configure.ac (--enable-linux-futex): Add new configure option.

libstdc++-v3/
	* configure.ac (--enable-linux-futex): Add new configure option.
	(HAVE_LINUX_FUTEX): New AC_DEFINE.
	* Makefile.in: Rebuilt.
	* aclocal.m4: Rebuilt.
	* configure: Rebuilt.
	* config.h.in: Rebuilt.
	* config/cpu/generic/cxxabi_tweaks.h (_GLIBCXX_GUARD_BIT,
	_GLIBCXX_GUARD_PENDING_BIT, _GLIBCXX_GUARD_WAITING_BIT): Define.
	* config/cpu/arm/cxxabi_tweaks.h (_GLIBCXX_GUARD_BIT,
	_GLIBCXX_GUARD_PENDING_BIT, _GLIBCXX_GUARD_WAITING_BIT): Define.
	* libsupc++/guard.cc: Include climits and syscall.h.
	(_GLIBCXX_USE_FUTEX): Define if futex syscall and atomic builtins
	are supported.
	(_GLIBCXX_FUTEX_WAIT, _GLIBCXX_FUTEX_WAKE): Likewise.
	(__guard_test_bit): New static inline.
	(__cxa_guard_acquire, __cxa_guard_release, __cxa_guard_abort): Use
	atomic builtins and futex syscall if _GLIBCXX_USE_FUTEX.
config/
	* futex.m4: New file.
libgomp/
	* configure.ac: Move futex checking into ../config/futex.m4.
	* configure: Rebuilt.
	* aclocal.m4: Rebuilt.
	* Makefile.in: Rebuilt.

	* configure.tgt: Rename have_tls to gcc_cv_have_tls to match
	2007-10-15 ../config/tls.m4 change.

From-SVN: r131399

9 files changed, 369 insertions, 21 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index e99e0500360..a5b54c46608 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,23 @@
+2008-01-08  Jakub Jelinek  <jakub@redhat.com>
+
+	* configure.ac (--enable-linux-futex): Add new configure option.
+	(HAVE_LINUX_FUTEX): New AC_DEFINE.
+	* Makefile.in: Rebuilt.
+	* aclocal.m4: Rebuilt.
+	* configure: Rebuilt.
+	* config.h.in: Rebuilt.
+	* config/cpu/generic/cxxabi_tweaks.h (_GLIBCXX_GUARD_BIT,
+	_GLIBCXX_GUARD_PENDING_BIT, _GLIBCXX_GUARD_WAITING_BIT): Define.
+	* config/cpu/arm/cxxabi_tweaks.h (_GLIBCXX_GUARD_BIT,
+	_GLIBCXX_GUARD_PENDING_BIT, _GLIBCXX_GUARD_WAITING_BIT): Define.
+	* libsupc++/guard.cc: Include climits and syscall.h.
+	(_GLIBCXX_USE_FUTEX): Define if futex syscall and atomic builtins
+	are supported.
+	(_GLIBCXX_FUTEX_WAIT, _GLIBCXX_FUTEX_WAKE): Likewise.
+	(__guard_test_bit): New static inline.
+	(__cxa_guard_acquire, __cxa_guard_release, __cxa_guard_abort): Use
+	atomic builtins and futex syscall if _GLIBCXX_USE_FUTEX.
+
 2008-01-07  Paolo Carlini  <pcarlini@suse.de>
 
