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Ruby Concurrency for Senior Engineering Interviews

Mutex

Explore how to use mutexes to synchronize threads in Ruby. Understand locking, unlocking, and ownership of mutexes to prevent concurrency issues. Learn to apply mutex for thread-safe operations through practical examples like the ping pong problem.

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Mutex

Mutex is the most basic or primitive synchronization construct available in Ruby. It offers two methods: lock() and unlock(). A Mutex object can only be unlocked by a thread that locked it in the first place. Consider the snippet below, where the child and the main thread alternatively acquire the mutex. The main thread blocks for the period the child holds the mutex.

Ruby
require 'date'
# Create a Mutex object
mutex = Mutex.new
# Spawn a child thread
Thread.new do
  puts("Child thread acquiring mutex")
  mutex.lock()
  sleep(3)
  puts("Child thread releasing mutex")
  mutex.unlock()
end
# Sleep main thread to give child thread a
# chance to acquire the mutex first
sleep(1)
puts("Main thread attempting to acquire mutex")
mutex.lock()
puts("Main thread acquires mutex")
mutex.unlock()

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