2)]
-           [_
-            (yield p "Not a module path index on right" v1 v2)])]
-        [(? string?)
-         (match v2
-           [(? string?)
-            (unless (string=? v1 v2)
-              (yield p "Unequal strings" v1 v2))]
-           [_
-            (yield p "Not a string on right" v1 v2)])]
-        [(? bytes?)
-         (match v2
-           [(? bytes?)
-            (unless (bytes=? v1 v2)
-              (yield p "Unequal bytes" v1 v2))]
-           [_
-            (yield p "Not a bytes on right" v1 v2)])]
-        [(? path?)
-         (match v2
-           [(? path?)
-            (unless (equal? v1 v2)
-              (yield p "Unequal paths" v1 v2))]
-           [_
-            (yield p "Not a path on right" v1 v2)])]
-        [(? number?)
-         (match v2
-           [(? number?)
-            (unless (equal? v1 v2)
-              (yield p "Unequal numbers" v1 v2))]
-           [_
-            (yield p "Not a number on right" v1 v2)])]
-        [(? regexp?)
-         (match v2
-           [(? regexp?)
-            (unless (string=? (object-name v1) (object-name v2))
-              (yield p "Unequal regexp" v1 v2))]
-           [_
-            (yield p "Not a regexp on right" v1 v2)])]
-        [(? byte-regexp?)
-         (match v2
-           [(? byte-regexp?)
-            (unless (bytes=? (object-name v1) (object-name v2))
-              (yield p "Unequal byte-regexp" v1 v2))]
-           [_
-            (yield p "Not a byte-regexp on right" v1 v2)])]
-        [(? box?)
-         (match v2
-           [(? box?)
-            (inner (list* 'unbox) (unbox v1) (unbox v2))]
-           [_
-            (yield p "Not a box on right" v1 v2)])]
-        [(? symbol?)
-         (match v2
-           [(? symbol?)
-            (unless (symbol=? v1 v2)
-              (cond
-                [(and (symbol-interned? v1) (not (symbol-interned? v1)))
-                 (yield p "Not interned symbol on right" v1 v2)]
-                [(and (symbol-unreadable? v1) (not (symbol-unreadable? v1)))
-                 (yield p "Not unreadable symbol on right" v1 v2)]
-                [(and (symbol-uninterned? v1) (not (symbol-uninterned? v1)))
-                 (yield p "Not uninterned symbol on right" v1 v2)]
-                [(and (symbol-uninterned? v1) (symbol-uninterned? v2))
-                 (unless (interned-symbol=? v1 v2)
-                   (yield p "Uninterned symbols don't align" v1 v2))]
-                [else
-                 (yield p "Other symbol-related problem" v1 v2)]))]
-           [_
-            (yield p "Not a symbol on right" v1 v2)])]
-        [(? empty?)
-         (yield p "Not empty on right" v1 v2)]
-        [_
-         (yield p "Cannot inspect values deeper" v1 v2)])))
-  (inner empty v1 v2))  
-
-(define (symbol-uninterned? s)
-  (not (or (symbol-interned? s) (symbol-unreadable? s))))
-
-;; Parameters
 (define stop-on-first-error (make-parameter #f))
 (define verbose-mode (make-parameter #f))
 (define care-about-nonserious? (make-parameter #t))
@@ -208,139 +19,23 @@ exec racket -t "$0" -- -s -t 60 -v -R $*
 (define time-limit (make-parameter +inf.0))
 (define randomize (make-parameter #f))
 
-;; Work
 (define errors (make-hash))
+(define (record-common-error! exn-msg)
+  (hash-update! errors (common-message exn-msg) add1 0))
 
