mirror of
https://github.com/matrix-construct/construct
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d9a4f06bf6
This is not a move to c++17. If the compiler happens to have support for c++17 namespace scope resolution, they have been kind enough to backport it to gnu++14. This limits our support for really old c++14 compilers, but that was limited anyway. GCC 6.1 and clang 3.6 tested.
65 lines
2.8 KiB
C++
65 lines
2.8 KiB
C++
/*
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* Copyright (C) 2016 Charybdis Development Team
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* Copyright (C) 2016 Jason Volk <jason@zemos.net>
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*
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* Permission to use, copy, modify, and/or distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice is present in all copies.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
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* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
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* IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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*/
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#pragma once
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#define HAVE_IRCD_CTX_OLE_H
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// Context OffLoad Engine (OLE)
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//
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// This system allows moving a task off the main IRCd thread by passing a function to a
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// worker thread for execution. The context on the main IRCd thread yields until the offload
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// function has returned (or thrown). Please read the last paragraph and be thoroughly dissuaded
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// from temptation to abuse this.
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//
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// The offload engine is for ye 'ole libraries or opaque function calls which may hang the
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// program with blocking I/O, extreme and time-consuming computation, or other uncooperative
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// behavior. IRCd is, at its core, still a single-threaded asynchronous environment and while
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// userspace context switching is provided to eliminate callbacks, the same rules for hanging
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// the program still apply.
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//
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// Before using this system, do everything you possibly can to figure out if you can participate
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// directly in the main boost::asio (glorified epoll()) system. If you have access to a file
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// descriptor, socket, or similar device exposed by the library YOU DO NOT NEED THIS SYSTEM.
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// We do not *prefer* to use threads just to have them wait on I/O. This system is also not for
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// moderately expensive computation; it is alright to be fairly liberal with the main thread.
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// You must factor in the round trip costs of kernel thread context switching, cache/bus
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// transfers and contention, and whether any concurrency will really even be produced at all
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// to make a good case for an offload that doesn't hurt more than it helps. And when it hurts,
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// it hurts _everything_.
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//
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namespace ircd::ctx::ole
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{
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struct init;
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void offload(const std::function<void ()> &);
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}
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namespace ircd::ctx
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{
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using ole::offload;
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}
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struct ircd::ctx::ole::init
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{
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init();
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~init() noexcept;
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};
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