libitm/stmlock.h

   1 /* Copyright (C) 2009, 2011 Free Software Foundation, Inc.
   2    Contributed by Richard Henderson <rth@redhat.com>.
   3
   4    This file is part of the GNU Transactional Memory Library (libitm).
   5
   6    Libitm is free software; you can redistribute it and/or modify it
   7    under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    Libitm is distributed in the hope that it will be useful, but WITHOUT ANY
  12    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  13    FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  14    more details.
  15
  16    Under Section 7 of GPL version 3, you are granted additional
  17    permissions described in the GCC Runtime Library Exception, version
  18    3.1, as published by the Free Software Foundation.
  19
  20    You should have received a copy of the GNU General Public License and
  21    a copy of the GCC Runtime Library Exception along with this program;
  22    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23    <http://www.gnu.org/licenses/>.  */
  24
  25 #ifndef LIBITM_STMLOCK_H
  26 #define LIBITM_STMLOCK_H 1
  27
  28 namespace GTM HIDDEN {
  29
  30 /* A versioned write lock on a cacheline.  This must be wide enough to
  31    store a pointer, and preferably wide enough to avoid overflowing the
  32    version counter.  Thus we use a "word", which should be 64-bits on
  33    64-bit systems even when their pointer size is forced smaller.  */
  34 typedef gtm_word gtm_stmlock;
  35
  36 /* This has to be the same size as gtm_stmlock, we just use this name
  37    for documentation purposes.  */
  38 typedef gtm_word gtm_version;
  39
  40 /* The maximum value a version number can have.  This is a consequence
  41    of having the low bit of gtm_stmlock reserved for the owned bit.  */
  42 #define GTM_VERSION_MAX         (~(gtm_version)0 >> 1)
  43
  44 /* A value that may be used to indicate "uninitialized" for a version.  */
  45 #define GTM_VERSION_INVALID     (~(gtm_version)0)
  46
  47 /* This bit is set when the write lock is held.  When set, the balance of
  48    the bits in the lock is a pointer that references STM backend specific
  49    data; it is up to the STM backend to determine if this thread holds the
  50    lock.  If this bit is clear, the balance of the bits are the last
  51    version number committed to the cacheline.  */
  52 static inline bool
  53 gtm_stmlock_owned_p (gtm_stmlock lock)
  54 {
  55   return lock & 1;
  56 }
  57
  58 static inline gtm_stmlock
  59 gtm_stmlock_set_owned (void *data)
  60 {
  61   return (gtm_stmlock)(uintptr_t)data | 1;
  62 }
  63
  64 static inline void *
  65 gtm_stmlock_get_addr (gtm_stmlock lock)
  66 {
  67   return (void *)((uintptr_t)lock & ~(uintptr_t)1);
  68 }
  69
  70 static inline gtm_version
  71 gtm_stmlock_get_version (gtm_stmlock lock)
  72 {
  73   return lock >> 1;
  74 }
  75
  76 static inline gtm_stmlock
  77 gtm_stmlock_set_version (gtm_version ver)
  78 {
  79   return ver << 1;
  80 }
  81
  82 /* We use a fixed set of locks for all memory, hashed into the
  83    following table.  */
  84 #define LOCK_ARRAY_SIZE  (1024 * 1024)
  85 extern gtm_stmlock gtm_stmlock_array[LOCK_ARRAY_SIZE];
  86
  87 static inline gtm_stmlock *
  88 gtm_get_stmlock (const gtm_cacheline *addr)
  89 {
  90   size_t idx = ((uintptr_t) addr / CACHELINE_SIZE) % LOCK_ARRAY_SIZE;
  91   return gtm_stmlock_array + idx;
  92 }
  93
  94 /* The current global version number.  */
  95 extern atomic<gtm_version> gtm_clock;
  96
  97 static inline gtm_version
  98 gtm_get_clock (void)
  99 {
 100   atomic_thread_fence(memory_order_release);
 101   return gtm_clock.load(memory_order_acquire);
 102 }
 103
 104 static inline gtm_version
 105 gtm_inc_clock (void)
 106 {
 107   /* ??? Here we have a choice, the pre-inc operator mapping to
 108      __atomic_add_fetch with memory_order_seq_cst, or fetch_add
 109      with memory_order_acq_rel plus another separate increment.
 110      We really ought to recognize and optimize fetch_op(x) op x... */
 111   gtm_version r = ++gtm_clock;
 112
 113   /* ??? Ought to handle wraparound for 32-bit.  */
 114   if (sizeof(r) < 8 && r > GTM_VERSION_MAX)
 115     abort ();
 116
 117   return r;
 118 }
 119
 120 } // namespace GTM
 121
 122 #endif // LIBITM_STMLOCK_H