pthread_once implementation for nptl on Alpha.

sysdeps/unix/sysv/linux/alpha/nptl/pthread_once.c

@@ -0,0 +1,96 @@
+/* Copyright (C) 2003 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include "pthreadP.h"
+#include <lowlevellock.h>
+
+
+unsigned long int __fork_generation attribute_hidden;
+
+static void
+clear_once_control (void *arg)
+{
+  pthread_once_t *once_control = (pthread_once_t *) arg;
+
+  *once_control = 0;
+  lll_futex_wake (once_control, INT_MAX);
+}
+
+int
+__pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
+{
+  for (;;)
+    {
+      int oldval;
+      int newval;
+      int tmp;
+
+      /* Pseudo code:
+	 newval = __fork_generation | 1;
+	 oldval = *once_control;
+	 if ((oldval & 2) == 0)
+	   *once_control = newval;
+	 Do this atomically.
+      */
+      newval = __fork_generation | 1;
+      __asm __volatile (
+		"1:	ldl_l	%0, %2\n"
+		"	and	%0, 2, %1\n"
+		"	bne	%1, 2f\n"
+		"	mov	%3, %1\n"
+		"	stl_c	%1, %2\n"
+		"	beq	%1, 1b\n"
+		"2:	mb"
+		: "=&r" (oldval), "=&r" (tmp), "=m" (*once_control)
+		: "r" (newval), "m" (*once_control));
+
+      /* Check if the initializer has already been done.  */
+      if ((oldval & 2) != 0)
+	return 0;
+
+      /* Check if another thread already runs the initializer.	*/
+      if ((oldval & 1) == 0)
+	break;
+
+      /* Check whether the initializer execution was interrupted by a fork.  */
+      if (oldval != newval)
+	break;
+
+      /* Same generation, some other thread was faster. Wait.  */
+      lll_futex_wait (once_control, oldval);
+    }
+
+  /* This thread is the first here.  Do the initialization.
+     Register a cleanup handler so that in case the thread gets
+     interrupted the initialization can be restarted.  */
+  pthread_cleanup_push (clear_once_control, once_control);
+
+  init_routine ();
+
+  pthread_cleanup_pop (0);
+
+  /* Add one to *once_control to take the bottom 2 bits from 01 to 10.  */
+  atomic_exchange_and_add (once_control, 1);
+
+  /* Wake up all other threads.  */
+  lll_futex_wake (once_control, INT_MAX);
+
+  return 0;
+}
+weak_alias (__pthread_once, pthread_once)
+strong_alias (__pthread_once, __pthread_once_internal)