Ruby » Ruby master

merge revision(s) 66242: [Backport #15387]

    io.c (io_write_nonblock): add RB_GC_GUARD, io_fflush may switch threads

    Since io_fflush may block on mutex or rb_io_wait_readable and
    switch threads, we need to ensure the `str' VALUE returned by
    `rb_obj_as_string` is visible to GC.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_5@66876 b2dd03c8-39d4-4d8f-98ff-823fe69b080e