2fd6d495fa
The compilation of wasm UDFs is performed by a call to a foreign function, which cannot be divided with yielding points and, as a result, causes long reactor stalls for big UDFs. We avoid them by submitting the compilation task to a non-seastar std::thread, and retrieving the result using seastar::alien. The thread is created at the start of the program. It executes tasks from a queue in an infinite loop. All seastar shards reference the thread through a std::shared_ptr to a `alien_thread_runner`. Considering that the compilation takes a long time anyway, the alien_thread_runner is implemented with focus on simplicity more than on performance. The tasks are stored in an std::queue, reading and writing to it is synchronized using an std::mutex for reading/ writing to the queue, and an std::condition_variable waiting until the queue has elements. When the destructor of the alien runner is called, an std::nullopt sentinel is pushed to the queue, and after all remaining tasks are finished and the sentinel is read, the thread finishes.
52 lines
1.2 KiB
C++
52 lines
1.2 KiB
C++
/*
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* Copyright (C) 2023-present ScyllaDB
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*/
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/*
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* SPDX-License-Identifier: AGPL-3.0-or-later
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*/
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#pragma once
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#include <functional>
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#include <mutex>
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#include <queue>
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#include <condition_variable>
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#include <thread>
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#include <seastar/core/future.hh>
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#include <seastar/util/noncopyable_function.hh>
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#include "rust/cxx.h"
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#include "rust/wasmtime_bindings.hh"
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namespace wasm {
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struct wasm_compile_task {
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seastar::noncopyable_function<void()> func;
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seastar::promise<rust::Box<wasmtime::Module>>& done;
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unsigned shard;
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};
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struct task_queue {
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std::mutex _mut;
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std::condition_variable _cv;
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std::queue<std::optional<wasm_compile_task>> _pending;
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public:
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std::optional<wasm_compile_task> pop_front();
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void push_back(std::optional<wasm_compile_task> work_item);
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};
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class alien_thread_runner {
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task_queue _pending_queue;
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std::thread _thread;
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public:
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alien_thread_runner();
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~alien_thread_runner();
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alien_thread_runner(const alien_thread_runner&) = delete;
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alien_thread_runner& operator=(const alien_thread_runner&) = delete;
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void submit(seastar::promise<rust::Box<wasmtime::Module>>& p, std::function<rust::Box<wasmtime::Module>()> f);
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};
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} // namespace wasm
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