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vector<bool>
Section: 24.2.3 [container.requirements.dataraces] Status: Resolved Submitter: Jeffrey Yaskin Opened: 2010-03-09 Last modified: 2016-01-28
Priority: Not Prioritized
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Discussion:
The common implementation of vector<bool>
is as an
unsynchronized bitfield. The addition of 24.2.3 [container.requirements.dataraces]/2 would require either a
change in representation or a change in access synchronization, both of
which are undesireable with respect to compatibility and performance.
[
2010 Pittsburgh: Moved to NAD EditorialResolved. Rationale added below.
]
Rationale:
Solved by N3069.
Proposed resolution:
Container data races 24.2.3 [container.requirements.dataraces]
Paragraph 1 is unchanged as follows:
1 For purposes of avoiding data races (17.6.4.8), implementations shall consider the following functions to be
const
:begin
,end
,rbegin
,rend
,front
,back
,data
,find
,lower_bound
,upper_bound
,equal_range
, and, except in associative containers,operator[]
.
Edit paragraph 2 as follows:
2 Notwithstanding (17.6.4.8), implementations are required to avoid data races when the contents of the contained object in different elements in the same sequence, excepting
vector<bool>
, are modified concurrently.
Edit paragraph 3 as follows:
3 [Note: For a
vector<int> x
with a size greater than one,x[1] = 5
and*x.begin() = 10
can be executed concurrently without a data race, butx[0] = 5
and*x.begin() = 10
executed concurrently may result in a data race. As an exception to the general rule, for avector<bool> y
,y[i] = true
may race withy[j] = true
. —end note]