// 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.

// This file is copied from

// https://github.com/apache/impala/blob/branch-2.9.0/be/src/util/threadpool.cc

// and modified by Doris

#include "util/threadpool.h"

#include <algorithm>

#include <cstdint>

#include <limits>

#include <ostream>

#include <thread>

#include <utility>

#include "common/logging.h"

#include "gutil/map-util.h"

#include "gutil/port.h"

#include "gutil/strings/substitute.h"

#include "util/debug/sanitizer_scopes.h"

#include "util/debug_points.h"

#include "util/doris_metrics.h"

#include "util/metrics.h"

#include "util/scoped_cleanup.h"

#include "util/stopwatch.hpp"

#include "util/thread.h"

namespace doris {

// The name of these varialbs will be useds as metric name in prometheus.

DEFINE_GAUGE_METRIC_PROTOTYPE_2ARG(thread_pool_active_threads, MetricUnit::NOUNIT);

DEFINE_GAUGE_METRIC_PROTOTYPE_2ARG(thread_pool_queue_size, MetricUnit::NOUNIT);

DEFINE_GAUGE_METRIC_PROTOTYPE_2ARG(thread_pool_max_queue_size, MetricUnit::NOUNIT);

DEFINE_GAUGE_METRIC_PROTOTYPE_2ARG(thread_pool_max_threads, MetricUnit::NOUNIT);

DEFINE_COUNTER_METRIC_PROTOTYPE_2ARG(thread_pool_submit_failed, MetricUnit::NOUNIT);

DEFINE_COUNTER_METRIC_PROTOTYPE_2ARG(thread_pool_task_execution_time_ns_total,

                                     MetricUnit::NANOSECONDS);

DEFINE_COUNTER_METRIC_PROTOTYPE_2ARG(thread_pool_task_execution_count_total, MetricUnit::NOUNIT);

DEFINE_COUNTER_METRIC_PROTOTYPE_2ARG(thread_pool_task_wait_worker_time_ns_total,

                                     MetricUnit::NANOSECONDS);

DEFINE_COUNTER_METRIC_PROTOTYPE_2ARG(thread_pool_task_wait_worker_count_total, MetricUnit::NOUNIT);

using namespace ErrorCode;

using std::string;

using strings::Substitute;

class FunctionRunnable : public Runnable {

public:

    explicit FunctionRunnable(std::function<void()> func) : _func(std::move(func)) {}

    void run() override { _func(); }

private:

    std::function<void()> _func;

};

ThreadPoolBuilder::ThreadPoolBuilder(string name, string workload_group)

        : _name(std::move(name)),

          _workload_group(std::move(workload_group)),

          _min_threads(0),

          _max_threads(std::thread::hardware_concurrency()),

          _max_queue_size(std::numeric_limits<int>::max()),

          _idle_timeout(std::chrono::milliseconds(500)) {}

ThreadPoolBuilder& ThreadPoolBuilder::set_min_threads(int min_threads) {

    CHECK_GE(min_threads, 0);

    _min_threads = min_threads;

    return *this;

}

ThreadPoolBuilder& ThreadPoolBuilder::set_max_threads(int max_threads) {

    CHECK_GT(max_threads, 0);

    _max_threads = max_threads;

    return *this;

}

ThreadPoolBuilder& ThreadPoolBuilder::set_max_queue_size(int max_queue_size) {

    _max_queue_size = max_queue_size;

    return *this;

}

ThreadPoolBuilder& ThreadPoolBuilder::set_cgroup_cpu_ctl(CgroupCpuCtl* cgroup_cpu_ctl) {

    _cgroup_cpu_ctl = cgroup_cpu_ctl;

    return *this;

}

ThreadPoolToken::ThreadPoolToken(ThreadPool* pool, ThreadPool::ExecutionMode mode,

                                 int max_concurrency)

        : _mode(mode),

          _pool(pool),

          _state(State::IDLE),

          _active_threads(0),

          _max_concurrency(max_concurrency),

          _num_submitted_tasks(0),

          _num_unsubmitted_tasks(0) {

    if (max_concurrency == 1 && mode != ThreadPool::ExecutionMode::SERIAL) {

        _mode = ThreadPool::ExecutionMode::SERIAL;

