[1/8] nptl: Add C11 threads thrd_* functions

Message ID 1506112024-22601-2-git-send-email-adhemerval.zanella@linaro.org
State New
Headers show
Series
  • Add support for ISO C threads.h
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Commit Message

Adhemerval Zanella Sept. 22, 2017, 8:26 p.m.
This patch adds the thrd_* definitions from C11 threads (ISO/IEC 9899:2011),
more specifically thrd_create, thrd_curent, rhd_detach, thrd_equal,
thrd_exit, thrd_join, thrd_sleep, thrd_yield, and required types.

Mostly of the definitions are composed based on POSIX conterparts, such as
thrd_t (using pthread_t).  For thrd_* function internally direct
POSIX pthread call are used with the exceptions:

  1. thrd_start uses pthread_create internal implementation, but changes
     how to actually calls the start routine.  This is due the difference
     in signature between POSIX and C11, where former return a 'void *'
     and latter 'int'.
     To avoid calling convention issues due 'void *' to int cast, routines
     from C11 threads are started slight different than default pthread one.
     Explicit cast to expected return are used internally on pthread_create
     and the result is stored back to void also with an explicit cast.

  2. thrd_sleep uses nanosleep internal direct syscall to avoid clobbering
     errno, to handle expected standard return codes, and to avoid making
     the call a POSIX cancellation entrypoint.

  3. thrd_yield also uses internal direct syscall to avoid errno clobbering.

Checked with a build for all major ABI (aarch64-linux-gnu, alpha-linux-gnu,
arm-linux-gnueabi, i386-linux-gnu, ia64-linux-gnu, m68k-linux-gnu,
microblaze-linux-gnu [1], mips{64}-linux-gnu, nios2-linux-gnu,
powerpc{64le}-linux-gnu, s390{x}-linux-gnu, sparc{64}-linux-gnu,
tile{pro,gx}-linux-gnu, and x86_64-linux-gnu).

Also ran a full check on aarch64-linux-gnu, x86_64-linux-gnu, i686-linux-gnu,
arm-linux-gnueabhf, and powerpc64le-linux-gnu.

	* conform/Makefile (conformtest-headers-ISO11): Add threads.h.
	(linknamespace-libs-ISO11): Add libpthread.a.
	* conform/data/threads.h-data: New file: add C11 thrd_* types and
	functions.
	* include/stdc-predef.h (__STDC_NO_THREADS__): Remove definition.
	* nptl/Makefile (headers): Add threads.h.
	(libpthread-routines): Add new C11 thread thrd_create, thrd_current,
	thrd_detach, thrd_equal, thrd_exit, thrd_join, thrd_sleep, and
	thrd_yield.
	* nptl/Versions (libpthread) [GLIBC_2.27]): Add new C11 thread
	thrd_create, thrd_current, thrd_detach, thrd_equal, thrd_exit,
	thrd_join, thrd_sleep, and thrd_yield symbols.
	* nptl/descr.h (struct pthread): Add c11 field.
	* nptl/pthreadP.h (ATTR_C11_THREAD): New define.
	* nptl/pthread_create.c (START_THREAD_DEFN): Call C11 thread start
	routine with expected function prototype.
	(__pthread_create_2_1): Add C11 threads check based on attribute
	value.
	* nptl/thrd_create.c: New file.
	* nptl/thrd_current.c: Likewise.
	* nptl/thrd_detach.c: Likewise.
	* nptl/thrd_equal.c: Likewise.
	* nptl/thrd_exit.c: Likewise.
	* nptl/thrd_join.c: Likewise.
	* nptl/thrd_priv.h: Likewise.
	* nptl/thrd_sleep.c: Likewise.
	* nptl/thrd_yield.c: Likewise.
	* sysdeps/nptl/threads.h: Likewise.
---
 ChangeLog                   | 31 ++++++++++++++++
 conform/Makefile            |  7 ++--
 conform/data/threads.h-data | 23 ++++++++++++
 include/stdc-predef.h       |  3 --
 nptl/Makefile               |  6 ++-
 nptl/Versions               |  6 +++
 nptl/descr.h                |  2 +
 nptl/pthreadP.h             |  3 ++
 nptl/pthread_create.c       | 18 ++++++++-
 nptl/thrd_create.c          | 32 ++++++++++++++++
 nptl/thrd_current.c         | 26 +++++++++++++
 nptl/thrd_detach.c          | 30 +++++++++++++++
 nptl/thrd_equal.c           | 26 +++++++++++++
 nptl/thrd_exit.c            | 27 ++++++++++++++
 nptl/thrd_join.c            | 32 ++++++++++++++++
 nptl/thrd_priv.h            | 46 +++++++++++++++++++++++
 nptl/thrd_sleep.c           | 41 +++++++++++++++++++++
 nptl/thrd_yield.c           | 29 +++++++++++++++
 sysdeps/nptl/threads.h      | 90 +++++++++++++++++++++++++++++++++++++++++++++
 19 files changed, 468 insertions(+), 10 deletions(-)
 create mode 100644 conform/data/threads.h-data
 create mode 100644 nptl/thrd_create.c
 create mode 100644 nptl/thrd_current.c
 create mode 100644 nptl/thrd_detach.c
 create mode 100644 nptl/thrd_equal.c
 create mode 100644 nptl/thrd_exit.c
 create mode 100644 nptl/thrd_join.c
 create mode 100644 nptl/thrd_priv.h
 create mode 100644 nptl/thrd_sleep.c
 create mode 100644 nptl/thrd_yield.c
 create mode 100644 sysdeps/nptl/threads.h

