brpc/src/bthread/timer_thread.cpp at master · apache/brpc · GitHub

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// Licensed to the Apache Software Foundation (ASF) under one

// or more contributor license agreements. See the NOTICE file

// distributed with this work for additional information

// regarding copyright ownership. The ASF licenses this file

// to you under the Apache License, Version 2.0 (the

// "License"); you may not use this file except in compliance

// with the License. You may obtain a copy of the License at

// http://www.apache.org/licenses/LICENSE-2.0

// Unless required by applicable law or agreed to in writing,

// software distributed under the License is distributed on an

// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY

// KIND, either express or implied. See the License for the

// specific language governing permissions and limitations

// under the License.

// bthread - An M:N threading library to make applications more concurrent.

#include <queue> // heap functions

#include <gflags/gflags.h>

#include "butil/scoped_lock.h"

#include "butil/logging.h"

#include "butil/third_party/murmurhash3/murmurhash3.h" // fmix64

#include "butil/resource_pool.h"

#include "butil/threading/platform_thread.h"

#include "bvar/bvar.h"

#include "bthread/sys_futex.h"

#include "bthread/timer_thread.h"

#include "bthread/log.h"

namespace bthread {

DEFINE_uint32(brpc_timer_num_buckets, 13, "brpc timer num buckets");

// Tasks unscheduled after being pulled into the timer thread's min-heap are

// only recycled when popped at their run_time, which can be far in the future

// for large timeouts. To bound the memory they occupy (~ qps * timeout), the

// timer thread periodically sweeps the heap and drops unscheduled tasks. The

// sweep only kicks in once the heap grows beyond this size, so that small

// heaps (where the retained memory is negligible) never pay the O(N) cost.

DEFINE_uint32(brpc_timer_heap_sweep_min_size, 4096,

"The timer thread sweeps unscheduled tasks out of its internal "

"heap only when the heap has at least this many tasks");

// The timer thread only consumes buckets and reclaims unscheduled tasks when

// it wakes up, which normally happens at the nearest task's run_time. If every

// pending task has a far-future run_time (e.g. minutes away), the thread would

// sleep that whole time while newly scheduled-then-unscheduled tasks pile up

// in the buckets, occupying pooled slots for the entire duration. Capping the

// sleep makes the thread wake up periodically to drain the buckets and sweep

// the heap, bounding that latency regardless of the timeout distribution.

// 0 (the default) disables the cap: sleep until the nearest run_time, the

// legacy behavior. Set it to a positive value to bound reclaim latency when

// tasks may have far-future run_times.

DEFINE_uint32(brpc_timer_max_wakeup_interval_ms, 0,

"The timer thread wakes up at least this often (in milliseconds) "

"to reclaim unscheduled tasks even when all pending tasks are far "

"in the future; 0 means no periodic wakeup");

// Defined in task_control.cpp

void run_worker_startfn();

const TimerThread::TaskId TimerThread::INVALID_TASK_ID = 0;

TimerThreadOptions::TimerThreadOptions()

: num_buckets(13) {

}

// A task contains the necessary information for running fn(arg).

// Tasks are created in Bucket::schedule and destroyed in TimerThread::run

struct BAIDU_CACHELINE_ALIGNMENT TimerThread::Task {

Task* next; // For linking tasks in a Bucket.

int64_t run_time; // run the task at this realtime

void (*fn)(void*); // the fn(arg) to run

void* arg;

// Current TaskId, checked against version in TimerThread::run to test

// if this task is unscheduled.

TaskId task_id;

// initial_version: not run yet

// initial_version + 1: running

// initial_version + 2: removed (also the version of next Task reused

// this struct)

butil::atomic<uint32_t> version;

Task() : version(2/*skip 0*/) {}

// Run this task and delete this struct.

// Returns true if fn(arg) did run.

bool run_and_delete();

// Delete this struct if this task was unscheduled.

// Returns true on deletion.

bool try_delete();

};

// Timer tasks are sharded into different Buckets to reduce contentions.

class BAIDU_CACHELINE_ALIGNMENT TimerThread::Bucket {

public:

Bucket()

: _nearest_run_time(std::numeric_limits<int64_t>::max())

, _task_head(nullptr) {

}

~Bucket() {}

struct ScheduleResult {

TimerThread::TaskId task_id;

bool earlier;

};

// Schedule a task into this bucket.

