[PATCH] Fix thread-unsafe lazy initializations

[Mark H Weaver]

Here's my proposed patch to fix these problems.
What do you think?

    Mark


>From dadcb1512569c1be039fc75f0a2967e370939e42 Mon Sep 17 00:00:00 2001
From: Mark H Weaver <address@hidden>
Date: Thu, 28 Feb 2013 17:56:58 -0500
Subject: [PATCH] Fix thread-unsafe lazy initializations.

* libguile/debug.c (scm_local_eval):
  libguile/ports.c (scm_current_warning_port):
  libguile/strports.c (scm_eval_string_in_module): Perform
  lazy-initialization while holding a mutex.  Use SCM_UNDEFINED as the
  uninitialized value.  Use 'scm_c_*_variable'.

* doc/ref/api-modules.texi (Accessing Modules from C): Fix
  'my_eval_string' example to be thread-safe.
---
 doc/ref/api-modules.texi |   13 +++++++------
 libguile/debug.c         |    8 ++++++--
 libguile/ports.c         |   12 ++++++++----
 libguile/strports.c      |    9 ++++++---
 4 files changed, 27 insertions(+), 15 deletions(-)

diff --git a/doc/ref/api-modules.texi b/doc/ref/api-modules.texi
index 17ab462..3d111c4 100644
--- a/doc/ref/api-modules.texi
+++ b/doc/ref/api-modules.texi
@@ -942,14 +942,15 @@ the @var{name} is not bound in the module, signals an 
error.  Returns a
 variable, always.
 
 @example
-SCM my_eval_string (SCM str)
address@hidden
-  static SCM eval_string_var = SCM_BOOL_F;
+static SCM eval_string_var;
 
-  if (scm_is_false (eval_string_var))
-    eval_string_var =
-      scm_c_public_lookup ("ice-9 eval-string", "eval-string");
+void my_init (void)
address@hidden
+  eval_string_var = scm_c_public_lookup ("ice-9 eval-string", "eval-string");
address@hidden
 
+SCM my_eval_string (SCM str)
address@hidden
   return scm_call_1 (scm_variable_ref (eval_string_var), str);
 @}
 @end example
diff --git a/libguile/debug.c b/libguile/debug.c
index b1a90d8..9e6328b 100644
--- a/libguile/debug.c
+++ b/libguile/debug.c
@@ -211,10 +211,14 @@ SCM_DEFINE (scm_debug_hang, "debug-hang", 0, 1, 0,
 SCM
 scm_local_eval (SCM exp, SCM env)
 {
-  static SCM local_eval_var = SCM_BOOL_F;
+  static SCM local_eval_var = SCM_UNDEFINED;
+  static scm_i_pthread_mutex_t local_eval_var_mutex
+    = SCM_I_PTHREAD_MUTEX_INITIALIZER;
 
-  if (scm_is_false (local_eval_var))
+  scm_i_scm_pthread_mutex_lock (&local_eval_var_mutex);
+  if (SCM_UNBNDP (local_eval_var))
     local_eval_var = scm_c_public_variable ("ice-9 local-eval", "local-eval");
+  scm_i_pthread_mutex_unlock (&local_eval_var_mutex);
 
   return scm_call_2 (SCM_VARIABLE_REF (local_eval_var), exp, env);
 }
diff --git a/libguile/ports.c b/libguile/ports.c
index 55808e2..8737a76 100644
--- a/libguile/ports.c
+++ b/libguile/ports.c
@@ -418,10 +418,14 @@ SCM_DEFINE (scm_current_error_port, "current-error-port", 
0, 0, 0,
 SCM
 scm_current_warning_port (void)
 {
-  static SCM cwp_var = SCM_BOOL_F;
-
-  if (scm_is_false (cwp_var))
-    cwp_var = scm_c_private_lookup ("guile", "current-warning-port");
+  static SCM cwp_var = SCM_UNDEFINED;
+  static scm_i_pthread_mutex_t cwp_var_mutex
+    = SCM_I_PTHREAD_MUTEX_INITIALIZER;
+
+  scm_i_scm_pthread_mutex_lock (&cwp_var_mutex);
+  if (SCM_UNBNDP (cwp_var))
+    cwp_var = scm_c_private_variable ("guile", "current-warning-port");
+  scm_i_pthread_mutex_unlock (&cwp_var_mutex);
   
   return scm_call_0 (scm_variable_ref (cwp_var));
 }
diff --git a/libguile/strports.c b/libguile/strports.c
index 14cc93f..d1b293c 100644
--- a/libguile/strports.c
+++ b/libguile/strports.c
@@ -534,13 +534,16 @@ SCM_DEFINE (scm_eval_string_in_module, "eval-string", 1, 
1, 0,
             "procedure returns.")
 #define FUNC_NAME s_scm_eval_string_in_module
 {
-  static SCM eval_string = SCM_BOOL_F, k_module = SCM_BOOL_F;
+  static SCM eval_string = SCM_UNDEFINED, k_module = SCM_UNDEFINED;
+  static scm_i_pthread_mutex_t init_mutex = SCM_I_PTHREAD_MUTEX_INITIALIZER;
 
-  if (scm_is_false (eval_string))
+  scm_i_scm_pthread_mutex_lock (&init_mutex);
+  if (SCM_UNBNDP (eval_string))
     {
-      eval_string = scm_c_public_lookup ("ice-9 eval-string", "eval-string");
+      eval_string = scm_c_public_variable ("ice-9 eval-string", "eval-string");
       k_module = scm_from_locale_keyword ("module");
     }
+  scm_i_pthread_mutex_unlock (&init_mutex);
   
   if (SCM_UNBNDP (module))
     module = scm_current_module ();
-- 
1.7.10.4