    }

}

ThreadPoolToken::~ThreadPoolToken() {

    shutdown();

    _pool->release_token(this);

}

Status ThreadPoolToken::submit(std::shared_ptr<Runnable> r) {

    return _pool->do_submit(std::move(r), this);

}

Status ThreadPoolToken::submit_func(std::function<void()> f) {

    return submit(std::make_shared<FunctionRunnable>(std::move(f)));

}

void ThreadPoolToken::shutdown() {

    std::unique_lock<std::mutex> l(_pool->_lock);

    _pool->check_not_pool_thread_unlocked();

    // Clear the queue under the lock, but defer the releasing of the tasks

    // outside the lock, in case there are concurrent threads wanting to access

    // the ThreadPool. The task's destructors may acquire locks, etc, so this

    // also prevents lock inversions.

    std::deque<ThreadPool::Task> to_release = std::move(_entries);

    _pool->_total_queued_tasks -= to_release.size();

    switch (state()) {

    case State::IDLE:

        // There were no tasks outstanding; we can quiesce the token immediately.

        transition(State::QUIESCED);

        break;

    case State::RUNNING:

        // There were outstanding tasks. If any are still running, switch to

        // QUIESCING and wait for them to finish (the worker thread executing

        // the token's last task will switch the token to QUIESCED). Otherwise,

        // we can quiesce the token immediately.

        // Note: this is an O(n) operation, but it's expected to be infrequent.

        // Plus doing it this way (rather than switching to QUIESCING and waiting

        // for a worker thread to process the queue entry) helps retain state

        // transition symmetry with ThreadPool::shutdown.

        for (auto it = _pool->_queue.begin(); it != _pool->_queue.end();) {

            if (*it == this) {

                it = _pool->_queue.erase(it);

            } else {

                it++;

            }

        }

        if (_active_threads == 0) {

            transition(State::QUIESCED);

            break;

        }

        transition(State::QUIESCING);

        [[fallthrough]];

    case State::QUIESCING:

        // The token is already quiescing. Just wait for a worker thread to

        // switch it to QUIESCED.

        _not_running_cond.wait(l, [this]() { return state() == State::QUIESCED; });

        break;

    default:

        break;

    }

}

void ThreadPoolToken::wait() {

    std::unique_lock<std::mutex> l(_pool->_lock);

    _pool->check_not_pool_thread_unlocked();

    _not_running_cond.wait(l, [this]() { return !is_active(); });

}

void ThreadPoolToken::transition(State new_state) {

#ifndef NDEBUG

    CHECK_NE(_state, new_state);

    switch (_state) {

    case State::IDLE:

        CHECK(new_state == State::RUNNING || new_state == State::QUIESCED);

        if (new_state == State::RUNNING) {

            CHECK(!_entries.empty());

        } else {

            CHECK(_entries.empty());

            CHECK_EQ(_active_threads, 0);

        }

        break;

    case State::RUNNING:

        CHECK(new_state == State::IDLE || new_state == State::QUIESCING ||

              new_state == State::QUIESCED);

        CHECK(_entries.empty());

        if (new_state == State::QUIESCING) {

            CHECK_GT(_active_threads, 0);

        }

        break;

    case State::QUIESCING:

        CHECK(new_state == State::QUIESCED);

        CHECK_EQ(_active_threads, 0);

        break;

    case State::QUIESCED:

        CHECK(false); // QUIESCED is a terminal state

        break;

    default:

        LOG(FATAL) << "Unknown token state: " << _state;

    }

#endif

    // Take actions based on the state we're entering.

    switch (new_state) {

    case State::IDLE:

    case State::QUIESCED:

        _not_running_cond.notify_all();

        break;

    default:

        break;

    }

    _state = new_state;

}

const char* ThreadPoolToken::state_to_string(State s) {

    switch (s) {

    case State::IDLE:

        return "IDLE";

        break;

    case State::RUNNING:

        return "RUNNING";

        break;

    case State::QUIESCING:

        return "QUIESCING";

        break;

    case State::QUIESCED:

        return "QUIESCED";

        break;

