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a2f0363f81
This adds new functions for futex operations, starting with wait, abstimed_wait, reltimed_wait, wake. They add documentation and error checking according to the current draft of the Linux kernel futex manpage. Waiting with absolute or relative timeouts is split into separate functions. This allows for removing a few cases of code duplication in pthreads code, which uses absolute timeouts; also, it allows us to put platform-specific code to go from an absolute to a relative timeout into the platform-specific futex abstractions.. Futex operations that can be canceled are also split out into separate functions suffixed by "_cancelable". There are separate versions for both Linux and NaCl; while they currently differ only slightly, my expectation is that the separate versions of lowlevellock-futex.h will eventually be merged into futex-internal.h when we get to move the lll_ functions over to the new futex API.
67 lines
2.4 KiB
C
67 lines
2.4 KiB
C
/* Copyright (C) 2002-2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include "pthreadP.h"
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#include <string.h>
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#include <kernel-features.h>
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static const struct pthread_rwlockattr default_rwlockattr =
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{
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.lockkind = PTHREAD_RWLOCK_DEFAULT_NP,
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.pshared = PTHREAD_PROCESS_PRIVATE
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};
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int
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__pthread_rwlock_init (rwlock, attr)
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pthread_rwlock_t *rwlock;
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const pthread_rwlockattr_t *attr;
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{
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const struct pthread_rwlockattr *iattr;
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iattr = ((const struct pthread_rwlockattr *) attr) ?: &default_rwlockattr;
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memset (rwlock, '\0', sizeof (*rwlock));
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rwlock->__data.__flags
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= iattr->lockkind == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP;
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/* The __SHARED field is computed to minimize the work that needs to
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be done while handling the futex. There are two inputs: the
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availability of private futexes and whether the rwlock is shared
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or private. Unfortunately the value of a private rwlock is
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fixed: it must be zero. The PRIVATE_FUTEX flag has the value
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0x80 in case private futexes are available and zero otherwise.
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This leads to the following table:
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| pshared | result
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| shared private | shared private |
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------------+-----------------+-----------------+
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!avail 0 | 0 0 | 0 0 |
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avail 0x80 | 0x80 0 | 0 0x80 |
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If the pshared value is in locking functions XORed with avail
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we get the expected result. */
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rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
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? 0 : FUTEX_PRIVATE_FLAG);
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return 0;
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}
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strong_alias (__pthread_rwlock_init, pthread_rwlock_init)
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