lib/redis/lock_manager.rb
# Redis::LockManager provides a simple mechanism to handle distributed locks using Redis.
# This class ensures that only one instance of a given operation runs at a given time across all processes/nodes.
# It uses the $alfred Redis namespace for all its operations.
#
# Example Usage:
#
# lock_manager = Redis::LockManager.new
#
# if lock_manager.lock("some_key")
# # Critical code that should not be run concurrently
# lock_manager.unlock("some_key")
# end
#
class Redis::LockManager
# Default lock timeout set to 1 second. This means that if the lock isn't released
# within 1 second, it will automatically expire.
# This helps to avoid deadlocks in case the process holding the lock crashes or fails to release it.
LOCK_TIMEOUT = 1.second
# Attempts to acquire a lock for the given key.
#
# If the lock is successfully acquired, the method returns true. If the key is
# already locked or if any other error occurs, it returns false.
#
# === Parameters
# * +key+ - The key for which the lock is to be acquired.
# * +timeout+ - Duration in seconds for which the lock is valid. Defaults to +LOCK_TIMEOUT+.
#
# === Returns
# * +true+ if the lock was successfully acquired.
# * +false+ if the lock was not acquired.
def lock(key, timeout = LOCK_TIMEOUT)
value = Time.now.to_f.to_s
# nx: true means set the key only if it does not exist
Redis::Alfred.set(key, value, nx: true, ex: timeout) ? true : false
end
# Releases a lock for the given key.
#
# === Parameters
# * +key+ - The key for which the lock is to be released.
#
# === Returns
# * +true+ indicating the lock release operation was initiated.
#
# Note: If the key wasn't locked, this operation will have no effect.
def unlock(key)
Redis::Alfred.delete(key)
true
end
# Checks if the given key is currently locked.
#
# === Parameters
# * +key+ - The key to check.
#
# === Returns
# * +true+ if the key is locked.
# * +false+ otherwise.
def locked?(key)
Redis::Alfred.exists?(key)
end
end