[SR-1771] DispatchTime should be Comparable

[glessard]

Previous ID	SR-1771
Radar	rdar://problem/26879337
Original Reporter	@glessard
Type	Bug
Status	Resolved
Resolution	Done

Environment

Xcode 8 (beta, 8S128d) with Swift 3.0 preview 1

Additional Detail from JIRA

Votes	0
Component/s	libdispatch
Labels	Bug
Assignee	mww (JIRA)
Priority	Medium

md5: 52712f7caaefd132adb681de084a9a62

Issue Description:

A workaround is to compare the .rawValue properties – clunky.

[swift-ci]

Comment by Daniel A. Steffen (JIRA)

the .rawValue is opaque and not guaranteed to be comparable (e.g. it does not compare numerically for DispatchWalltime)

[belkadan]

Out of curiosity (I'm not part of the Dispatch team) when do you need to compare them?

[glessard]

Jordan:
I compared dispatch_time_t values in a simple rate-limiting algorithm of sorts. When issuing an asynchronous task, I'd save a target time (from dispatch_time(DISPATCH_TIME_NOW, offset)), and in the callback I'd compare it to the current time (from dispatch_time(DISPATCH_TIME_NOW, 0)). If the current time is too early (smaller), I'd post the result in a dispatch_after block, otherwise I'd post it immediately.

This could be done in other ways, but since dispatch_time_t is the native representation for libdispatch, this was straightforward (and has behaved as I expected in testing.)

Daniel:
As far as I can tell the values returned from the old dispatch_time() function were comparable; since the new system splits DispatchTime and DispatchWallTime into separate types, comparability is now achievable as a public feature.

[swift-ci]

Comment by Daniel A. Steffen (JIRA)

yes, I'm not saying that it is not achievable, I agree that it is.
I was warning you that using the workaround of comparing .rawValue is not guaranteed to work going forward (the raw value encoding is private) (and dispatch_time_t in the old API was definitely not comparable since multiple representations were mixed together)

[swift-ci]

Comment by Matt Wright (JIRA)

Addressed in 8ac413a0b5a9f927f44438df3376a7757f607953.