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Module import obarrays are accessed in a critical section.

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Fixes <https://bugs.gnu.org/31879>.

* libguile/modules.c (import_obarray_mutex): New variable.
(resolve_duplicate_binding, module_imported_variable): Acquire it before
accessing an obarray.
This commit is contained in:
Ludovic Courtès 2018-06-18 17:39:35 +02:00 • committed by Andy Wingo
parent f075641051
commit edc80bd595
1 changed files with 17 additions and 0 deletions
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17
libguile/modules.c
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@ -275,6 +275,13 @@ default_duplicate_binding_handlers (void)
return (scm_call_0 (get_handlers)); return (scm_call_0 (get_handlers));
} }
/* Each module has an "import obarray" that may be accessed concurrently
by several threads. This mutex protects access to any obarray. This
is coarse-grain but (1) pthread mutexes are quite cheap, and (2)
Scheme "programs" have a cache for free variables anyway. */
static scm_i_pthread_mutex_t import_obarray_mutex =
SCM_I_PTHREAD_MUTEX_INITIALIZER;
/* Resolve the import of SYM in MODULE, where SYM is currently provided by /* Resolve the import of SYM in MODULE, where SYM is currently provided by
both IFACE1 as VAR1 and IFACE2 as VAR2. Return the variable chosen by the both IFACE1 as VAR1 and IFACE2 as VAR2. Return the variable chosen by the
duplicate binding handlers or `#f'. */ duplicate binding handlers or `#f'. */
@ -300,7 +307,11 @@ resolve_duplicate_binding (SCM module, SCM sym,
args[5] = SCM_VARIABLE_REF (var2); args[5] = SCM_VARIABLE_REF (var2);
if (SCM_UNBNDP (args[5])) if (SCM_UNBNDP (args[5]))
args[5] = SCM_BOOL_F; args[5] = SCM_BOOL_F;
scm_i_pthread_mutex_lock (&import_obarray_mutex);
args[6] = scm_hashq_ref (SCM_MODULE_IMPORT_OBARRAY (module), sym, SCM_BOOL_F); args[6] = scm_hashq_ref (SCM_MODULE_IMPORT_OBARRAY (module), sym, SCM_BOOL_F);
scm_i_pthread_mutex_unlock (&import_obarray_mutex);
args[7] = SCM_BOOL_F; args[7] = SCM_BOOL_F;
handlers = SCM_MODULE_DUPLICATE_HANDLERS (module); handlers = SCM_MODULE_DUPLICATE_HANDLERS (module);
@ -338,7 +349,11 @@ module_imported_variable (SCM module, SCM sym)
/* Search cached imported bindings. */ /* Search cached imported bindings. */
imports = SCM_MODULE_IMPORT_OBARRAY (module); imports = SCM_MODULE_IMPORT_OBARRAY (module);
scm_i_pthread_mutex_lock (&import_obarray_mutex);
var = scm_hashq_ref (imports, sym, SCM_UNDEFINED); var = scm_hashq_ref (imports, sym, SCM_UNDEFINED);
scm_i_pthread_mutex_unlock (&import_obarray_mutex);
if (SCM_BOUND_THING_P (var)) if (SCM_BOUND_THING_P (var))
return var; return var;
@ -386,7 +401,9 @@ module_imported_variable (SCM module, SCM sym)
if (SCM_BOUND_THING_P (found_var)) if (SCM_BOUND_THING_P (found_var))
{ {
/* Save the lookup result for future reference. */ /* Save the lookup result for future reference. */
scm_i_pthread_mutex_lock (&import_obarray_mutex);
(void) scm_hashq_set_x (imports, sym, found_var); (void) scm_hashq_set_x (imports, sym, found_var);
scm_i_pthread_mutex_unlock (&import_obarray_mutex);
return found_var; return found_var;
} }
} }