Use TLS when available for `SCM_I_CURRENT_THREAD'.

* acinclude.m4 (GUILE_THREAD_LOCAL_STORAGE): New macro.

* configure.ac: Use it.

* libguile/__scm.h (SCM_THREAD_LOCAL): New macro.

* libguile/gen-scmconfig.c (main): Define `SCM_HAVE_THREAD_STORAGE_CLASS'.

* libguile/gen-scmconfig.h.in (SCM_I_GSC_HAVE_THREAD_STORAGE_CLASS):
  New.

* libguile/threads.c
  (scm_i_current_thread)[SCM_HAVE_THREAD_STORAGE_CLASS]: New.
  (SET_CURRENT_THREAD): New macro.
  (guilify_self_1, on_thread_exit, init_thread_key): Use it.

* libguile/threads.h
  (scm_i_current_thread)[SCM_HAVE_THREAD_STORAGE_CLASS]: New
  declaration.
  (SCM_I_CURRENT_THREAD)[SCM_HAVE_THREAD_STORAGE_CLASS]: New macro.
  (init_thread_key_once, init_thread_key): Conditionalize on
  `!defined SCM_HAVE_THREAD_STORAGE_CLASS'.
  (scm_i_init_thread_for_guile): Update accordingly.

acinclude.m4

@@ -335,6 +335,26 @@ AC_DEFUN([GUILE_GNU_LD_RELRO], [
   AC_SUBST([GNU_LD_FLAGS])
 ])
 
+dnl GUILE_THREAD_LOCAL_STORAGE
+dnl
+dnl Check for compiler thread-local storage (TLS) support.
+AC_DEFUN([GUILE_THREAD_LOCAL_STORAGE], [
+  AC_CACHE_CHECK([whether the `__thread' storage class is available],
+    [ac_cv_have_thread_storage_class],
+    [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([__thread int tls_integer;],
+			  [tls_integer = 123;])],
+       [ac_cv_have_thread_storage_class="yes"],
+       [ac_cv_have_thread_storage_class="no"])])
+
+  if test "x$ac_cv_have_thread_storage_class" = "xyes"; then
+     SCM_I_GSC_HAVE_THREAD_STORAGE_CLASS=1
+  else
+     SCM_I_GSC_HAVE_THREAD_STORAGE_CLASS=0
+  fi
+
+  AC_SUBST([SCM_I_GSC_HAVE_THREAD_STORAGE_CLASS])
+])
+
 dnl GUILE_READLINE
 dnl
 dnl Check all the things needed by `guile-readline', the Readline

configure.ac

@@ -1380,6 +1380,8 @@ AC_DEFINE(PTHREAD_ATTR_GETSTACK_WORKS, [1], [Define when pthread_att_get_stack w
 CFLAGS="$old_CFLAGS"
 AC_MSG_RESULT($works)
 
+GUILE_THREAD_LOCAL_STORAGE
+
 fi # with_threads=pthreads
 
 

libguile/__scm.h

@@ -679,6 +679,14 @@ SCM_API SCM scm_apply_generic (SCM gf, SCM args);
 #define SCM_C_INLINE_KEYWORD
 #endif
 
+/* Handling thread-local storage (TLS).  */
+
+#ifdef SCM_HAVE_THREAD_STORAGE_CLASS
+# define SCM_THREAD_LOCAL __thread
+#else
+# define SCM_THREAD_LOCAL
+#endif
+
 #endif  /* SCM___SCM_H */
 
 /*

libguile/gen-scmconfig.c

@@ -404,6 +404,13 @@ main (int argc, char *argv[])
   pf ("typedef long int scm_t_off;\n");
 #endif
 
+  pf ("/* Define to 1 if the compiler supports the "
+      "`__thread' storage class.  */\n");
+  if (SCM_I_GSC_HAVE_THREAD_STORAGE_CLASS)
+    pf ("#define SCM_HAVE_THREAD_STORAGE_CLASS\n");
+  else
+    pf ("/* #undef SCM_HAVE_THREAD_STORAGE_CLASS */\n");
+
 #if USE_DLL_IMPORT
   pf ("\n");
   pf ("/* Define some additional CPP macros on Win32 platforms. */\n");

libguile/gen-scmconfig.h.in

@@ -30,6 +30,7 @@
 #define SCM_I_GSC_USE_NULL_THREADS @SCM_I_GSC_USE_NULL_THREADS@
 #define SCM_I_GSC_NEED_BRACES_ON_PTHREAD_ONCE_INIT @SCM_I_GSC_NEED_BRACES_ON_PTHREAD_ONCE_INIT@
 #define SCM_I_GSC_NEED_BRACES_ON_PTHREAD_MUTEX_INITIALIZER @SCM_I_GSC_NEED_BRACES_ON_PTHREAD_MUTEX_INITIALIZER@
+#define SCM_I_GSC_HAVE_THREAD_STORAGE_CLASS @SCM_I_GSC_HAVE_THREAD_STORAGE_CLASS@
 #define SCM_I_GSC_HAVE_STRUCT_DIRENT64 @SCM_I_GSC_HAVE_STRUCT_DIRENT64@
 