// Returns the TaskId and if it has the nearest run time.

ScheduleResult schedule(void (*fn)(void*), void* arg,

const timespec& abstime);

// Pull all scheduled tasks.

// This function is called in timer thread.

Task* consume_tasks();

private:

FastPthreadMutex _mutex;

int64_t _nearest_run_time;

Task* _task_head;

};

// Utilies for making and extracting TaskId.

inline TimerThread::TaskId make_task_id(

butil::ResourceId<TimerThread::Task> slot, uint32_t version) {

return TimerThread::TaskId((((uint64_t)version) << 32) | slot.value);

}

inline

butil::ResourceId<TimerThread::Task> slot_of_task_id(TimerThread::TaskId id) {

butil::ResourceId<TimerThread::Task> slot = { (id & 0xFFFFFFFFul) };

return slot;

}

inline uint32_t version_of_task_id(TimerThread::TaskId id) {

return (uint32_t)(id >> 32);

}

inline bool task_greater(const TimerThread::Task* a, const TimerThread::Task* b) {

return a->run_time > b->run_time;

}

void* TimerThread::run_this(void* arg) {

butil::PlatformThread::SetNameSimple("brpc_timer");

static_cast<TimerThread*>(arg)->run();

return nullptr;

}

TimerThread::TimerThread()

: _started(false)

, _stop(false)

, _buckets(nullptr)

, _nearest_run_time(std::numeric_limits<int64_t>::max())

, _nsignals(0)

, _npending(0)

, _thread(0) {

}

TimerThread::~TimerThread() {

stop_and_join();

delete [] _buckets;

_buckets = nullptr;

}

int TimerThread::start(const TimerThreadOptions* options_in) {

if (_started) {

return 0;

}

if (options_in) {

_options = *options_in;

}

if (_options.num_buckets == 0) {

LOG(ERROR) << "num_buckets can't be 0";

return EINVAL;

}

if (_options.num_buckets > 1024) {

LOG(ERROR) << "num_buckets=" << _options.num_buckets << " is too big";

return EINVAL;

}

_buckets = new Bucket[_options.num_buckets];

const int ret = pthread_create(&_thread, nullptr, TimerThread::run_this, this);

if (ret) {

return ret;

}

_started = true;

return 0;

}

TimerThread::Task* TimerThread::Bucket::consume_tasks() {

Task* head = nullptr;

if (_task_head) { // NOTE: schedule() and consume_tasks() are sequenced

// by TimerThread._nearest_run_time and fenced by TimerThread._mutex.

// We can avoid touching the mutex and related cacheline when the

// bucket is actually empty.

BAIDU_SCOPED_LOCK(_mutex);

if (_task_head) {

head = _task_head;

_task_head = nullptr;

_nearest_run_time = std::numeric_limits<int64_t>::max();

}

return head;

}

TimerThread::Bucket::ScheduleResult

TimerThread::Bucket::schedule(void (*fn)(void*), void* arg,

const timespec& abstime) {

butil::ResourceId<Task> slot_id;

Task* task = butil::get_resource<Task>(&slot_id);

if (task == nullptr) {

ScheduleResult result = { INVALID_TASK_ID, false };

return result;

}

task->next = nullptr;

task->fn = fn;

task->arg = arg;

task->run_time = butil::timespec_to_microseconds(abstime);

uint32_t version = task->version.load(butil::memory_order_relaxed);

if (version == 0) { // skip 0.

task->version.fetch_add(2, butil::memory_order_relaxed);

version = 2;

}

const TaskId id = make_task_id(slot_id, version);

task->task_id = id;

bool earlier = false;

{

BAIDU_SCOPED_LOCK(_mutex);

task->next = _task_head;

_task_head = task;

if (task->run_time < _nearest_run_time) {

_nearest_run_time = task->run_time;

earlier = true;

}

ScheduleResult result = { id, earlier };

return result;

