mirror of
https://github.com/matrix-construct/construct
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123 lines
2.8 KiB
C++
123 lines
2.8 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<it> when_any(it first, const it &last);
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template<class it> future<void> when_all(it first, const it &last);
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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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static const auto then
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{
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[](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 remove(p.state(), p);
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}
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};
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promise<void> p;
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const auto set_then
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{
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[&p](it &f)
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{
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f->state().then = [p]
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(shared_state_base &) mutable
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{
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then(p);
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};
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}
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};
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future<void> ret(p);
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for(; first != last; ++first)
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if(is(first->state(), future_state::PENDING))
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set_then(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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/// 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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static const auto then
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{
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[](promise<it> &p, it &f)
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{
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if(!p.valid())
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return;
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set(f->state(), future_state::OBSERVED);
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p.set_value(f);
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}
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};
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promise<it> p;
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const auto set_then
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{
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[&p](it &f)
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{
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f->state().then = [p, f] // alloc
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(shared_state_base &) mutable
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{
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then(p, f);
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};
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}
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};
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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(f->state(), future_state::READY))
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{
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set(f->state(), 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(first->state(), future_state::PENDING))
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set_then(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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