123 lines
3.8 KiB
C++
123 lines
3.8 KiB
C++
/* Copyright (C) 2009-2016 Free Software Foundation, Inc.
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Contributed by Richard Henderson <rth@redhat.com>.
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This file is part of the GNU Transactional Memory Library (libitm).
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Libitm is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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Libitm is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef LIBITM_STMLOCK_H
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#define LIBITM_STMLOCK_H 1
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namespace GTM HIDDEN {
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/* A versioned write lock on a cacheline. This must be wide enough to
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store a pointer, and preferably wide enough to avoid overflowing the
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version counter. Thus we use a "word", which should be 64-bits on
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64-bit systems even when their pointer size is forced smaller. */
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typedef gtm_word gtm_stmlock;
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/* This has to be the same size as gtm_stmlock, we just use this name
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for documentation purposes. */
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typedef gtm_word gtm_version;
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/* The maximum value a version number can have. This is a consequence
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of having the low bit of gtm_stmlock reserved for the owned bit. */
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#define GTM_VERSION_MAX (~(gtm_version)0 >> 1)
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/* A value that may be used to indicate "uninitialized" for a version. */
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#define GTM_VERSION_INVALID (~(gtm_version)0)
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/* This bit is set when the write lock is held. When set, the balance of
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the bits in the lock is a pointer that references STM backend specific
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data; it is up to the STM backend to determine if this thread holds the
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lock. If this bit is clear, the balance of the bits are the last
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version number committed to the cacheline. */
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static inline bool
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gtm_stmlock_owned_p (gtm_stmlock lock)
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{
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return lock & 1;
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}
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static inline gtm_stmlock
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gtm_stmlock_set_owned (void *data)
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{
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return (gtm_stmlock)(uintptr_t)data | 1;
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}
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static inline void *
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gtm_stmlock_get_addr (gtm_stmlock lock)
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{
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return (void *)((uintptr_t)lock & ~(uintptr_t)1);
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}
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static inline gtm_version
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gtm_stmlock_get_version (gtm_stmlock lock)
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{
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return lock >> 1;
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}
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static inline gtm_stmlock
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gtm_stmlock_set_version (gtm_version ver)
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{
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return ver << 1;
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}
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/* We use a fixed set of locks for all memory, hashed into the
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following table. */
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#define LOCK_ARRAY_SIZE (1024 * 1024)
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extern gtm_stmlock gtm_stmlock_array[LOCK_ARRAY_SIZE];
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static inline gtm_stmlock *
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gtm_get_stmlock (const gtm_cacheline *addr)
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{
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size_t idx = ((uintptr_t) addr / CACHELINE_SIZE) % LOCK_ARRAY_SIZE;
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return gtm_stmlock_array + idx;
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}
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/* The current global version number. */
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extern atomic<gtm_version> gtm_clock;
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static inline gtm_version
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gtm_get_clock (void)
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{
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atomic_thread_fence(memory_order_release);
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return gtm_clock.load(memory_order_acquire);
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}
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static inline gtm_version
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gtm_inc_clock (void)
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{
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/* ??? Here we have a choice, the pre-inc operator mapping to
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__atomic_add_fetch with memory_order_seq_cst, or fetch_add
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with memory_order_acq_rel plus another separate increment.
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We really ought to recognize and optimize fetch_op(x) op x... */
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gtm_version r = ++gtm_clock;
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/* ??? Ought to handle wraparound for 32-bit. */
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if (sizeof(r) < 8 && r > GTM_VERSION_MAX)
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abort ();
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return r;
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}
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} // namespace GTM
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#endif // LIBITM_STMLOCK_H
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