a752c7ab
 elopes
add first test an...
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/*
* POSIX compatible implementation of barriers.
*
* Copyright (C) 2014 Freie Universität Berlin
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License v2.1. See the file LICENSE in the top level
* directory for more details.
*/
/**
* @ingroup pthread
* @{
* @file
* @brief Synchronization barriers.
* @author René Kijewski <kijewski@inf.fu-berlin.de>
* @}
*/
#include "sched.h"
#include "pthread.h"
#define ENABLE_DEBUG (0)
#include "debug.h"
int pthread_barrier_init(pthread_barrier_t *barrier,
const pthread_barrierattr_t *attr,
unsigned int count)
{
(void) attr;
barrier->next = NULL;
mutex_init(&barrier->mutex);
barrier->count = count;
return 0;
}
int pthread_barrier_destroy(pthread_barrier_t *barrier)
{
barrier->count = -1;
return 0;
}
static inline int priority_min(int a, int b)
{
if (a == -1) {
return b;
}
return a < b ? a : b;
}
int pthread_barrier_wait(pthread_barrier_t *barrier)
{
/* Idea: the count is decreased by every thread that waits on the barrier.
* If the value is bigger than zero afterwards, then the thread has to wait
* to be woken up. Once the value reaches zero, everyone gets woken up. */
mutex_lock(&barrier->mutex);
DEBUG("%s: hit a synchronization barrier. pid=%" PRIkernel_pid"\n",
sched_active_thread->name, sched_active_pid);
int switch_prio = -1;
if (--barrier->count > 0) {
/* need to wait for further threads */
DEBUG("%s: waiting for %u threads. pid=%" PRIkernel_pid "\n",
sched_active_thread->name, barrier->count, sched_active_pid);
pthread_barrier_waiting_node_t node;
node.pid = sched_active_pid;
node.next = barrier->next;
node.cont = 0;
barrier->next = &node;
mutex_unlock(&barrier->mutex);
while (1) {
/* The mutex is reacquired before checking if we should continue,
* so that the waiting thread don't accidentially run before the
* wake up loop has ended. Otherwise the thread could run into the
* the barrier again before `barrier->count` was reset. */
mutex_lock(&barrier->mutex);
if (node.cont) {
break;
}
mutex_unlock_and_sleep(&barrier->mutex);
}
}
else {
/* all threads have arrived, wake everybody up */
DEBUG("%s: waking every other thread up. pid=%" PRIkernel_pid "\n",
sched_active_thread->name, sched_active_pid);
int count = 1; /* Count number of woken up threads.
* The first thread is the current thread. */
pthread_barrier_waiting_node_t *next;
for (next = barrier->next; next; next = next->next) {
++count;
next->cont = 1;
thread_t *other = (thread_t *) sched_threads[next->pid];
switch_prio = priority_min(switch_prio, other->priority);
sched_set_status(other, STATUS_PENDING);
}
barrier->next = NULL;
barrier->count = count;
}
mutex_unlock(&barrier->mutex);
if (switch_prio != -1) {
sched_switch(switch_prio);
}
return 0;
}
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