YugabyteDB (2.13.1.0-b60, 21121d69985fbf76aa6958d8f04a9bfa936293b5)

// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-

/* Copyright (c) 2010, Google Inc.

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions are

 * met:

 *

 *     * Redistributions of source code must retain the above copyright

 * notice, this list of conditions and the following disclaimer.

 *     * Redistributions in binary form must reproduce the above

 * copyright notice, this list of conditions and the following disclaimer

 * in the documentation and/or other materials provided with the

 * distribution.

 *     * Neither the name of Google Inc. nor the names of its

 * contributors may be used to endorse or promote products derived from

 * this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR

 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT

 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 *

 * The following only applies to changes made to this file as part of YugaByte development.

 *

 * Portions Copyright (c) YugaByte, Inc.

 *

 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except

 * in compliance with the License.  You may obtain a copy of the License at

 *

 * http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software distributed under the License

 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express

 * or implied.  See the License for the specific language governing permissions and limitations

 * under the License.

 *

 */

// The OS-specific header included below must provide two calls:

// yb::base::internal::SpinLockDelay() and yb::base::internal::SpinLockWake().

// See spinlock_internal.h for the spec of SpinLockWake().

// void SpinLockDelay(volatile Atomic32 *w, int32 value, int loop)

// SpinLockDelay() generates an apprproate spin delay on iteration "loop" of a

// spin loop on location *w, whose previously observed value was "value".

// SpinLockDelay() may do nothing, may yield the CPU, may sleep a clock tick,

// or may wait for a delay that can be truncated by a call to SpinLockWake(w).

// In all cases, it must return in bounded time even if SpinLockWake() is not

// called.

#include "yb/gutil/spinlock_internal.h"

// forward declaration for use by spinlock_*-inl.h

namespace yb {

namespace base {

namespace internal {

static int SuggestedDelayNS(int loop);

}  // namespace internal

}  // namespace base

}  // namespace yb

#if defined(_WIN32)

#include "yb/gutil/spinlock_win32-inl.h"

#elif defined(__linux__)

#include "yb/gutil/spinlock_linux-inl.h"

#else

#include "yb/gutil/spinlock_posix-inl.h"

#endif

namespace yb {

namespace base {

namespace internal {

// See spinlock_internal.h for spec.

int32 SpinLockWait(volatile Atomic32 *w, int n,

                   const SpinLockWaitTransition trans[]) {

  int32 v;

  bool done = false;

  for (int loop = 0; !done; 
loop++15.5k
) {

    v = ::base::subtle::Acquire_Load(w);

    int i;

    for (i = 0; i != n && 
v != trans[i].from43.9k
; 
i++36.3k
) {

    }

    if (i == n) {

      SpinLockDelay(w, v, loop);     // no matching transition

    } else 
if (7.49k
trans[i].to == v7.49k
 ||   // null transition

               
::base::subtle::Acquire_CompareAndSwap(w, v, trans[i].to) == v2.83k
) {

      done = trans[i].done;

    }

  }

  return v;

}

// Return a suggested delay in nanoseconds for iteration number "loop"

static int SuggestedDelayNS(int loop) {

  // Weak pseudo-random number generator to get some spread between threads

  // when many are spinning.

#ifdef BASE_HAS_ATOMIC64

  static ::base::subtle::Atomic64 rand;

  uint64 r = ::base::subtle::NoBarrier_Load(&rand);

  r = 0x5deece66dLL * r + 0xb;   // numbers from nrand48()

  ::base::subtle::NoBarrier_Store(&rand, r);

  r <<= 16;   // 48-bit random number now in top 48-bits.

  if (loop < 0 || 
loop > 3210.9M
) {   // limit loop to 0..32

    loop = 32;

  }

  // loop>>3 cannot exceed 4 because loop cannot exceed 32.

  // Select top 20..24 bits of lower 48 bits,

  // giving approximately 0ms to 16ms.

  // Mean is exponential in loop for first 32 iterations, then 8ms.

  // The futex path multiplies this by 16, since we expect explicit wakeups

  // almost always on that path.

  return static_cast<int>(r >> (44 - (loop >> 3)));

#else

  static Atomic32 rand;

  uint32 r = ::base::subtle::NoBarrier_Load(&rand);

  r = 0x343fd * r + 0x269ec3;   // numbers from MSVC++

  ::base::subtle::NoBarrier_Store(&rand, r);

  r <<= 1;   // 31-bit random number now in top 31-bits.

  if (loop < 0 || loop > 32) {   // limit loop to 0..32

    loop = 32;

  }

  // loop>>3 cannot exceed 4 because loop cannot exceed 32.

  // Select top 20..24 bits of lower 31 bits,

  // giving approximately 0ms to 16ms.

  // Mean is exponential in loop for first 32 iterations, then 8ms.

  // The futex path multiplies this by 16, since we expect explicit wakeups

  // almost always on that path.

  return r >> (12 - (loop >> 3));

#endif

}

} // namespace internal

} // namespace base

} // namespace yb