 	PR libstdc++/34680
diff --git a/libstdc++-v3/Makefile.in b/libstdc++-v3/Makefile.in
index c3d4cc592e0..75241af5f5d 100644
--- a/libstdc++-v3/Makefile.in
+++ b/libstdc++-v3/Makefile.in
@@ -54,6 +54,7 @@ am__aclocal_m4_deps = $(top_srcdir)/../config/enable.m4 \
 	$(top_srcdir)/../config/multi.m4 \
 	$(top_srcdir)/../config/no-executables.m4 \
 	$(top_srcdir)/../config/unwind_ipinfo.m4 \
+	$(top_srcdir)/../config/futex.m4 \
 	$(top_srcdir)/../libtool.m4 $(top_srcdir)/../ltoptions.m4 \
 	$(top_srcdir)/../ltsugar.m4 $(top_srcdir)/../ltversion.m4 \
 	$(top_srcdir)/crossconfig.m4 $(top_srcdir)/linkage.m4 \
diff --git a/libstdc++-v3/aclocal.m4 b/libstdc++-v3/aclocal.m4
index 66a69892520..02b6b899cd5 100644
--- a/libstdc++-v3/aclocal.m4
+++ b/libstdc++-v3/aclocal.m4
@@ -589,6 +589,7 @@ m4_include([../config/lib-prefix.m4])
 m4_include([../config/multi.m4])
 m4_include([../config/no-executables.m4])
 m4_include([../config/unwind_ipinfo.m4])
+m4_include([../config/futex.m4])
 m4_include([../libtool.m4])
 m4_include([../ltoptions.m4])
 m4_include([../ltsugar.m4])
diff --git a/libstdc++-v3/config.h.in b/libstdc++-v3/config.h.in
index 1c7bcd3f9cc..f25ab541dff 100644
--- a/libstdc++-v3/config.h.in
+++ b/libstdc++-v3/config.h.in
@@ -232,6 +232,9 @@
 /* Only used in build directory testsuite_hooks.h. */
 #undef HAVE_LIMIT_VMEM
 
+/* Define if futex syscall is available. */
+#undef HAVE_LINUX_FUTEX
+
 /* Define to 1 if you have the <locale.h> header file. */
 #undef HAVE_LOCALE_H
 
diff --git a/libstdc++-v3/config/cpu/arm/cxxabi_tweaks.h b/libstdc++-v3/config/cpu/arm/cxxabi_tweaks.h
index e56c20067ca..b6b88e41431 100644
--- a/libstdc++-v3/config/cpu/arm/cxxabi_tweaks.h
+++ b/libstdc++-v3/config/cpu/arm/cxxabi_tweaks.h
@@ -1,6 +1,6 @@
 // Control various target specific ABI tweaks.  ARM version.
 
-// Copyright (C) 2004, 2006 Free Software Foundation, Inc.
+// Copyright (C) 2004, 2006, 2008 Free Software Foundation, Inc.
 //
 // This file is part of the GNU ISO C++ Library.  This library is free
 // software; you can redistribute it and/or modify it under the
@@ -46,6 +46,9 @@ namespace __cxxabiv1
   // guard variable.  */
 #define _GLIBCXX_GUARD_TEST(x) ((*(x) & 1) != 0)
 #define _GLIBCXX_GUARD_SET(x) *(x) = 1
+#define _GLIBCXX_GUARD_BIT 1
+#define _GLIBCXX_GUARD_PENDING_BIT __guard_test_bit (1, 1)
+#define _GLIBCXX_GUARD_WAITING_BIT __guard_test_bit (2, 1)
   typedef int __guard;
 
   // We also want the element size in array cookies.
@@ -62,6 +65,9 @@ namespace __cxxabiv1
   // The generic ABI uses the first byte of a 64-bit guard variable.
 #define _GLIBCXX_GUARD_TEST(x) (*(char *) (x) != 0)
 #define _GLIBCXX_GUARD_SET(x) *(char *) (x) = 1
+#define _GLIBCXX_GUARD_BIT __guard_test_bit (0, 1)
+#define _GLIBCXX_GUARD_PENDING_BIT __guard_test_bit (1, 1)
+#define _GLIBCXX_GUARD_WAITING_BIT __guard_test_bit (2, 1)
   __extension__ typedef int __guard __attribute__((mode (__DI__)));
 
   // __cxa_vec_ctor has void return type.
diff --git a/libstdc++-v3/config/cpu/generic/cxxabi_tweaks.h b/libstdc++-v3/config/cpu/generic/cxxabi_tweaks.h
index 95fd3066c04..2859e83c9be 100644
--- a/libstdc++-v3/config/cpu/generic/cxxabi_tweaks.h
+++ b/libstdc++-v3/config/cpu/generic/cxxabi_tweaks.h
@@ -1,6 +1,6 @@
 // Control various target specific ABI tweaks.  Generic version.
 
