ceph/src/rocksdb/third-party/folly/folly/synchronization/AtomicUtil.h

   1 //  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under both the GPLv2 (found in the
   3 //  COPYING file in the root directory) and Apache 2.0 License
   4 //  (found in the LICENSE.Apache file in the root directory).
   5
   6 #pragma once
   7
   8 #include <atomic>
   9 #include <cstdint>
  10
  11 namespace folly {
  12
  13 /**
  14  * Sets a bit at the given index in the binary representation of the integer
  15  * to 1.  Returns the previous value of the bit, so true if the bit was not
  16  * changed, false otherwise
  17  *
  18  * On some architectures, using this is more efficient than the corresponding
  19  * std::atomic::fetch_or() with a mask.  For example to set the first (least
  20  * significant) bit of an integer, you could do atomic.fetch_or(0b1)
  21  *
  22  * The efficiency win is only visible in x86 (yet) and comes from the
  23  * implementation using the x86 bts instruction when possible.
  24  *
  25  * When something other than std::atomic is passed, the implementation assumed
  26  * incompatibility with this interface and calls Atomic::fetch_or()
  27  */
  28 template <typename Atomic>
  29 bool atomic_fetch_set(
  30     Atomic& atomic,
  31     std::size_t bit,
  32     std::memory_order order = std::memory_order_seq_cst);
  33
  34 /**
  35  * Resets a bit at the given index in the binary representation of the integer
  36  * to 0.  Returns the previous value of the bit, so true if the bit was
  37  * changed, false otherwise
  38  *
  39  * This follows the same underlying principle and implementation as
  40  * fetch_set().  Using the optimized implementation when possible and falling
  41  * back to std::atomic::fetch_and() when in debug mode or in an architecture
  42  * where an optimization is not possible
  43  */
  44 template <typename Atomic>
  45 bool atomic_fetch_reset(
  46     Atomic& atomic,
  47     std::size_t bit,
  48     std::memory_order order = std::memory_order_seq_cst);
  49
  50 } // namespace folly
  51
  52 #include <folly/synchronization/AtomicUtil-inl.h>