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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