    }

    return "<cannot reach here>";

}

bool ThreadPoolToken::need_dispatch() {

    return _state == ThreadPoolToken::State::IDLE ||

           (_mode == ThreadPool::ExecutionMode::CONCURRENT &&

            _num_submitted_tasks < _max_concurrency);

}

ThreadPool::ThreadPool(const ThreadPoolBuilder& builder)

        : _name(builder._name),

          _workload_group(builder._workload_group),

          _min_threads(builder._min_threads),

          _max_threads(builder._max_threads),

          _max_queue_size(builder._max_queue_size),

          _idle_timeout(builder._idle_timeout),

          _pool_status(Status::Uninitialized("The pool was not initialized.")),

          _num_threads(0),

          _num_threads_pending_start(0),

          _active_threads(0),

          _total_queued_tasks(0),

          _cgroup_cpu_ctl(builder._cgroup_cpu_ctl),

          _tokenless(new_token(ExecutionMode::CONCURRENT)),

          _id(UniqueId::gen_uid()) {}

ThreadPool::~ThreadPool() {

    // There should only be one live token: the one used in tokenless submission.

    CHECK_EQ(1, _tokens.size()) << strings::Substitute(

            "Threadpool $0 destroyed with $1 allocated tokens", _name, _tokens.size());

    shutdown();

}

Status ThreadPool::init() {

    if (!_pool_status.is<UNINITIALIZED>()) {

        return Status::NotSupported("The thread pool {} is already initialized", _name);

    }

    _pool_status = Status::OK();

    _num_threads_pending_start = _min_threads;

    for (int i = 0; i < _min_threads; i++) {

        Status status = create_thread();

        if (!status.ok()) {

            shutdown();

            return status;

        }

    }

    // _id of thread pool is used to make sure when we create thread pool with same name, we can

    // get different _metric_entity

    // If not, we will have problem when we deregister entity and register hook.

    _metric_entity = DorisMetrics::instance()->metric_registry()->register_entity(

            fmt::format("thread_pool_{}", _name), {{"thread_pool_name", _name},

                                                   {"workload_group", _workload_group},

                                                   {"id", _id.to_string()}});

    INT_GAUGE_METRIC_REGISTER(_metric_entity, thread_pool_active_threads);

    INT_GAUGE_METRIC_REGISTER(_metric_entity, thread_pool_max_threads);

    INT_GAUGE_METRIC_REGISTER(_metric_entity, thread_pool_queue_size);

    INT_GAUGE_METRIC_REGISTER(_metric_entity, thread_pool_max_queue_size);

    INT_COUNTER_METRIC_REGISTER(_metric_entity, thread_pool_task_execution_time_ns_total);

    INT_COUNTER_METRIC_REGISTER(_metric_entity, thread_pool_task_execution_count_total);

    INT_COUNTER_METRIC_REGISTER(_metric_entity, thread_pool_task_wait_worker_time_ns_total);

    INT_COUNTER_METRIC_REGISTER(_metric_entity, thread_pool_task_wait_worker_count_total);

    INT_COUNTER_METRIC_REGISTER(_metric_entity, thread_pool_submit_failed);

    _metric_entity->register_hook("update", [this]() {

        {

            std::lock_guard<std::mutex> l(_lock);

            if (!_pool_status.ok()) {

                return;

            }

        }

        thread_pool_active_threads->set_value(num_active_threads());

        thread_pool_queue_size->set_value(get_queue_size());

        thread_pool_max_queue_size->set_value(get_max_queue_size());

        thread_pool_max_threads->set_value(max_threads());

    });

    return Status::OK();

}

void ThreadPool::shutdown() {

    // Why access to doris_metrics is safe here?

    // Since DorisMetrics is a singleton, it will be destroyed only after doris_main is exited.

    // The shutdown/destroy of ThreadPool is guaranteed to take place before doris_main exits by

    // ExecEnv::destroy().

