[Feature][ZXW-33]merge ZXW 0428 version

Change-Id: I11f167edfea428d9fab198ff00ff1364932d1b0b
diff --git a/ap/libc/glibc/glibc-2.23/sysdeps/nacl/exit-thread.h b/ap/libc/glibc/glibc-2.23/sysdeps/nacl/exit-thread.h
new file mode 100644
index 0000000..864ed4b
--- /dev/null
+++ b/ap/libc/glibc/glibc-2.23/sysdeps/nacl/exit-thread.h
@@ -0,0 +1,80 @@
+/* Call to terminate the current thread.  NaCl version.
+   Copyright (C) 2015-2016 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 <assert.h>
+#include <atomic.h>
+#include <futex-internal.h>
+#include <nacl-interfaces.h>
+#include <nptl/pthreadP.h>
+
+/* This causes the current thread to exit, without affecting other
+   threads in the process if there are any.  If there are no other
+   threads left, then this has the effect of _exit (0).  */
+
+static inline void __attribute__ ((noreturn, always_inline, unused))
+__exit_thread (void)
+{
+  struct pthread *pd = THREAD_SELF;
+
+  /* The generic logic for pthread_join and stack/descriptor reuse is
+     based on the Linux kernel feature that will clear and futex-wake
+     a designated address as a final part of thread teardown.  Correct
+     synchronization relies on the fact that these happen only after
+     there is no possibility of user code touching or examining the
+     late thread's stack.
+
+     The NaCl system interface implements half of this: it clears a
+     word after the thread's user stack is safely dead, but it does
+     not futex-wake the location.  So, some shenanigans are required.
+     We change and futex-wake the location here, so as to wake up any
+     blocked pthread_join (i.e. lll_wait_tid) or pthread_timedjoin_np
+     (i.e. lll_timedwait_tid).  However, that's before we have safely
+     vacated the stack.  So instead of clearing the location, we set
+     it to a special magic value, NACL_EXITING_TID.  This counts as a
+     "live thread" value for all the generic logic, but is recognized
+     specially in lll_wait_tid and lll_timedwait_tid (lowlevellock.h).
+     Once it has this value, lll_wait_tid will busy-wait for the
+     location to be cleared to zero by the NaCl system code.  Only then
+     is the stack actually safe to reuse.  */
+
+  if (!IS_DETACHED (pd))
+    {
+      /* The magic value must not be one that could ever be a valid
+	 TID value.  See pthread-pids.h about the low bit.  */
+      assert (NACL_EXITING_TID & 1);
+
+      /* The magic value must not be one that has the "free" flag
+	 (i.e. sign bit) set.  If that bit is set, then the
+	 descriptor could be reused for a new thread.  */
+      assert (NACL_EXITING_TID > 0);
+
+      atomic_store_relaxed (&pd->tid, NACL_EXITING_TID);
+      futex_wake ((unsigned int *) &pd->tid, 1, FUTEX_PRIVATE);
+    }
+
+  /* This clears PD->tid some time after the thread stack can never
+     be touched again.  Unfortunately, it does not also do a
+     futex-wake at that time (as Linux does via CLONE_CHILD_CLEARTID
+     and set_tid_address).  So lll_wait_tid does some busy-waiting.  */
+  __nacl_irt_thread.thread_exit (&pd->tid);
+
+  /* That never returns unless something is severely and unrecoverably wrong.
+     If it ever does, try to make sure we crash.  */
+  while (1)
+    __builtin_trap ();
+}