3b73576ab9
* Instead of reading the output line-by-line, figure out what lines we need ahead-of-time and issue as few read calls as possible. On Windows 8 and up, we issue just one read call. On earlier versions, we avoid reading more than a certain amount. * This change reduces the CPU usage. e.g. In my Windows 10 VM, the idle CPU usage of winpty-agent.exe+conhost.exe combined, with an empty console, dropped from ~3.6% to ~1.4%. In a Windows 7 VM, I measured a reduction of CPU from ~1.6% to 0.6%. * Increase the MAX_CONSOLE_WIDTH from 500 to 2500. The limiting factor now is that LargeConsoleRead reads at least one line at a line, but we don't want to read more than 2500 characters in one call on old operating systems. * Fix the attribute handling in scanForDirtyLines. (The assignment to newAttr was dead.) The 2500 limit is arbitrary and could probably be increased. The actual hard limit depends on the OS and is around 17000. My understanding is that the limit is based upon the need to allocate I/O buffers within a shared 64KiB heap, and I'm worried about heap fragmentation. I know that 2500 is safe, because winpty has been issuing reads of almost 3000 characters already to find the sync marker. Fixes https://github.com/rprichard/winpty/issues/44
66 lines
1.9 KiB
C++
Executable File
66 lines
1.9 KiB
C++
Executable File
#include "LargeConsoleRead.h"
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#include <stdlib.h>
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#include "Agent.h"
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#include "Win32Console.h"
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namespace {
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// Returns true if the OS version is at least Windows 8 (6.2). This function
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// should work correctly regardless of how the executable is manifested.
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static bool isWindows8OrGreater() {
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OSVERSIONINFO info = {0};
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info.dwOSVersionInfoSize = sizeof(info);
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if (!GetVersionEx(&info)) {
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return false;
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}
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if (info.dwMajorVersion > 6) {
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return true;
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}
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if (info.dwMajorVersion < 6) {
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return false;
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}
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return info.dwMinorVersion >= 2;
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}
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} // anonymous namespace
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LargeConsoleReadBuffer::LargeConsoleReadBuffer() :
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m_rect(0, 0, 0, 0), m_rectWidth(0)
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{
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}
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void largeConsoleRead(LargeConsoleReadBuffer &out,
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Win32Console &console,
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const SmallRect &readArea) {
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ASSERT(readArea.Left >= 0 &&
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readArea.Top >= 0 &&
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readArea.Right >= readArea.Left &&
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readArea.Bottom >= readArea.Top &&
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readArea.width() <= MAX_CONSOLE_WIDTH);
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const size_t count = readArea.width() * readArea.height();
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if (out.m_data.size() < count) {
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out.m_data.resize(count);
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}
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out.m_rect = readArea;
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out.m_rectWidth = readArea.width();
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static const bool useLargeReads = isWindows8OrGreater();
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if (useLargeReads) {
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console.read(readArea, out.m_data.data());
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} else {
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const int maxReadLines = std::max(1, MAX_CONSOLE_WIDTH / readArea.width());
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int curLine = readArea.Top;
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while (curLine <= readArea.Bottom) {
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const SmallRect subReadArea(
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readArea.Left,
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curLine,
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readArea.width(),
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std::min(maxReadLines, readArea.Bottom + 1 - curLine));
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console.read(subReadArea, out.lineDataMut(curLine));
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curLine = subReadArea.Bottom + 1;
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}
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}
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}
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