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9b7aa536ba
This "quiescent state based reclamation" module provides support for
the qp-trie module in dns/qp. It is a replacement for liburcu, written
without reference to the urcu source code, and in fact it works in a
significantly different way.
A few specifics of BIND make this variant of QSBR somewhat simpler:
* We can require that wait-free access to a qp-trie only happens in
an isc_loop callback. The loop provides a natural quiescent state,
after the callbacks are done, when no qp-trie access occurs.
* We can dispense with any API like rcu_synchronize(). In practice,
it takes far too long to wait for a grace period to elapse for each
write to a data structure.
* We use the idea of "phases" (aka epochs or eras) from EBR to
reduce the amount of bookkeeping needed to track memory that is no
longer needed, knowing that the qp-trie does most of that work
already.
I considered hazard pointers for safe memory reclamation. They have
more read-side overhead (updating the hazard pointers) and it wasn't
clear to me how to nicely schedule the cleanup work. Another
alternative, epoch-based reclamation, is designed for fine-grained
lock-free updates, so it needs some rethinking to work well with the
heavily read-biased design of the qp-trie. QSBR has the fastest read
side of the basic SMR algorithms (with no barriers), and fits well
into a libuv loop. More recent hybrid SMR algorithms do not appear to
have enough benefits to justify the extra complexity.
156 lines
3 KiB
C
156 lines
3 KiB
C
/*
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* Copyright (C) Internet Systems Consortium, Inc. ("ISC")
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*
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* SPDX-License-Identifier: MPL-2.0
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*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, you can obtain one at https://mozilla.org/MPL/2.0/.
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*
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* See the COPYRIGHT file distributed with this work for additional
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* information regarding copyright ownership.
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*/
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#pragma once
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#include <inttypes.h>
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#include <isc/barrier.h>
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#include <isc/lang.h>
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#include <isc/loop.h>
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#include <isc/magic.h>
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#include <isc/mem.h>
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#include <isc/qsbr.h>
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#include <isc/refcount.h>
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#include <isc/result.h>
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#include <isc/signal.h>
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#include <isc/stack.h>
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#include <isc/thread.h>
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#include <isc/types.h>
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#include <isc/uv.h>
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#include <isc/work.h>
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/*
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* Per-thread loop
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*/
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#define LOOP_MAGIC ISC_MAGIC('L', 'O', 'O', 'P')
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#define VALID_LOOP(t) ISC_MAGIC_VALID(t, LOOP_MAGIC)
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typedef ISC_LIST(isc_job_t) isc_joblist_t;
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typedef ISC_ASTACK(isc_job_t) isc_jobstack_t;
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struct isc_loop {
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int magic;
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isc_refcount_t references;
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isc_thread_t thread;
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isc_loopmgr_t *loopmgr;
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uv_loop_t loop;
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uint32_t tid;
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isc_mem_t *mctx;
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/* states */
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bool paused;
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bool shuttingdown;
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/* Async queue */
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uv_async_t queue_trigger;
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isc_jobstack_t queue_jobs;
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/* Pause */
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uv_async_t pause_trigger;
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/* Shutdown */
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uv_async_t shutdown_trigger;
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isc_joblist_t setup_jobs;
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isc_joblist_t teardown_jobs;
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/* Destroy */
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uv_async_t destroy_trigger;
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/* safe memory reclamation */
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uv_async_t wakeup_trigger;
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uv_prepare_t quiescent;
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isc_qsbr_phase_t qsbr_phase;
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};
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/*
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* Loop Manager
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*/
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#define LOOPMGR_MAGIC ISC_MAGIC('L', 'o', 'o', 'M')
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#define VALID_LOOPMGR(t) ISC_MAGIC_VALID(t, LOOPMGR_MAGIC)
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struct isc_loopmgr {
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int magic;
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isc_mem_t *mctx;
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uint_fast32_t nloops;
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atomic_bool shuttingdown;
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atomic_bool running;
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atomic_bool paused;
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/* signal handling */
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isc_signal_t *sigint;
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isc_signal_t *sigterm;
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/* pause/resume */
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isc_barrier_t pausing;
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isc_barrier_t resuming;
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/* start/stop */
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isc_barrier_t starting;
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/* stopping */
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isc_barrier_t stopping;
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/* per-thread objects */
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isc_loop_t *loops;
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/* safe memory reclamation */
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isc_qsbr_t qsbr;
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};
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/*
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* Signal Handler
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*/
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struct isc_signal {
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uv_signal_t signal;
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isc_loop_t *loop;
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isc_signal_cb cb;
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void *cbarg;
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int signum;
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};
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/*
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* Job to be scheduled in an event loop
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*/
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#define JOB_MAGIC ISC_MAGIC('J', 'O', 'B', ' ')
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#define VALID_JOB(t) ISC_MAGIC_VALID(t, JOB_MAGIC)
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struct isc_job {
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int magic;
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uv_idle_t idle;
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isc_loop_t *loop;
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isc_job_cb cb;
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void *cbarg;
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ISC_LINK(isc_job_t) link;
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};
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/*
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* Work to be offloaded to an external thread.
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*/
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struct isc_work {
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uv_work_t work;
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isc_loop_t *loop;
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isc_work_cb work_cb;
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isc_after_work_cb after_work_cb;
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void *cbarg;
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};
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#define DEFAULT_LOOP(loopmgr) (&(loopmgr)->loops[0])
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#define CURRENT_LOOP(loopmgr) (&(loopmgr)->loops[isc_tid()])
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#define LOOP(loopmgr, tid) (&(loopmgr)->loops[tid])
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#define ON_LOOP(loop) ((loop) == CURRENT_LOOP((loop)->loopmgr))
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