-(define (common-message exn)
-  (define given-messages (regexp-match #rx".*given" (exn-message exn)))
+(define (common-message exn-msg)
+  (define given-messages (regexp-match #rx".*given" exn-msg))
   (if (and given-messages (not (empty? given-messages)))
       (first given-messages)
-      (exn-message exn)))
-
-(define (exn-printer file phase serious? exn)
-  (hash-update! errors (common-message exn) add1 0)
-  (unless (and (not (care-about-nonserious?)) (not serious?))
-    (when (or (verbose-mode) (stop-on-first-error))
-      (fprintf (current-error-port) "~a -- ~a: ~a~n" file phase (exn-message exn)))
-    (when (stop-on-first-error)
-      exn)))
-
-(define (run-with-time-limit t thnk)
-  (define th (thread thnk))
-  (sync th
-        (handle-evt (alarm-evt (+ (current-inexact-milliseconds)
-                                  (* 1000 t)))
-                    (lambda _
-                      (kill-thread th)))))
-
-(define (run-with-limit file k thnk)
-  (define file-custodian (make-custodian))
-  (define ch (make-channel))
-  (custodian-limit-memory file-custodian k)
-  (local [(define worker-thread
-            (parameterize ([current-custodian file-custodian])
-              (thread
-               (lambda ()
-                 (define r (thnk))
-                 (channel-put ch r)
-                 (channel-get ch)))))]
-    (begin0
-      (sync
-       (handle-evt ch
-                   (lambda (v)
-                     (when (exn? v) (raise v))
-                     v))
-       (handle-evt worker-thread
-                   (lambda _
-                     (failure! file 'memory))))
-      (custodian-shutdown-all file-custodian))))
+      exn-msg))
 
 (define success-ht (make-hasheq))
 (define success! (make-recorder! success-ht))
 (define failure-ht (make-hasheq))
 (define failure! (make-recorder! failure-ht))
 
-(define-syntax run/stages*
-  (syntax-rules ()
-    [(_ file) (success! file 'everything)]
-    [(_ file [step1 serious? e] . rst)
-     (let/ec esc
-       (let ([step1 (with-handlers ([exn:fail? 
-                                     (lambda (x)
-                                       (failure! file 'step1)
-                                       (esc (exn-printer file 'step1 serious? x)))])
-                      e)])
-         (success! file 'step1)
-         (run/stages* file . rst)))]))
-
-(define-syntax-rule (define-stages (stages run!)
-                      file
-                      [stage serious? e] ...)
-  (define-values (stages run!)
-    (values '(stage ...)
-            (lambda (file)
-              (run/stages* file [stage serious? e] ...)))))
-
 (define debugging? (make-parameter #f))
 
-(define (print-bytes orig new)
-  (when (debugging?)
-    (show-bytes-side-by-side orig new))
-  #t)
-
-(define-stages (stages run!)
-  file
-  [read-orig 
-   #t
-   (bytes-gulp file)]
-  [parse-orig 
-   #t
-   (zo-parse/bytes read-orig)]
-  [marshal-parsed 
-   #t
-   (zo-marshal parse-orig)]
-  #;[ignored 
-     #f
-     (printf "orig: ~a, marshalled: ~a~n"
-             (bytes-length read-orig)
-             (bytes-length marshal-parsed))]
-  [parse-marshalled 
-   #t
-   (zo-parse/bytes marshal-parsed)]
-  [compare-parsed-to-parsed-marshalled 
-   #f
-   (equal?/why-not parse-orig parse-marshalled)]
-  [marshal-marshalled 
-   #t
-   (zo-marshal parse-marshalled)]
-  [compare-marshalled-to-marshalled-marshalled 
-   #f
-   (bytes-not-equal?-error marshal-parsed marshal-marshalled)]
-  #;[show-orig-and-marshal-parsed
-   #f
-   (print-bytes read-orig marshal-parsed)]
-  #;[replace-with-marshalled 
-     #t
-     (replace-file file marshal-marshalled)]
-  [decompile-parsed 
-   #t
-   (decompile parse-orig)]
-  [c-parse-marshalled
-   #t
-   (read-compiled-bytes marshal-parsed)]
-  [compare-orig-to-marshalled 
-   #f
-   (bytes-not-equal?-error read-orig marshal-parsed)])
-
-(define (run-test file)
-  (when (debugging?)
-    (printf "~a\n" file))
-  (run-with-limit 
-   file
-   (* 1024 1024 128)
-   (lambda ()
-     (run! file))))
-
 (define (randomize-list l)
   (define ll (length l))
   (define seen? (make-hasheq))
@@ -366,59 +61,162 @@ exec racket -t "$0" -- -s -t 60 -v -R $*
     [(regexp-match #rx"\\.zo$" p-str)
      (! p-str)]))
 
