Common: Add HTTPDownloader implementation

common/ThreadPool.cpp

@@ -0,0 +1,137 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2022 Colion Braley
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+// From https://raw.githubusercontent.com/cbraley/threadpool/master/src/thread_pool.cc
+
+#include "common/PrecompiledHeader.h"
+
+#include "common/ThreadPool.h"
+
+#include <cassert>
+
+namespace cb {
+
+// static
+unsigned int ThreadPool::GetNumLogicalCores() {
+  // TODO(cbraley): Apparently this is broken in some older stdlib
+  // implementations?
+  const unsigned int dflt = std::thread::hardware_concurrency();
+  if (dflt == 0) {
+    // TODO(cbraley): Return some error code instead.
+    return 16;
+  } else {
+    return dflt;
+  }
+}
+
+ThreadPool::~ThreadPool() {
+  // TODO(cbraley): The current thread could help out to drain the work_ queue
+  // faster - for example, if there is work that hasn't yet been scheduled this
+  // thread could "pitch in" to help finish faster.
+
+  {
+    std::lock_guard<std::mutex> scoped_lock(mu_);
+    exit_ = true;
+  }
+  condvar_.notify_all();  // Tell *all* workers we are ready.
+
+  for (std::thread& thread : workers_) {
+    thread.join();
+  }
+}
+
+void ThreadPool::Wait() {
+  std::unique_lock<std::mutex> lock(mu_);
+  if (!work_.empty()) {
+    work_done_condvar_.wait(lock, [this] { return work_.empty(); });
+  }
+}
+
+ThreadPool::ThreadPool(int num_workers)
+    : num_workers_(num_workers), exit_(false) {
+  assert(num_workers_ > 0);
+  // TODO(cbraley): Handle thread construction exceptions.
+  workers_.reserve(num_workers_);
+  for (int i = 0; i < num_workers_; ++i) {
+    workers_.emplace_back(&ThreadPool::ThreadLoop, this);
+  }
+}
+
+void ThreadPool::Schedule(std::function<void(void)> func) {
+  ScheduleAndGetFuture(std::move(func));  // We ignore the returned std::future.
+}
+
+void ThreadPool::ThreadLoop() {
+  // Wait until the ThreadPool sends us work.
+  while (true) {
+    WorkItem work_item;
+
+    int prev_work_size = -1;
+    {
+      std::unique_lock<std::mutex> lock(mu_);
+      condvar_.wait(lock, [this] { return exit_ || (!work_.empty()); });
+      // ...after the wait(), we hold the lock.
+
+      // If all the work is done and exit_ is true, break out of the loop.
+      if (exit_ && work_.empty()) {
+        break;
+      }
+
+      // Pop the work off of the queue - we are careful to execute the
+      // work_item.func callback only after we have released the lock.
+      prev_work_size = work_.size();
+      work_item = std::move(work_.front());
+      work_.pop();
+    }
+
+    // We are careful to do the work without the lock held!
+    // TODO(cbraley): Handle exceptions properly.
+    work_item.func();  // Do work.
+
+    if (work_done_callback_) {
+      work_done_callback_(prev_work_size - 1);
+    }
+
+    // Notify a condvar is all work is done.
+    {
+      std::unique_lock<std::mutex> lock(mu_);
+      if (work_.empty() && prev_work_size == 1) {
+        work_done_condvar_.notify_all();
+      }
+    }
+  }
+}
+
+int ThreadPool::OutstandingWorkSize() const {
+  std::lock_guard<std::mutex> scoped_lock(mu_);
+  return work_.size();
+}
+
+int ThreadPool::NumWorkers() const { return num_workers_; }
+
+void ThreadPool::SetWorkDoneCallback(std::function<void(int)> func) {
+  work_done_callback_ = std::move(func);
+}
+
+}  // namespace cb