mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-10 23:30:07 +00:00
81 lines
3.5 KiB
C
81 lines
3.5 KiB
C
/* Call to terminate the current thread. NaCl version.
|
|
Copyright (C) 2015 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 <lowlevellock.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);
|
|
lll_futex_wake (&pd->tid, 1, LLL_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 ();
|
|
}
|