 /*

libguile/threads.c

@@ -290,8 +290,27 @@ unblock_from_queue (SCM queue)
 /* Getting into and out of guile mode.
  */
 
+#ifdef SCM_HAVE_THREAD_STORAGE_CLASS
+
+/* When thread-local storage (TLS) is available, a pointer to the
+   current-thread object is kept in TLS.  Note that storing the thread-object
+   itself in TLS (rather than a pointer to some malloc'd memory) is not
+   possible since thread objects may live longer than the actual thread they
+   represent.  */
+SCM_THREAD_LOCAL scm_i_thread *scm_i_current_thread = NULL;
+
+# define SET_CURRENT_THREAD(_t)  scm_i_current_thread = (_t)
+
+#else /* !SCM_HAVE_THREAD_STORAGE_CLASS */
+
+/* Key used to retrieve the current thread with `pthread_getspecific ()'.  */
 scm_i_pthread_key_t scm_i_thread_key;
 
+# define SET_CURRENT_THREAD(_t)				\
+  scm_i_pthread_setspecific (scm_i_thread_key, (_t))
+
+#endif /* !SCM_HAVE_THREAD_STORAGE_CLASS */
+
 
 static scm_i_pthread_mutex_t thread_admin_mutex = SCM_I_PTHREAD_MUTEX_INITIALIZER;
 static scm_i_thread *all_threads = NULL;
@@ -357,7 +376,7 @@ guilify_self_1 (SCM_STACKITEM *base)
   t->exited = 0;
   t->guile_mode = 0;
 
-  scm_i_pthread_setspecific (scm_i_thread_key, t);
+  SET_CURRENT_THREAD (t);
 
   scm_i_pthread_mutex_lock (&thread_admin_mutex);
   t->next_thread = all_threads;
@@ -475,7 +494,7 @@ on_thread_exit (void *v)
       t->held_mutex = NULL;
     }
 
-  scm_i_pthread_setspecific (scm_i_thread_key, v);
+  SET_CURRENT_THREAD (v);
 
   /* Ensure the signal handling thread has been launched, because we might be
      shutting it down.  */
@@ -514,9 +533,11 @@ on_thread_exit (void *v)
 
   scm_i_pthread_mutex_unlock (&thread_admin_mutex);
 
-  scm_i_pthread_setspecific (scm_i_thread_key, NULL);
+  SET_CURRENT_THREAD (NULL);
 }
 
+#ifndef SCM_HAVE_THREAD_STORAGE_CLASS
+
 static scm_i_pthread_once_t init_thread_key_once = SCM_I_PTHREAD_ONCE_INIT;
 
 static void
@@ -525,6 +546,8 @@ init_thread_key (void)
   scm_i_pthread_key_create (&scm_i_thread_key, NULL);
 }
 
+#endif
+
 /* Perform any initializations necessary to bring the current thread
    into guile mode, initializing Guile itself, if necessary.
 
@@ -542,9 +565,12 @@ scm_i_init_thread_for_guile (SCM_STACKITEM *base, SCM parent)
 {
   scm_i_thread *t;
 
+#ifndef SCM_HAVE_THREAD_STORAGE_CLASS
   scm_i_pthread_once (&init_thread_key_once, init_thread_key);
+#endif
 
-  if ((t = SCM_I_CURRENT_THREAD) == NULL)
+  t = SCM_I_CURRENT_THREAD;
+  if (t == NULL)
     {
       /* This thread has not been guilified yet.
        */

libguile/threads.h

@@ -194,9 +194,18 @@ SCM_API void scm_dynwind_critical_section (SCM mutex);
 
 #ifdef BUILDING_LIBGUILE
 
-# define SCM_I_CURRENT_THREAD						\
-  ((scm_i_thread *) scm_i_pthread_getspecific (scm_i_thread_key))
-SCM_API scm_i_pthread_key_t scm_i_thread_key;
+# ifdef SCM_HAVE_THREAD_STORAGE_CLASS
+
+SCM_INTERNAL SCM_THREAD_LOCAL scm_i_thread *scm_i_current_thread;
+#  define SCM_I_CURRENT_THREAD (scm_i_current_thread)
+
+# else /* !SCM_HAVE_THREAD_STORAGE_CLASS */
+
+SCM_INTERNAL scm_i_pthread_key_t scm_i_thread_key;
+#  define SCM_I_CURRENT_THREAD						\
+    ((scm_i_thread *) scm_i_pthread_getspecific (scm_i_thread_key))
+
+# endif /* !SCM_HAVE_THREAD_STORAGE_CLASS */
 
 # define scm_i_dynwinds()         (SCM_I_CURRENT_THREAD->dynwinds)
 # define scm_i_set_dynwinds(w)    (SCM_I_CURRENT_THREAD->dynwinds = (w))