-- 
2.7.4

Patch

diff --git a/conform/Makefile b/conform/Makefile
index 3883a4b..9e00d41 100644
--- a/conform/Makefile
+++ b/conform/Makefile
@@ -34,9 +34,9 @@  conformtest-headers-ISO := assert.h ctype.h errno.h float.h limits.h locale.h \
 conformtest-headers-ISO99 := $(conformtest-headers-ISO) complex.h fenv.h \
 			     inttypes.h iso646.h stdbool.h stdint.h tgmath.h \
 			     wchar.h wctype.h
-# Missing ISO11 expectations for: stdatomic.h threads.h.
+# Missing ISO11 expectations for: stdatomic.h
 conformtest-headers-ISO11 := $(conformtest-headers-ISO99) stdalign.h \
-			     stdnoreturn.h uchar.h
+			     stdnoreturn.h threads.h uchar.h
 conformtest-headers-POSIX := $(conformtest-headers-ISO) aio.h dirent.h \
 			     fcntl.h fnmatch.h glob.h grp.h mqueue.h \
 			     pthread.h pwd.h regex.h sched.h semaphore.h \
@@ -197,7 +197,8 @@  linknamespace-libs-xsi = $(linknamespace-libs-posix) \
 			 $(common-objpfx)crypt/libcrypt.a
 linknamespace-libs-ISO = $(linknamespace-libs-isoc)
 linknamespace-libs-ISO99 = $(linknamespace-libs-isoc)
-linknamespace-libs-ISO11 = $(linknamespace-libs-isoc)
+linknamespace-libs-ISO11 = $(linknamespace-libs-isoc) \
+			   $(common-objpfx)nptl/libpthread.a
 linknamespace-libs-XPG4 = $(linknamespace-libs-isoc) \
 			  $(common-objpfx)crypt/libcrypt.a
 linknamespace-libs-XPG42 = $(linknamespace-libs-XPG4)
diff --git a/conform/data/threads.h-data b/conform/data/threads.h-data
new file mode 100644
index 0000000..bc2d857
--- /dev/null
+++ b/conform/data/threads.h-data
@@ -0,0 +1,23 @@ 
+#if defined ISO11
+
+constant thrd_success
+constant thrd_busy
+constant thrd_error
+constant thrd_nomem
+constant thrd_timedout
+
+type thrd_t
+type thrd_start_t
+
+function int thrd_create (thrd_t*, thrd_start_t, void*)
+function int thrd_equal (thrd_t, thrd_t)
+function thrd_t thrd_current (void)
+function int thrd_sleep (const struct timespec*, struct timespec*)
+function void thrd_exit (int)
+function int thrd_detach (thrd_t)
+function int thrd_join (thrd_t, int*)
+function void thrd_yield (void)
+
+#include "time.h-data"
+
+#endif
diff --git a/include/stdc-predef.h b/include/stdc-predef.h
index 74ade90..1cd3d73 100644
--- a/include/stdc-predef.h
+++ b/include/stdc-predef.h
@@ -57,7 +57,4 @@ 
    - 3 additional Zanabazar Square characters */
 #define __STDC_ISO_10646__		201706L
 
