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3b9e9a3a56
Note effect of BOOST_USE_SEGMENTED_STACKS if StackAllocator is not explicitly passed. Introduce function_heading_for QuickBook template to allow separate descriptions of swap(fiber), swap(packaged_task) and swap(promise). Document async() using C++14 std::result_of_t and std::decay_t, aligning with std::async() documentation. Rework when_any / when_all examples to use unbounded_channel throughout, since we always close() the channel after the first value anyway. bounded_channel doesn't really add much value here. Make wait_first_outcome_impl() infer its channel pointer type. That way we can reuse that function instead of coding a separate wait_all_until_error_impl(), which differs only in using the nchannel facade instead of directly pushing to unbounded_channel. Explain use of std::bind() to bind a lambda. Use a more nuanced discussion of promise lifetime in write_ec() example function. Use condition_variable::wait(lock, predicate) in a couple places in work_sharing.cpp example.
183 lines
5.2 KiB
Plaintext
183 lines
5.2 KiB
Plaintext
[/
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Copyright Oliver Kowalke 2013.
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt
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]
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[#class_packaged_task]
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[section:packaged_task Template `packaged_task<>`]
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A __packaged_task__ wraps a callable target that returns a value so that the
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return value can be computed asynchronously.
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Conventional usage of `packaged_task<>` is like this:
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# Instantiate `packaged_task<>` with template arguments matching the signature
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of the callable. Pass the callable to the [link packaged_task_packaged_task
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constructor].
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# Call [member_link packaged_task..get_future] and capture the returned
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[template_link future] instance.
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# Launch a [class_link fiber] to run the new `packaged_task<>`, passing any
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arguments required by the original callable.
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# Call [member_link fiber..detach] on the newly-launched `fiber`.
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# At some later point, retrieve the result from the `future<>`.
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This is, in fact, pretty much what [ns_function_link fibers..async]
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encapsulates.
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template< class R, typename ... Args >
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class packaged_task< R( Args ... ) > {
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public:
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packaged_task() noexcept;
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template< typename Fn >
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explicit packaged_task( Fn &&);
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template< typename Fn, typename Allocator >
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packaged_task( std::allocator_arg_t, Allocator const&, Fn &&);
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packaged_task( packaged_task &&) noexcept;
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packaged_task & operator=( packaged_task &&) noexcept;
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packaged_task( packaged_task const&) = delete;
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packaged_task & operator=( packaged_task const&) = delete;
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~packaged_task();
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void swap( packaged_task &) noexcept;
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bool valid() const noexcept;
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future< R > get_future();
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void operator()( Args ...);
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void reset();
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};
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template< typename Signature >
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void swap( packaged_task< Signature > &, packaged_task< Signature > &) noexcept;
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[heading Default constructor `packaged_task()`]
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packaged_task() noexcept;
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[variablelist
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[[Effects:] [Constructs an object of class `packaged_task` with no [link
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shared_state shared state].]]
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[[Throws:] [Nothing.]]
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]
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[#packaged_task_packaged_task]
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[heading Templated constructor `template<> packaged_task()`]
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template< typename Fn >
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explicit packaged_task( Fn && fn);
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template< typename Fn, typename Allocator >
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packaged_task( std::allocator_arg_t, Allocator const& alloc, Fn && fn);
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[variablelist
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[[Effects:] [Constructs an object of class `packaged_task` with a [link
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shared_state shared state] and stores the callable target `fn` internally.]]
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[[Throws:] [Exceptions caused by memory allocation.]]
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[[Note:] [The signature of `Fn` should have a return type convertible to `R`.]]
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[[See also:] [__allocator_arg_t__]]
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]
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[heading Move constructor]
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packaged_task( packaged_task && other) noexcept;
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[variablelist
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[[Effects:] [Creates a packaged_task by moving the [link shared_state shared
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state] from `other`.]]
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[[Postcondition:] [`other` contains no valid shared state.]]
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[[Throws:] [Nothing.]]
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]
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[heading Destructor]
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~packaged_task();
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[variablelist
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[[Effects:] [Destroys `*this` and abandons the [link shared_state shared
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state] if shared state is ready; otherwise stores __future_error__ with error
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condition __broken_promise__.]]
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]
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[operator_heading packaged_task..operator_assign..operator=]
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packaged_task & operator=( packaged_task && other) noexcept;
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[variablelist
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[[Effects:] [Transfers the ownership of [link shared_state shared state] to
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`*this`.]]
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[[Postcondition:] [`other` contains no valid shared state.]]
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[[Throws:] [Nothing.]]
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]
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[member_heading packaged_task..swap]
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void swap( packaged_task & other) noexcept;
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[variablelist
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[[Effects:] [Swaps the [link shared_state shared state] between other and
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`*this`.]]
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[[Throws:] [Nothing.]]
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]
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[member_heading packaged_task..valid]
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bool valid() const noexcept;
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[variablelist
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[[Effects:] [Returns `true` if `*this` contains a [link shared_state shared
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state].]]
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[[Throws:] [Nothing.]]
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]
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[member_heading packaged_task..get_future]
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future< R > get_future();
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[variablelist
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[[Returns:] [A __future__ with the same [link shared_state shared state].]]
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[[Throws:] [__future_error__ with __already_retrieved__ or __no_state__.]]
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]
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[operator_heading packaged_task..operator_apply..operator()]
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void operator()( Args && ... args);
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[variablelist
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[[Effects:] [Invokes the stored callable target. Any exception thrown by the
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callable target `fn` is stored in the [link shared_state shared state].
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Otherwise, the value returned by `fn` is stored in the shared state.]]
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[[Throws:] [__future_error__ with __no_state__.]]
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]
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[member_heading packaged_task..reset]
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void reset();
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[variablelist
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[[Effects:] [Resets the [link shared_state shared state] and abondons the
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result of previous executions. A new shared state is constructed.]]
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[[Throws:] [__future_error__ with __no_state__.]]
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]
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[function_heading_for swap..packaged_task]
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template< typename Signature >
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void swap( packaged_task< Signature > & l, packaged_task< Signature > & r) noexcept;
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[variablelist
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[[Effects:] [Same as `l.swap( r)`.]]
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]
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[endsect]
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