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Section: 29.7 [time.clock] Status: NAD Submitter: Beman Dawes Opened: 2008-11-24 Last modified: 2019-02-26
Priority: Not Prioritized
View all issues with NAD status.
Discussion:
Each of the three clocks specified in Clocks 29.7 [time.clock] provides the member function:
static time_point now();
The semantics specified by Clock requirements 29.3 [time.clock.req]
make no mention of error handling. Thus the function may throw bad_alloc
or an implementation-defined exception (16.4.6.13 [res.on.exception.handling]
paragraph 4).
Some implementations of these functions on POSIX, Windows, and
presumably on other operating systems, may fail in ways only detectable
at runtime. Some failures on Windows are due to supporting chipset
errata and can even occur after successful calls to a clock's now()
function.
These functions are used in cases where exceptions are not appropriate or where the specifics of the exception or cause of error need to be available to the user. See N2828, Library Support for hybrid error handling (Rev 1), for more specific discussion of use cases. Thus some change in the interface of now is required.
The proposed resolution has been implemented in the Boost version of the chrono library. No problems were encountered.
[ Batavia (2009-05): ]
We recommend this issue be deferred until the next Committee Draft has been issued and the prerequisite paper has been accepted.
Move to Open.
[ 2009-10 Santa Cruz: ]
Mark as NAD future. Too late to make this change without having already accepted the hybrid error handling proposal.
[LEWG Kona 2017]
Recommend NAD. Needs a paper. Proposed resolution no longer applies.
Proposed resolution:
Accept the proposed wording of N2828, Library Support for hybrid error handling (Rev 1).
Change Clock
requirements 29.3 [time.clock.req] as indicated:
-2- In Table 55
C1
andC2
denote clock types.t1
andt2
are values returned byC1::now()
where the call returningt1
happens before (1.10) the call returningt2
and both of these calls happen beforeC1::time_point::max()
.ec
denotes an object of typeerror_code
(19.5.4.1 [syserr.errcode.overview]).
Table 55 — Clock requirements Expression Return type Operational semantics ... ... ... C1::now()
C1::time_point
Returns a time_point
object representing the current point in time.C1::now(ec)
C1::time_point
Returns a time_point
object representing the current point in time.
Change class system_clock
29.7.2 [time.clock.system] as indicated:
static time_point now(error_code& ec=throws());
Change class monotonic_clock
99 [time.clock.monotonic] as indicated:
static time_point now(error_code& ec=throws());
Change class high_resolution_clock
29.7.8 [time.clock.hires] as indicated:
static time_point now(error_code& ec=throws());