/* Hurd helpers for lowlevellocks.

   Copyright (C) 1999-2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or

   modify it under the terms of the GNU Lesser General Public

   License as published by the Free Software Foundation; either

   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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

   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public

   License along with the GNU C Library; if not, see

   <http://www.gnu.org/licenses/>.  */

#include "hurdlock.h"

#include <hurd.h>

#include <hurd/hurd.h>

#include <time.h>

#include <errno.h>

#include <unistd.h>

/* Convert an absolute timeout in nanoseconds to a relative

   timeout in milliseconds.  */

static inline int __attribute__ ((gnu_inline))

compute_reltime (const struct timespec *abstime, clockid_t clk)

{

  struct timespec ts;

  __clock_gettime (clk, &ts);

  ts.tv_sec = abstime->tv_sec - ts.tv_sec;

  ts.tv_nsec = abstime->tv_nsec - ts.tv_nsec;

  if (ts.tv_nsec < 0)

    {

      --ts.tv_sec;

      ts.tv_nsec += 1000000000;

    }

  return ts.tv_sec < 0 ? -1 : (int)(ts.tv_sec * 1000 + ts.tv_nsec / 1000000);

}

int

__lll_abstimed_wait (void *ptr, int val,

  const struct timespec *tsp, int flags, int clk)

{

  int mlsec = compute_reltime (tsp, clk);

  return mlsec < 0 ? KERN_TIMEDOUT : lll_timed_wait (ptr, val, mlsec, flags);

}

int

__lll_abstimed_xwait (void *ptr, int lo, int hi,

  const struct timespec *tsp, int flags, int clk)

{

  int mlsec = compute_reltime (tsp, clk);

  return mlsec < 0 ? KERN_TIMEDOUT : lll_timed_xwait (ptr, lo, hi, mlsec,

	                                              flags);

}

int

__lll_abstimed_lock (void *ptr,

  const struct timespec *tsp, int flags, int clk)

{

  if (lll_trylock (ptr) == 0)

    return 0;

  while (1)

    {

      if (atomic_exchange_acq ((int *)ptr, 2) == 0)

        return 0;

      else if (tsp->tv_nsec < 0 || tsp->tv_nsec >= 1000000000)

        return EINVAL;

      int mlsec = compute_reltime (tsp, clk);

      if (mlsec < 0 || lll_timed_wait (ptr, 2, mlsec, flags) == KERN_TIMEDOUT)

        return ETIMEDOUT;

    }

}

/* Robust locks.  */

/* Test if a given process id is still valid.  */

static inline int

valid_pid (int pid)

{

  task_t task = __pid2task (pid);

  if (task == MACH_PORT_NULL)

    return 0;

  __mach_port_deallocate (__mach_task_self (), task);

  return 1;

}

/* Robust locks have currently no support from the kernel; they

   are simply implemented with periodic polling. When sleeping, the

   maximum blocking time is determined by this constant.  */

#define MAX_WAIT_TIME   1500

int

__lll_robust_lock (void *ptr, int flags)

{

  int *iptr = (int *)ptr;

  int id = __getpid ();

  int wait_time = 25;

  unsigned int val;

  /* Try to set the lock word to our PID if it's clear. Otherwise,

     mark it as having waiters.  */

  while (1)

    {

      val = *iptr;

      if (!val && atomic_compare_and_exchange_bool_acq (iptr, id, 0) == 0)

        return 0;

      else if (atomic_compare_and_exchange_bool_acq (iptr,

               val | LLL_WAITERS, val) == 0)

        break;

    }

  for (id |= LLL_WAITERS ; ; )

    {

      val = *iptr;

      if (!val && atomic_compare_and_exchange_bool_acq (iptr, id, 0) == 0)

        return 0;

      else if (val && !valid_pid (val & LLL_OWNER_MASK))

        {

          if (atomic_compare_and_exchange_bool_acq (iptr, id, val) == 0)

            return EOWNERDEAD;

        }

      else

        {

          lll_timed_wait (iptr, val, wait_time, flags);

          if (wait_time < MAX_WAIT_TIME)

            wait_time <<= 1;

        }

    }

}

int

__lll_robust_abstimed_lock (void *ptr,

  const struct timespec *tsp, int flags, int clk)

{

  int *iptr = (int *)ptr;

  int id = __getpid ();

  int wait_time = 25;

  unsigned int val;

  while (1)

    {

      val = *iptr;

      if (!val && atomic_compare_and_exchange_bool_acq (iptr, id, 0) == 0)

        return 0;

      else if (atomic_compare_and_exchange_bool_acq (iptr,

          val | LLL_WAITERS, val) == 0)

        break;

    }

  for (id |= LLL_WAITERS ; ; )

    {

      val = *iptr;

      if (!val && atomic_compare_and_exchange_bool_acq (iptr, id, 0) == 0)

        return 0;

      else if (val && !valid_pid (val & LLL_OWNER_MASK))

        {

          if (atomic_compare_and_exchange_bool_acq (iptr, id, val) == 0)

            return EOWNERDEAD;

        }

      else

        {

          int mlsec = compute_reltime (tsp, clk);

          if (mlsec < 0)

            return ETIMEDOUT;

          else if (mlsec > wait_time)

            mlsec = wait_time;

          int res = lll_timed_wait (iptr, val, mlsec, flags);

          if (res == KERN_TIMEDOUT)

            return ETIMEDOUT;

          else if (wait_time < MAX_WAIT_TIME)

            wait_time <<= 1;

        }

    }

}

int

__lll_robust_trylock (void *ptr)

{

  int *iptr = (int *)ptr;

  int id = __getpid ();

  unsigned int val = *iptr;

  if (!val)

    {

      if (atomic_compare_and_exchange_bool_acq (iptr, id, 0) == 0)

        return 0;

    }

  else if (!valid_pid (val & LLL_OWNER_MASK)

           && atomic_compare_and_exchange_bool_acq (iptr, id, val) == 0)

    return EOWNERDEAD;

  return EBUSY;

}

void

__lll_robust_unlock (void *ptr, int flags)

{

  unsigned int val = atomic_load_relaxed ((unsigned int *)ptr);

  while (1)

    {

      if (val & LLL_WAITERS)

        {

          lll_set_wake (ptr, 0, flags);

          break;

        }

      else if (atomic_compare_exchange_weak_release ((unsigned int *)ptr, &val, 0))

        break;

    }

}