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/* Thread Priority Protect helpers.
Copyright (C) 2006-2022 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 <assert.h>
#include <atomic.h>
#include <errno.h>
#include <pthreadP.h>
#include <sched.h>
#include <stdlib.h>
#include <atomic.h>
int __sched_fifo_min_prio = -1;
libc_hidden_data_def (__sched_fifo_min_prio)
int __sched_fifo_max_prio = -1;
libc_hidden_data_def (__sched_fifo_max_prio)
/* We only want to initialize __sched_fifo_min_prio and __sched_fifo_max_prio
once. The standard solution would be similar to pthread_once, but then
readers would need to use an acquire fence. In this specific case,
initialization is comprised of just idempotent writes to two variables
that have an initial value of -1. Therefore, we can treat each variable as
a separate, at-least-once initialized value. This enables using just
relaxed MO loads and stores, but requires that consumers check for
initialization of each value that is to be used; see
__pthread_tpp_change_priority for an example.
*/
void
__init_sched_fifo_prio (void)
{
atomic_store_relaxed (&__sched_fifo_max_prio,
__sched_get_priority_max (SCHED_FIFO));
atomic_store_relaxed (&__sched_fifo_min_prio,
__sched_get_priority_min (SCHED_FIFO));
}
libc_hidden_def (__init_sched_fifo_prio)
int
__pthread_tpp_change_priority (int previous_prio, int new_prio)
{
struct pthread *self = THREAD_SELF;
struct priority_protection_data *tpp = THREAD_GETMEM (self, tpp);
int fifo_min_prio = atomic_load_relaxed (&__sched_fifo_min_prio);
int fifo_max_prio = atomic_load_relaxed (&__sched_fifo_max_prio);
if (tpp == NULL)
{
/* See __init_sched_fifo_prio. We need both the min and max prio,
so need to check both, and run initialization if either one is
not initialized. The memory model's write-read coherence rule
makes this work. */
if (fifo_min_prio == -1 || fifo_max_prio == -1)
{
__init_sched_fifo_prio ();
fifo_min_prio = atomic_load_relaxed (&__sched_fifo_min_prio);
fifo_max_prio = atomic_load_relaxed (&__sched_fifo_max_prio);
}
size_t size = sizeof *tpp;
size += (fifo_max_prio - fifo_min_prio + 1)
* sizeof (tpp->priomap[0]);
tpp = calloc (size, 1);
if (tpp == NULL)
return ENOMEM;
tpp->priomax = fifo_min_prio - 1;
THREAD_SETMEM (self, tpp, tpp);
}
assert (new_prio == -1
|| (new_prio >= fifo_min_prio
&& new_prio <= fifo_max_prio));
assert (previous_prio == -1
|| (previous_prio >= fifo_min_prio
&& previous_prio <= fifo_max_prio));
int priomax = tpp->priomax;
int newpriomax = priomax;
if (new_prio != -1)
{
if (tpp->priomap[new_prio - fifo_min_prio] + 1 == 0)
return EAGAIN;
++tpp->priomap[new_prio - fifo_min_prio];
if (new_prio > priomax)
newpriomax = new_prio;
}
if (previous_prio != -1)
{
if (--tpp->priomap[previous_prio - fifo_min_prio] == 0
&& priomax == previous_prio
&& previous_prio > new_prio)
{
int i;
for (i = previous_prio - 1; i >= fifo_min_prio; --i)
if (tpp->priomap[i - fifo_min_prio])
break;
newpriomax = i;
}
}
if (priomax == newpriomax)
return 0;
/* See CREATE THREAD NOTES in nptl/pthread_create.c. */
lll_lock (self->lock, LLL_PRIVATE);
tpp->priomax = newpriomax;
int result = 0;
if ((self->flags & ATTR_FLAG_SCHED_SET) == 0)
{
if (__sched_getparam (self->tid, &self->schedparam) != 0)
result = errno;
else
self->flags |= ATTR_FLAG_SCHED_SET;
}
if ((self->flags & ATTR_FLAG_POLICY_SET) == 0)
{
self->schedpolicy = __sched_getscheduler (self->tid);
if (self->schedpolicy == -1)
result = errno;
else
self->flags |= ATTR_FLAG_POLICY_SET;
}
if (result == 0)
{
struct sched_param sp = self->schedparam;
if (sp.sched_priority < newpriomax || sp.sched_priority < priomax)
{
if (sp.sched_priority < newpriomax)
sp.sched_priority = newpriomax;
if (__sched_setscheduler (self->tid, self->schedpolicy, &sp) < 0)
result = errno;
}
}
lll_unlock (self->lock, LLL_PRIVATE);
return result;
}
libc_hidden_def (__pthread_tpp_change_priority)
int
__pthread_current_priority (void)
{
struct pthread *self = THREAD_SELF;
if ((self->flags & (ATTR_FLAG_POLICY_SET | ATTR_FLAG_SCHED_SET))
== (ATTR_FLAG_POLICY_SET | ATTR_FLAG_SCHED_SET))
return self->schedparam.sched_priority;
int result = 0;
/* See CREATE THREAD NOTES in nptl/pthread_create.c. */
lll_lock (self->lock, LLL_PRIVATE);
if ((self->flags & ATTR_FLAG_SCHED_SET) == 0)
{
if (__sched_getparam (self->tid, &self->schedparam) != 0)
result = -1;
else
self->flags |= ATTR_FLAG_SCHED_SET;
}
if ((self->flags & ATTR_FLAG_POLICY_SET) == 0)
{
self->schedpolicy = __sched_getscheduler (self->tid);
if (self->schedpolicy == -1)
result = -1;
else
self->flags |= ATTR_FLAG_POLICY_SET;
}
if (result != -1)
result = self->schedparam.sched_priority;
lll_unlock (self->lock, LLL_PRIVATE);
return result;
}
libc_hidden_def (__pthread_current_priority)
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