Rubyスクリプトの外部コマンド呼び出しが本番で予期しない遅延を起こす理由──プロセス管理とタイムアウト設計

# よく見かける書き方
result = `convert input.jpg -resize 100x100 output.jpg`

require 'open3'
require 'timeout'

def run_command_with_timeout(command, timeout_sec = 30)
  begin
    Timeout.timeout(timeout_sec) do
      stdout, stderr, status = Open3.capture3(command)
      
      if status.success?
        { success: true, output: stdout }
      else
        { success: false, error: stderr, exit_code: status.exitstatus }
      end
    end
  rescue Timeout::Error
    { success: false, error: "Command timed out after #{timeout_sec}s" }
  rescue => e
    { success: false, error: e.message }
  end
end

# 使用例
result = run_command_with_timeout("convert input.jpg -resize 100x100 output.jpg", 60)
unless result[:success]
  Rails.logger.warn("Command failed: #{result[:error]}")
  # エラーハンドリング
end

require 'thread'

class CommandQueue
  def initialize(max_workers = 3)
    @queue = Queue.new
    @max_workers = max_workers
    @workers = []
  end

  def start
    @max_workers.times do
      @workers << Thread.new do
        while job = @queue.pop
          break if job == :stop
          execute_job(job)
        end
      end
    end
  end

  def add_job(command, timeout = 30)
    @queue.push({ command: command, timeout: timeout })
  end

  def shutdown
    @max_workers.times { @queue.push(:stop) }
    @workers.each(&:join)
  end

  private

  def execute_job(job)
    result = run_command_with_timeout(job[:command], job[:timeout])
    # ログ出力やエラーハンドリング
  end
end

# 使用例
queue = CommandQueue.new(3)  # 同時実行数を3に制限
queue.start

1000.times do |i|
  queue.add_job("process_file_#{i}.jpg")
end

queue.shutdown

def run_command_with_logging(command, timeout_sec = 30)
  start_time = Time.now
  
  result = run_command_with_timeout(command, timeout_sec)
  elapsed = Time.now - start_time
  
  log_entry = {
    command: command,
    success: result[:success],
    elapsed_ms: (elapsed * 1000).round,
    timeout_sec: timeout_sec,
    error: result[:error]
  }
  
  Rails.logger.info("External command executed: #{log_entry.to_json}")
  
  result
end

# 危険：ファイル名にスペースがあると失敗する可能性
`convert "my file.jpg" output.jpg`

# 安全：配列で渡すとシェルを経由しない
Open3.capture3("convert", "my file.jpg", "output.jpg")