[rubygems/rubygems] Fewer allocations in gem installation

For now, on a small rails app I have hanging around:

```
==> memprof.after.txt <==
Total allocated: 872.51 MB (465330 objects)
Total retained:  40.48 kB (326 objects)

==> memprof.before.txt <==
Total allocated: 890.79 MB (1494026 objects)
Total retained:  40.40 kB (328 objects)
```

Not a huge difference in memory usage, but it's a drastic improvement
in total number of allocations.

Additionally, this will pay huge dividends once
https://github.com/ruby/zlib/pull/61 is merged, as it will allow us to
completely avoid allocations in the repeated calls to readpartial,
which currently accounts for most of the memory usage shown above.

https://github.com/rubygems/rubygems/commit/f78d45d927

1 files changed, 21 insertions, 17 deletions

diff --git a/lib/rubygems/package/tar_header.rb b/lib/rubygems/package/tar_header.rb
index 7deafa994f..087f13f6c9 100644
--- a/lib/rubygems/package/tar_header.rb
+++ b/lib/rubygems/package/tar_header.rb
@@ -127,7 +127,8 @@ class Gem::Package::TarHeader
   end
 
   def self.strict_oct(str)
-    return str.strip.oct if /\A[0-7]*\z/.match?(str.strip)
+    str.strip!
+    return str.oct if /\A[0-7]*\z/.match?(str)
 
     raise ArgumentError, "#{str.inspect} is not an octal string"
   end
@@ -137,7 +138,8 @@ class Gem::Package::TarHeader
     # \ff flags a negative 256-based number
     # In case we have a match, parse it as a signed binary value
     # in big-endian order, except that the high-order bit is ignored.
-    return str.unpack("N2").last if /\A[\x80\xff]/n.match?(str)
+
+    return str.unpack1("@4N") if /\A[\x80\xff]/n.match?(str)
     strict_oct(str)
   end
 
@@ -149,21 +151,23 @@ class Gem::Package::TarHeader
       raise ArgumentError, ":name, :size, :prefix and :mode required"
     end
 
-    vals[:uid] ||= 0
-    vals[:gid] ||= 0
-    vals[:mtime] ||= 0
-    vals[:checksum] ||= ""
-    vals[:typeflag] = "0" if vals[:typeflag].nil? || vals[:typeflag].empty?
-    vals[:magic] ||= "ustar"
-    vals[:version] ||= "00"
-    vals[:uname] ||= "wheel"
-    vals[:gname] ||= "wheel"
-    vals[:devmajor] ||= 0
-    vals[:devminor] ||= 0
-
-    FIELDS.each do |name|
-      instance_variable_set "@#{name}", vals[name]
-    end
+    @checksum = vals[:checksum] || ""
+    @devmajor = vals[:devmajor] || 0
+    @devminor = vals[:devminor] || 0
+    @gid = vals[:gid] || 0
+    @gname = vals[:gname] || "wheel"
+    @linkname = vals[:linkname]
+    @magic = vals[:magic] || "ustar"
+    @mode = vals[:mode]
+    @mtime = vals[:mtime] || 0
+    @name = vals[:name]
+    @prefix = vals[:prefix]
+    @size = vals[:size]
+    @typeflag = vals[:typeflag]
+    @typeflag = "0" if @typeflag.nil? || @typeflag.empty?
+    @uid = vals[:uid] || 0
+    @uname = vals[:uname] || "wheel"
+    @version = vals[:version] || "00"
 
     @empty = vals[:empty]
   end