hi, thanks for replying, but i didn't understand much of what you said.
i think you're saying that my code (the CRC library) is calling array_try_unshare or jl_array_grow_end? i don't see either of those in my code at https://github.com/andrewcooke/CRC.jl/blob/master/src/CRC.jl what i do see is a call to reinterpret(). that seems to cause this problem. so i guess my question is - is there any way to specify that the reinterpret has a finite scope? by the time that this error occurs the reinterpreted array is no longer used. i'm happy to raise an issue, but i'm still not sure what the issue is. it seems like julia is trying too hard to rotect me from something that isn't happening? here's my demo of the issue with reinterpret: julia> a = b"1234" 4-element Array{UInt8,1}: 0x31 0x32 0x33 0x34 julia> resize!(a, 2) 2-element Array{UInt8,1}: 0x31 0x32 julia> resize!(a, 4) 4-element Array{UInt8,1}: 0x31 0x32 0x00 0x34 julia> reinterpret(Uint32, a); julia> resize!(a, 2) ERROR: cannot resize array with shared data in resize! at ./array.jl:545 thanks, andrew On Thursday, 19 February 2015 11:37:06 UTC-3, Kevin Squire wrote: > > Hi Andrew, > > A very similar issue came up in > https://github.com/JuliaLang/julia/issues/4592, which was addressed by > > > https://github.com/JuliaLang/julia/commit/2570b4a60e5ab5c438c57ed9a3eafa5c881bc39a > > If you look at the fix, you'll see that the error in your code comes from > array_try_unshare or jl_array_grow_end. In either case, > unsharing/resizing doesn't work for arrays sharing data with "how == 3", > which means that the data being resized is actually just a pointer to the > original data (defined here > <https://github.com/JuliaLang/julia/blob/master/src/julia.h#L104-L108>). > > In your case, what is happening is that a string is created ("hello world"), > and the variable a simply gets a pointer to the underlying string data (the > b_str macro does just that > <https://github.com/JuliaLang/julia/blob/master/base/string.jl#L1077>), > so it's sharing data (with a string that isn't referenced anymore), and > therefore can't be resized. > > At a minimum, it would be great to have this information somewhere in the > docs. A more informative error might also be useful. Would you mind > opening up an issue (and/or if you're so motivated, a pull request)? > > Cheers, > > Kevin > > > > On Thu, Feb 19, 2015 at 2:39 AM, andrew cooke <and...@acooke.org > <javascript:>> wrote: > >> Hi, >> >> I'm trying to understand the bug report at >> https://github.com/andrewcooke/CRC.jl/issues/4 which has >> >> julia> using CRC >> >> julia> crc32c = crc(CRC_32_C) >> handler (generic function with 3 methods) >> >> julia> a = b"hello world"; >> >> julia> crc32c(a) >> 0xc99465aa >> >> julia> resize!(a, 5) >> ERROR: cannot resize array with shared data >> in resize! at ./array.jl:545 >> >> but I can find no docs on what "shared data" for arrays means. All I >> have found is the C code at >> https://github.com/JuliaLang/julia/blob/master/src/array.c which, tbh, >> is a little opaque (what is a->how? how can i reset a->shared?) >> >> It sounds like the array code is doing something like reference counting >> and refusing to be mutable when there are references? How do I decrement >> the count? >> >> Is there any documentation on sharing of arrays? >> >> My guess is that a caller could work round this by making a copy, but >> that seems inefficient. Especially since my code simply iterates through >> the data and then "no longer cares". >> >> Sorry, this email is very vague. Given the lack of docs (nothing about >> sharing in the manual i can see) I wonder if I've stumbled over some >> internal detail that should not be exposed to users? >> >> Any help appreciated, >> Andrew >> > >
