Class: MultiJSON::OptionsCache::Store Private

Inherits:
Object
  • Object
show all
Defined in:
lib/multi_json/options_cache/mutex_store.rb

Overview

This class is part of a private API. You should avoid using this class if possible, as it may be removed or be changed in the future.

Thread-safe cache store backed by a Hash guarded by a Mutex

Used on MRI and TruffleRuby, where a runtime dependency on concurrent-ruby would be overkill: the GVL on MRI makes single lookups atomic, and locking on both reads and writes keeps the small perf cost predictable across engines without adding a runtime dependency.

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Store

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Create a new cache store



19
20
21
22
 
# File 'lib/multi_json/options_cache/mutex_store.rb', line 19

def initialize
  @cache = {}
  @mutex = Mutex.new
end

Instance Method Details

#fetch(key, default = nil) { ... } ⇒ Object

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Fetch a value from cache or compute it

When called with a block, returns the cached value or computes a new one. When called without a block, returns the cached value or the supplied default if the key is missing. Nil cached values are preserved because “Hash#fetch“ only falls through to the default block when the key is truly missing. The “block_given?“ check is hoisted out of the mutex so the no-block read path runs the check once per call instead of once inside the critical section.

Parameters:

  • key (Object) —

    cache key

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

    value to return when key is missing and no block is given

Yields:

  • block to compute value if not cached

Returns:

  • (Object) —

    cached, computed, or default value



53
54
55
56
57
58
59
60
61
62
 
# File 'lib/multi_json/options_cache/mutex_store.rb', line 53

def fetch(key, default = nil)
  return @mutex.synchronize { @cache.fetch(key) { default } } unless block_given?

  @mutex.synchronize do
    @cache.fetch(key) do
      @cache.shift if @cache.size >= OptionsCache.max_cache_size
      @cache[key] = yield
    end
  end
end

#reset ⇒ void

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

This method returns an undefined value.

Clear all cached entries

Held under the mutex because TruffleRuby (which also uses this backend via the ruby-platform gem) has true parallelism: a concurrent “fetch“ racing with “Hash#clear“ could corrupt iteration in a way that MRI’s GVL would otherwise prevent.



33
34
35
 
# File 'lib/multi_json/options_cache/mutex_store.rb', line 33

def reset
  @mutex.synchronize { @cache.clear }
end