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 (c) 2018-2026 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



81
82
83
84
85
86
87
 
# File 'lib/zache.rb', line 81

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



228
229
230
231
232
233
234
235
236
237
238
239
240
241
 
# File 'lib/zache.rb', line 228

def clean
  sync do
    count = 0
    @hash.delete_if do |key, _value|
      expired = overdue?(key)
      if expired
        @locks.delete(key)
        count += 1
      end
      expired
    end
    count
  end
end

#empty? ⇒ Boolean

Returns TRUE if the cache is empty, FALSE otherwise.

Returns:

  • (Boolean) —

    True if the cache is empty



246
247
248
 
# File 'lib/zache.rb', line 246

def empty?
  sync { @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)



133
134
135
136
137
138
139
140
141
142
 
# File 'lib/zache.rb', line 133

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



149
150
151
 
# File 'lib/zache.rb', line 149

def expired?(key)
  sync { overdue?(key) }
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



116
117
118
119
120
121
122
123
124
 
# File 'lib/zache.rb', line 116

def get(key, lifetime: 2**32, dirty: false, placeholder: nil, eager: false, &block)
  if block_given?
    return cached(key) if dirt?(key, dirty)
    return eager(key, lifetime, placeholder, &block) if eager
    lock(key) { calc(key, lifetime, &block) }
  else
    fetch(key, dirty)
  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



169
170
171
 
# File 'lib/zache.rb', line 169

def locked?(key)
  sync { @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



158
159
160
161
162
163
 
# File 'lib/zache.rb', line 158

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



179
180
181
182
183
 
# File 'lib/zache.rb', line 179

def put(key, value, lifetime: 2**32)
  lock(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



191
192
193
194
 
# File 'lib/zache.rb', line 191

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

#remove_all ⇒ Hash

Remove all keys from the cache.

Returns:

  • (Hash) —

    Empty hash



199
200
201
202
203
204
 
# File 'lib/zache.rb', line 199

def remove_all
  sync do
    @hash = {}
    @locks = {}
  end
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



211
212
213
214
215
216
217
218
219
220
221
222
 
# File 'lib/zache.rb', line 211

def remove_by
  sync do
    count = 0
    @hash.each_key do |k|
      next unless yield(k)
      @hash.delete(k)
      @locks.delete(k)
      count += 1
    end
    count
  end
end

#size ⇒ Integer

Total number of keys currently in cache.

Returns:

  • (Integer) —

    Number of keys in the cache



92
93
94
 
# File 'lib/zache.rb', line 92

def size
  sync { @hash.size }
end