    DorisMetrics::instance()->metric_registry()->deregister_entity(_metric_entity);

    debug::ScopedTSANIgnoreReadsAndWrites ignore_tsan;

    std::unique_lock<std::mutex> l(_lock);

    check_not_pool_thread_unlocked();

    // Note: this is the same error seen at submission if the pool is at

    // capacity, so clients can't tell them apart. This isn't really a practical

    // concern though because shutting down a pool typically requires clients to

    // be quiesced first, so there's no danger of a client getting confused.

    // Not print stack trace here

    _pool_status = Status::Error<SERVICE_UNAVAILABLE, false>(

            "The thread pool {} has been shut down.", _name);

    // Clear the various queues under the lock, but defer the releasing

    // of the tasks outside the lock, in case there are concurrent threads

    // wanting to access the ThreadPool. The task's destructors may acquire

    // locks, etc, so this also prevents lock inversions.

    _queue.clear();

    std::deque<std::deque<Task>> to_release;

    for (auto* t : _tokens) {

        if (!t->_entries.empty()) {

            to_release.emplace_back(std::move(t->_entries));

        }

        switch (t->state()) {

        case ThreadPoolToken::State::IDLE:

            // The token is idle; we can quiesce it immediately.

            t->transition(ThreadPoolToken::State::QUIESCED);

            break;

        case ThreadPoolToken::State::RUNNING:

            // The token has tasks associated with it. If they're merely queued

            // (i.e. there are no active threads), the tasks will have been removed

            // above and we can quiesce immediately. Otherwise, we need to wait for

            // the threads to finish.

            t->transition(t->_active_threads > 0 ? ThreadPoolToken::State::QUIESCING

                                                 : ThreadPoolToken::State::QUIESCED);

            break;

        default:

            break;

        }

    }

    // The queues are empty. Wake any sleeping worker threads and wait for all

    // of them to exit. Some worker threads will exit immediately upon waking,

    // while others will exit after they finish executing an outstanding task.

    _total_queued_tasks = 0;

    while (!_idle_threads.empty()) {

        _idle_threads.front().not_empty.notify_one();

        _idle_threads.pop_front();

    }

    _no_threads_cond.wait(l, [this]() { return _num_threads + _num_threads_pending_start == 0; });

    // All the threads have exited. Check the state of each token.

    for (auto* t : _tokens) {

        DCHECK(t->state() == ThreadPoolToken::State::IDLE ||

               t->state() == ThreadPoolToken::State::QUIESCED);

    }

}

std::unique_ptr<ThreadPoolToken> ThreadPool::new_token(ExecutionMode mode, int max_concurrency) {

    std::lock_guard<std::mutex> l(_lock);

    std::unique_ptr<ThreadPoolToken> t(new ThreadPoolToken(this, mode, max_concurrency));

    InsertOrDie(&_tokens, t.get());

    return t;

}

void ThreadPool::release_token(ThreadPoolToken* t) {

    std::lock_guard<std::mutex> l(_lock);

    CHECK(!t->is_active()) << strings::Substitute("Token with state $0 may not be released",

                                                  ThreadPoolToken::state_to_string(t->state()));

    CHECK_EQ(1, _tokens.erase(t));

}

Status ThreadPool::submit(std::shared_ptr<Runnable> r) {

    return do_submit(std::move(r), _tokenless.get());

}

Status ThreadPool::submit_func(std::function<void()> f) {

    return submit(std::make_shared<FunctionRunnable>(std::move(f)));

}

Status ThreadPool::do_submit(std::shared_ptr<Runnable> r, ThreadPoolToken* token) {

    DCHECK(token);

    std::unique_lock<std::mutex> l(_lock);

    if (PREDICT_FALSE(!_pool_status.ok())) {

        return _pool_status;

    }

    if (PREDICT_FALSE(!token->may_submit_new_tasks())) {

        return Status::Error<SERVICE_UNAVAILABLE>("Thread pool({}) token was shut down", _name);

    }

    // Size limit check.

    int64_t capacity_remaining = static_cast<int64_t>(_max_threads) - _active_threads +

                                 static_cast<int64_t>(_max_queue_size) - _total_queued_tasks;

    if (capacity_remaining < 1) {

        thread_pool_submit_failed->increment(1);

        return Status::Error<SERVICE_UNAVAILABLE>(

                "Thread pool {} is at capacity ({}/{} tasks running, {}/{} tasks queued)", _name,

                _num_threads + _num_threads_pending_start, _max_threads, _total_queued_tasks,

                _max_queue_size);

    }

    // Should we create another thread?

