From: "ioquatix (Samuel Williams)" <noreply@...>
Date: 2022-09-26T12:50:24+00:00
Subject: [ruby-core:110088] [Ruby master Feature#14900] Extra allocation in String#byteslice

Issue #14900 has been updated by ioquatix (Samuel Williams).


By the way, ideally, I think you can implement this:

```ruby
buffer = String.new # allocation
while true
	# Efficiently read into the buffer:
	if buffer.empty?
		io.read(1024, buffer)
	else
		buffer << io.read(1024)
	end

	# Consume the buffer in chunks:
	while size = consume(buffer)
		buffer.byteslice!(size..-1) # shared root string - no memcpy or allocation
	end
end
```

----------------------------------------
Feature #14900: Extra allocation in String#byteslice
https://bugs.ruby-lang.org/issues/14900#change-99343

* Author: janko (Janko Marohni��)
* Status: Open
* Priority: Normal
----------------------------------------
When executing `String#byteslice` with a range, I noticed that sometimes the original string is allocated again. When I run the following script:

~~~ ruby
require "objspace"

string = "a" * 100_000

GC.start
GC.disable
generation = GC.count

ObjectSpace.trace_object_allocations do
  string.byteslice(50_000..-1)

  ObjectSpace.each_object(String) do |string|
    p string.bytesize if ObjectSpace.allocation_generation(string) == generation
  end
end
~~~

it outputs

~~~
50000
100000
6
5
~~~

The one with 50000 bytes is the result of `String#byteslice`, but the one with 100000 bytes is the duplicated original string. I expected only the result of `String#byteslice` to be amongst new allocations.

If instead of the last 50000 bytes I slice the *first* 50000 bytes, the extra duplication doesn't occur.

~~~ ruby
# ...
  string.byteslice(0, 50_000)
# ...
~~~

~~~
50000
5
~~~

It's definitely ok if the implementation of `String#bytesize` allocates extra strings as part of the implementation, but it would be nice if they were deallocated before returning the result.

EDIT: It seems that `String#slice` has the same issue.



-- 
https://bugs.ruby-lang.org/

Unsubscribe: <mailto:ruby-core-request@ruby-lang.org?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>