feat(storage): implement multi stream manager for async downloads #15858
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| Original file line number | Diff line number | Diff line change |
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| // Copyright 2025 Google LLC | ||
| // | ||
| // 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 | ||
| // | ||
| // https://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. | ||
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| #include "google/cloud/storage/internal/async/multi_stream_manager.h" | ||
| #include "google/cloud/storage/internal/async/object_descriptor_impl.h" | ||
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| namespace google { | ||
| namespace cloud { | ||
| namespace storage_internal { | ||
| GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_BEGIN | ||
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| // Explicit instantiation for ObjectDescriptorImpl usage. | ||
| template class MultiStreamManager<ReadStream, ReadRange>; | ||
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| GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END | ||
| } // namespace storage_internal | ||
| } // namespace cloud | ||
| } // namespace google |
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| // Copyright 2025 Google LLC | ||
| // | ||
| // 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 | ||
| // | ||
| // https://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. | ||
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| #ifndef GOOGLE_CLOUD_CPP_GOOGLE_CLOUD_STORAGE_INTERNAL_ASYNC_MULTI_STREAM_MANAGER_H | ||
| #define GOOGLE_CLOUD_CPP_GOOGLE_CLOUD_STORAGE_INTERNAL_ASYNC_MULTI_STREAM_MANAGER_H | ||
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| #include "google/cloud/status.h" | ||
| #include "google/cloud/version.h" | ||
| #include <cstdint> | ||
| #include <functional> | ||
| #include <list> | ||
| #include <memory> | ||
| #include <unordered_map> | ||
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| namespace google { | ||
| namespace cloud { | ||
| namespace storage_internal { | ||
| GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_BEGIN | ||
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| // Defines the interface contract that any stream type (e.g., ReadStream, | ||
| // WriteStream) managed by MultiStreamManager must implement. This explicit base | ||
| // class ensures we have a clear, enforceable interface for operations like | ||
| // CancelAll(). | ||
| class StreamBase { | ||
| public: | ||
| virtual ~StreamBase() = default; | ||
| virtual void Cancel() = 0; | ||
| }; | ||
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| // Manages a collection of streams. | ||
| // | ||
| // This class implements the "Subsequent Stream" logic where idle streams | ||
| // are moved to the front of the queue for reuse. | ||
| // | ||
| // THREAD SAFETY: | ||
| // This class is NOT thread-safe. The owner (e.g. ObjectDescriptorImpl | ||
| // or AsyncWriterImpl etc) must serialize access, typically by holding | ||
| // an external mutex while calling these methods. | ||
| // | ||
| // EXAMPLE USAGE: | ||
| // class MyOwner { | ||
| // std::mutex mu_; | ||
| // MultiStreamManager<MyStream, MyRange> manager_; | ||
| // | ||
| // void StartRead() { | ||
| // std::unique_lock<std::mutex> lk(mu_); | ||
| // auto it = manager_.GetLeastBusyStream(); | ||
| // } | ||
| // }; | ||
| template <typename StreamT, typename RangeT> | ||
| class MultiStreamManager { | ||
| public: | ||
| struct Stream { | ||
| std::shared_ptr<StreamT> stream; | ||
| std::unordered_map<std::int64_t, std::shared_ptr<RangeT>> active_ranges; | ||
| }; | ||
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| using StreamIterator = typename std::list<Stream>::iterator; | ||
| using StreamFactory = std::function<std::shared_ptr<StreamT>()>; | ||
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| // Constructor creates the first stream using the factory immediately. | ||
| explicit MultiStreamManager(StreamFactory stream_factory) | ||
| : stream_factory_(std::move(stream_factory)) { | ||
| streams_.push_back(Stream{stream_factory_(), {}}); | ||
| } | ||
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| // Constructor accepts an already-created initial stream. | ||