    // We assume that each current inactive thread will grab one item from the

    // queue.  If it seems like we'll need another thread, we create one.

    //

    // Rather than creating the thread here, while holding the lock, we defer

    // it to down below. This is because thread creation can be rather slow

    // (hundreds of milliseconds in some cases) and we'd like to allow the

    // existing threads to continue to process tasks while we do so.

    //

    // In theory, a currently active thread could finish immediately after this

    // calculation but before our new worker starts running. This would mean we

    // created a thread we didn't really need. However, this race is unavoidable

    // and harmless.

    //

    // Of course, we never create more than _max_threads threads no matter what.

    int threads_from_this_submit =

            token->is_active() && token->mode() == ExecutionMode::SERIAL ? 0 : 1;

    int inactive_threads = _num_threads + _num_threads_pending_start - _active_threads;

    int additional_threads =

            static_cast<int>(_queue.size()) + threads_from_this_submit - inactive_threads;

    bool need_a_thread = false;

    if (additional_threads > 0 && _num_threads + _num_threads_pending_start < _max_threads) {

        need_a_thread = true;

        _num_threads_pending_start++;

    }

    Task task;

    task.runnable = std::move(r);

    task.submit_time_wather.start();

    // Add the task to the token's queue.

    ThreadPoolToken::State state = token->state();

    DCHECK(state == ThreadPoolToken::State::IDLE || state == ThreadPoolToken::State::RUNNING);

    token->_entries.emplace_back(std::move(task));

    // When we need to execute the task in the token, we submit the token object to the queue.

    // There are currently two places where tokens will be submitted to the queue:

    // 1. When submitting a new task, if the token is still in the IDLE state,

    //    or the concurrency of the token has not reached the online level, it will be added to the queue.

    // 2. When the dispatch thread finishes executing a task:

    //    1. If it is a SERIAL token, and there are unsubmitted tasks, submit them to the queue.

    //    2. If it is a CONCURRENT token, and there are still unsubmitted tasks, and the upper limit of concurrency is not reached,

    //       then submitted to the queue.

    if (token->need_dispatch()) {

        _queue.emplace_back(token);

        ++token->_num_submitted_tasks;

        if (state == ThreadPoolToken::State::IDLE) {

            token->transition(ThreadPoolToken::State::RUNNING);

        }

    } else {

        ++token->_num_unsubmitted_tasks;

    }

    _total_queued_tasks++;

    // Wake up an idle thread for this task. Choosing the thread at the front of

    // the list ensures LIFO semantics as idling threads are also added to the front.

    //

    // If there are no idle threads, the new task remains on the queue and is

    // processed by an active thread (or a thread we're about to create) at some

    // point in the future.

    if (!_idle_threads.empty()) {

        _idle_threads.front().not_empty.notify_one();

        _idle_threads.pop_front();

    }

    l.unlock();

    if (need_a_thread) {

        Status status = create_thread();

        if (!status.ok()) {

            l.lock();

            _num_threads_pending_start--;

            if (_num_threads + _num_threads_pending_start == 0) {

                // If we have no threads, we can't do any work.

                return status;

            }

            // If we failed to create a thread, but there are still some other

            // worker threads, log a warning message and continue.

            LOG(WARNING) << "Thread pool " << _name

                         << " failed to create thread: " << status.to_string();

        }

    }

    return Status::OK();

}

void ThreadPool::wait() {

    std::unique_lock<std::mutex> l(_lock);

    check_not_pool_thread_unlocked();

    _idle_cond.wait(l, [this]() { return _total_queued_tasks == 0 && _active_threads == 0; });

}

void ThreadPool::dispatch_thread() {

    std::unique_lock<std::mutex> l(_lock);

    debug::ScopedTSANIgnoreReadsAndWrites ignore_tsan;

    InsertOrDie(&_threads, Thread::current_thread());

    DCHECK_GT(_num_threads_pending_start, 0);

    _num_threads++;

    _num_threads_pending_start--;

    if (_cgroup_cpu_ctl != nullptr) {

        static_cast<void>(_cgroup_cpu_ctl->add_thread_to_cgroup());

    }

    // Owned by this worker thread and added/removed from _idle_threads as needed.

