null-threads: keys are destroyed too early

null-threads: keys are destroyed too early

[Matthias Drochner]

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The "autogen" program crashes on exit if built against
a guile which doesn't use threads.
Here is a stacktrace:
#0  0xbbb902d1 in scm_make_srcprops () from /usr/pkg/lib/libguile.so.17
#1  0xbbb8b322 in scm_read_sexp () from /usr/pkg/lib/libguile.so.17
#2  0xbbb8a3f9 in scm_read_expression () from /usr/pkg/lib/libguile.so.17
#3  0xbbb8b1dc in scm_read_sexp () from /usr/pkg/lib/libguile.so.17
#4  0xbbb8a3f9 in scm_read_expression () from /usr/pkg/lib/libguile.so.17
#5  0xbbb8b1dc in scm_read_sexp () from /usr/pkg/lib/libguile.so.17
#6  0xbbb8a3f9 in scm_read_expression () from /usr/pkg/lib/libguile.so.17
#7  0x08050b3b in ag_scm_c_eval_string_from_file_line ()
#8  0x0805bbbd in doneCheck ()
#9  0xbba6b999 in __cxa_finalize () from /usr/lib/libc.so.12
#10 0xbba6b822 in exit () from /usr/lib/libc.so.12

The following happens: autogen registers an atexit() function
which calls ag_scm_c_eval_string_from_file_line().
On exit, this eventually calls scm_make_srcprops(), which
uses SCM_CRITICAL_SECTION_START, which in turn references
SCM_I_CURRENT_THREAD. The latter is implemented by
pthread_getspecific(), or rather its replacement in null-threads.c.

The emulated pthread_key_create() in null-threads.c also
registers an atexit() function which destroys the pthread_keys
allocated by the process. Since atexit() functions are
called in reverse order, this destroy_keys() function is
called before the doneCheck() above.

So SCM_I_CURRENT_THREAD tries to use a destroyed key,
leading to the crash.

The appended patch avoids the problem.

best regards
Matthias





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Dr. Sebastian M. Schmidt
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$NetBSD$

--- libguile/null-threads.c.orig	2008-01-04 14:43:50.000000000 +0100
+++ libguile/null-threads.c
@@ -47,8 +47,10 @@ int
 scm_i_pthread_key_create (scm_i_pthread_key_t *key,
 			  void (*destr_func) (void *))
 {
+#if 0 /* keys are needed by other atexit() functions */
   if (all_keys == NULL)
     atexit (destroy_keys);
+#endif
 
   key->next = all_keys;
   all_keys = key;