diff options
Diffstat (limited to 'sysdeps/nacl')
| -rw-r--r-- | sysdeps/nacl/exit-thread.h | 49 | ||||
| -rw-r--r-- | sysdeps/nacl/lll_timedwait_tid.c | 61 | ||||
| -rw-r--r-- | sysdeps/nacl/lowlevellock.h | 45 | ||||
| -rw-r--r-- | sysdeps/nacl/pthread-pids.h | 3 |
4 files changed, 156 insertions, 2 deletions
diff --git a/sysdeps/nacl/exit-thread.h b/sysdeps/nacl/exit-thread.h index a08a5b1d5c..c809405cf1 100644 --- a/sysdeps/nacl/exit-thread.h +++ b/sysdeps/nacl/exit-thread.h @@ -16,8 +16,11 @@ License along with the GNU C Library; if not, see <http://www.gnu.org/licenses/>. */ -#include <stddef.h> +#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 @@ -26,7 +29,49 @@ static inline void __attribute__ ((noreturn, always_inline, unused)) __exit_thread (void) { - __nacl_irt_thread.thread_exit (NULL); + 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. */ diff --git a/sysdeps/nacl/lll_timedwait_tid.c b/sysdeps/nacl/lll_timedwait_tid.c new file mode 100644 index 0000000000..ecaf0b113a --- /dev/null +++ b/sysdeps/nacl/lll_timedwait_tid.c @@ -0,0 +1,61 @@ +/* Timed waiting for thread death. 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 <errno.h> +#include <lowlevellock.h> +#include <sys/time.h> + +int +__lll_timedwait_tid (int *tidp, const struct timespec *abstime) +{ + /* Reject invalid timeouts. */ + if (__glibc_unlikely (abstime->tv_nsec < 0) + || __glibc_unlikely (abstime->tv_nsec >= 1000000000)) + return EINVAL; + + /* Repeat until thread terminated. */ + int tid; + while ((tid = atomic_load_relaxed (tidp)) != 0) + { + /* See exit-thread.h for details. */ + if (tid == NACL_EXITING_TID) + /* The thread should now be in the process of exiting, so it will + finish quick enough that the timeout doesn't matter. If any + thread ever stays in this state for long, there is something + catastrophically wrong. */ + BUSY_WAIT_NOP; + else + { + assert (tid > 0); + + /* If *FUTEX == TID, wait until woken or timeout. */ + int err = __nacl_irt_futex.futex_wait_abs ((volatile int *) tidp, + tid, abstime); + if (err != 0) + { + if (__glibc_likely (err == ETIMEDOUT)) + return err; + assert (err == EAGAIN); + } + } + } + + return 0; +} diff --git a/sysdeps/nacl/lowlevellock.h b/sysdeps/nacl/lowlevellock.h new file mode 100644 index 0000000000..0b85d8d317 --- /dev/null +++ b/sysdeps/nacl/lowlevellock.h @@ -0,0 +1,45 @@ +/* Low-level lock implementation. 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/>. */ + +#ifndef _LOWLEVELLOCK_H + +/* Everything except the exit handling is the same as the generic code. */ +# include <sysdeps/nptl/lowlevellock.h> + +# ifndef BUSY_WAIT_NOP +# define BUSY_WAIT_NOP __sync_synchronize () +# endif + +/* See exit-thread.h for details. */ +# define NACL_EXITING_TID 1 + +# undef lll_wait_tid +# define lll_wait_tid(tid) \ + do { \ + __typeof (tid) __tid; \ + volatile __typeof (tid) *__tidp = &(tid); \ + while ((__tid = atomic_load_relaxed (__tidp)) != 0) \ + { \ + if (__tid == NACL_EXITING_TID) \ + BUSY_WAIT_NOP; \ + else \ + lll_futex_wait (__tidp, __tid, LLL_PRIVATE); \ + } \ + } while (0) + +#endif /* lowlevellock.h */ diff --git a/sysdeps/nacl/pthread-pids.h b/sysdeps/nacl/pthread-pids.h index ccb99d6b0c..1589e5b342 100644 --- a/sysdeps/nacl/pthread-pids.h +++ b/sysdeps/nacl/pthread-pids.h @@ -50,6 +50,9 @@ __nacl_get_tid (struct pthread *pd) assert ((id & 1) == 0); assert (sizeof id == sizeof tid); assert (tid > 0); + /* This ensures that NACL_EXITING_TID (lowlevellock.h) can never + be a valid TID value. */ + assert ((tid & 1) == 0); return tid; } |