Class: SupportTableCache::MemoryCache

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

Overview

An optimized cache implementation that can be used when all records can easily fit in memory and are never changed. It is intended for use with small, static support tables only.

This cache will not store nil values. This is to prevent the cache from filling up with cache misses because there is no purging mechanism.

Instance Method Summary collapse

Constructor Details

#initialize ⇒ SupportTableCache::MemoryCache

Create a new memory cache.



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# File 'lib/support_table_cache/memory_cache.rb', line 14

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

Instance Method Details

#clear ⇒ void

This method returns an undefined value.

Clear all values from the cache.



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# File 'lib/support_table_cache/memory_cache.rb', line 75

def clear
  @cache.clear
end

#delete(key) ⇒ void

This method returns an undefined value.

Delete a value from the cache.

Parameters:

  • key (Object) —

    The cache key.



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# File 'lib/support_table_cache/memory_cache.rb', line 68

def delete(key)
  @cache.delete(key)
end

#fetch(key, expires_in: nil) { ... } ⇒ Object?

Fetch a value from the cache. If the key is not found or has expired, yields to get a new value.

Parameters:

  • key (Object) —

    The cache key.

  • expires_in (Integer, nil) (defaults to: nil) —

    Time in seconds until the cached value expires.

Yields:

  • Block to execute to get a new value if the key is not cached.

Returns:

  • (Object, nil) —

    The cached value or the result of the block, or nil if no value is found.



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# File 'lib/support_table_cache/memory_cache.rb', line 25

def fetch(key, expires_in: nil)
  serialized_value, expire_at = @cache[key]
  if serialized_value.nil? || (expire_at && expire_at < Process.clock_gettime(Process::CLOCK_MONOTONIC))
    value = yield if block_given?
    return nil if value.nil?
    write(key, value, expires_in: expires_in)
    serialized_value = Marshal.dump(value)
  end
  Marshal.load(serialized_value)
end

#read(key) ⇒ Object?

Read a value from the cache.

Parameters:

  • key (Object) —

    The cache key.

Returns:

  • (Object, nil) —

    The cached value or nil if not found.



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# File 'lib/support_table_cache/memory_cache.rb', line 40

def read(key)
  fetch(key)
end

#write(key, value, expires_in: nil) ⇒ void

This method returns an undefined value.

Write a value to the cache.

Parameters:

  • key (Object) —

    The cache key.

  • value (Object) —

    The value to cache. Nil values are not cached.

  • expires_in (Integer, nil) (defaults to: nil) —

    Time in seconds until the cached value expires.



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# File 'lib/support_table_cache/memory_cache.rb', line 50

def write(key, value, expires_in: nil)
  return if value.nil?

  if expires_in
    expire_at = Process.clock_gettime(Process::CLOCK_MONOTONIC) + expires_in
  end

  serialized_value = Marshal.dump(value)

  @mutex.synchronize do
    @cache[key] = [serialized_value, expire_at]
  end
end