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[SR-9597] DispatchData.copyBytes allocates #627

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weissi opened this issue Jan 3, 2019 · 5 comments
Open

[SR-9597] DispatchData.copyBytes allocates #627

weissi opened this issue Jan 3, 2019 · 5 comments
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bug libdispatch

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@weissi
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weissi commented Jan 3, 2019

Previous ID SR-9597
Radar rdar://problem/52529586
Original Reporter @weissi
Type Bug
Additional Detail from JIRA
Votes 0
Component/s libdispatch
Labels Bug
Assignee None
Priority Medium

md5: 63ced7a174d79c5fd0d6f317c1e088e1

Issue Description:

every method I can see to copy bytes out of a DispatchData into some other container of bytes allocates.

DispatchData.copyBytes looks really benign but internally calls (https://github.com/apple/swift-corelibs-libdispatch/blob/9c48a809693b78bd5ad89718c6f9712aaa1cfb1e/src/swift/Data.swift#L221) _copyBytesHelper which calls CDispatch.dispatch_data_apply which needs a closure. That closure has a non-nil context pointer and therefore allocates.

Possible solutions:

  • fix SR-904

  • make enough things inlinable/usableFromInline that we don't actually need to create a proper closure

CC @jckarter, phabouzit (JIRA User), @phausler, @parkera, phabouzit (JIRA User)
@jckarter
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jckarter commented Jan 3, 2019

Sounds like a dup of SR-904. aschwaighofer@apple.com (JIRA User) are you still working on that?

@weissi
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weissi commented Jan 3, 2019

@jckarter well, kind of a dup. It would certainly be possible to implement DispatchData.copyBytes without using any closures. But fixing SR-904 would obviously be the most awesome fix and it would fix so many other similarly surprising issues too.

@jckarter
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jckarter commented Jan 3, 2019

If it doesn't overly uglify the implementation, sure.

@weissi
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weissi commented Jan 3, 2019

@jckarter don't get me wrong, I would love for SR-904 to be fixed. I didn't file it as a dupe because I wan't sure if SR-904 will be fixed soon and I still think that DispatchData must be able to copy the bytes out of itself without allocating, regardless of Swift's ability to allocate non-escaping closures on the heap. But if fixing SR-904 is the fix to this bug I'll be very very happy 🙂

@weissi
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weissi commented Jul 2, 2019

@swift-ci create

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
@shahmishal shahmishal transferred this issue from apple/swift May 5, 2022
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@jckarter @weissi