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Section: 31.6.9 [futures.async] Status: C++11 Submitter: Alberto Ganesh Barbati Opened: 2011-02-17 Last modified: 2019-01-01
Priority: Not Prioritized
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Clause 31.6.9 [futures.async] has undergone significant rewording in Batavia. Due to co-presence of at least three different sources of modification there is a part where changes have overlapped (marked by an Editor's note), which should be reconciled. Moreover, I believe that a few non-overlapping sentences are now incorrect and should be fixed, so the problem cannot be handled editorially. (See c++std-lib-29667.)
[Adopted in Madrid, 2011-03]
Edit 31.6.5 [futures.state], paragraph 3 as follows.
An asynchronous return object is an object that reads results from an associated asynchronous state. A waiting function of an asynchronous return object is one that potentially blocks to wait for the associated asynchronous state to be made ready.
Edit within 31.6.9 [futures.async] paragraph 3 bullet 2 as follows.
policy & launch::deferredis non-zero — [...] The associated asynchronous state is not made ready until the function has completed. The first call to a function
requiring a non-timed waiton an asynchronous return object referring to theassociated asynchronous state created by thisshall invoke the deferred function in the thread that called the waiting function
asynccall to become ready
; onceevaluation of
INVOKE(g, xyz)begins, the function is no longer considered deferred. [...]
Edit 31.6.9 [futures.async] paragraph 5 as follows.
Synchronization: Regardless of the provided
- the invocation of
asyncsynchronizes with (1.10) the invocation of
f. [Note: this statement applies even when the corresponding future object is moved to another thread. —end note]; and
- the completion of the function
fis sequenced before (1.10) the associated asynchronous state is made ready. [Note:
fmight not be called at all, so its completion might never happen. —end note]
policy & launch::asyncis non-zero,
- a call to a waiting function on an asynchronous return object that shares the associated asynchronous state created by this
asynccall shall block until the associated thread has completed, as if joined (22.214.171.124);
thesynchronizes with (1.10) the return from the first function that successfully detects the ready status of the associated asynchronous state or with the return from the last function that releases the associated asynchronous state
join()on the created thread object
returns, whichever happens first. [Editor's note: N3196 changes the following sentence as indicated. N3188 removes the sentence. Please pick one.] If the invocation is deferred, the completion of the invocation of the deferred function synchronizes with the successful return from a call to a waiting function on the associated asynchronous state.