-// Copyright (C) 2004, 2006 Free Software Foundation, Inc.
+// Copyright (C) 2004, 2006, 2008 Free Software Foundation, Inc.
 //
 // This file is part of the GNU ISO C++ Library.  This library is free
 // software; you can redistribute it and/or modify it under the
@@ -44,6 +44,9 @@ namespace __cxxabiv1
   // The generic ABI uses the first byte of a 64-bit guard variable.
 #define _GLIBCXX_GUARD_TEST(x) (*(char *) (x) != 0)
 #define _GLIBCXX_GUARD_SET(x) *(char *) (x) = 1
+#define _GLIBCXX_GUARD_BIT __guard_test_bit (0, 1)
+#define _GLIBCXX_GUARD_PENDING_BIT __guard_test_bit (1, 1)
+#define _GLIBCXX_GUARD_WAITING_BIT __guard_test_bit (2, 1)
   __extension__ typedef int __guard __attribute__((mode (__DI__)));
 
   // __cxa_vec_ctor has void return type.
diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index 5e57fd651c6..403b8183bbe 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -1053,6 +1053,8 @@ Optional Features:
                           memory [default=no]
   --enable-tls            Use thread-local storage [default=yes]
   --disable-rpath         do not hardcode runtime library paths
+  --enable-linux-futex    use the Linux futex system call
+                          [default=default]
   --enable-symvers=STYLE  enables symbol versioning of the shared library
                           [default=yes]
   --enable-visibility     enables visibility safe usage [default=yes]
@@ -114116,8 +114118,222 @@ _ACEOF
 #define HAVE_GETIPINFO 1
 _ACEOF
 
+fi
+
+ # Check whether --enable-linux-futex or --disable-linux-futex was given.
+if test "${enable_linux_futex+set}" = set; then
+  enableval="$enable_linux_futex"
+
+      case "$enableval" in
+       yes|no|default) ;;
+       *) { { echo "$as_me:$LINENO: error: Unknown argument to enable/disable linux-futex" >&5
+echo "$as_me: error: Unknown argument to enable/disable linux-futex" >&2;}
+   { (exit 1); exit 1; }; } ;;
+                          esac
+
+else
+  enable_linux_futex=default
+fi;
+
+case "$target" in
+  *-linux*)
+    case "$enable_linux_futex" in
+      default)
+	# If headers don't have gettid/futex syscalls definition, then
+	# default to no, otherwise there will be compile time failures.
+	# Otherwise, default to yes.  If we don't detect we are
+	# compiled/linked against NPTL and not cross-compiling, check
+	# if programs are run by default against NPTL and if not, issue
+	# a warning.
+	enable_linux_futex=no
+	if test x$gcc_no_link = xyes; then
+  { { echo "$as_me:$LINENO: error: Link tests are not allowed after GCC_NO_EXECUTABLES." >&5
+echo "$as_me: error: Link tests are not allowed after GCC_NO_EXECUTABLES." >&2;}
+   { (exit 1); exit 1; }; }
+fi
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+#include <sys/syscall.h>
+	   int lk;
+int
+main ()
+{
+syscall (SYS_gettid); syscall (SYS_futex, &lk, 0, 0, 0);
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext conftest$ac_exeext
+if { (eval echo "$as_me:$LINENO: \"$ac_link\"") >&5
+  (eval $ac_link) 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } &&
+	 { ac_try='test -z "$ac_c_werror_flag"
+			 || test ! -s conftest.err'
+  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; } &&
+	 { ac_try='test -s conftest$ac_exeext'
+  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; }; then
+  save_LIBS="$LIBS"
+	   LIBS="-lpthread $LIBS"
+	   if test x$gcc_no_link = xyes; then
+  { { echo "$as_me:$LINENO: error: Link tests are not allowed after GCC_NO_EXECUTABLES." >&5
+echo "$as_me: error: Link tests are not allowed after GCC_NO_EXECUTABLES." >&2;}
+   { (exit 1); exit 1; }; }
+fi
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+#ifndef _GNU_SOURCE
+	     #define _GNU_SOURCE 1
+	     #endif
+	     #include <pthread.h>
+	     pthread_t th; void *status;
+int
+main ()
+{
+pthread_tryjoin_np (th, &status);
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext conftest$ac_exeext
+if { (eval echo "$as_me:$LINENO: \"$ac_link\"") >&5
+  (eval $ac_link) 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } &&
+	 { ac_try='test -z "$ac_c_werror_flag"
+			 || test ! -s conftest.err'
+  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; } &&
+	 { ac_try='test -s conftest$ac_exeext'
+  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; }; then
+  enable_linux_futex=yes
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
 
