mirror of
https://github.com/matrix-construct/construct
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68 lines
2.3 KiB
C++
68 lines
2.3 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_FAULT_H
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namespace ircd::ctx
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{
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IRCD_EXCEPTION(error, aborted)
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IRCD_EXCEPTION(aborted, unhandled_fault)
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template<class... args> struct fault;
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}
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// Faults add the notion of recoverable exceptions. C++ exceptions are not, as
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// they destruct the stack and then clobber everything with the catch branch.
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// A fault is an error handling device alternative to throwing an exception;
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// Hitting a fault may stop the context until the fault is serviced to continue
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// or a real exception is thrown to abort the context.
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//
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// A compelling example is std::bad_alloc, or an out of memory condition. A
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// fault allows other contexts to free up their resources after which the
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// faulty context can continue without having to unwind the work it's already
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// made progress on to try again.
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//
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// Faults begin with the cost of a function call to a handler at the point of
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// the fault. The handler's template specifies the argument list so the fault
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// can safely observe or modify your data. The call to fault has no return
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// value. If it returns the fault has been successfully serviced.
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//
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// Fault handlers must return true to default the faulty context. Handlers are
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// also responsible for detecting if they are executing with an active
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// exception which makes returning false considered a DOUBLE FAULT. This may
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// lead to program termination because it's basically throwing an exception from
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// a destructor (and can be useful proper behavior).
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//
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template<class... args>
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struct ircd::ctx::fault
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{
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using handler = std::function<bool (args&&...)>;
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handler h;
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virtual bool handle(args&&... a)
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{
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if(unlikely(!h))
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throw unhandled_fault{};
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return h(std::forward<args>(a)...);
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}
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void operator()(args&&... a)
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{
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if(!handle(std::forward<args>(a)...))
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throw aborted{};
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}
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fault(handler h)
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:h{std::move(h)}
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{}
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};
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