}

TimerThread::TaskId TimerThread::schedule(

void (*fn)(void*), void* arg, const timespec& abstime) {

if (_stop.load(butil::memory_order_relaxed) || !_started) {

// Not add tasks when TimerThread is about to stop.

return INVALID_TASK_ID;

}

// Hashing by pthread id is better for cache locality.

const Bucket::ScheduleResult result =

_buckets[butil::fmix64(pthread_numeric_id()) % _options.num_buckets]

.schedule(fn, arg, abstime);

if (result.earlier) {

bool earlier = false;

const int64_t run_time = butil::timespec_to_microseconds(abstime);

{

BAIDU_SCOPED_LOCK(_mutex);

if (run_time < _nearest_run_time) {

_nearest_run_time = run_time;

++_nsignals;

earlier = true;

}

if (earlier) {

futex_wake_private(&_nsignals, 1);

}

return result.task_id;

}

// Notice that we don't recycle the Task in this function, let TimerThread::run

// do it. The side effect is that we may allocate many unscheduled tasks before

// TimerThread wakes up. The number is approximately qps * timeout_s. Under the

// precondition that ResourcePool<Task> caches 128K for each thread, with some

// further calculations, we can conclude that in a RPC scenario:

// when timeout / latency < 2730 (128K / sizeof(Task))

// unscheduled tasks do not occupy additional memory. 2730 is a large ratio

// between timeout and latency in most RPC scenarios, this is why we don't

// try to reuse tasks right now inside unschedule() with more complicated code.

int TimerThread::unschedule(TaskId task_id) {

const butil::ResourceId<Task> slot_id = slot_of_task_id(task_id);

Task* const task = butil::address_resource(slot_id);

if (task == nullptr) {

LOG(ERROR) << "Invalid task_id=" << task_id;

return -1;

}

const uint32_t id_version = version_of_task_id(task_id);

uint32_t expected_version = id_version;

// This CAS is rarely contended, should be fast.

// The acquire fence is paired with release fence in Task::run_and_delete

// to make sure that we see all changes brought by fn(arg).

if (task->version.compare_exchange_strong(

expected_version, id_version + 2,

butil::memory_order_acquire)) {

return 0;

}

return (expected_version == id_version + 1) ? 1 : -1;

}

bool TimerThread::Task::run_and_delete() {

const uint32_t id_version = version_of_task_id(task_id);

uint32_t expected_version = id_version;

// This CAS is rarely contended, should be fast.

if (version.compare_exchange_strong(

expected_version, id_version + 1, butil::memory_order_relaxed)) {

fn(arg);

// The release fence is paired with acquire fence in

// TimerThread::unschedule to make changes of fn(arg) visible.

version.store(id_version + 2, butil::memory_order_release);

butil::return_resource(slot_of_task_id(task_id));

return true;

} else if (expected_version == id_version + 2) {

// already unscheduled.

butil::return_resource(slot_of_task_id(task_id));

return false;

} else {

// Impossible.

LOG(ERROR) << "Invalid version=" << expected_version

<< ", expecting " << id_version + 2;

return false;

}

bool TimerThread::Task::try_delete() {

const uint32_t id_version = version_of_task_id(task_id);

if (version.load(butil::memory_order_relaxed) != id_version) {

CHECK_EQ(version.load(butil::memory_order_relaxed), id_version + 2);

butil::return_resource(slot_of_task_id(task_id));

return true;

}

return false;

}

template <typename T>

static T deref_value(void* arg) {

return *(T*)arg;

}

void TimerThread::run() {

run_worker_startfn();

#ifdef BAIDU_INTERNAL

logging::ComlogInitializer comlog_initializer;

#endif

int64_t last_sleep_time = butil::gettimeofday_us();

BT_VLOG << "Started TimerThread=" << pthread_self();

// min heap of tasks (ordered by run_time)

std::vector<Task*> tasks;

tasks.reserve(4096);

// Heap size at the last sweep. Used to trigger the next sweep only after

// the heap has roughly doubled, keeping the amortized cost of sweeping at

// O(1) per task. It also follows the heap down when tasks are run, so a

// regrowth (e.g. filled with newly-unscheduled tasks) triggers a sweep.

