file_locking.md

🔒 Locking Files with File#flock

Use flock to prevent race conditions when multiple processes access the same file. Shared lock (LOCK_SH) for reading; exclusive lock (LOCK_EX) for writing.

File.open('shared.log', 'a') do |f|
  f.flock(File::LOCK_EX)
  f.puts("#{Time.now}: new entry")
  f.flock(File::LOCK_UN)
end