Freeze absolute paths for reduce allocations on file operations

[casperisfine]

Most of the File methods cast the paths it receives with FilePathValue / rb_get_path which ultimately delegate to rb_new_str_frozen (aliased as rb_str_new4).

rb_new_str_frozen could be experessed as str.frozen? ? str : str.dup.

So by freezing the paths passed to the various File. methods, we
save at least one useless allocation each time, unless the string encoding
is incompatible with the file system.

s = __FILE__
alloc = GC.stat[:total_allocated_objects]
File.realpath(s)
p GC.stat[:total_allocated_objects] - alloc # => 3

s = __FILE__.freeze
alloc = GC.stat[:total_allocated_objects]
File.realpath(s)
p GC.stat[:total_allocated_objects] - alloc # => 2

[fxn]

I've checked with Module#autoload too. It saves three allocations!

s = __FILE__
alloc = GC.stat[:total_allocated_objects]
Object.autoload(:A, s)
p GC.stat[:total_allocated_objects] - alloc # => 5

s = __FILE__.freeze
alloc = GC.stat[:total_allocated_objects]
Object.autoload(:B, s)
p GC.stat[:total_allocated_objects] - alloc # => 2

[casperisfine]

I've checked with Module#autoload too. It saves three allocations!

Yeah, autoload calls realpath, which itself allocates a bit too much. I'm currently working on upstream PRs to improve that (ruby/ruby#3267).

But it seems like all File operation always allocate at least one object:

s = __FILE__.freeze
alloc = GC.stat[:total_allocated_objects]
File.exist?(s)
p GC.stat[:total_allocated_objects] - alloc # => 1

It's not allocating a String though, I'm trying to pinpoint that alloc. Anyway it's a bit unrelated.

[fxn]

Perfect!

[casperisfine]

But it seems like all File operation always allocate at least one object:

Ok so self answer, even calling an empty method cause 1 alloc, so 1 is the minimum.