feat: thread pool object

include/dpp/dpp.h

@@ -76,3 +76,4 @@
 #include <dpp/timed_listener.h>
 #include <dpp/collector.h>
 #include <dpp/bignum.h>
+#include <dpp/thread_pool.h>

include/dpp/thread_pool.h

@@ -0,0 +1,50 @@
+/************************************************************************************
+ *
+ * D++, A Lightweight C++ library for Discord
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright 2021 Craig Edwards and D++ contributors
+ * (https://github.com/brainboxdotcc/DPP/graphs/contributors)
+ *
+ * Licensed 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.
+ *
+ ************************************************************************************/
+
+#pragma once
+#include <thread>
+#include <queue>
+#include <vector>
+#include <condition_variable>
+#include <mutex>
+#include <functional>
+
+/**
+ * A task within a thread pool. A simple lambda that accepts no parameters and returns void.
+ */
+using thread_pool_task = std::function<void()>;
+
+/**
+ * @brief A thread pool contains 1 or more worker threads which accept thread_pool_task lambadas
+ * into a queue, which is processed in-order by whichever thread is free.
+ */
+struct thread_pool {
+	std::vector<std::thread> threads;
+	std::queue<thread_pool_task> tasks;
+	std::mutex queue_mutex;
+	std::condition_variable cv;
+	bool stop{false};
+
+	explicit thread_pool(size_t num_threads = std::thread::hardware_concurrency());
+	~thread_pool();
+	void enqueue(thread_pool_task task);
+};

src/dpp/thread_pool.cpp

@@ -0,0 +1,74 @@
+/************************************************************************************
+ *
+ * D++, A Lightweight C++ library for Discord
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright 2021 Craig Edwards and D++ contributors
+ * (https://github.com/brainboxdotcc/DPP/graphs/contributors)
+ *
+ * Licensed 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.
+ *
+ ************************************************************************************/
+
+#include <dpp/utility.h>
+#include <ssod/thread_pool.h>
+#include <shared_mutex>
+
+thread_pool::thread_pool(size_t num_threads) {
+	for (size_t i = 0; i < num_threads; ++i) {
+		threads.emplace_back([this, i]() {
+			dpp::utility::set_thread_name("pool/exec/" + std::to_string(i));
+			while (true) {
+				thread_pool_task task;
+				{
+					std::unique_lock<std::mutex> lock(queue_mutex);
+
+					cv.wait(lock, [this] {
+						return !tasks.empty() || stop;
+					});
+
+					if (stop && tasks.empty()) {
+						return;
+					}
+
+					task = std::move(tasks.front());
+					tasks.pop();
+				}
+
+				task();
+			}
+		});
+	}
+}
+
+thread_pool::~thread_pool()
+{
+	{
+		std::unique_lock<std::mutex> lock(queue_mutex);
+		stop = true;
+	}
+
+	cv.notify_all();
+	for (auto& thread : threads) {
+		thread.join();
+	}
+}
+
+void thread_pool::enqueue(thread_pool_task task)
+{
+	{
+		std::unique_lock<std::mutex> lock(queue_mutex);
+		tasks.emplace(std::move(task));
+	}
+	cv.notify_one();
+}