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/* Delayed deallocation of port_info objects.
Copyright (C) 2015 Free Software Foundation, Inc.
Written by Justus Winter <4winter@informatik.uni-hamburg.de>
This file is part of the GNU Hurd.
The GNU Hurd is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2, or (at
your option) any later version.
The GNU Hurd 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
General Public License for more details.
You should have received a copy of the GNU General Public License
along with the GNU Hurd. If not, see <http://www.gnu.org/licenses/>. */
#include <assert.h>
#include <pthread.h>
#include "ports.h"
/*
* A threadpool has a color indicating which threads belong to the old
* generation.
*/
#define COLOR_BLACK 0
#define COLOR_WHITE 1
#define COLOR_INVALID ~0U
static inline int
valid_color (unsigned int c)
{
return c == COLOR_BLACK || c == COLOR_WHITE;
}
static inline unsigned int
flip_color (unsigned int c)
{
assert (valid_color (c));
return ! c;
}
/* Initialize the thread pool. */
void
_ports_threadpool_init (struct ports_threadpool *pool)
{
pthread_spin_init (&pool->lock, PTHREAD_PROCESS_PRIVATE);
pool->color = COLOR_BLACK;
pool->old_threads = 0;
pool->old_objects = NULL;
pool->young_threads = 0;
pool->young_objects = NULL;
}
/* Turn all young objects and threads into old ones. */
static inline void
flip_generations (struct ports_threadpool *pool)
{
assert (pool->old_threads == 0);
pool->old_threads = pool->young_threads;
pool->old_objects = pool->young_objects;
pool->young_threads = 0;
pool->young_objects = NULL;
pool->color = flip_color (pool->color);
}
/* Called by a thread to join a thread pool. */
void
_ports_thread_online (struct ports_threadpool *pool,
struct ports_thread *thread)
{
pthread_spin_lock (&pool->lock);
thread->color = flip_color (pool->color);
pool->young_threads += 1;
pthread_spin_unlock (&pool->lock);
}
struct pi_list
{
struct pi_list *next;
struct port_info *pi;
};
/* Called by a thread that enters its quiescent period. */
void
_ports_thread_quiescent (struct ports_threadpool *pool,
struct ports_thread *thread)
{
struct pi_list *free_list = NULL, *p;
assert (valid_color (thread->color));
pthread_spin_lock (&pool->lock);
if (thread->color == pool->color)
{
pool->old_threads -= 1;
pool->young_threads += 1;
thread->color = flip_color (thread->color);
if (pool->old_threads == 0)
{
free_list = pool->old_objects;
flip_generations (pool);
}
}
pthread_spin_unlock (&pool->lock);
for (p = free_list; p;)
{
struct pi_list *old = p;
p = p->next;
ports_port_deref (old->pi);
free (old);
}
}
/* Called by a thread to leave a thread pool. */
void
_ports_thread_offline (struct ports_threadpool *pool,
struct ports_thread *thread)
{
assert (valid_color (thread->color));
retry:
pthread_spin_lock (&pool->lock);
if (thread->color == pool->color)
{
pthread_spin_unlock (&pool->lock);
_ports_thread_quiescent (pool, thread);
goto retry;
}
thread->color = COLOR_INVALID;
pool->young_threads -= 1;
pthread_spin_unlock (&pool->lock);
}
/* Schedule an object for deallocation. */
void
_ports_port_deref_deferred (struct port_info *pi)
{
struct ports_threadpool *pool = &pi->bucket->threadpool;
struct pi_list *pl = malloc (sizeof *pl);
if (pl == NULL)
return;
pl->pi = pi;
pthread_spin_lock (&pool->lock);
pl->next = pool->young_objects;
pool->young_objects = pl;
if (pool->old_threads == 0)
{
assert (pool->old_objects == NULL);
flip_generations (pool);
}
pthread_spin_unlock (&pool->lock);
}
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