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LibLine: Avoid excessive write() syscalls when refreshing the display

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Previously, we were generating the display update one character at a
time, and writing them one at a time to stderr, which is not buffered,
doing so caused one syscall per character printed which is s l o w (TM)
This commit makes LibLine write the update contents into a buffer, and
flush it after all the update is generated :^)
This commit is contained in:
Ali Mohammad Pur 2021-07-19 23:12:28 +04:30 • committed by Ali Mohammad Pur
parent 0f6654fef2
commit 3184086679
5 changed files with 126 additions and 110 deletions
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46
Userland/Libraries/LibLine/XtermSuggestionDisplay.cpp
View file

@ -5,6 +5,7 @@
*/
#include <AK/BinarySearch.h>
#include <AK/FileStream.h>
#include <AK/Function.h>
#include <AK/StringBuilder.h>
#include <LibLine/SuggestionDisplay.h>
@ -17,6 +18,8 @@ void XtermSuggestionDisplay::display(const SuggestionManager& manager)
{
did_display();
OutputFileStream stderr_stream { stderr };
size_t longest_suggestion_length = 0;
size_t longest_suggestion_byte_length = 0;
@ -30,9 +33,9 @@ void XtermSuggestionDisplay::display(const SuggestionManager& manager)
size_t num_printed = 0;
size_t lines_used = 1;
VT::save_cursor();
VT::clear_lines(0, m_lines_used_for_last_suggestions);
VT::restore_cursor();
VT::save_cursor(stderr_stream);
VT::clear_lines(0, m_lines_used_for_last_suggestions, stderr_stream);
VT::restore_cursor(stderr_stream);
auto spans_entire_line { false };
Vector<StringMetrics::LineMetrics> lines;
@ -45,14 +48,13 @@ void XtermSuggestionDisplay::display(const SuggestionManager& manager)
// We should make enough space for the biggest entry in
// the suggestion list to fit in the prompt line.
auto start = max_line_count - m_prompt_lines_at_suggestion_initiation;
for (size_t i = start; i < max_line_count; ++i) {
fputc('\n', stderr);
}
for (size_t i = start; i < max_line_count; ++i)
stderr_stream.write("\n"sv.bytes());
lines_used += max_line_count;
longest_suggestion_length = 0;
}
VT::move_absolute(max_line_count + m_origin_row, 1);
VT::move_absolute(max_line_count + m_origin_row, 1, stderr_stream);
if (m_pages.is_empty()) {
size_t num_printed = 0;
@ -89,14 +91,13 @@ void XtermSuggestionDisplay::display(const SuggestionManager& manager)
auto page_index = fit_to_page_boundary(manager.next_index());
manager.set_start_index(m_pages[page_index].start);
manager.for_each_suggestion([&](auto& suggestion, auto index) {
size_t next_column = num_printed + suggestion.text_view.length() + longest_suggestion_length + 2;
if (next_column > m_num_columns) {
auto lines = (suggestion.text_view.length() + m_num_columns - 1) / m_num_columns;
lines_used += lines;
fputc('\n', stderr);
stderr_stream.write("\n"sv.bytes());
num_printed = 0;
}
@ -107,22 +108,19 @@ void XtermSuggestionDisplay::display(const SuggestionManager& manager)
// Only apply color to the selection if something is *actually* added to the buffer.
if (manager.is_current_suggestion_complete() && index == manager.next_index()) {
VT::apply_style({ Style::Foreground(Style::XtermColor::Blue) });
fflush(stderr);
VT::apply_style({ Style::Foreground(Style::XtermColor::Blue) }, stderr_stream);
}
if (spans_entire_line) {
num_printed += m_num_columns;
fprintf(stderr, "%s", suggestion.text_string.characters());
stderr_stream.write(suggestion.text_string.bytes());
} else {
fprintf(stderr, "%-*s", static_cast<int>(longest_suggestion_byte_length) + 2, suggestion.text_string.characters());
stderr_stream.write(String::formatted("{: <{}}", suggestion.text_string, longest_suggestion_byte_length + 2).bytes());
num_printed += longest_suggestion_length + 2;
}
if (manager.is_current_suggestion_complete() && index == manager.next_index()) {
VT::apply_style(Style::reset_style());
fflush(stderr);
}
if (manager.is_current_suggestion_complete() && index == manager.next_index())
VT::apply_style(Style::reset_style(), stderr_stream);
return IterationDecision::Continue;
});
@ -140,17 +138,14 @@ void XtermSuggestionDisplay::display(const SuggestionManager& manager)
if (string.length() > m_num_columns - 1) {
// This would overflow into the next line, so just don't print an indicator.
fflush(stderr);
return;
}
VT::move_absolute(m_origin_row + lines_used, m_num_columns - string.length() - 1);
VT::apply_style({ Style::Background(Style::XtermColor::Green) });
fputs(string.characters(), stderr);
VT::apply_style(Style::reset_style());
VT::move_absolute(m_origin_row + lines_used, m_num_columns - string.length() - 1, stderr_stream);
VT::apply_style({ Style::Background(Style::XtermColor::Green) }, stderr_stream);
stderr_stream.write(string.bytes());
VT::apply_style(Style::reset_style(), stderr_stream);
}
fflush(stderr);
}
bool XtermSuggestionDisplay::cleanup()
@ -158,7 +153,8 @@ bool XtermSuggestionDisplay::cleanup()
did_cleanup();
if (m_lines_used_for_last_suggestions) {
VT::clear_lines(0, m_lines_used_for_last_suggestions);
OutputFileStream stderr_stream { stderr };
VT::clear_lines(0, m_lines_used_for_last_suggestions, stderr_stream);
m_lines_used_for_last_suggestions = 0;
return true;
}