+if test x$cross_compiling = xno; then
+	       if getconf GNU_LIBPTHREAD_VERSION 2>/dev/null \
+		  | LC_ALL=C grep -i NPTL > /dev/null 2>/dev/null; then :; else
+		 { echo "$as_me:$LINENO: WARNING: The kernel might not support futex or gettid syscalls.
+If so, please configure with --disable-linux-futex" >&5
+echo "$as_me: WARNING: The kernel might not support futex or gettid syscalls.
+If so, please configure with --disable-linux-futex" >&2;}
+	       fi
+	     fi
+	     enable_linux_futex=yes
 fi
+rm -f conftest.err conftest.$ac_objext \
+      conftest$ac_exeext conftest.$ac_ext
+	   LIBS="$save_LIBS"
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+fi
+rm -f conftest.err conftest.$ac_objext \
+      conftest$ac_exeext conftest.$ac_ext
+	;;
+        yes)
+	if test x$gcc_no_link = xyes; then
+  { { echo "$as_me:$LINENO: error: Link tests are not allowed after GCC_NO_EXECUTABLES." >&5
+echo "$as_me: error: Link tests are not allowed after GCC_NO_EXECUTABLES." >&2;}
+   { (exit 1); exit 1; }; }
+fi
+cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+#include <sys/syscall.h>
+	   int lk;
+int
+main ()
+{
+syscall (SYS_gettid); syscall (SYS_futex, &lk, 0, 0, 0);
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext conftest$ac_exeext
+if { (eval echo "$as_me:$LINENO: \"$ac_link\"") >&5
+  (eval $ac_link) 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } &&
+	 { ac_try='test -z "$ac_c_werror_flag"
+			 || test ! -s conftest.err'
+  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; } &&
+	 { ac_try='test -s conftest$ac_exeext'
+  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; }; then
+  :
+else
+  echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+{ { echo "$as_me:$LINENO: error: SYS_gettid and SYS_futex required for --enable-linux-futex" >&5
+echo "$as_me: error: SYS_gettid and SYS_futex required for --enable-linux-futex" >&2;}
+   { (exit 1); exit 1; }; }
+fi
+rm -f conftest.err conftest.$ac_objext \
+      conftest$ac_exeext conftest.$ac_ext
+	;;
+    esac
+    ;;
+  *)
+    enable_linux_futex=no
+    ;;
+esac
+if test x$enable_linux_futex = xyes; then
+
+cat >>confdefs.h <<\_ACEOF
+#define HAVE_LINUX_FUTEX 1
+_ACEOF
+
+fi
+
 
 # This depends on GLIBCXX CHECK_LINKER_FEATURES, but without it assumes no.
 
diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac
index 72471f15795..3411b97afc8 100644
--- a/libstdc++-v3/configure.ac
+++ b/libstdc++-v3/configure.ac
@@ -295,9 +295,10 @@ else
 
   # Assume we have _Unwind_GetIPInfo for cross-compiles.
   AC_DEFINE(HAVE_GETIPINFO)
-
 fi
 
+GCC_LINUX_FUTEX([AC_DEFINE(HAVE_LINUX_FUTEX, 1, [Define if futex syscall is available.])])
+
 # This depends on GLIBCXX CHECK_LINKER_FEATURES, but without it assumes no.
 GLIBCXX_ENABLE_SYMVERS([yes])
 GLIBCXX_ENABLE_VISIBILITY([yes])
diff --git a/libstdc++-v3/libsupc++/guard.cc b/libstdc++-v3/libsupc++/guard.cc
index 6cf83b1c1f4..e4665773ca2 100644
--- a/libstdc++-v3/libsupc++/guard.cc
+++ b/libstdc++-v3/libsupc++/guard.cc
@@ -35,12 +35,21 @@
 #include <new>
 #include <ext/atomicity.h>
 #include <ext/concurrence.h>
+#if defined(__GTHREADS) && defined(__GTHREAD_HAS_COND) \
+    && defined(_GLIBCXX_ATOMIC_BUILTINS) && defined(_GLIBCXX_HAVE_LINUX_FUTEX)
+# include <climits>
+# include <syscall.h>
+# define _GLIBCXX_USE_FUTEX
+# define _GLIBCXX_FUTEX_WAIT 0
+# define _GLIBCXX_FUTEX_WAKE 1
+#endif
 
 // The IA64/generic ABI uses the first byte of the guard variable.
 // The ARM EABI uses the least significant bit.
 