    IdleThread me;

    while (true) {

        // Note: Status::Aborted() is used to indicate normal shutdown.

        if (!_pool_status.ok()) {

            VLOG_CRITICAL << "DispatchThread exiting: " << _pool_status.to_string();

            break;

        }

        if (_num_threads + _num_threads_pending_start > _max_threads) {

            break;

        }

        if (_queue.empty()) {

            // There's no work to do, let's go idle.

            //

            // Note: if FIFO behavior is desired, it's as simple as changing this to push_back().

            _idle_threads.push_front(me);

            SCOPED_CLEANUP({

                // For some wake ups (i.e. shutdown or do_submit) this thread is

                // guaranteed to be unlinked after being awakened. In others (i.e.

                // spurious wake-up or Wait timeout), it'll still be linked.

                if (me.is_linked()) {

                    _idle_threads.erase(_idle_threads.iterator_to(me));

                }

            });

            if (me.not_empty.wait_for(l, _idle_timeout) == std::cv_status::timeout) {

                // After much investigation, it appears that pthread condition variables have

                // a weird behavior in which they can return ETIMEDOUT from timed_wait even if

                // another thread did in fact signal. Apparently after a timeout there is some

                // brief period during which another thread may actually grab the internal mutex

                // protecting the state, signal, and release again before we get the mutex. So,

                // we'll recheck the empty queue case regardless.

                if (_queue.empty() && _num_threads + _num_threads_pending_start > _min_threads) {

                    VLOG_NOTICE << "Releasing worker thread from pool " << _name << " after "

                                << std::chrono::duration_cast<std::chrono::milliseconds>(

                                           _idle_timeout)

                                           .count()

                                << "ms of idle time.";

                    break;

                }

            }

            continue;

        }

        MonotonicStopWatch task_execution_time_watch;

        task_execution_time_watch.start();

        // Get the next token and task to execute.

        ThreadPoolToken* token = _queue.front();

        _queue.pop_front();

        DCHECK_EQ(ThreadPoolToken::State::RUNNING, token->state());

        DCHECK(!token->_entries.empty());

        Task task = std::move(token->_entries.front());

        thread_pool_task_wait_worker_time_ns_total->increment(

                task.submit_time_wather.elapsed_time());

        thread_pool_task_wait_worker_count_total->increment(1);

        token->_entries.pop_front();

        token->_active_threads++;

        --_total_queued_tasks;

        ++_active_threads;

        l.unlock();

        // Execute the task

        task.runnable->run();

        // Destruct the task while we do not hold the lock.

        //

        // The task's destructor may be expensive if it has a lot of bound

        // objects, and we don't want to block submission of the threadpool.

        // In the worst case, the destructor might even try to do something

        // with this threadpool, and produce a deadlock.

        task.runnable.reset();

        l.lock();

        thread_pool_task_execution_time_ns_total->increment(

                task_execution_time_watch.elapsed_time());

        thread_pool_task_execution_count_total->increment(1);

        // Possible states:

        // 1. The token was shut down while we ran its task. Transition to QUIESCED.

        // 2. The token has no more queued tasks. Transition back to IDLE.

        // 3. The token has more tasks. Requeue it and transition back to RUNNABLE.

        ThreadPoolToken::State state = token->state();

        DCHECK(state == ThreadPoolToken::State::RUNNING ||

               state == ThreadPoolToken::State::QUIESCING);

        --token->_active_threads;

        --token->_num_submitted_tasks;

        // handle shutdown && idle

        if (token->_active_threads == 0) {

            if (state == ThreadPoolToken::State::QUIESCING) {

                DCHECK(token->_entries.empty());

                token->transition(ThreadPoolToken::State::QUIESCED);

            } else if (token->_entries.empty()) {

                token->transition(ThreadPoolToken::State::IDLE);

            }

        }

        // We decrease _num_submitted_tasks holding lock, so the following DCHECK works.

