optimizing-io-operations

.NET High-Performance I/O

A guide for APIs optimizing large-scale data input/output.

Quick Reference: See QUICKREF.md for essential patterns at a glance.

1. Core APIs

2. High-Speed Standard I/O

2.1 Basic Pattern

// Use buffer stream directly for large I/O
using var inputStream = Console.OpenStandardInput();
using var outputStream = Console.OpenStandardOutput();
using var reader = new StreamReader(inputStream, bufferSize: 65536);
using var writer = new StreamWriter(outputStream, bufferSize: 65536);

// Disable buffer flush for performance improvement
writer.AutoFlush = false;

string? line;
while ((line = reader.ReadLine()) is not null)
{
    writer.WriteLine(ProcessLine(line));
}

// Manual flush at the end
writer.Flush();

2.2 For Algorithm Problem Solving

using System.Text;

// High-speed input
using var reader = new StreamReader(
    Console.OpenStandardInput(),
    Encoding.ASCII,
    bufferSize: 65536);

// High-speed output
using var writer = new StreamWriter(
    Console.OpenStandardOutput(),
    Encoding.ASCII,
    bufferSize: 65536);

var sb = new StringBuilder();

// Collect large output in StringBuilder and write at once
for (int i = 0; i < 100000; i++)
{
    sb.AppendLine(i.ToString());
}

writer.Write(sb);
writer.Flush();

3. File I/O Optimization

3.1 Buffer Size Optimization

// Use larger buffer than default (4KB)
const int bufferSize = 64 * 1024; // 64KB

using var fileStream = new FileStream(
    path,
    FileMode.Open,
    FileAccess.Read,
    FileShare.Read,
    bufferSize: bufferSize);

3.2 Async File I/O

// Open file with async option
using var fileStream = new FileStream(
    path,
    FileMode.Open,
    FileAccess.Read,
    FileShare.Read,
    bufferSize: 4096,
    options: FileOptions.Asynchronous);

var buffer = new byte[4096];
int bytesRead = await fileStream.ReadAsync(buffer);