Synchronization.c - Android社区 - https://www.androidos.net.cn/

/** @file
  Implementation of synchronization functions.

Copyright (c) 2006 - 2012, Intel Corporation. All rights reserved.<BR>
  This program and the accompanying materials
  are licensed and made available under the terms and conditions of the BSD License
  which accompanies this distribution.  The full text of the license may be found at
  http://opensource.org/licenses/bsd-license.php.

THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.

**/

#include "BaseSynchronizationLibInternals.h"

#define SPIN_LOCK_RELEASED          ((UINTN) 1)
#define SPIN_LOCK_ACQUIRED          ((UINTN) 2)

/**
  Retrieves the architecture specific spin lock alignment requirements for
  optimal spin lock performance.

This function retrieves the spin lock alignment requirements for optimal
  performance on a given CPU architecture. The spin lock alignment is byte alignment. 
  It must be a power of two and is returned by this function. If there are no alignment
  requirements, then 1 must be returned. The spin lock synchronization
  functions must function correctly if the spin lock size and alignment values
  returned by this function are not used at all. These values are hints to the
  consumers of the spin lock synchronization functions to obtain optimal spin
  lock performance.

@return The architecture specific spin lock alignment.

**/
UINTN
EFIAPI
GetSpinLockProperties (
  VOID
  )
{
  return 32;
}

/**
  Initializes a spin lock to the released state and returns the spin lock.

This function initializes the spin lock specified by SpinLock to the released
  state, and returns SpinLock. Optimal performance can be achieved by calling
  GetSpinLockProperties() to determine the size and alignment requirements for
  SpinLock.

If SpinLock is NULL, then ASSERT().

@param  SpinLock  A pointer to the spin lock to initialize to the released
                    state.

@return SpinLock is in release state.

**/
SPIN_LOCK *
EFIAPI
InitializeSpinLock (
  OUT      SPIN_LOCK                 *SpinLock
  )
{
  ASSERT (SpinLock != NULL);
  *SpinLock = SPIN_LOCK_RELEASED;
  return SpinLock;
}

/**
  Waits until a spin lock can be placed in the acquired state.

This function checks the state of the spin lock specified by SpinLock. If
  SpinLock is in the released state, then this function places SpinLock in the
  acquired state and returns SpinLock. Otherwise, this function waits
  indefinitely for the spin lock to be released, and then places it in the
  acquired state and returns SpinLock. All state transitions of SpinLock must
  be performed using MP safe mechanisms.

If SpinLock is NULL, then ASSERT().
  If SpinLock was not initialized with InitializeSpinLock(), then ASSERT().
  If PcdSpinLockTimeout is not zero, and SpinLock is can not be acquired in
  PcdSpinLockTimeout microseconds, then ASSERT().

@param  SpinLock  A pointer to the spin lock to place in the acquired state.

@return SpinLock acquired the lock.

**/
SPIN_LOCK *
EFIAPI
AcquireSpinLock (
  IN OUT  SPIN_LOCK                 *SpinLock
  )
{
  UINT64  Current;
  UINT64  Previous;
  UINT64  Total;
  UINT64  Start;
  UINT64  End;
  UINT64  Timeout;
  INT64   Cycle;
  INT64   Delta;

if (PcdGet32 (PcdSpinLockTimeout) > 0) {
    //
    // Get the current timer value
    //
    Current = GetPerformanceCounter();

//
    // Initialize local variables
    //
    Start = 0;
    End   = 0;
    Total = 0;

//
    // Retrieve the performance counter properties and compute the number of performance
    // counter ticks required to reach the timeout
    //
    Timeout = DivU64x32 (
                MultU64x32 (
                  GetPerformanceCounterProperties (&Start, &End),
                  PcdGet32 (PcdSpinLockTimeout)
                  ),
                1000000
                );
    Cycle = End - Start;
    if (Cycle < 0) {
      Cycle = -Cycle;
    }
    Cycle++;

while (!AcquireSpinLockOrFail (SpinLock)) {
      CpuPause ();
      Previous = Current;
      Current  = GetPerformanceCounter();
      Delta = (INT64) (Current - Previous);
      if (Start > End) {
        Delta = -Delta;
      }
      if (Delta < 0) {
        Delta += Cycle;
      }
      Total += Delta;
      ASSERT (Total < Timeout);
    }
  } else {
    while (!AcquireSpinLockOrFail (SpinLock)) {
      CpuPause ();
    }
  }
  return SpinLock;
}

/**
  Attempts to place a spin lock in the acquired state.

This function checks the state of the spin lock specified by SpinLock. If
  SpinLock is in the released state, then this function places SpinLock in the
  acquired state and returns TRUE. Otherwise, FALSE is returned. All state
  transitions of SpinLock must be performed using MP safe mechanisms.

If SpinLock is NULL, then ASSERT().
  If SpinLock was not initialized with InitializeSpinLock(), then ASSERT().

@param  SpinLock  A pointer to the spin lock to place in the acquired state.

@retval TRUE  SpinLock was placed in the acquired state.
  @retval FALSE SpinLock could not be acquired.

**/
BOOLEAN
EFIAPI
AcquireSpinLockOrFail (
  IN OUT  SPIN_LOCK                 *SpinLock
  )
{
  SPIN_LOCK    LockValue;

ASSERT (SpinLock != NULL);

LockValue = *SpinLock;
  ASSERT (SPIN_LOCK_ACQUIRED == LockValue || SPIN_LOCK_RELEASED == LockValue);

return (BOOLEAN)(
           InterlockedCompareExchangePointer (
             (VOID**)SpinLock,
             (VOID*)SPIN_LOCK_RELEASED,
             (VOID*)SPIN_LOCK_ACQUIRED
             ) == (VOID*)SPIN_LOCK_RELEASED
           );
}

/**
  Releases a spin lock.

This function places the spin lock specified by SpinLock in the release state
  and returns SpinLock.

If SpinLock is NULL, then ASSERT().
  If SpinLock was not initialized with InitializeSpinLock(), then ASSERT().

@param  SpinLock  A pointer to the spin lock to release.

@return SpinLock released lock.

**/
SPIN_LOCK *
EFIAPI
ReleaseSpinLock (
  IN OUT  SPIN_LOCK                 *SpinLock
  )
{
  SPIN_LOCK    LockValue;

ASSERT (SpinLock != NULL);

LockValue = *SpinLock;
  ASSERT (SPIN_LOCK_ACQUIRED == LockValue || SPIN_LOCK_RELEASED == LockValue);

*SpinLock = SPIN_LOCK_RELEASED;
  return SpinLock;
}

/**
  Performs an atomic increment of an 32-bit unsigned integer.

Performs an atomic increment of the 32-bit unsigned integer specified by
  Value and returns the incremented value. The increment operation must be
  performed using MP safe mechanisms. The state of the return value is not
  guaranteed to be MP safe.