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Diffstat (limited to 'REORG.TODO/sysdeps/nptl/lowlevellock.h')
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diff --git a/REORG.TODO/sysdeps/nptl/lowlevellock.h b/REORG.TODO/sysdeps/nptl/lowlevellock.h new file mode 100644 index 0000000000..54e3c28b0b --- /dev/null +++ b/REORG.TODO/sysdeps/nptl/lowlevellock.h @@ -0,0 +1,205 @@ +/* Low-level lock implementation. Generic futex-based version. + Copyright (C) 2005-2017 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 _LOWLEVELLOCK_H +#define _LOWLEVELLOCK_H 1 + +#include <atomic.h> +#include <lowlevellock-futex.h> + +/* Low-level locks use a combination of atomic operations (to acquire and + release lock ownership) and futex operations (to block until the state + of a lock changes). A lock can be in one of three states: + 0: not acquired, + 1: acquired with no waiters; no other threads are blocked or about to block + for changes to the lock state, + >1: acquired, possibly with waiters; there may be other threads blocked or + about to block for changes to the lock state. + + We expect that the common case is an uncontended lock, so we just need + to transition the lock between states 0 and 1; releasing the lock does + not need to wake any other blocked threads. If the lock is contended + and a thread decides to block using a futex operation, then this thread + needs to first change the state to >1; if this state is observed during + lock release, the releasing thread will wake one of the potentially + blocked threads. + + Much of this code takes a 'private' parameter. This may be: + LLL_PRIVATE: lock only shared within a process + LLL_SHARED: lock may be shared across processes. + + Condition variables contain an optimization for broadcasts that requeues + waiting threads on a lock's futex. Therefore, there is a special + variant of the locks (whose name contains "cond") that makes sure to + always set the lock state to >1 and not just 1. + + Robust locks set the lock to the id of the owner. This allows detection + of the case where the owner exits without releasing the lock. Flags are + OR'd with the owner id to record additional information about lock state. + Therefore the states of robust locks are: + 0: not acquired + id: acquired (by user identified by id & FUTEX_TID_MASK) + + The following flags may be set in the robust lock value: + FUTEX_WAITERS - possibly has waiters + FUTEX_OWNER_DIED - owning user has exited without releasing the futex. */ + + +/* If LOCK is 0 (not acquired), set to 1 (acquired with no waiters) and return + 0. Otherwise leave lock unchanged and return non-zero to indicate that the + lock was not acquired. */ +#define lll_trylock(lock) \ + __glibc_unlikely (atomic_compare_and_exchange_bool_acq (&(lock), 1, 0)) + +/* If LOCK is 0 (not acquired), set to 2 (acquired, possibly with waiters) and + return 0. Otherwise leave lock unchanged and return non-zero to indicate + that the lock was not acquired. */ +#define lll_cond_trylock(lock) \ + __glibc_unlikely (atomic_compare_and_exchange_bool_acq (&(lock), 2, 0)) + +extern void __lll_lock_wait_private (int *futex) attribute_hidden; +extern void __lll_lock_wait (int *futex, int private) attribute_hidden; + +/* This is an expression rather than a statement even though its value is + void, so that it can be used in a comma expression or as an expression + that's cast to void. */ +/* The inner conditional compiles to a call to __lll_lock_wait_private if + private is known at compile time to be LLL_PRIVATE, and to a call to + __lll_lock_wait otherwise. */ +/* If FUTEX is 0 (not acquired), set to 1 (acquired with no waiters) and + return. Otherwise, ensure that it is >1 (acquired, possibly with waiters) + and then block until we acquire the lock, at which point FUTEX will still be + >1. The lock is always acquired on return. */ +#define __lll_lock(futex, private) \ + ((void) \ + ({ \ + int *__futex = (futex); \ + if (__glibc_unlikely \ + (atomic_compare_and_exchange_bool_acq (__futex, 1, 0))) \ + { \ + if (__builtin_constant_p (private) && (private) == LLL_PRIVATE) \ + __lll_lock_wait_private (__futex); \ + else \ + __lll_lock_wait (__futex, private); \ + } \ + })) +#define lll_lock(futex, private) \ + __lll_lock (&(futex), private) + + +/* This is an expression rather than a statement even though its value is + void, so that it can be used in a comma expression or as an expression + that's cast to void. */ +/* Unconditionally set FUTEX to 2 (acquired, possibly with waiters). If FUTEX + was 0 (not acquired) then return. Otherwise, block until the lock is + acquired, at which point FUTEX is 2 (acquired, possibly with waiters). The + lock is always acquired on return. */ +#define __lll_cond_lock(futex, private) \ + ((void) \ + ({ \ + int *__futex = (futex); \ + if (__glibc_unlikely (atomic_exchange_acq (__futex, 2) != 0)) \ + __lll_lock_wait (__futex, private); \ + })) +#define lll_cond_lock(futex, private) __lll_cond_lock (&(futex), private) + + +extern int __lll_timedlock_wait (int *futex, const struct timespec *, + int private) attribute_hidden; + + +/* As __lll_lock, but with a timeout. If the timeout occurs then return + ETIMEDOUT. If ABSTIME is invalid, return EINVAL. */ +#define __lll_timedlock(futex, abstime, private) \ + ({ \ + int *__futex = (futex); \ + int __val = 0; \ + \ + if (__glibc_unlikely \ + (atomic_compare_and_exchange_bool_acq (__futex, 1, 0))) \ + __val = __lll_timedlock_wait (__futex, abstime, private); \ + __val; \ + }) +#define lll_timedlock(futex, abstime, private) \ + __lll_timedlock (&(futex), abstime, private) + + +/* This is an expression rather than a statement even though its value is + void, so that it can be used in a comma expression or as an expression + that's cast to void. */ +/* Unconditionally set FUTEX to 0 (not acquired), releasing the lock. If FUTEX + was >1 (acquired, possibly with waiters), then wake any waiters. The waiter + that acquires the lock will set FUTEX to >1. + Evaluate PRIVATE before releasing the lock so that we do not violate the + mutex destruction requirements. Specifically, we need to ensure that + another thread can destroy the mutex (and reuse its memory) once it + acquires the lock and when there will be no further lock acquisitions; + thus, we must not access the lock after releasing it, or those accesses + could be concurrent with mutex destruction or reuse of the memory. */ +#define __lll_unlock(futex, private) \ + ((void) \ + ({ \ + int *__futex = (futex); \ + int __private = (private); \ + int __oldval = atomic_exchange_rel (__futex, 0); \ + if (__glibc_unlikely (__oldval > 1)) \ + lll_futex_wake (__futex, 1, __private); \ + })) +#define lll_unlock(futex, private) \ + __lll_unlock (&(futex), private) + + +#define lll_islocked(futex) \ + ((futex) != LLL_LOCK_INITIALIZER) + + +/* Our internal lock implementation is identical to the binary-compatible + mutex implementation. */ + +/* Initializers for lock. */ +#define LLL_LOCK_INITIALIZER (0) +#define LLL_LOCK_INITIALIZER_LOCKED (1) + + +/* The kernel notifies a process which uses CLONE_CHILD_CLEARTID via futex + wake-up when the clone terminates. The memory location contains the + thread ID while the clone is running and is reset to zero by the kernel + afterwards. The kernel up to version 3.16.3 does not use the private futex + operations for futex wake-up when the clone terminates. */ +#define lll_wait_tid(tid) \ + do { \ + __typeof (tid) __tid; \ + while ((__tid = (tid)) != 0) \ + lll_futex_wait (&(tid), __tid, LLL_SHARED);\ + } while (0) + +extern int __lll_timedwait_tid (int *, const struct timespec *) + attribute_hidden; + +/* As lll_wait_tid, but with a timeout. If the timeout occurs then return + ETIMEDOUT. If ABSTIME is invalid, return EINVAL. */ +#define lll_timedwait_tid(tid, abstime) \ + ({ \ + int __res = 0; \ + if ((tid) != 0) \ + __res = __lll_timedwait_tid (&(tid), (abstime)); \ + __res; \ + }) + + +#endif /* lowlevellock.h */ |