-/* We do not support C11 <threads.h>.  */
-#define __STDC_NO_THREADS__		1
-
 #endif
diff --git a/nptl/Makefile b/nptl/Makefile
index d819349..31761a6 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -22,7 +22,7 @@  subdir	:= nptl
 
 include ../Makeconfig
 
-headers := pthread.h semaphore.h bits/semaphore.h
+headers := pthread.h semaphore.h bits/semaphore.h threads.h
 
 extra-libs := libpthread
 extra-libs-others := $(extra-libs)
@@ -138,7 +138,9 @@  libpthread-routines = nptl-init vars events version pt-interp \
 		      pthread_mutex_getprioceiling \
 		      pthread_mutex_setprioceiling \
 		      pthread_setname pthread_getname \
-		      pthread_setattr_default_np pthread_getattr_default_np
+		      pthread_setattr_default_np pthread_getattr_default_np \
+		      thrd_create thrd_current thrd_detach thrd_equal \
+		      thrd_exit thrd_join thrd_sleep thrd_yield
 #		      pthread_setuid pthread_seteuid pthread_setreuid \
 #		      pthread_setresuid \
 #		      pthread_setgid pthread_setegid pthread_setregid \
diff --git a/nptl/Versions b/nptl/Versions
index 0ae5def..a282ceb 100644
--- a/nptl/Versions
+++ b/nptl/Versions
@@ -265,6 +265,12 @@  libpthread {
   GLIBC_2.22 {
   }
 
+  # C11 thread symbols.
+  GLIBC_2.27 {
+    thrd_create; thrd_current; thrd_detach; thrd_equal; thrd_exit; thrd_join;
+    thrd_sleep; thrd_yield;
+  }
+
   GLIBC_PRIVATE {
     __pthread_initialize_minimal;
     __pthread_clock_gettime; __pthread_clock_settime;
diff --git a/nptl/descr.h b/nptl/descr.h
index c5ad0c8..c1ff711 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -371,6 +371,8 @@  struct pthread
      to the function.  */
   void *(*start_routine) (void *);
   void *arg;
+  /* Indicates whether is a C11 thread created by thrd_creat.  */
+  bool c11;
 
   /* Debug state.  */
   td_eventbuf_t eventbuf;
diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
index dbf46b0..ded7547 100644
--- a/nptl/pthreadP.h
+++ b/nptl/pthreadP.h
@@ -173,6 +173,9 @@  enum
 #define __PTHREAD_ONCE_DONE		2
 #define __PTHREAD_ONCE_FORK_GEN_INCR	4
 
+/* Attribute to indicate thread creation was issued from C11 thrd_create.  */
+#define ATTR_C11_THREAD ((void*)(uintptr_t)-1)
+
 
