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LibCore: Introduce SharedSingleProducerCircularQueue
This new class with an admittedly long OOP-y name provides a circular queue in shared memory. The queue is a lock-free synchronous queue implemented with atomics, and its implementation is significantly simplified by only accounting for one producer (and multiple consumers). It is intended to be used as a producer-consumer communication datastructure across processes. The original motivation behind this class is efficient short-period transfer of audio data in userspace. This class includes formal proofs of several correctness properties of the main queue operations `enqueue` and `dequeue`. These proofs are not 100% complete in their existing form as the invariants they depend on are "handwaved". This seems fine to me right now, as any proof is better than no proof :^). Anyways, the proofs should build confidence that the implemented algorithms, which are only roughly based on existing work, operate correctly in even the worst-case concurrency scenarios.
This commit is contained in:
kleines Filmröllchen
Linus Groh
parent
b0a2572577
commit
6b13436ef6
5 changed files with 440 additions and 0 deletions
203
Tests/LibCore/TestLibCoreSharedSingleProducerCircularQueue.cpp
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Tests/LibCore/TestLibCoreSharedSingleProducerCircularQueue.cpp
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/*
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* Copyright (c) 2022, kleines Filmröllchen <filmroellchen@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include "sched.h"
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#include <LibCore/SharedCircularQueue.h>
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#include <LibTest/TestCase.h>
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#include <LibThreading/Thread.h>
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using TestQueue = Core::SharedSingleProducerCircularQueue<int>;
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using QueueError = ErrorOr<int, TestQueue::QueueStatus>;
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Function<intptr_t()> dequeuer(TestQueue& queue, Atomic<size_t>& dequeue_count, size_t test_count);
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// These first two cases don't multithread at all.
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TEST_CASE(simple_enqueue)
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{
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auto queue = MUST(TestQueue::try_create());
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for (size_t i = 0; i < queue.size() - 1; ++i)
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EXPECT(!queue.try_enqueue((int)i).is_error());
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auto result = queue.try_enqueue(0);
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EXPECT(result.is_error());
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EXPECT_EQ(result.release_error(), TestQueue::QueueStatus::Full);
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}
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TEST_CASE(simple_dequeue)
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{
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auto queue = MUST(TestQueue::try_create());
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auto const test_count = 10;
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for (int i = 0; i < test_count; ++i)
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(void)queue.try_enqueue(i);
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for (int i = 0; i < test_count; ++i) {
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auto const element = queue.try_dequeue();
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EXPECT(!element.is_error());
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EXPECT_EQ(element.value(), i);
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}
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}
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// There is one parallel consumer, but nobody is producing at the same time.
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TEST_CASE(simple_multithread)
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{
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auto queue = MUST(TestQueue::try_create());
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auto const test_count = 10;
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for (int i = 0; i < test_count; ++i)
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(void)queue.try_enqueue(i);
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auto second_thread = Threading::Thread::construct([&queue]() {
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auto copied_queue = queue;
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for (int i = 0; i < test_count; ++i) {
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QueueError result = TestQueue::QueueStatus::Invalid;
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do {
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result = copied_queue.try_dequeue();
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if (!result.is_error())
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EXPECT_EQ(result.value(), i);
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} while (result.is_error() && result.error() == TestQueue::QueueStatus::Empty);
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if (result.is_error())
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FAIL("Unexpected error while dequeueing.");
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}
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return 0;
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});
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second_thread->start();
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(void)second_thread->join();
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EXPECT_EQ(queue.weak_used(), (size_t)0);
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}
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// There is one parallel consumer and one parallel producer.
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TEST_CASE(producer_consumer_multithread)
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{
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auto queue = MUST(TestQueue::try_create());
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// Ensure that we have the possibility of filling the queue up.
