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/* Hurd helpers for lowlevellocks.
Copyright (C) 1999-2020 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
<https://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 (! valid_nanoseconds (tsp->tv_nsec))
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;
}
}
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