Bug #13085
Updated by nobu (Nobuyoshi Nakada) over 7 years ago
Relying on rb_str_new_frozen for unconverted strings does not save memory because copy-on-write is always triggered in read-write I/O loops were subsequent IO#read calls will clobber the given write buffer. ```ruby buf = ''.b while input.read(16384, buf) output.write(buf) end ``` This generates a lot of garbage starting with Ruby 2.2 (r44471). For my use case, even `IO.copy_stream` IO.copy_stream generates garbage, since I wrap "write" to do Digest calculation in a single pass. I tried using rb_str_replace and reusing the string as a hidden `(klass (klass == 0)` 0) thread-local, but `rb_str_replace` rb_str_replace attempts CoW optimization by creating new frozen objects, too: https://80x24.org/spew/20161229004417.12304-1-e@80x24.org/raw So, I'm not sure what to do, temporal locking seems wrong for writing strings (I guess it's for reading?). I get `test_threaded_flush` test_threaded_flush failures with the following: https://80x24.org/spew/20161229005701.9712-1-e@80x24.org/raw `IO#syswrite` IO#syswrite has the same problem with garbage. I can use `IO#write_nonblock` IO#write_nonblock on fast filesystems while holding GVL, I guess...