From: Kevin Ryde <user42@zip.com.au>
Subject: gensym thread safety
Date: Wed, 28 Jul 2004 08:58:20 +1000 [thread overview]
Message-ID: <87smbd12ib.fsf@zip.com.au> (raw)
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The chance of two threads hitting the read+increment at the same time
is obviously small, but a mutex will guarantee it.
* symbols.c (scm_gensym): Use scm_i_misc_mutex around gensym_counter
update, for thread safety.
(gensym_counter): Move into scm_gensym which is its only user.
(scm_init_symbols): No need to explicitly initialize gensym_counter.
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--- symbols.c.~1.112.~ 2004-07-24 09:09:00.000000000 +1000
+++ symbols.c 2004-07-24 16:53:36.000000000 +1000
@@ -1,4 +1,4 @@
-/* Copyright (C) 1995,1996,1997,1998,2000,2001, 2003 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,1997,1998,2000,2001, 2003, 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
@@ -264,8 +264,6 @@
#define MAX_PREFIX_LENGTH 30
-static int gensym_counter;
-
SCM_DEFINE (scm_gensym, "gensym", 0, 1, 0,
(SCM prefix),
"Create a new symbol with a name constructed from a prefix and\n"
@@ -275,6 +273,8 @@
"resetting the counter.")
#define FUNC_NAME s_scm_gensym
{
+ static int gensym_counter = 0;
+
char buf[MAX_PREFIX_LENGTH + SCM_INTBUFLEN];
char *name = buf;
size_t len;
@@ -293,7 +293,14 @@
memcpy (name, SCM_STRING_CHARS (prefix), len);
}
{
- int n_digits = scm_iint2str (gensym_counter++, 10, &name[len]);
+ int n, n_digits;
+
+ /* mutex in case another thread looks and incs at the exact same moment */
+ scm_mutex_lock (&scm_i_misc_mutex);
+ n = gensym_counter++;
+ scm_mutex_unlock (&scm_i_misc_mutex);
+
+ n_digits = scm_iint2str (count, 10, &name[len]);
SCM res = scm_mem2symbol (name, len + n_digits);
if (name != buf)
free (name);
@@ -414,7 +421,6 @@
void
scm_init_symbols ()
{
- gensym_counter = 0;
#include "libguile/symbols.x"
}
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