size_t last_sweep_size = 0;

// vars

size_t nscheduled = 0;

bvar::PassiveStatus<size_t> nscheduled_var(deref_value<size_t>, &nscheduled);

bvar::PerSecond<bvar::PassiveStatus<size_t> > nscheduled_second(&nscheduled_var);

size_t ntriggered = 0;

bvar::PassiveStatus<size_t> ntriggered_var(deref_value<size_t>, &ntriggered);

bvar::PerSecond<bvar::PassiveStatus<size_t> > ntriggered_second(&ntriggered_var);

double busy_seconds = 0;

bvar::PassiveStatus<double> busy_seconds_var(deref_value<double>, &busy_seconds);

bvar::PerSecond<bvar::PassiveStatus<double> > busy_seconds_second(&busy_seconds_var);

if (!_options.bvar_prefix.empty()) {

nscheduled_second.expose_as(_options.bvar_prefix, "scheduled_second");

ntriggered_second.expose_as(_options.bvar_prefix, "triggered_second");

busy_seconds_second.expose_as(_options.bvar_prefix, "usage");

}

while (!_stop.load(butil::memory_order_relaxed)) {

// Clear _nearest_run_time before consuming tasks from buckets.

// This helps us to be aware of earliest task of the new tasks before we

// would run the consumed tasks.

{

BAIDU_SCOPED_LOCK(_mutex);

// This check of _stop ensures we won't miss the reset of _nearest_run_time

// to 0 in stop_and_join, avoiding potential race conditions.

if (BAIDU_UNLIKELY(_stop.load(butil::memory_order_relaxed))) {

break;

}

_nearest_run_time = std::numeric_limits<int64_t>::max();

}

// Pull tasks from buckets.

for (size_t i = 0; i < _options.num_buckets; ++i) {

Bucket& bucket = _buckets[i];

for (Task* p = bucket.consume_tasks(); p != nullptr; ++nscheduled) {

// p->next should be kept first

// in case of the deletion of Task p which is unscheduled

Task* next_task = p->next;

if (!p->try_delete()) { // remove the task if it's unscheduled

tasks.push_back(p);

std::push_heap(tasks.begin(), tasks.end(), task_greater);

}

p = next_task;

}

// A task is only checked by try_delete() once, right when it is pulled

// out of its bucket. If it gets unscheduled afterwards, it lingers in

// the heap (occupying a pooled Task slot) until it is popped at its

// run_time. For large timeouts this keeps a lot of dead tasks around.

// Sweep them out here. The sweep is gated on the heap having grown to

// twice its post-sweep size (and past a minimum), so the O(N) pass is

// amortized O(1) per task and small heaps never pay for it.

if (tasks.size() >= FLAGS_brpc_timer_heap_sweep_min_size &&

tasks.size() >= last_sweep_size * 2) {

size_t j = 0;

for (size_t i = 0; i < tasks.size(); ++i) {

Task* task = tasks[i];

if (!task->try_delete()) { // still scheduled, keep it

tasks[j++] = task;

}

if (j != tasks.size()) {

tasks.resize(j);

std::make_heap(tasks.begin(), tasks.end(), task_greater);

}

last_sweep_size = tasks.size();

}

bool pull_again = false;

while (!tasks.empty()) {

Task* task1 = tasks[0]; // the about-to-run task

if (butil::gettimeofday_us() < task1->run_time) { // not ready yet.

break;

}

// Each time before we run the earliest task (that we think),

// check the globally shared _nearest_run_time. If a task earlier

// than task1 was scheduled during pulling from buckets, we'll

// know. In RPC scenarios, _nearest_run_time is not often changed by

// threads because the task needs to be the earliest in its bucket,

// since run_time of scheduled tasks are often in ascending order,

// most tasks are unlikely to be "earliest". (If run_time of tasks

// are in descending orders, all tasks are "earliest" after every

// insertion, and they'll grab _mutex and change _nearest_run_time

// frequently, fortunately this is not true at most of time).

