From: Kevin Ryde <user42@zip.com.au>
Subject: strerror thread safety
Date: Wed, 28 Jul 2004 09:02:47 +1000 [thread overview]
Message-ID: <87hdrt12aw.fsf@zip.com.au> (raw)
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* error.c (scm_strerror): Use scm_i_misc_mutex around strerror since
it's not thread safe.
(scm_syserror): Use scm_strerror rather than SCM_I_STRERROR, to take
advantage of this.
* fports.c (scm_open_file): Use scm_strerror likewise.
* filesys.c (scm_stat, scm_lstat): Ditto.
A program provoking the problem (in glibc at least),
(use-modules (ice-9 threads))
(define e1 9999)
(define s1 (strerror e1))
(define e2 7777)
(define s2 (strerror e2))
(begin-thread
(while #t
(display "-")
(let ((s (strerror e1)))
(if (not (string=? s1 s))
(begin
(format #t "oops, wrong s1, got ~s want ~s\n" s s1)
(primitive-exit 1))))))
(while #t
(display ".")
(let ((s (strerror e2)))
(if (not (string=? s2 s))
(begin
(format #t "oops, wrong s2, got ~s want ~s\n" s s2)
(primitive-exit 1)))))
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Index: error.c
===================================================================
RCS file: /cvsroot/guile/guile/guile-core/libguile/error.c,v
retrieving revision 1.75
diff -u -u -r1.75 error.c
--- error.c 23 Jul 2004 15:43:01 -0000 1.75
+++ error.c 27 Jul 2004 23:01:30 -0000
@@ -1,4 +1,4 @@
-/* Copyright (C) 1995,1996,1997,1998,2000,2001 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,1997,1998,2000,2001, 2004 Free Software Foundation, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
@@ -26,6 +26,7 @@
#include <errno.h>
#include "libguile/_scm.h"
+#include "libguile/dynwind.h"
#include "libguile/pairs.h"
#include "libguile/strings.h"
#include "libguile/throw.h"
@@ -142,13 +143,34 @@
# define SCM_I_ERRNO() errno
#endif /* __MINGW32__ */
+/* strerror may not be thread safe, for instance in glibc (version 2.3.2) an
+ error number not among the known values results in a string like "Unknown
+ error 9999" formed in a static buffer, which will be overwritten by a
+ similar call in another thread. A test program running two threads with
+ different unknown error numbers can trip this problem fairly quickly.
+
+ Some systems don't do what glibc does, instead just giving a single
+ "Unknown error" for unrecognised numbers. It doesn't seem worth trying
+ to tell if that's the case, a mutex is reasonably fast, and in any case
+ strerror isn't needed very often. */
+
SCM_DEFINE (scm_strerror, "strerror", 1, 0, 0,
(SCM err),
"Return the Unix error message corresponding to @var{err}, which\n"
"must be an integer value.")
#define FUNC_NAME s_scm_strerror
{
- return scm_makfrom0str (SCM_I_STRERROR (scm_to_int (err)));
+ SCM ret;
+ scm_frame_begin (0);
+ scm_frame_unwind_handler ((void(*)(void*)) scm_mutex_unlock,
+ &scm_i_misc_mutex,
+ SCM_F_WIND_EXPLICITLY);
+ scm_mutex_lock (&scm_i_misc_mutex);
+
+ ret = scm_makfrom0str (SCM_I_STRERROR (scm_to_int (err)));
+
+ scm_frame_end ();
+ return ret;
}
#undef FUNC_NAME
@@ -156,13 +178,12 @@
void
scm_syserror (const char *subr)
{
- int save_errno = SCM_I_ERRNO ();
-
+ SCM err = scm_from_int (SCM_I_ERRNO ());
scm_error (scm_system_error_key,
subr,
"~A",
- scm_cons (scm_makfrom0str (SCM_I_STRERROR (save_errno)), SCM_EOL),
- scm_cons (scm_from_int (save_errno), SCM_EOL));
+ scm_cons (scm_strerror (err), SCM_EOL),
+ scm_cons (err, SCM_EOL));
}
void
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