 /* Condition variable definitions.  See __pthread_cond_wait_common.
    Need to be defined here so there is one place from which
diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
index 992331e..bef3042 100644
--- a/nptl/pthread_create.c
+++ b/nptl/pthread_create.c
@@ -460,7 +460,19 @@  START_THREAD_DEFN
       LIBC_PROBE (pthread_start, 3, (pthread_t) pd, pd->start_routine, pd->arg);
 
       /* Run the code the user provided.  */
-      THREAD_SETMEM (pd, result, pd->start_routine (pd->arg));
+      void *ret;
+      if (pd->c11)
+	{
+	  /* The function pointer of the c11 thread start is cast to an incorrect
+	     type on __pthread_create_2_1 call, however it is casted back to correct
+	     one so the call behavior is well-defined (it is assumed that pointers
+	     to void are able to represent all values of int.  */
+	  int (*start)(void*) = (int (*) (void*)) pd->start_routine;
+	  ret = (void*) (intptr_t) start (pd->arg);
+	}
+      else
+	ret = pd->start_routine (pd->arg);
+      THREAD_SETMEM (pd, result, ret);
     }
 
   /* Call destructors for the thread_local TLS variables.  */
@@ -613,7 +625,8 @@  __pthread_create_2_1 (pthread_t *newthread, const pthread_attr_t *attr,
   const struct pthread_attr *iattr = (struct pthread_attr *) attr;
   struct pthread_attr default_attr;
   bool free_cpuset = false;
-  if (iattr == NULL)
+  bool c11 = (attr == ATTR_C11_THREAD);
+  if (iattr == NULL || c11)
     {
       lll_lock (__default_pthread_attr_lock, LLL_PRIVATE);
       default_attr = __default_pthread_attr;
@@ -671,6 +684,7 @@  __pthread_create_2_1 (pthread_t *newthread, const pthread_attr_t *attr,
      get the information from its thread descriptor.  */
   pd->start_routine = start_routine;
   pd->arg = arg;
+  pd->c11 = c11;
 
