Class: Cymometer::Counter

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

Defined Under Namespace

Classes: LimitExceeded

Constant Summary collapse

DEFAULT_WINDOW =

Default window is 1 hour

3600
INCREMENT_LUA_SCRIPT = 
<<-LUA.freeze
  local key = KEYS[1]
  local current_time = tonumber(ARGV[1])
  local window = tonumber(ARGV[2])
  local limit = tonumber(ARGV[3])

  -- Remove entries older than the window size
  redis.call('ZREMRANGEBYSCORE', key, 0, current_time - window)

  -- Get the current count
  local count = redis.call('ZCOUNT', key, current_time - window, '+inf')

  if count >= limit then
    -- Limit exceeded, do not increment
    return {0, count}
  else
    -- Increment the counter
    redis.call('ZADD', key, current_time, current_time)
    redis.call('EXPIRE', key, math.floor(window / 1000000))
    return {1, count + 1}
  end
LUA
DECREMENT_LUA_SCRIPT = 
<<-LUA.freeze
  local key = KEYS[1]
  local current_time = tonumber(ARGV[1])
  local window = tonumber(ARGV[2])

  -- Remove entries older than the window size
  redis.call('ZREMRANGEBYSCORE', key, 0, current_time - window)

  -- Attempt to remove the entry with the lowest score (oldest entry)
  local entries = redis.call('ZRANGEBYSCORE', key, current_time - window, '+inf', 'LIMIT', 0, 1)

  if next(entries) == nil then
    -- No entries to remove, safe no-op
    local count = 0
    return {1, count}
  else
    local member = entries[1]
    redis.call('ZREM', key, member)
    local count = redis.call('ZCOUNT', key, current_time - window, '+inf')
    return {1, count}
  end
LUA

Class Attribute Summary collapse

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(key_namespace: nil, key: nil, limit: nil, window: nil, redis: nil) ⇒ Counter

Returns a new instance of Counter.



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# File 'lib/cymometer/counter.rb', line 65

def initialize(key_namespace: nil, key: nil, limit: nil, window: nil, redis: nil)
  @redis = redis || Cymometer.redis
  @key = "#{key_namespace || "cymometer"}:#{key || generate_key}"
  @window = window || DEFAULT_WINDOW
  @limit = limit || 1
end

Class Attribute Details

.decrement_sha ⇒ Object (readonly)

Returns the value of attribute decrement_sha.



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# File 'lib/cymometer/counter.rb', line 62

def decrement_sha
  @decrement_sha
end

.increment_sha ⇒ Object (readonly)

Returns the value of attribute increment_sha.



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# File 'lib/cymometer/counter.rb', line 62

def increment_sha
  @increment_sha
end

Instance Attribute Details

#key ⇒ Object (readonly)

Returns the value of attribute key.



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# File 'lib/cymometer/counter.rb', line 10

def key
  @key
end

#limit ⇒ Object (readonly)

Returns the value of attribute limit.



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# File 'lib/cymometer/counter.rb', line 10

def limit
  @limit
end

#window ⇒ Object (readonly)

Returns the value of attribute window.



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# File 'lib/cymometer/counter.rb', line 10

def window
  @window
end

Instance Method Details

#count ⇒ Object

Returns the current count



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# File 'lib/cymometer/counter.rb', line 106

def count
  current_time = (Time.now.to_f * 1_000_000).to_i
  window = @window * 1_000_000

  # Clean expired entries
  @redis.zremrangebyscore(@key, 0, current_time - window)
  @redis.zcount(@key, current_time - window, "+inf").to_i
end

#decrement! ⇒ Object

Atomically decrements the counter by removing the oldest entry



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# File 'lib/cymometer/counter.rb', line 92

def decrement!
  current_time = (Time.now.to_f * 1_000_000).to_i
  window = @window * 1_000_000

  result = evalsha_with_fallback(
    :decrement,
    keys: [@key],
    argv: [current_time, window]
  )

  result[1].to_i
end

#increment! ⇒ Object

Atomically increments the counter and checks the limit

Raises:



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# File 'lib/cymometer/counter.rb', line 73

def increment!
  current_time = (Time.now.to_f * 1_000_000).to_i # Microseconds
  window = @window * 1_000_000 # Convert to microseconds

  result = evalsha_with_fallback(
    :increment,
    keys: [@key],
    argv: [current_time, window, @limit]
  )

  success = result[0] == 1
  count = result[1].to_i

  raise LimitExceeded, "Limit of #{@limit} exceeded with count #{count}" unless success

  count
end

#transaction(rollback: true) ⇒ Object

Executes a block if the counter can be incremented. If the block raises an exception, decrements the counter and re-raises the exception.



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# File 'lib/cymometer/counter.rb', line 117

def transaction(rollback: true)
  increment!
  begin
    yield
  rescue => e
    decrement! if rollback
    raise e
  end
end