From 6b39c6b1bf62218edf6478c8f55a543e069ea51a Mon Sep 17 00:00:00 2001 From: Daniel Bertalan Date: Wed, 29 Dec 2021 18:37:31 +0100 Subject: Shell: Avoid many single byte write() syscalls when printing the prompt Whenever the prompt is printed, we write a line's worth of space characters to the terminal to ensure that the prompt ends up on a new line even if there is dangling output on the current line. We write these to the stderr, which is unbuffered, so each putc() call would come with the overhead of a system call. Let's use a buffer + fwrite() instead, since heap allocation is much faster. --- Userland/Shell/Shell.cpp | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'Userland/Shell') diff --git a/Userland/Shell/Shell.cpp b/Userland/Shell/Shell.cpp index 0b31ed99f6..d0630ffe7d 100644 --- a/Userland/Shell/Shell.cpp +++ b/Userland/Shell/Shell.cpp @@ -1660,8 +1660,11 @@ void Shell::bring_cursor_to_beginning_of_a_line() const fputs(eol_mark.characters(), stderr); - for (auto i = eol_mark_length; i < ws.ws_col; ++i) - putc(' ', stderr); + // We write a line's worth of whitespace to the terminal. This way, we ensure that + // the prompt ends up on a new line even if there is dangling output on the current line. + size_t fill_count = ws.ws_col - eol_mark_length; + auto fill_buffer = String::repeated(' ', fill_count); + fwrite(fill_buffer.characters(), 1, fill_count, stderr); putc('\r', stderr); } -- cgit v1.2.3