-(define (zo-test paths)
-  (run-with-time-limit 
-   (time-limit)
-   (lambda ()
-     (for-each (curry for-zos run-test) paths)))
-  
-  (unless (invariant-output)
-    (for ([kind-name (list* 'memory stages)])
-      (define fails (length (hash-ref failure-ht kind-name empty)))
-      (define succs (length (hash-ref success-ht kind-name empty)))
-      (define all (+ fails succs))
-      (unless (zero? all)
-        (printf "~S~n"
-                `(,kind-name
-                  (#f ,fails)
-                  (#t ,succs)
-                  ,all))))
-    (printf "~a tests passed~n" (length (hash-ref success-ht 'everything empty)))
-    
-    (printf "Common Errors:~n")
-    
-    (for ([p (in-list (sort (filter (λ (p) ((car p) . > . 10))
-                                    (hash-map errors (λ (k v) (cons v k))))
-                            > #:key car))])
-      (printf "~a:~n~a~n~n" (car p) (cdr p)))))
+(define-runtime-path zo-test-worker-path "zo-test-worker.rkt")
+(define racket-path (path->string (find-executable-path "racket")))
 
-; Run
-#;(current-command-line-arguments #("-s" "/home/bjohn3x/development/plt/collects/browser/compiled/browser_scrbl.zo"))
-(command-line #:program "zo-test" 
-              #:once-each
-              [("-D") 
-               "Enable debugging output"
-               (debugging? #t)]
-              [("-s" "--stop-on-first-error") 
-               "Stop testing when first error is encountered"
-               (stop-on-first-error #t)]
-              [("-S")
-               "Don't take some errors seriously"
-               (care-about-nonserious? #f)]
-              [("-v" "--verbose")
-               "Display verbose error messages"
-               (verbose-mode #t)]
-              [("-I")
-               "Invariant output"
-               (invariant-output #t)]
-              [("-R")
-               "Randomize"
-               (randomize #t)]
-              [("-t") 
-               number
-               "Limit the run to a given amount of time"
-               (time-limit (string->number number))]
-              #:args p
-              (zo-test (if (empty? p)
-                           (list (find-collects-dir))
-                           p)))
\ No newline at end of file
+(define p
+  (command-line #:program "zo-test" 
+                #:once-each
+                [("-D") 
+                 "Enable debugging output"
+                 (debugging? #t)]
+                [("-s" "--stop-on-first-error") 
+                 "Stop testing when first error is encountered"
+                 (stop-on-first-error #t)]
+                [("-S")
+                 "Don't take some errors seriously"
+                 (care-about-nonserious? #f)]
+                [("-v" "--verbose")
+                 "Display verbose error messages"
+                 (verbose-mode #t)]
+                [("-I")
+                 "Invariant output"
+                 (invariant-output #t)]
+                [("-R")
+                 "Randomize"
+                 (randomize #t)]
+                [("-t") 
+                 number
+                 "Limit the run to a given amount of time"
+                 (time-limit (string->number number))]
+                #:args p
+                (if (empty? p)
+                    (list (find-collects-dir))
+                    p)))
+
+(define to-worker-ch (make-channel))
+(define stop-ch (make-channel))
+(define from-worker-ch (make-channel))
+
+(define worker-threads
+  (for/list ([i (in-range (processor-count))])
+    (thread
+     (λ ()
+       (let loop ()
+         (sync
+          (handle-evt to-worker-ch
+                      (λ (p)
+                        (when (debugging?)
