Class: Zache

Inherits:
Object
  • Object
show all
Defined in:
lib/zache.rb

Overview

It is a very simple thread-safe in-memory cache with an ability to expire keys automatically, when their lifetime is over. Use it like this:

require 'zache'
zache = Zache.new
# Expires in 5 minutes
v = zache.get(:count, lifetime: 5 * 60) { expensive() }

For more information read README file.

Author

Yegor Bugayenko ([email protected])

Copyright

Copyright © 2018-2025 Yegor Bugayenko

License

MIT

Defined Under Namespace

Classes: Fake

Instance Method Summary collapse

Constructor Details

#initialize(sync: true, dirty: false) ⇒ Zache

Makes a new object of the cache.

“sync” is whether the hash is thread-safe (‘true`) or not (`false`); it is recommended to leave this parameter untouched, unless you really know what you are doing.

If the dirty argument is set to true, a previously calculated result will be returned if it exists, even if it is already expired.

Parameters:

  • sync (Boolean) (defaults to: true) —

    Whether the hash is thread-safe

  • dirty (Boolean) (defaults to: false) —

    Whether to return expired values



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# File 'lib/zache.rb', line 88

def initialize(sync: true, dirty: false)
  @hash = {}
  @sync = sync
  @dirty = dirty
  @mutex = Mutex.new
  @locks = {}
end

Instance Method Details

#clean ⇒ Integer

Remove keys that are expired. This cleans up the cache by removing all keys where the lifetime has been exceeded.

Returns:

  • (Integer) —

    Number of keys removed



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# File 'lib/zache.rb', line 251

def clean
  synchronize_all do
    size_before = @hash.size
    @hash.delete_if { |key, _value| expired?(key) }
    size_before - @hash.size
  end
end

#empty? ⇒ Boolean

Returns TRUE if the cache is empty, FALSE otherwise.

Returns:

  • (Boolean) —

    True if the cache is empty



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# File 'lib/zache.rb', line 262

def empty?
  @hash.empty?
end

#exists?(key, dirty: false) ⇒ Boolean

Checks whether the value exists in the cache by the provided key. Returns TRUE if the value is here. If the key is already expired in the cache, it will be removed by this method and the result will be FALSE.

Parameters:

  • key (Object) —

    The key to check in the cache

  • dirty (Boolean) (defaults to: false) —

    Whether to consider expired values as existing

Returns:

  • (Boolean) —

    True if the key exists and is not expired (unless dirty is true)



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# File 'lib/zache.rb', line 159

def exists?(key, dirty: false)
  rec = @hash[key]
  if expired?(key) && !dirty && !@dirty
    @hash.delete(key)
    rec = nil
  end
  !rec.nil?
end

#expired?(key) ⇒ Boolean

Checks whether the key exists in the cache and is expired. If the key is absent FALSE is returned.

Parameters:

  • key (Object) —

    The key to check in the cache

Returns:

  • (Boolean) —

    True if the key exists and is expired



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# File 'lib/zache.rb', line 173

def expired?(key)
  rec = @hash[key]
  !rec.nil? && rec[:start] < Time.now - rec[:lifetime]
end

#get(key, lifetime: 2**32, dirty: false, placeholder: nil, eager: false) { ... } ⇒ Object

Gets the value from the cache by the provided key.

If the value is not found in the cache, it will be calculated via the provided block. If the block is not given and the key doesn’t exist or is expired, an exception will be raised (unless dirty is set to true). The lifetime must be in seconds. The default lifetime is huge, which means that the key will never be expired.

If the dirty argument is set to true, a previously calculated result will be returned if it exists, even if it is already expired.

Parameters:

  • key (Object) —

    The key to retrieve from the cache

  • lifetime (Integer) (defaults to: 2**32) —

    Time in seconds until the key expires

  • dirty (Boolean) (defaults to: false) —

    Whether to return expired values

  • eager (Boolean) (defaults to: false) —

    Whether to return placeholder while working?

  • placeholder (Object) (defaults to: nil) —

    The placeholder to return in eager mode

Yields:

  • Block to calculate the value if not in cache

Yield Returns:

  • (Object) —

    The value to cache

Returns:

  • (Object) —

    The cached value



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# File 'lib/zache.rb', line 123

def get(key, lifetime: 2**32, dirty: false, placeholder: nil, eager: false, &block)
  if block_given?
    return @hash[key][:value] if (dirty || @dirty) && locked?(key) && expired?(key) && @hash.key?(key)
    if eager
      return @hash[key][:value] if @hash.key?(key)
      put(key, placeholder, lifetime: 0)
      Thread.new do
        synchronize_one(key) do
          calc(key, lifetime, &block)
        end
      end
      placeholder
    else
      synchronize_one(key) do
        calc(key, lifetime, &block)
      end
    end
  else
    rec = @hash[key]
    if expired?(key)
      return rec[:value] if dirty || @dirty
      @hash.delete(key)
      rec = nil
    end
    raise 'The key is absent in the cache' if rec.nil?
    rec[:value]
  end
end

#locked?(key) ⇒ Boolean

Is key currently locked doing something?

Parameters:

  • key (Object) —

    The key to check

Returns:

  • (Boolean) —

    True if the cache is locked



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# File 'lib/zache.rb', line 192

def locked?(key)
  @locks[key]&.locked?
end

#mtime(key) ⇒ Time

Returns the modification time of the key, if it exists. If not, current time is returned.

Parameters:

  • key (Object) —

    The key to get the modification time for

Returns:

  • (Time) —

    The modification time of the key or current time if key doesn’t exist



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# File 'lib/zache.rb', line 183

def mtime(key)
  rec = @hash[key]
  rec.nil? ? Time.now : rec[:start]
end

#put(key, value, lifetime: 2**32) ⇒ Object

Put a value into the cache.

Parameters:

  • key (Object) —

    The key to store the value under

  • value (Object) —

    The value to store in the cache

  • lifetime (Integer) (defaults to: 2**32) —

    Time in seconds until the key expires (default: never expires)

Returns:

  • (Object) —

    The value stored



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# File 'lib/zache.rb', line 202

def put(key, value, lifetime: 2**32)
  synchronize_one(key) do
    @hash[key] = {
      value: value,
      start: Time.now,
      lifetime: lifetime
    }
  end
end

#remove(key) { ... } ⇒ Object

Removes the value from the cache, by the provided key. If the key is absent and the block is provided, the block will be called.

Parameters:

  • key (Object) —

    The key to remove from the cache

Yields:

  • Block to call if the key is not found

Returns:

  • (Object) —

    The removed value or the result of the block



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# File 'lib/zache.rb', line 218

def remove(key)
  synchronize_one(key) { @hash.delete(key) { yield if block_given? } }
end

#remove_all ⇒ Hash

Remove all keys from the cache.

Returns:

  • (Hash) —

    Empty hash



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# File 'lib/zache.rb', line 225

def remove_all
  synchronize_all { @hash = {} }
end

#remove_by {|key| ... } ⇒ Integer

Remove all keys that match the block.

Yields:

  • (key) —

    Block that should return true for keys to be removed

Yield Parameters:

  • key (Object) —

    The cache key to evaluate

Returns:

  • (Integer) —

    Number of keys removed



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# File 'lib/zache.rb', line 234

def remove_by
  synchronize_all do
    count = 0
    @hash.each_key do |k|
      if yield(k)
        @hash.delete(k)
        count += 1
      end
    end
    count
  end
end

#size ⇒ Integer

Total number of keys currently in cache.

Returns:

  • (Integer) —

    Number of keys in the cache



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# File 'lib/zache.rb', line 99

def size
  @hash.size
end