| // This is required by ObjectDescriptorImpl which receives an OpenStream. | ||
| MultiStreamManager(StreamFactory stream_factory, | ||
| std::shared_ptr<StreamT> initial_stream) | ||
| : stream_factory_(std::move(stream_factory)) { | ||
| streams_.push_back(Stream{std::move(initial_stream), {}}); | ||
| } | ||
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| StreamIterator GetFirstStream() { | ||
| if (streams_.empty()) return streams_.end(); | ||
| return streams_.begin(); | ||
| } | ||
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| StreamIterator GetLeastBusyStream() { | ||
| if (streams_.empty()) return streams_.end(); | ||
| auto least_busy_it = streams_.begin(); | ||
| // Track min_ranges to avoid calling .size() repeatedly if possible, | ||
| // though for std::unordered_map .size() is O(1). | ||
| std::size_t min_ranges = least_busy_it->active_ranges.size(); | ||
| if (min_ranges == 0) return least_busy_it; | ||
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| // Start checking from the second element | ||
| for (auto it = std::next(streams_.begin()); it != streams_.end(); ++it) { | ||
| // Strict less-than ensures stability (preferring older streams if tied) | ||
| auto size = it->active_ranges.size(); | ||
| if (size < min_ranges) { | ||
| least_busy_it = it; | ||
| min_ranges = size; | ||
| if (min_ranges == 0) return least_busy_it; | ||
| } | ||
| } | ||
| return least_busy_it; | ||
| } | ||
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| StreamIterator AddStream(std::shared_ptr<StreamT> stream) { | ||
| streams_.push_front(Stream{std::move(stream), {}}); | ||
| return streams_.begin(); | ||
| } | ||
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| void CancelAll() { | ||
| for (auto& s : streams_) { | ||
| if (s.stream) s.stream->Cancel(); | ||
| } | ||
| } | ||
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| void RemoveStreamAndNotifyRanges(StreamIterator it, Status const& status) { | ||
| auto ranges = std::move(it->active_ranges); | ||
| streams_.erase(it); | ||
| for (auto const& kv : ranges) { | ||
| kv.second->OnFinish(status); | ||
| } | ||
| } | ||
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| void MoveActiveRanges(StreamIterator from, StreamIterator to) { | ||
| to->active_ranges = std::move(from->active_ranges); | ||
| } | ||
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| void CleanupDoneRanges(StreamIterator it) { | ||
| auto& active_ranges = it->active_ranges; | ||
| for (auto i = active_ranges.begin(); i != active_ranges.end();) { | ||
| if (i->second->IsDone()) { | ||
| i = active_ranges.erase(i); | ||
| } else { | ||
| ++i; | ||
| } | ||
| } | ||
| } | ||
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| template <typename Pred> | ||
| bool ReuseIdleStreamToFront(Pred pred) { | ||
| for (auto it = streams_.begin(); it != streams_.end(); ++it) { | ||
| if (!pred(*it)) continue; | ||
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| // If the idle stream is already at the front, we don't | ||
| // need to move it. Otherwise splice to the front in O(1). | ||
| if (it != streams_.begin()) { | ||
| streams_.splice(streams_.begin(), streams_, it); | ||
| } | ||
| return true; | ||
| } | ||
| return false; | ||
| } | ||
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| bool Empty() const { return streams_.empty(); } | ||
| StreamIterator End() { return streams_.end(); } | ||
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| std::size_t Size() const { return streams_.size(); } | ||
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| private: | ||
| std::list<Stream> streams_; | ||
| StreamFactory stream_factory_; | ||
| }; | ||
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| GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END | ||
| } // namespace storage_internal | ||
| } // namespace cloud | ||
| } // namespace google | ||
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| #endif // GOOGLE_CLOUD_CPP_GOOGLE_CLOUD_STORAGE_INTERNAL_ASYNC_MULTI_STREAM_MANAGER_H | ||
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nit: here and other places where push_back or push_front is called while constructing the element at the same time are good opportunities to use emplace_back or emplace_front instead.