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/* Copyright (C) 2009, 2011 Free Software Foundation, Inc.
Contributed by Richard Henderson <rth@redhat.com>.
This file is part of the GNU Transactional Memory Library (libitm).
Libitm is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
Libitm 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 General Public License for
more details.
Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.
You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
<http://www.gnu.org/licenses/>. */
#ifndef LIBITM_STMLOCK_H
#define LIBITM_STMLOCK_H 1
namespace GTM HIDDEN {
/* A versioned write lock on a cacheline. This must be wide enough to
store a pointer, and preferably wide enough to avoid overflowing the
version counter. Thus we use a "word", which should be 64-bits on
64-bit systems even when their pointer size is forced smaller. */
typedef gtm_word gtm_stmlock;
/* This has to be the same size as gtm_stmlock, we just use this name
for documentation purposes. */
typedef gtm_word gtm_version;
/* The maximum value a version number can have. This is a consequence
of having the low bit of gtm_stmlock reserved for the owned bit. */
#define GTM_VERSION_MAX (~(gtm_version)0 >> 1)
/* A value that may be used to indicate "uninitialized" for a version. */
#define GTM_VERSION_INVALID (~(gtm_version)0)
/* This bit is set when the write lock is held. When set, the balance of
the bits in the lock is a pointer that references STM backend specific
data; it is up to the STM backend to determine if this thread holds the
lock. If this bit is clear, the balance of the bits are the last
version number committed to the cacheline. */
static inline bool
gtm_stmlock_owned_p (gtm_stmlock lock)
{
return lock & 1;
}
static inline gtm_stmlock
gtm_stmlock_set_owned (void *data)
{
return (gtm_stmlock)(uintptr_t)data | 1;
}
static inline void *
gtm_stmlock_get_addr (gtm_stmlock lock)
{
return (void *)((uintptr_t)lock & ~(uintptr_t)1);
}
static inline gtm_version
gtm_stmlock_get_version (gtm_stmlock lock)
{
return lock >> 1;
}
static inline gtm_stmlock
gtm_stmlock_set_version (gtm_version ver)
{
return ver << 1;
}
/* We use a fixed set of locks for all memory, hashed into the
following table. */
#define LOCK_ARRAY_SIZE (1024 * 1024)
extern gtm_stmlock gtm_stmlock_array[LOCK_ARRAY_SIZE];
static inline gtm_stmlock *
gtm_get_stmlock (const gtm_cacheline *addr)
{
size_t idx = ((uintptr_t) addr / CACHELINE_SIZE) % LOCK_ARRAY_SIZE;
return gtm_stmlock_array + idx;
}
/* The current global version number. */
extern atomic<gtm_version> gtm_clock;
static inline gtm_version
gtm_get_clock (void)
{
atomic_thread_fence(memory_order_release);
return gtm_clock.load(memory_order_acquire);
}
static inline gtm_version
gtm_inc_clock (void)
{
/* ??? Here we have a choice, the pre-inc operator mapping to
__atomic_add_fetch with memory_order_seq_cst, or fetch_add
with memory_order_acq_rel plus another separate increment.
We really ought to recognize and optimize fetch_op(x) op x... */
gtm_version r = ++gtm_clock;
/* ??? Ought to handle wraparound for 32-bit. */
if (sizeof(r) < 8 && r > GTM_VERSION_MAX)
abort ();
return r;
}
} // namespace GTM
#endif // LIBITM_STMLOCK_H
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