Re: port-for-each vs lazy sweep

[Kevin Ryde <user42@zip.com.au>]

[-- Attachment #1: Type: text/plain, Size: 380 bytes --]

Actually I see the flush func of a soft port is entirely unused, it's
never called by a force-output because nothing is ever put in the port
buffer as such.  The manual could be clearer about what it's supposed to
be for :-(.

At any rate, I put in the failing test below for port-for-each, and I
think flush-all could benefit from the rewrite below, just on general
principles.


[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: ports.test.diff --]
[-- Type: text/x-diff, Size: 1397 bytes --]

--- ports.test	27 Jan 2007 11:06:20 +1100	1.33.2.5
+++ ports.test	22 Aug 2007 16:43:39 +1000	
@@ -550,6 +550,38 @@
       (eqv? n (port-line port)))))
 
 ;;;
+;;; port-for-each
+;;;
+
+(with-test-prefix "port-for-each"
+
+  ;; In guile 1.8.0 through 1.8.2, port-for-each could pass a freed cell to
+  ;; its iterator func if a port was inaccessible in the last gc mark but
+  ;; the lazy sweeping has not yet reached it to remove it from the port
+  ;; table (scm_i_port_table).  Provoking those gc conditions is a little
+  ;; tricky, but the following code made it happen in 1.8.2.
+  (pass-if "passing freed cell"
+    (throw 'unresolved)
+    (let ((lst '()))
+      ;; clear out the heap
+      (gc) (gc) (gc)
+      ;; allocate cells so the opened ports aren't at the start of the heap
+      (make-list 1000)
+      (open-input-file "/dev/null")
+      (make-list 1000)
+      (open-input-file "/dev/null")
+      ;; this gc leaves the above ports unmarked, ie. inaccessible
+      (gc)
+      ;; but they're still in the port table, so this sees them
+      (port-for-each (lambda (port)
+		       (set! lst (cons port lst))))
+      ;; this forces completion of the sweeping
+      (gc) (gc) (gc)
+      ;; and (if the bug is present) the cells accumulated in LST are now
+      ;; freed cells, which give #f from `port?'
+      (not (memq #f (map port? lst))))))
+
+;;;
 ;;; seek
 ;;;
 

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #3: ports.c.flush-all.diff --]
[-- Type: text/x-diff, Size: 1040 bytes --]

--- ports.c	27 Jan 2007 10:51:48 +1100	1.204.2.14
+++ ports.c	21 Aug 2007 17:02:53 +1000	
@@ -929,25 +929,26 @@
 }
 #undef FUNC_NAME
 
+
+static void
+scm_flush_all_ports_one (void *dummy, SCM port)
+{
+  if (SCM_OPOUTPORTP (port))
+    scm_flush (port);
+}
+
 SCM_DEFINE (scm_flush_all_ports, "flush-all-ports", 0, 0, 0,
             (),
 	    "Equivalent to calling @code{force-output} on\n"
 	    "all open output ports.  The return value is unspecified.")
 #define FUNC_NAME s_scm_flush_all_ports
 {
-  size_t i;
-
-  scm_i_scm_pthread_mutex_lock (&scm_i_port_table_mutex);
-  for (i = 0; i < scm_i_port_table_size; i++)
-    {
-      if (SCM_OPOUTPORTP (scm_i_port_table[i]->port))
-	scm_flush (scm_i_port_table[i]->port);
-    }
-  scm_i_pthread_mutex_unlock (&scm_i_port_table_mutex);
+  scm_c_port_for_each (scm_flush_all_ports_one);
   return SCM_UNSPECIFIED;
 }
 #undef FUNC_NAME
 
+
 SCM_DEFINE (scm_read_char, "read-char", 0, 1, 0,
            (SCM port),
 	    "Return the next character available from @var{port}, updating\n"

[-- Attachment #4: Type: text/plain, Size: 143 bytes --]

_______________________________________________
Guile-devel mailing list
Guile-devel@gnu.org
http://lists.gnu.org/mailman/listinfo/guile-devel