mirror of
https://github.com/matrix-construct/construct
synced 2024-11-03 04:18:55 +01:00
142 lines
3.7 KiB
C++
142 lines
3.7 KiB
C++
// Matrix Construct
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//
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// Copyright (C) Matrix Construct Developers, Authors & Contributors
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// Copyright (C) 2016-2018 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. The
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// full license for this software is available in the LICENSE file.
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#pragma once
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#define HAVE_IRCD_CTX_WHEN_H
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namespace ircd::ctx
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{
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template<class it> future<void> when_all(it first, const it &last);
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template<class it> future<it> when_any(it first, const it &last);
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}
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// Internal interface
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namespace ircd::ctx::when
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{
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template<class T> auto &state(const future<T> &);
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void all_then(promise<void> &p);
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template<class it> void any_then(promise<it> &p, it &f);
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template<class it> void set_all_then(promise<void> &p, it &f);
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template<class it> void set_any_then(promise<it> &p, it &f);
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}
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/// Returns a future which becomes ready when any of the futures in the
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/// iteration become ready or are already ready. The future that when_any()
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/// eventually indicates is then considered "observed" which means you
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/// are required to do nothing when including it in the next invocation of
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/// when_any() and it won't be considered ready or pending again and the
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/// collection does not have to be modified in any way.
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///
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/// The returned future's payload is an iterator into the collection as if
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/// it were the result of an std::find() etc; thus to know its index an
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/// std::distance is often satisfactory.
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template<class it>
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ircd::ctx::future<it>
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ircd::ctx::when_any(it first,
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const it &last)
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{
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promise<it> p;
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future<it> ret(p);
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for(auto f(first); f != last; ++f)
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if(is(state(*f), future_state::READY))
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{
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set(when::state(*f), future_state::OBSERVED);
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p.set_value(f);
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return ret;
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}
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for(; first != last; ++first)
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if(is(state(*first), future_state::PENDING))
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when::set_any_then(p, first);
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if(refcount(p.state()) <= 1)
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p.set_value(first);
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return ret;
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}
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/// Returns a future which becomes ready when all of the futures in the
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/// collection become ready. This future has a void payload to minimize
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/// its cost since this indication is positively unate.
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template<class it>
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ircd::ctx::future<void>
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ircd::ctx::when_all(it first,
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const it &last)
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{
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promise<void> p;
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future<void> ret(p);
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for(; first != last; ++first)
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if(is(state(*first), future_state::PENDING))
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when::set_all_then(p, first);
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if(refcount(p.state()) <= 1)
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p.set_value();
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return ret;
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}
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template<class it>
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void
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ircd::ctx::when::set_any_then(promise<it> &p,
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it &f)
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{
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when::state(*f).then = [p, f] // TODO: quash this alloc
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(shared_state_base &sb) mutable
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{
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if(sb.then)
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any_then(p, f);
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};
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}
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template<class it>
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void
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ircd::ctx::when::set_all_then(promise<void> &p,
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it &f)
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{
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when::state(*f).then = [p] // TODO: quash this alloc
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(shared_state_base &sb) mutable
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{
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if(sb.then)
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all_then(p);
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};
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}
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template<class it>
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void
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ircd::ctx::when::any_then(promise<it> &p,
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it &f)
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{
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if(!p.valid())
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return;
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set(when::state(*f), future_state::OBSERVED);
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p.set_value(f);
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}
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inline void
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ircd::ctx::when::all_then(promise<void> &p)
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{
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if(!p.valid())
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return;
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if(refcount(p.state()) < 2)
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return p.set_value();
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return p.remove(p.state(), p);
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}
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/// In order for this template to be reusable with std::set iterations we
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/// have to make a const_cast at some point; this internal function does that.
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template<class T>
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auto &
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ircd::ctx::when::state(const future<T> &f)
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{
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return const_cast<future<T> &>(f).state();
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}
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