784e03aa31
swapcontext() is expensive as it invokes system calls. Replace it with setjmp()/longjmp(). We still use setcontext() initially, since that's the most reasonable portable method of setting up a stack. Context switch time (measured by thread_context_switch) is reduced to 120ns (from 450ns), with inefficiencies in the test itself and in future<> dominating.
116 lines
3.4 KiB
C++
116 lines
3.4 KiB
C++
/*
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* This file is open source software, licensed to you under the terms
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* of the Apache License, Version 2.0 (the "License"). See the NOTICE file
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* distributed with this work for additional information regarding copyright
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* ownership. You may not use this file except in compliance with the License.
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*
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing,
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* software distributed under the License is distributed on an
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* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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* KIND, either express or implied. See the License for the
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* specific language governing permissions and limitations
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* under the License.
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*/
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/*
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* Copyright (C) 2015 Cloudius Systems, Ltd.
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*/
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#pragma once
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#include "future.hh"
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#include <memory>
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#include <setjmp.h>
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namespace seastar {
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class thread;
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class thread_context;
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namespace thread_impl {
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thread_context* get();
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void switch_in(thread_context* to);
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void switch_out(thread_context* from);
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void init();
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}
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extern thread_local jmp_buf g_unthreaded_context;
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// Internal class holding thread state. We can't hold this in
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// \c thread itself because \c thread is movable, and we want pointers
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// to this state to be captured.
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class thread_context {
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static constexpr const size_t _stack_size = 128*1024;
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std::unique_ptr<char[]> _stack{new char[_stack_size]};
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std::function<void ()> _func;
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jmp_buf _context;
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promise<> _done;
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bool _joined = false;
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private:
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static void s_main(unsigned int lo, unsigned int hi);
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void setup();
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void main();
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public:
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thread_context(std::function<void ()> func);
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void switch_in();
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void switch_out();
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friend class thread;
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friend void thread_impl::switch_in(thread_context*);
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friend void thread_impl::switch_out(thread_context*);
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};
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/// \brief thread - stateful thread of execution
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///
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/// Threads allow using seastar APIs in a blocking manner,
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/// by calling future::get() on a non-ready future. When
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/// this happens, the thread is put to sleep until the future
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/// becomes ready.
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class thread {
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std::unique_ptr<thread_context> _context;
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static thread_local thread* _current;
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public:
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/// \brief Constructs a \c thread object that does not represent a thread
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/// of execution.
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thread() = default;
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/// \brief Constructs a \c thread object that represents a thread of execution
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///
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/// \param func Callable object to execute in thread. The callable is
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/// called immediately.
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template <typename Func>
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thread(Func func);
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/// \brief Moves a thread object.
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thread(thread&& x) noexcept = default;
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/// \brief Move-assigns a thread object.
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thread& operator=(thread&& x) noexcept = default;
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/// \brief Destroys a \c thread object.
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///
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/// The thread must not represent a running thread of execution (see join()).
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~thread() { assert(!_context || _context->_joined); }
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/// \brief Waits for thread execution to terminate.
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///
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/// Waits for thread execution to terminate, and marks the thread object as not
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/// representing a running thread of execution.
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future<> join();
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};
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template <typename Func>
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inline
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thread::thread(Func func)
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: _context(std::make_unique<thread_context>(func)) {
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}
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inline
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future<>
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thread::join() {
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_context->_joined = true;
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return _context->_done.get_future();
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}
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}
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