        DCHECK(token->_num_submitted_tasks < token->_max_concurrency);

        // If token->state is running and there are unsubmitted tasks in the token, we put

        // the token back.

        if (token->_num_unsubmitted_tasks > 0 && state == ThreadPoolToken::State::RUNNING) {

            // SERIAL: if _entries is not empty, then num_unsubmitted_tasks must be greater than 0.

            // CONCURRENT: we have to check _num_unsubmitted_tasks because there may be at least 2

            // threads are running for the token.

            _queue.emplace_back(token);

            ++token->_num_submitted_tasks;

            --token->_num_unsubmitted_tasks;

        }

        if (--_active_threads == 0) {

            _idle_cond.notify_all();

        }

    }

    // It's important that we hold the lock between exiting the loop and dropping

    // _num_threads. Otherwise it's possible someone else could come along here

    // and add a new task just as the last running thread is about to exit.

    CHECK(l.owns_lock());

    CHECK_EQ(_threads.erase(Thread::current_thread()), 1);

    _num_threads--;

    if (_num_threads + _num_threads_pending_start == 0) {

        _no_threads_cond.notify_all();

        // Sanity check: if we're the last thread exiting, the queue ought to be

        // empty. Otherwise it will never get processed.

        CHECK(_queue.empty());

        DCHECK_EQ(0, _total_queued_tasks);

    }

}

Status ThreadPool::create_thread() {

    return Thread::create("thread pool", strings::Substitute("$0 [worker]", _name),

                          &ThreadPool::dispatch_thread, this, nullptr);

}

void ThreadPool::check_not_pool_thread_unlocked() {

    Thread* current = Thread::current_thread();

    if (ContainsKey(_threads, current)) {

        LOG(FATAL) << strings::Substitute(

                "Thread belonging to thread pool '$0' with "

                "name '$1' called pool function that would result in deadlock",

                _name, current->name());

    }

}

Status ThreadPool::set_min_threads(int min_threads) {

    std::lock_guard<std::mutex> l(_lock);

    if (min_threads > _max_threads) {

        // min threads can not be set greater than max threads

        return Status::InternalError("set thread pool {} min_threads failed", _name);

    }

    _min_threads = min_threads;

    if (min_threads > _num_threads + _num_threads_pending_start) {

        int addition_threads = min_threads - _num_threads - _num_threads_pending_start;

        _num_threads_pending_start += addition_threads;

        for (int i = 0; i < addition_threads; i++) {

            Status status = create_thread();

            if (!status.ok()) {

                _num_threads_pending_start--;

                LOG(WARNING) << "Thread pool " << _name

                             << " failed to create thread: " << status.to_string();

                return status;

            }

        }

    }

    return Status::OK();

}

Status ThreadPool::set_max_threads(int max_threads) {

    std::lock_guard<std::mutex> l(_lock);

    DBUG_EXECUTE_IF("ThreadPool.set_max_threads.force_set", {

        _max_threads = max_threads;

        return Status::OK();

    })

    if (_min_threads > max_threads) {

        // max threads can not be set less than min threads

        return Status::InternalError("set thread pool {} max_threads failed", _name);

    }

    _max_threads = max_threads;

    if (_max_threads > _num_threads + _num_threads_pending_start) {

        int addition_threads = _max_threads - _num_threads - _num_threads_pending_start;

        addition_threads = std::min(addition_threads, _total_queued_tasks);

        _num_threads_pending_start += addition_threads;

        for (int i = 0; i < addition_threads; i++) {

            Status status = create_thread();

            if (!status.ok()) {

                _num_threads_pending_start--;

                LOG(WARNING) << "Thread pool " << _name

                             << " failed to create thread: " << status.to_string();

                return status;

            }

        }

    }

    return Status::OK();

}

std::ostream& operator<<(std::ostream& o, ThreadPoolToken::State s) {

    return o << ThreadPoolToken::state_to_string(s);

}

} // namespace doris