Danny Robson
9bfefb3dab
clearing the tasks on the worker threads can cause the queue to stall while the cookie is notified, released, and deleted. we punt the cleanup off to a reaper thread so that the workers can continue.
147 lines
4.1 KiB
C++
147 lines
4.1 KiB
C++
/*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* Copyright 2018 Danny Robson <danny@nerdcruft.net>
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*/
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#include "./queue.hpp"
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#include "../raii.hpp"
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#include <iostream>
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using util::job::queue;
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///////////////////////////////////////////////////////////////////////////////
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queue::queue (unsigned thread_count, unsigned pool_size):
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m_tasks {
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{}, util::pool<task> {pool_size}, {}, {}
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},
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m_pending (0),
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m_threads (thread_count),
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m_doomed (0),
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m_reaper (&queue::reap, this)
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{
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CHECK_GE (m_tasks.finishing.capacity (), thread_count);
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for (auto &t: m_threads)
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t = std::thread (&queue::loop, this);
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}
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//-----------------------------------------------------------------------------
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queue::~queue ()
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{
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m_stopping = true;
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// raise the semaphore enough times to resume all the worker threads
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for (size_t i = 0; i < m_threads.size (); ++i)
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m_pending.release ();
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// wait for everyone to tidy up. perhaps we'd like to use a timeout, but
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// if things deadlock then it's the users fault currently.
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for (auto &t: m_threads)
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t.join ();
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// wake the reaper up with enough tasks that it's guaranteed to resume.
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// it will bail early and drain the queue, so the validity of the increment
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// isn't super important.
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m_doomed.release (m_tasks.finishing.capacity ());
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m_reaper.join ();
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}
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///////////////////////////////////////////////////////////////////////////////
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#include <iostream>
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void
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queue::loop ()
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{
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while (true) {
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m_pending.acquire ();
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if (m_stopping)
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return;
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util::scoped_counter running_count (m_running);
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CHECK (!m_tasks.pending->empty ());
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auto todo = [this] () {
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auto obj = m_tasks.pending.acquire ();
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auto res = obj->front ();
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obj->pop_front ();
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return res;
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} ();
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util::scoped_function cleanup ([&, this] () {
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while (!m_tasks.finishing.push (todo))
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;
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m_doomed.release ();
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});
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todo->function (*todo);
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}
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}
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//-----------------------------------------------------------------------------
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void
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queue::reap ()
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{
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while (true) {
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// wait until we might have something to work with
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m_doomed.acquire ();
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if (m_stopping)
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break;
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// pop and notify as many doomed tasks as we can
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int count = 0;
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for (task *item; m_tasks.finishing.pop (item); ++count) {
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item->done.notify ();
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m_tasks.notified.push_back (item);
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}
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// destroy any tasks that have a zero reference count
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m_tasks.notified.erase (
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std::remove_if (
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m_tasks.notified.begin (),
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m_tasks.notified.end (),
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[&] (auto i) {
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if (i->references.value () < 1)
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return false;
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m_tasks.store.destroy (i);
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return true;
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}
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),
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m_tasks.notified.end ()
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);
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// subtract the number of tasks we've dealt with (remembering we've
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// already claimed one in the process of waking).
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m_doomed.acquire (count - 1);
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}
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// pre-notify everyone. this lets any observers release the task before
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// we wait for them at destruction time. otherwise we tend to find
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// deadlocks amongst remaining tasks.
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std::vector<task*> doomed;
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for (auto &i: m_tasks.notified)
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m_tasks.store.destroy (i);
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for (auto &i: doomed)
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i->done.notify ();
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for (auto &i: doomed)
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m_tasks.store.destroy (i);
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}
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