improved the setup for the front-end method so that

printing to stdout and stderr is safe and to better document
the issues

collects/drracket/private/rep.rkt

@@ -1312,7 +1312,7 @@ TODO
                   (let ([run-on-user-thread (lambda (t) 
                                               (queue-user/wait 
                                                (λ ()
-                                                 (with-handlers ((exn? (λ (x) (printf "~s\n" (exn-message x)))))
+                                                 (with-handlers ((exn? (λ (x) (oprintf "~s\n" (exn-message x)))))
                                                    (t)))))])
                     run-on-user-thread))
             
@@ -1653,10 +1653,39 @@ TODO
         (let ([lang (drracket:language-configuration:language-settings-language user-language-settings)]
               [drr-evtspace (current-eventspace)]
               [s (make-semaphore 0)])
+          
+          (define-values (sp-err-other-end sp-err) (make-pipe))
+          (define-values (sp-out-other-end sp-out) (make-pipe))
+          (define io-chan (make-channel))
+          
+          ;; collect the IO to replay later
+          (thread
+           (λ () 
+             (let loop ([ports (list sp-err-other-end sp-out-other-end)]
+                        [io '()])
+               (cond
+                 [(null? ports) (channel-put io-chan io)]
+                 [else
+                  (apply sync
+                         (map (λ (port) (handle-evt 
+                                         port 
+                                         (λ (_) 
+                                           (define byte (read-byte port))
+                                           (if (eof-object? byte)
+                                               (loop (remq port ports) io)
+                                               (loop ports (cons (cons port byte) 
+                                                                 io))))))
+                              ports))]))))
+             
           (run-in-evaluation-thread
            (λ ()
              (let/ec k
-               (parameterize ([error-escape-handler (λ () (k (void)))])
+               ;; we set the io ports here to ones that just collect the data
+               ;; since we're blocking the eventspace handler thread (and thus IO to 
+               ;; the user's ports can deadlock)
+               (parameterize ([error-escape-handler (λ () (k (void)))]
+                              [current-output-port sp-out]
+                              [current-error-port sp-err])
                  (cond
                    ;; this is for backwards compatibility; drracket used to
                    ;; expect this method to be a thunk (but that was a bad decision)
@@ -1667,7 +1696,21 @@ TODO
                     ;; this is the backwards compatible case.
                     (send lang first-opened)])))
              (semaphore-post s)))
-          (semaphore-wait s))
+          
+          ;; wait for the first-opened method to finish up
+          (semaphore-wait s)
+          
+          ;; close the output ports to get the above thread to terminate
+          (close-output-port sp-err)
+          (close-output-port sp-out)
+          
+          ;; duplicate it over to the user's ports, now that there is
+          ;; no danger of deadlock
+          (for ([i (in-list (reverse (channel-get io-chan)))])
+            (write-byte (cdr i)
+                        (if (eq? (car i) sp-err-other-end)
+                            (get-err-port)
+                            (get-out-port)))))
         
         (send context enable-evaluation)
         (end-edit-sequence)

collects/scribblings/tools/language.scrbl

@@ -440,7 +440,7 @@ This method is the same as
 }
 
 @defmethod[(on-execute [settings settings]
-                       [run-in-user-thread ((-> void) -> void)])
+                       [run-on-user-thread ((-> void) -> void)])
            vod]{
 This method is the same as
 @method[drracket:language:language<%> on-execute].
@@ -628,7 +628,7 @@ default settings obtained via
 
 }
 
-@defmethod*[([(first-opened [settings settings]) void?])]{
+@defmethod[(first-opened [settings settings]) void?]{
 
 This method is called after the language is initialized, but
 no program has yet been run. It is called from the user's 
@@ -637,8 +637,8 @@ eventspace's main thread.
 See also
 @method[drracket:rep:text% initialize-console].
 
-Calling this method should not raise an exception (or otherwise
+Calling this method should not escape. 
-try to escape). DrRacket calls this method in a @racket[parameterize]
+DrRacket calls this method in a @racket[parameterize]
 where the @racket[error-escape-handler] is set to an escaping
 continuation that continues initializing the interactions window.
 Thus, raising an exception will report the error in the user's
@@ -646,7 +646,14 @@ interactions window as if this were a bug in the user's program.
 Escaping in any other way, however, can cause DrRacket to fail
 to start up.
 
-Contrary to the method contract space, DrRacket will also invoke this
+Also, IO system will deadlock if the @racket[first-opened] method
+does IO on the user's IO ports, so the calling context of
+@racket[first-opened] sets the @racket[current-output-port] and
+@racket[current-error-port] to ports that just collect all of the
+IO that happened and then replay it later in the initialization of the
+user's program.
+
+Contrary to the method contract spec, DrRacket will also invoke this
 method if it has zero arguments, passing nothing; the zero argument
 version is for backwards compatibility and is not recommended.
 
@@ -932,7 +939,7 @@ the settings for this language.
 }
 
 @defmethod[(on-execute [settings settings]
-                       [run-in-user-thread ((-> any) -> any)])
+                       [run-on-user-thread ((-> any) -> any)])
            any]{
 The @scheme[on-execute] method is called on DrRacket's
 eventspace's main thread before any evaluation happens
@@ -1015,13 +1022,16 @@ that error message into the definitions window.}
 
 ]
 
-The @scheme[run-in-user-thread] arguments accepts thunks and
+The @scheme[run-on-user-thread] arguments accepts thunks and
-runs them on the user's eventspace's main thread. These
+runs them on the user's eventspace's main thread. 
-thunks must not raise an exceptions (or DrRacket itself will
+The output ports are not yet
-get stuck). In addition, the output ports are not yet
 functioning, so print outs should be directed to the
 original DrRacket output port, if necessary.
 
+This thunk is wrapped in a @racket[with-handlers] that 
+catches all exceptions matching @racket[exn:fail?] and
+then prints out the exception message to the original
+output port of the DrRacket process.
 }
 
 @defmethod[(order-manuals [manuals (listof bytes?)])

collects/scribblings/tools/rep.scrbl

@@ -111,7 +111,9 @@ The @scheme[complete-program?] argument determines if the
   how it finishes).
 }
 
-@defmethod[#:mode augment (on-execute [run-on-user-thread (-> any)]) any]{
+@defmethod[(on-execute [run-on-user-thread (-> any)]) any]{
+
+  Use @scheme[run-on-user-thread] to initialize the user's parameters, etc.
 
   Called from the DrRacket thread after the language's
   @method[drracket:language:language<%> on-execute]
@@ -119,7 +121,11 @@ The @scheme[complete-program?] argument determines if the
   special values have been setup (the ones registered
   via @scheme[drracket:language:add-snip-value]).
 
-  Use @scheme[run-on-user-thread] to initialize the user's parameters, etc.
+  Do not print to @racket[current-output-port] or @racket[current-error-port]
+  during the dynamic extent of the thunk passed to @racket[run-on-user-thread] becuase
+  this can deadlock. IO is still, in general, fine, but the @racket[current-error-port]
+  and @racket[current-output-port] are set to the user's ports that print
+  into the interactions window and are not in a good state during those calls.
   
 }