   /* Copy the thread attribute flags.  */
   struct pthread *self = THREAD_SELF;
diff --git a/nptl/thrd_create.c b/nptl/thrd_create.c
new file mode 100644
index 0000000..0b6b822
--- /dev/null
+++ b/nptl/thrd_create.c
@@ -0,0 +1,32 @@ 
+/* C11 threads thread creation implementation.
+   Copyright (C) 2017 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "thrd_priv.h"
+
+/* Create a new thread executing the function func.  Arguments to func
+   are passed through arg.  If succesful, thr is set to new thread
+   identifier.  */
+int
+thrd_create (thrd_t *thr, thrd_start_t func, void *arg)
+{
+  _Static_assert (sizeof (thr) == sizeof (pthread_t), "thrd_t size");
+
+  int err_code = __pthread_create_2_1 (thr, ATTR_C11_THREAD,
+				       (void* (*) (void*))func, arg);
+  return thrd_err_map (err_code);
+}
diff --git a/nptl/thrd_current.c b/nptl/thrd_current.c
new file mode 100644
index 0000000..7269d4b
--- /dev/null
+++ b/nptl/thrd_current.c
@@ -0,0 +1,26 @@ 
+/* C11 threads current thread implementation.
+   Copyright (C) 2017 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "thrd_priv.h"
+
+/* Return current thread identifier.  */
+thrd_t
+thrd_current (void)
+{
+  return __pthread_self ();
+}
diff --git a/nptl/thrd_detach.c b/nptl/thrd_detach.c
new file mode 100644
index 0000000..187d078
--- /dev/null
+++ b/nptl/thrd_detach.c
@@ -0,0 +1,30 @@ 
+/* C11 threads thread detach implementation.
+   Copyright (C) 2017 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "thrd_priv.h"
+
+/* Detache the thread identified by thr from the current environment.
+   It does not allow join or wait for the thread.  */
+int
+thrd_detach (thrd_t thr)
+{
+  int err_code;
+
+  err_code = __pthread_detach (thr);
+  return thrd_err_map (err_code);
+}
diff --git a/nptl/thrd_equal.c b/nptl/thrd_equal.c
new file mode 100644
index 0000000..fcda488
--- /dev/null
+++ b/nptl/thrd_equal.c
@@ -0,0 +1,26 @@ 
+/* C11 threads thread equality check implementation.
+   Copyright (C) 2017 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "thrd_priv.h"
+
+/* Check if lhs and rhs point to the same thread.  */
+int
+thrd_equal (thrd_t lhs, thrd_t rhs)
+{
+  return __pthread_equal (lhs, rhs);
+}
diff --git a/nptl/thrd_exit.c b/nptl/thrd_exit.c
new file mode 100644
index 0000000..a49d8e0
--- /dev/null
+++ b/nptl/thrd_exit.c
@@ -0,0 +1,27 @@ 
+/* C11 threads thread exit implementation.
+   Copyright (C) 2017 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "thrd_priv.h"
+
+/* Terminate current thread execution, cleaning up any thread local
+   storage and freeing resources.  Returns the value specified in res.  */
+_Noreturn void
+thrd_exit (int res)
+{
+  __pthread_exit ((void*)(uintptr_t) res);
+}
diff --git a/nptl/thrd_join.c b/nptl/thrd_join.c
new file mode 100644
index 0000000..1d69918
--- /dev/null
+++ b/nptl/thrd_join.c
@@ -0,0 +1,32 @@ 
+/* C11 threads thread join implementation.
+   Copyright (C) 2017 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "thrd_priv.h"
+
+/* Block current thread until execution of thr is complete.  In case that
+   res is not NULL, will store the return value of thr when exiting.  */
+int
+thrd_join (thrd_t thr, int *res)
+{
+  void *pthread_res;
+  int err_code = __pthread_join (thr, &pthread_res);
+  if (res)
+   *res = (int)((uintptr_t) pthread_res);
+
+  return thrd_err_map (err_code);
+}
diff --git a/nptl/thrd_priv.h b/nptl/thrd_priv.h
new file mode 100644
index 0000000..a431d60
--- /dev/null
+++ b/nptl/thrd_priv.h
@@ -0,0 +1,46 @@ 
+/* Internal C11 threads definitions.
+   Copyright (C) 2017 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef THRD_PRIV_H
+# define THRD_PRIV_H
+
+#include <features.h>
+#include <threads.h>
+#include <errno.h>
+#include "pthreadP.h"	/* For pthread_{mutex,cond}_t definitions.  */
+
+/* Maps pthread error codes with thrd error codes.  */
+static __always_inline int
+thrd_err_map (int err_code)
+{
+  switch (err_code)
+  {
+    case 0:
+      return thrd_success;
+    case ENOMEM:
+      return thrd_nomem;
+    case ETIMEDOUT:
+      return thrd_timedout;
+    case EBUSY:
+      return thrd_busy;
+    default:
+      return thrd_error;
+  }
+}
+
+#endif
