Use a constant empty tar header to avoid extra allocations #7484
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martinemde
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Feb 22, 2024
lib/rubygems/package/tar_header.rb
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| EMPTY = new({ # :nodoc: | ||
| mode: 0, | ||
| name: "", | ||
| prefix: "", | ||
| size: 0, | ||
| empty: true, | ||
| }).freeze |
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To really be identical you need the following. The default values are not the same as what an empty header outputs.
Suggested change
| EMPTY = new({ # :nodoc: | |
| mode: 0, | |
| name: "", | |
| prefix: "", | |
| size: 0, | |
| empty: true, | |
| }).freeze | |
| EMPTY = new({ # :nodoc: | |
| checksum: 0, | |
| gname: "", | |
| linkname: "", | |
| magic: "", | |
| mode: 0, | |
| name: "", | |
| prefix: "", | |
| size: 0, | |
| uname: "", | |
| version: 0, | |
| empty: true, | |
| }).freeze |
Here's my irb doublecheck:
irb(main):033> EMPTY = Gem::Package::TarHeader.new({ checksum: 0, gname: "", linkname: "", magic: "", mode: 0, name: "", prefix: "", size: 0, uname: "", version: 0, empty: true, })
=> #<Gem::Package::TarHeader:0x00000001203e60e0 @checksum=0, @devmajor=0, @devminor=0, @empty=true, @gid=0, @gname="", @linkname="", @magic="", @mode=0, @mtime=0, @name="", @prefix="", @size=0, @typeflag="0", @uid=0, @uname="", @version=0>
irb(main):034> Gem::Package::TarHeader.from(StringIO.new(Gem::Package::TarHeader::EMPTY_HEADER))
=> #<Gem::Package::TarHeader:0x00000001204cde90 @checksum=0, @devmajor=0, @devminor=0, @empty=true, @gid=0, @gname="", @linkname="", @magic="", @mode=0, @mtime=0, @name="", @prefix="", @size=0, @typeflag="0", @uid=0, @uname="", @version=0>We should also add a test.
simi
approved these changes
Feb 22, 2024
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@simi are you thinking the tar header is expected to be mutable? That's worth considering... |
No, I was just wondering what's memory footprint impact. |
deivid-rodriguez
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Apr 3, 2024
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There is one empty tar header per tar file read, in my experience. each gem requires reading 2 tar files. |
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deivid-rodriguez
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May 3, 2024
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Should we squash into a single commit? Right now there's three commits, two of them with the same commit message, which seems a bit confusing! Other than that, seems great! |
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@segiddins I squashed commits myself and will be merging this, hope it's ok. |
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…-tar-header-to-avoid-extra-allocations Use a constant empty tar header to avoid extra allocations (cherry picked from commit 90d0ceb)
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