{

BAIDU_SCOPED_LOCK(_mutex);

if (task1->run_time > _nearest_run_time) {

// a task is earlier than task1. We need to check buckets.

pull_again = true;

break;

}

std::pop_heap(tasks.begin(), tasks.end(), task_greater);

tasks.pop_back();

if (task1->run_and_delete()) {

++ntriggered;

}

// Publish the heap size before possibly looping back on pull_again,

// so the observability counter doesn't go stale during the retry spin.

_npending.store((int64_t)tasks.size(), butil::memory_order_relaxed);

if (pull_again) {

BT_VLOG << "pull again, tasks=" << tasks.size();

continue;

}

// Let the sweep baseline follow the heap down as tasks are run, so

// that a heap refilled with (soon unscheduled) tasks is swept again.

if (tasks.size() < last_sweep_size) {

last_sweep_size = tasks.size();

}

// The realtime to wait for.

int64_t next_run_time = std::numeric_limits<int64_t>::max();

if (!tasks.empty()) {

next_run_time = tasks[0]->run_time;

}

// Similarly with the situation before running tasks, we check

// _nearest_run_time to prevent us from waiting on a non-earliest

// task. We also use the _nsignal to make sure that if new task

// is earlier than the realtime that we wait for, we'll wake up.

int expected_nsignals = 0;

{

BAIDU_SCOPED_LOCK(_mutex);

if (next_run_time > _nearest_run_time) {

// a task is earlier than what we would wait for.

// We need to check the buckets.

continue;

} else {

_nearest_run_time = next_run_time;

expected_nsignals = _nsignals;

}

timespec* ptimeout = nullptr;

timespec next_timeout = { 0, 0 };

const int64_t now = butil::gettimeofday_us();

if (next_run_time != std::numeric_limits<int64_t>::max()) {

int64_t wait_us = next_run_time - now;

// Cap the sleep so we periodically wake up to drain buckets and

// sweep the heap even when the nearest task is far in the future.

// Note: an empty heap keeps ptimeout nullptr (sleep until woken by a

// schedule()), which is safe because the first task after the heap

// empties is always earlier than _nearest_run_time and wakes us.

const int64_t max_wakeup_us =

(int64_t)FLAGS_brpc_timer_max_wakeup_interval_ms * 1000;

if (max_wakeup_us > 0 && wait_us > max_wakeup_us) {

wait_us = max_wakeup_us;

}

next_timeout = butil::microseconds_to_timespec(wait_us);

ptimeout = &next_timeout;

}

busy_seconds += (now - last_sleep_time) / 1000000.0;

futex_wait_private(&_nsignals, expected_nsignals, ptimeout);

last_sleep_time = butil::gettimeofday_us();

}

BT_VLOG << "Ended TimerThread=" << pthread_self();

}

void TimerThread::stop_and_join() {

if (_stop.exchange(true, butil::memory_order_relaxed)) {

return;

}

if (_started) {

{

BAIDU_SCOPED_LOCK(_mutex);

// trigger pull_again and wakeup TimerThread

_nearest_run_time = 0;

++_nsignals;

}

if (pthread_self() != _thread) {

// stop_and_join was not called from a running task.

// wake up the timer thread in case it is sleeping.

futex_wake_private(&_nsignals, 1);

pthread_join(_thread, nullptr);

}

static pthread_once_t g_timer_thread_once = PTHREAD_ONCE_INIT;

static TimerThread* g_timer_thread = nullptr;

static void init_global_timer_thread() {

g_timer_thread = new TimerThread;

TimerThreadOptions options;

options.bvar_prefix = "bthread_timer";

options.num_buckets = FLAGS_brpc_timer_num_buckets;

const int rc = g_timer_thread->start(&options);

if (rc != 0) {

LOG(FATAL) << "Fail to start timer_thread, " << berror(rc);

delete g_timer_thread;

g_timer_thread = nullptr;

return;

}

TimerThread* get_or_create_global_timer_thread() {

pthread_once(&g_timer_thread_once, init_global_timer_thread);

return g_timer_thread;

}

TimerThread* get_global_timer_thread() {

return g_timer_thread;

}

} // end namespace bthread

brpc/src/bthread/timer_thread.cpp at master · apache/brpc · GitHub

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