diff --git a/nptl/thrd_sleep.c b/nptl/thrd_sleep.c
new file mode 100644
index 0000000..a49fdc4
--- /dev/null
+++ b/nptl/thrd_sleep.c
@@ -0,0 +1,41 @@ 
+/* C11 threads thread sleep implementation.
+   Copyright (C) 2017 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "thrd_priv.h"
+#include <time.h>
+
+/* Block current thread execution for at least the time pointed by time_point.
+   The current thread may resume if receives a signal.  In that case, if
+   remaining is not NULL, the remaining time is stored in the object pointed
+   by it.  */
+int
+thrd_sleep (const struct timespec* time_point, struct timespec* remaining)
+{
+  INTERNAL_SYSCALL_DECL (err);
+  int ret = INTERNAL_SYSCALL_CALL (nanosleep, err, time_point, remaining);
+  if (INTERNAL_SYSCALL_ERROR_P (ret, err))
+    {
+      /* C11 states thrd_sleep function returns -1 if it has been interrupted
+         by a signal, or a negative value if it fails.  */
+      ret = INTERNAL_SYSCALL_ERRNO (ret, err);
+      if (ret == EINTR)
+	return -1;
+      return -2;
+    }
+  return 0;
+}
diff --git a/nptl/thrd_yield.c b/nptl/thrd_yield.c
new file mode 100644
index 0000000..13a02f3
--- /dev/null
+++ b/nptl/thrd_yield.c
@@ -0,0 +1,29 @@ 
+/* C11 threads thread yield implementation.
+   Copyright (C) 2017 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "thrd_priv.h"
+
+/* Stop current thread execution and call the scheduler to decide which
+   thread should execute next.  The current thread may be selected by the
+   scheduler to keep running.  */
+void
+thrd_yield (void)
+{
+  INTERNAL_SYSCALL_DECL (err);
+  INTERNAL_SYSCALL_CALL (sched_yield, err);
+}
diff --git a/sysdeps/nptl/threads.h b/sysdeps/nptl/threads.h
new file mode 100644
index 0000000..4b89a30
--- /dev/null
+++ b/sysdeps/nptl/threads.h
@@ -0,0 +1,90 @@ 
+/* ISO C11 Standard: 7.26 - Thread support library  <threads.h>.
+   Copyright (C) 2017 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, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _THREADS_H
+#define _THREADS_H	1
+
+#include <features.h>
+#include <time.h>
+
+__BEGIN_DECLS
+
+#include <bits/types/struct_timespec.h>
+
+typedef unsigned long int thrd_t;
+typedef int (*thrd_start_t) (void*);
+
+/* Exit and error codes.  */
+enum
+{
+  thrd_success  = 0,
+  thrd_busy     = 1,
+  thrd_error    = 2,
+  thrd_nomem    = 3,
+  thrd_timedout = 4
+};
+
+/* Threads functions.  */
+
+/* Create a new thread executing the function __func.  Arguments to __func
+   are passed through __arg.  If succesful, __thr is set to new thread
+   identifier.  */
+extern int thrd_create (thrd_t *__thr, thrd_start_t __func, void *__arg);
+
+/* Check if __lhs and __rhs point to the same thread.  */
+extern int thrd_equal (thrd_t __lhs, thrd_t __rhs);
+
+/* Return current thread identifier.  */
+extern thrd_t thrd_current (void);
+
+/* Block current thread execution for at least the time pointed by
+   __time_point.  The current thread may resume if receives a signal.  In
+   that case, if __remaining is not NULL, the remaining time is stored in
+   the object pointed by it.  */
+extern int thrd_sleep (const struct timespec *__time_point,
+		       struct timespec *__remaining);
+
+/* Terminate current thread execution, cleaning up any thread local
+   storage and freeing resources.  Returns the value specified in __res.  */
+extern void thrd_exit (int __res) __attribute__ ((__noreturn__));
+
+/* Detache the thread identified by __thr from the current environment.
+   It does not allow join or wait for __thr.  */
+extern int thrd_detach (thrd_t __thr);
+
+/* Block current thread until execution of __thr is complete.  In case that
+   __res is not NULL, will store the return value of __thr when exiting.  */
+extern int thrd_join (thrd_t __thr, int *__res);
+
+/* Stop current thread execution and call the scheduler to decide which
+   thread should execute next.  The current thread may be selected by the
+   scheduler to keep running.  */
+extern void thrd_yield (void);
+
+#ifdef __USE_EXTERN_INLINES
+/* Optimizations.  */
+__extern_inline int
+thrd_equal (thrd_t __thread1, thrd_t __thread2)
+{
+  return __thread1 == __thread2;
+}
+#endif
+
+__END_DECLS
+
+#endif /* _THREADS_H */