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auto const test_count = queue.size() * 4;
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Atomic<bool> other_thread_running { false };
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auto second_thread = Threading::Thread::construct([&queue, &other_thread_running]() {
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auto copied_queue = queue;
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other_thread_running.store(true);
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for (size_t i = 0; i < test_count; ++i) {
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QueueError result = TestQueue::QueueStatus::Invalid;
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do {
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result = copied_queue.try_dequeue();
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if (!result.is_error())
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EXPECT_EQ(result.value(), (int)i);
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} while (result.is_error() && result.error() == TestQueue::QueueStatus::Empty);
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if (result.is_error())
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FAIL("Unexpected error while dequeueing.");
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}
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return 0;
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});
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second_thread->start();
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while (!other_thread_running.load())
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;
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for (size_t i = 0; i < test_count; ++i) {
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ErrorOr<void, TestQueue::QueueStatus> result = TestQueue::QueueStatus::Invalid;
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do {
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result = queue.try_enqueue((int)i);
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} while (result.is_error() && result.error() == TestQueue::QueueStatus::Full);
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if (result.is_error())
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FAIL("Unexpected error while enqueueing.");
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}
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(void)second_thread->join();
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EXPECT_EQ(queue.weak_used(), (size_t)0);
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}
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// There are multiple parallel consumers, but nobody is producing at the same time.
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TEST_CASE(multi_consumer)
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{
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auto queue = MUST(TestQueue::try_create());
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// This needs to be divisible by 4!
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size_t const test_count = queue.size() - 4;
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Atomic<size_t> dequeue_count = 0;
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auto threads = {
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Threading::Thread::construct(dequeuer(queue, dequeue_count, test_count)),
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Threading::Thread::construct(dequeuer(queue, dequeue_count, test_count)),
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Threading::Thread::construct(dequeuer(queue, dequeue_count, test_count)),
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Threading::Thread::construct(dequeuer(queue, dequeue_count, test_count)),
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};
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for (size_t i = 0; i < test_count; ++i)
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(void)queue.try_enqueue((int)i);
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for (auto thread : threads)
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thread->start();
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for (auto thread : threads)
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(void)thread->join();
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EXPECT_EQ(queue.weak_used(), (size_t)0);
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EXPECT_EQ(dequeue_count.load(), (size_t)test_count);
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}
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// There are multiple parallel consumers and one parallel producer.
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TEST_CASE(single_producer_multi_consumer)
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{
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auto queue = MUST(TestQueue::try_create());
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// Choose a higher number to provoke possible race conditions.
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size_t const test_count = queue.size() * 8;
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Atomic<size_t> dequeue_count = 0;
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auto threads = {
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Threading::Thread::construct(dequeuer(queue, dequeue_count, test_count)),
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Threading::Thread::construct(dequeuer(queue, dequeue_count, test_count)),
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Threading::Thread::construct(dequeuer(queue, dequeue_count, test_count)),
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Threading::Thread::construct(dequeuer(queue, dequeue_count, test_count)),
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};
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for (auto thread : threads)
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thread->start();
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for (size_t i = 0; i < test_count; ++i) {
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ErrorOr<void, TestQueue::QueueStatus> result = TestQueue::QueueStatus::Invalid;
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do {
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result = queue.try_enqueue((int)i);
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// After we put something in the first time, let's wait while nobody has dequeued yet.
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while (dequeue_count.load() == 0)
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;
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// Give others time to do something.
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sched_yield();
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} while (result.is_error() && result.error() == TestQueue::QueueStatus::Full);
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if (result.is_error())
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FAIL("Unexpected error while enqueueing.");
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}
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for (auto thread : threads)
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(void)thread->join();
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EXPECT_EQ(queue.weak_used(), (size_t)0);
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EXPECT_EQ(dequeue_count.load(), (size_t)test_count);
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}
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Function<intptr_t()> dequeuer(TestQueue& queue, Atomic<size_t>& dequeue_count, size_t const test_count)
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{
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return [&queue, &dequeue_count, test_count]() {
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auto copied_queue = queue;
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for (size_t i = 0; i < test_count / 4; ++i) {
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QueueError result = TestQueue::QueueStatus::Invalid;
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do {
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result = copied_queue.try_dequeue();
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if (!result.is_error())
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dequeue_count.fetch_add(1);
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// Give others time to do something.
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sched_yield();
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} while (result.is_error() && result.error() == TestQueue::QueueStatus::Empty);
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if (result.is_error())
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FAIL("Unexpected error while dequeueing.");
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}
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return (intptr_t)0;
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};
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}
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