+                          (printf "~a\n" p))
+                        (define-values
+                          (sp stdout stdin _stderr)
+                          (subprocess #f #f #f racket-path (path->string zo-test-worker-path) p))
+                        (define r
+                          (dynamic-wind
+                           void
+                           (λ ()
+                             (read stdout))
+                           (λ ()
+                             (close-input-port stdout)
+                             (close-output-port stdin)
+                             (subprocess-kill sp #t))))
+                        (channel-put from-worker-ch (cons p r))
+                        (loop)))
+          (handle-evt stop-ch
+                      (λ (die)
+                        (void)))))))))          
+
+(define (process-result p r)
+  (match r
+    [(success phase)
+     (success! p phase)]
+    [(failure phase serious? exn-msg)
+     (record-common-error! exn-msg)
+     (failure! p phase)
+     
+     (unless (and (not (care-about-nonserious?)) (not serious?))
+       (when (or (verbose-mode) (stop-on-first-error))
+         (fprintf (current-error-port) "~a -- ~a: ~a\n" p phase exn-msg))
+       (when (stop-on-first-error)
+         (stop!)))]))     
+
+(define timing-thread
+  (thread
+   (λ ()
+     (sync 
+      (alarm-evt (+ (current-inexact-milliseconds)
+                    (* 1000 (time-limit)))))
+     (stop!))))
+
+(define server-thread
+  (thread
+   (λ ()
+     (let loop ([ts worker-threads])
+       (if (empty? ts)
+           (stop!)
+           (apply
+            sync
+            (handle-evt from-worker-ch
+                        (match-lambda
+                          [(cons p rs)
+                           (for-each (curry process-result p) rs)
+                           (loop ts)]))
+            (for/list ([t (in-list ts)])
+              (handle-evt t (λ _ (loop (remq t ts)))))))))))
+
+(define (spawn-worker p)
+  (channel-put to-worker-ch p))
+
+(define (zo-test paths)
+  (for-each (curry for-zos spawn-worker) paths)
+  
+  (for ([i (in-range (processor-count))])
+    (channel-put stop-ch #t)))
+
+(define root-thread
+  (thread
+   (λ ()
+     (zo-test p))))
+
+(define final-sema (make-semaphore 0))
+(define (stop!)
+  (semaphore-post final-sema))
+
+(define (hash-keys ht)
+  (hash-map ht (λ (k v) k)))
+
+(define final-thread
+  (thread
+   (λ ()
+     (semaphore-wait final-sema)
+     (for-each kill-thread
+               (list* root-thread server-thread worker-threads))
+     (unless (invariant-output)
+       (newline)
+       (for ([kind-name 
+              (remove-duplicates 
+               (append
+                (hash-keys failure-ht)
+                (hash-keys success-ht)))])
+         (define fails (length (hash-ref failure-ht kind-name empty)))
+         (define succs (length (hash-ref success-ht kind-name empty)))
+         (define all (+ fails succs))
+         (unless (zero? all)
+           (printf "~S~n"
+                   `(,kind-name
+                     (#f ,fails)
+                     (#t ,succs)
+                     ,all))))
+       (newline)
+       (printf "~a tests passed~n" (length (hash-ref success-ht 'everything empty)))
+       
+       (let ([common-errors 
+              (sort (filter (λ (p) ((car p) . > . 10))
+                            (hash-map errors (λ (k v) (cons v k))))
+                    > #:key car)])
+         (unless (empty? common-errors)
+           (printf "Common Errors:~n")
+           (for ([p (in-list common-errors)])
+             (printf "~a:~n~a~n~n" (car p) (cdr p)))))))))
+
+(thread-wait final-thread)
\ No newline at end of file