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