 // Thread-safe static local initialization support.
 #ifdef __GTHREADS
+# ifndef _GLIBCXX_USE_FUTEX
 namespace
 {
   // A single mutex controlling all static initializations.
@@ -75,8 +84,9 @@ namespace
     }
   };
 }
+# endif
 
-#ifdef __GTHREAD_HAS_COND
+# if defined(__GTHREAD_HAS_COND) && !defined(_GLIBCXX_USE_FUTEX)
 namespace
 {
   // A single conditional variable controlling all static initializations.
@@ -98,9 +108,9 @@ namespace
     return *static_cond;
   }
 }
-#endif
+# endif
 
-#ifndef _GLIBCXX_GUARD_TEST_AND_ACQUIRE
+# ifndef _GLIBCXX_GUARD_TEST_AND_ACQUIRE
 inline bool
 __test_and_acquire (__cxxabiv1::__guard *g)
 {
@@ -108,24 +118,24 @@ __test_and_acquire (__cxxabiv1::__guard *g)
   _GLIBCXX_READ_MEM_BARRIER;
   return b;
 }
-#define _GLIBCXX_GUARD_TEST_AND_ACQUIRE(G) __test_and_acquire (G)
-#endif
+#  define _GLIBCXX_GUARD_TEST_AND_ACQUIRE(G) __test_and_acquire (G)
+# endif
 
-#ifndef _GLIBCXX_GUARD_SET_AND_RELEASE
+# ifndef _GLIBCXX_GUARD_SET_AND_RELEASE
 inline void
 __set_and_release (__cxxabiv1::__guard *g)
 {
   _GLIBCXX_WRITE_MEM_BARRIER;
   _GLIBCXX_GUARD_SET (g);
 }
-#define _GLIBCXX_GUARD_SET_AND_RELEASE(G) __set_and_release (G)
-#endif
+#  define _GLIBCXX_GUARD_SET_AND_RELEASE(G) __set_and_release (G)
+# endif
 
 #else /* !__GTHREADS */
 
-#undef _GLIBCXX_GUARD_TEST_AND_ACQUIRE
-#undef _GLIBCXX_GUARD_SET_AND_RELEASE
-#define _GLIBCXX_GUARD_SET_AND_RELEASE(G) _GLIBCXX_GUARD_SET (G)
+# undef _GLIBCXX_GUARD_TEST_AND_ACQUIRE
+# undef _GLIBCXX_GUARD_SET_AND_RELEASE
+# define _GLIBCXX_GUARD_SET_AND_RELEASE(G) _GLIBCXX_GUARD_SET (G)
 
 #endif /* __GTHREADS */
 
@@ -176,8 +186,35 @@ namespace __gnu_cxx
 // headers define a symbol __GTHREAD_HAS_COND for platforms that support POSIX
 // like conditional variables. For platforms that do not support conditional
 // variables, we need to fall back to the old code.
+
+// If _GLIBCXX_USE_FUTEX, no global mutex or conditional variable is used,
+// only atomic operations are used together with futex syscall.
+// Valid values of the first integer in guard are:
+// 0				  No thread encountered the guarded init
+//				  yet or it has been aborted.
+// _GLIBCXX_GUARD_BIT		  The guarded static var has been successfully
+//				  initialized.
+// _GLIBCXX_GUARD_PENDING_BIT	  The guarded static var is being initialized
+//				  and no other thread is waiting for its
+//				  initialization.
+// (_GLIBCXX_GUARD_PENDING_BIT    The guarded static var is being initialized
+//  | _GLIBCXX_GUARD_WAITING_BIT) and some other threads are waiting until
+//				  it is initialized.
+
 namespace __cxxabiv1 
 {
+#ifdef _GLIBCXX_USE_FUTEX
+  namespace
+  {
+    static inline int __guard_test_bit (const int __byte, const int __val)
+    {
+      union { int __i; char __c[sizeof (int)]; } __u = { 0 };
+      __u.__c[__byte] = __val;
+      return __u.__i;
+    }
+  }
+#endif
+
   static inline int
   init_in_progress_flag(__guard* g)
   { return ((char *)g)[1]; }
@@ -207,7 +244,7 @@ namespace __cxxabiv1
       return 0;
 
     if (init_in_progress_flag(g))
-	throw_recursive_init_exception();
+      throw_recursive_init_exception();
 
     set_init_in_progress_flag(g, 1);
     return 1;
@@ -223,14 +260,46 @@ namespace __cxxabiv1
     if (_GLIBCXX_GUARD_TEST_AND_ACQUIRE (g))
       return 0;
 
