lib/lock_and_cache.rb
require 'logger'
require 'timeout'
require 'digest/sha1'
require 'base64'
require 'redis'
require 'active_support'
require 'active_support/core_ext'
require_relative 'lock_and_cache/version'
require_relative 'lock_and_cache/action'
require_relative 'lock_and_cache/key'
# Lock and cache using redis!
#
# Most caching libraries don't do locking, meaning that >1 process can be calculating a cached value at the same time. Since you presumably cache things because they cost CPU, database reads, or money, doesn't it make sense to lock while caching?
module LockAndCache
DEFAULT_MAX_LOCK_WAIT = 60 * 60 * 24 # 1 day in seconds
DEFAULT_HEARTBEAT_EXPIRES = 32 # 32 seconds
class TimeoutWaitingForLock < StandardError; end
# @param redis_connection [Redis] A redis connection to be used for lock storage
def LockAndCache.lock_storage=(redis_connection)
raise "only redis for now" unless redis_connection.class.to_s == 'Redis'
@lock_storage = redis_connection
end
# @return [Redis] The redis connection used for lock and cached value storage
def LockAndCache.lock_storage
@lock_storage
end
# @param redis_connection [Redis] A redis connection to be used for cached value storage
def LockAndCache.cache_storage=(redis_connection)
raise "only redis for now" unless redis_connection.class.to_s == 'Redis'
@cache_storage = redis_connection
end
# @return [Redis] The redis connection used for cached value storage
def LockAndCache.cache_storage
@cache_storage
end
# @param logger [Logger] A logger.
def LockAndCache.logger=(logger)
@logger = logger
end
# @return [Logger] The logger.
def LockAndCache.logger
@logger
end
# Flush LockAndCache's cached value storage.
#
# @note If you are sharing a redis database, it will clear it...
#
# @note If you want to clear a single key, try `LockAndCache.clear(key)` (standalone mode) or `#lock_and_cache_clear(method_id, *key_parts)` in context mode.
def LockAndCache.flush_cache
cache_storage.flushdb
end
# Flush LockAndCache's lock storage.
#
# @note If you are sharing a redis database, it will clear it...
#
# @note If you want to clear a single key, try `LockAndCache.clear(key)` (standalone mode) or `#lock_and_cache_clear(method_id, *key_parts)` in context mode.
def LockAndCache.flush_locks
lock_storage.flushdb
end
# Lock and cache based on a key.
#
# @param key_parts [*] Parts that should be used to construct a key.
#
# @note Standalone mode. See also "context mode," where you mix LockAndCache into a class and call it from within its methods.
#
# @note A single hash arg is treated as a cache key, e.g. `LockAndCache.lock_and_cache(foo: :bar, expires: 100)` will be treated as a cache key of `foo: :bar, expires: 100` (which is probably wrong!!!). Try `LockAndCache.lock_and_cache({ foo: :bar }, expires: 100)` instead. This is the opposite of context mode.
def LockAndCache.lock_and_cache(*key_parts_and_options, &blk)
options = (key_parts_and_options.last.is_a?(Hash) && key_parts_and_options.length > 1) ? key_parts_and_options.pop : {}
raise "need a cache key" unless key_parts_and_options.length > 0
key = LockAndCache::Key.new key_parts_and_options
action = LockAndCache::Action.new key, options, blk
action.perform
end
# Clear a single key
#
# @note Standalone mode. See also "context mode," where you mix LockAndCache into a class and call it from within its methods.
def LockAndCache.clear(*key_parts)
key = LockAndCache::Key.new key_parts
key.clear
end
# Check if a key is locked
#
# @note Standalone mode. See also "context mode," where you mix LockAndCache into a class and call it from within its methods.
def LockAndCache.locked?(*key_parts)
key = LockAndCache::Key.new key_parts
key.locked?
end
# Check if a key is cached already
#
# @note Standalone mode. See also "context mode," where you mix LockAndCache into a class and call it from within its methods.
def LockAndCache.cached?(*key_parts)
key = LockAndCache::Key.new key_parts
key.cached?
end
# @param seconds [Numeric] Maximum wait time to get a lock
#
# @note Can be overridden by putting `max_lock_wait:` in your call to `#lock_and_cache`
def LockAndCache.max_lock_wait=(seconds)
@max_lock_wait = seconds.to_f
end
# @private
def LockAndCache.max_lock_wait
@max_lock_wait || DEFAULT_MAX_LOCK_WAIT
end
# @param seconds [Numeric] How often a process has to heartbeat in order to keep a lock
#
# @note Can be overridden by putting `heartbeat_expires:` in your call to `#lock_and_cache`
def LockAndCache.heartbeat_expires=(seconds)
memo = seconds.to_f
raise "heartbeat_expires must be greater than 2 seconds" unless memo >= 2
@heartbeat_expires = memo
end
# @private
def LockAndCache.heartbeat_expires
@heartbeat_expires || DEFAULT_HEARTBEAT_EXPIRES
end
# Check if a method is locked on an object.
#
# @note Subject mode - this is expected to be called on an object whose class has LockAndCache mixed in. See also standalone mode.
def lock_and_cache_locked?(method_id, *key_parts)
key = LockAndCache::Key.new key_parts, context: self, method_id: method_id
key.locked?
end
# Clear a lock and cache given exactly the method and exactly the same arguments
#
# @note Subject mode - this is expected to be called on an object whose class has LockAndCache mixed in. See also standalone mode.
def lock_and_cache_clear(method_id, *key_parts)
key = LockAndCache::Key.new key_parts, context: self, method_id: method_id
key.clear
end
# Lock and cache a method given key parts.
#
# The cache key will automatically include the class name of the object calling it (the context!) and the name of the method it is called from.
#
# @param key_parts_and_options [*] Parts that you want to include in the lock and cache key. If the last element is a Hash, it will be treated as options.
#
# @return The cached value (possibly newly calculated).
#
# @note Subject mode - this is expected to be called on an object whose class has LockAndCache mixed in. See also standalone mode.
#
# @note A single hash arg is treated as an options hash, e.g. `lock_and_cache(expires: 100)` will be treated as options `expires: 100`. This is the opposite of standalone mode.
def lock_and_cache(*key_parts_and_options, &blk)
options = key_parts_and_options.last.is_a?(Hash) ? key_parts_and_options.pop : {}
key = LockAndCache::Key.new key_parts_and_options, context: self, caller: caller
action = LockAndCache::Action.new key, options, blk
action.perform
end
end
logger = Logger.new $stderr
logger.level = (ENV['LOCK_AND_CACHE_DEBUG'] == 'true') ? Logger::DEBUG : Logger::INFO
LockAndCache.logger = logger