0
0
mirror of https://gitlab.nic.cz/labs/bird.git synced 2024-12-25 03:01:55 +00:00
bird/lib/rcu.c
2024-06-28 22:03:45 +02:00

107 lines
2.9 KiB
C

/*
* BIRD Library -- Read-Copy-Update Basic Operations
*
* (c) 2021 Maria Matejka <mq@jmq.cz>
* (c) 2021 CZ.NIC z.s.p.o.
*
* Can be freely distributed and used under the terms of the GNU GPL.
* Note: all the relevant patents shall be expired.
*
* Using the Supplementary Material for User-Level Implementations of Read-Copy-Update
* by Matthieu Desnoyers, Paul E. McKenney, Alan S. Stern, Michel R. Dagenais and Jonathan Walpole
* obtained from https://www.efficios.com/pub/rcu/urcu-supp-accepted.pdf
*/
#include "lib/rcu.h"
#include "lib/io-loop.h"
#include "lib/locking.h"
_Atomic u64 rcu_global_phase = RCU_GP_PHASE;
_Thread_local struct rcu_thread this_rcu_thread;
static struct rcu_thread * _Atomic rcu_thread_list = NULL;
static _Atomic uint rcu_thread_spinlock = 0;
static int
rcu_critical(struct rcu_thread *t, u64 phase)
{
uint val = atomic_load_explicit(&t->ctl, memory_order_acquire);
return
(val & RCU_NEST_MASK) /* Active */
&& ((val & ~RCU_NEST_MASK) <= phase); /* In an older phase */
}
void
synchronize_rcu(void)
{
/* Increment phase */
u64 phase = atomic_fetch_add_explicit(&rcu_global_phase, RCU_GP_PHASE, memory_order_acq_rel);
while (1) {
/* Spinlock */
while (atomic_exchange_explicit(&rcu_thread_spinlock, 1, memory_order_acq_rel))
birdloop_yield();
/* Check all threads */
bool critical = 0;
for (struct rcu_thread * _Atomic *tp = &rcu_thread_list, *t;
t = atomic_load_explicit(tp, memory_order_acquire);
tp = &t->next)
/* Found a critical */
if (critical = rcu_critical(t, phase))
break;
/* Unlock */
ASSERT_DIE(atomic_exchange_explicit(&rcu_thread_spinlock, 0, memory_order_acq_rel));
/* Done if no critical */
if (!critical)
return;
/* Wait and retry if critical */
birdloop_yield();
}
}
void
rcu_thread_start(void)
{
/* Insert this thread to the thread list, no spinlock is needed */
struct rcu_thread *next = atomic_load_explicit(&rcu_thread_list, memory_order_acquire);
do atomic_store_explicit(&this_rcu_thread.next, next, memory_order_relaxed);
while (!atomic_compare_exchange_strong_explicit(
&rcu_thread_list, &next, &this_rcu_thread,
memory_order_acq_rel, memory_order_acquire));
}
void
rcu_thread_stop(void)
{
/* Spinlock */
while (atomic_exchange_explicit(&rcu_thread_spinlock, 1, memory_order_acq_rel))
birdloop_yield();
/* Find this thread */
for (struct rcu_thread * _Atomic *tp = &rcu_thread_list, *t;
t = atomic_load_explicit(tp, memory_order_acquire);
tp = &t->next)
if (t == &this_rcu_thread)
{
/* Remove this thread */
atomic_store_explicit(tp, atomic_load_explicit(&t->next, memory_order_acquire), memory_order_release);
/* Unlock and go */
ASSERT_DIE(atomic_exchange_explicit(&rcu_thread_spinlock, 0, memory_order_acq_rel));
return;
}
bug("Failed to find a stopped rcu thread");
}
void
rcu_init(void)
{
rcu_thread_start();
}