+# ifdef _GLIBCXX_USE_FUTEX
+    // If __sync_* and futex syscall are supported, don't use any global
+    // mutex.
+    if (__gthread_active_p ())
+      {
+	int *gi = (int *) (void *) g;
+	const int guard_bit = _GLIBCXX_GUARD_BIT;
+	const int pending_bit = _GLIBCXX_GUARD_PENDING_BIT;
+	const int waiting_bit = _GLIBCXX_GUARD_WAITING_BIT;
+
+	while (1)
+	  {
+	    int old = __sync_val_compare_and_swap (gi, 0, pending_bit);
+	    if (old == 0)
+	      return 1;	// This thread should do the initialization.
+
+	    if (old == guard_bit)
+	      return 0;	// Already initialized.
+
+	    if (old == pending_bit)
+	      {
+		int newv = old | waiting_bit;
+		if (__sync_val_compare_and_swap (gi, old, newv) != old)
+		  continue;
+
+		old = newv;
+	      }
+
+	    syscall (SYS_futex, gi, _GLIBCXX_FUTEX_WAIT, old, 0);
+	  }
+      }
+# else
     if (__gthread_active_p ())
       {
 	mutex_wrapper mw;
 
 	while (1)	// When this loop is executing, mutex is locked.
 	  {
-#ifdef __GTHREAD_HAS_COND
-	    // The static is allready initialized.
+#  ifdef __GTHREAD_HAS_COND
+	    // The static is already initialized.
 	    if (_GLIBCXX_GUARD_TEST(g))
 	      return 0;	// The mutex will be unlocked via wrapper
 
@@ -247,7 +316,7 @@ namespace __cxxabiv1
 		set_init_in_progress_flag(g, 1);
 		return 1; // The mutex will be unlocked via wrapper.
 	      }
-#else
+#  else
 	    // This provides compatibility with older systems not supporting
 	    // POSIX like conditional variables.
 	    if (acquire(g))
@@ -256,9 +325,10 @@ namespace __cxxabiv1
 		return 1; // The mutex still locked.
 	      }
 	    return 0; // The mutex will be unlocked via wrapper.
-#endif
+#  endif
 	  }
       }
+# endif
 #endif
 
     return acquire (g);
@@ -267,7 +337,20 @@ namespace __cxxabiv1
   extern "C"
   void __cxa_guard_abort (__guard *g)
   {
-#ifdef __GTHREAD_HAS_COND
+#ifdef _GLIBCXX_USE_FUTEX
+    // If __sync_* and futex syscall are supported, don't use any global
+    // mutex.
+    if (__gthread_active_p ())
+      {
+	int *gi = (int *) (void *) g;
+	const int waiting_bit = _GLIBCXX_GUARD_WAITING_BIT;
+	int old = __sync_lock_test_and_set (gi, 0);
+
+	if ((old & waiting_bit) != 0)
+	  syscall (SYS_futex, gi, _GLIBCXX_FUTEX_WAKE, INT_MAX);
+	return;
+      }
+#elif defined(__GTHREAD_HAS_COND)
     if (__gthread_active_p())
       {	
 	mutex_wrapper mw;
@@ -293,7 +376,21 @@ namespace __cxxabiv1
   extern "C"
   void __cxa_guard_release (__guard *g)
   {
-#ifdef __GTHREAD_HAS_COND
+#ifdef _GLIBCXX_USE_FUTEX
+    // If __sync_* and futex syscall are supported, don't use any global
+    // mutex.
+    if (__gthread_active_p ())
+      {
+	int *gi = (int *) (void *) g;
+	const int guard_bit = _GLIBCXX_GUARD_BIT;
+	const int waiting_bit = _GLIBCXX_GUARD_WAITING_BIT;
+	int old = __sync_lock_test_and_set (gi, guard_bit);
+
+	if ((old & waiting_bit) != 0)
+	  syscall (SYS_futex, gi, _GLIBCXX_FUTEX_WAKE, INT_MAX);
+	return;
+      }
+#elif defined(__GTHREAD_HAS_COND)
     if (__gthread_active_p())
       {
 	mutex_wrapper mw;