Class: MemCache

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

Overview

A Ruby client library for memcached.

Defined Under Namespace

Classes: MemCacheError, Server

Constant Summary collapse

VERSION =

The version of MemCache you are using.

'1.7.0'
DEFAULT_OPTIONS =

Default options for the cache object.

{
  :namespace   => nil,
  :readonly    => false,
  :multithread => true,
  :failover    => true,
  :timeout     => 0.5,
  :logger      => nil,
  :no_reply    => false,
}
DEFAULT_PORT =

Default memcached port.

11211
DEFAULT_WEIGHT =

Default memcached server weight.

1
ONE_MB =

Add key to the cache with value value that expires in expiry seconds. If raw is true, value will not be Marshalled.

Warning: Readers should not call this method in the event of a cache miss; see MemCache#add.

1024 * 1024

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(*args) ⇒ MemCache

Accepts a list of servers and a list of opts. servers may be omitted. See servers= for acceptable server list arguments.

Valid options for opts are:

[:namespace]   Prepends this value to all keys added or retrieved.
[:readonly]    Raises an exception on cache writes when true.
[:multithread] Wraps cache access in a Mutex for thread safety. Defaults to true.
[:failover]    Should the client try to failover to another server if the
               first server is down?  Defaults to true.
[:timeout]     Time to use as the socket read timeout.  Defaults to 0.5 sec,
               set to nil to disable timeouts (this is a major performance penalty in Ruby 1.8,
               "gem install SystemTimer' to remove most of the penalty).
[:logger]      Logger to use for info/debug output, defaults to nil
[:no_reply]    Don't bother looking for a reply for write operations (i.e. they
               become 'fire and forget'), memcached 1.2.5 and later only, speeds up
               set/add/delete/incr/decr significantly.

Other options are ignored.



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# File 'lib/memcache.rb', line 120

def initialize(*args)
  servers = []
  opts = {}

  case args.length
  when 0 then # NOP
  when 1 then
    arg = args.shift
    case arg
    when Hash   then opts = arg
    when Array  then servers = arg
    when String then servers = [arg]
    else raise ArgumentError, 'first argument must be Array, Hash or String'
    end
  when 2 then
    servers, opts = args
  else
    raise ArgumentError, "wrong number of arguments (#{args.length} for 2)"
  end

  opts = DEFAULT_OPTIONS.merge opts
  @namespace   = opts[:namespace]
  @readonly    = opts[:readonly]
  @multithread = opts[:multithread]
  @timeout     = opts[:timeout]
  @failover    = opts[:failover]
  @logger      = opts[:logger]
  @no_reply    = opts[:no_reply]
  @mutex       = Mutex.new if @multithread

  logger.info { "memcache-client #{VERSION} #{Array(servers).inspect}" } if logger

  Thread.current[:memcache_client] = self.object_id if !@multithread

  self.servers = servers
end

Instance Attribute Details

#failover ⇒ Object (readonly)

Should the client try to failover to another server if the first server is down? Defaults to true.



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# File 'lib/memcache.rb', line 86

def failover
  @failover
end

#logger ⇒ Object (readonly)

Log debug/info/warn/error to the given Logger, defaults to nil.



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# File 'lib/memcache.rb', line 91

def logger
  @logger
end

#multithread ⇒ Object (readonly)

The multithread setting for this instance



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# File 'lib/memcache.rb', line 69

def multithread
  @multithread
end

#namespace ⇒ Object (readonly)

The namespace for this instance



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# File 'lib/memcache.rb', line 64

def namespace
  @namespace
end

#no_reply ⇒ Object (readonly)

Don’t send or look for a reply from the memcached server for write operations. Please note this feature only works in memcached 1.2.5 and later. Earlier versions will reply with “ERROR”.



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# File 'lib/memcache.rb', line 97

def no_reply
  @no_reply
end

#servers ⇒ Object

The servers this client talks to. Play at your own peril.



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# File 'lib/memcache.rb', line 74

def servers
  @servers
end

#timeout ⇒ Object (readonly)

Socket timeout limit with this client, defaults to 0.5 sec. Set to nil to disable timeouts.



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# File 'lib/memcache.rb', line 80

def timeout
  @timeout
end

Instance Method Details

#[]=(key, value) ⇒ Object

Shortcut to save a value in the cache. This method does not set an expiration on the entry. Use set to specify an explicit expiry.



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# File 'lib/memcache.rb', line 629

def []=(key, value)
  set key, value
end

#active? ⇒ Boolean

Returns whether there is at least one active server for the object.

Returns:

  • (Boolean) 


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# File 'lib/memcache.rb', line 168

def active?
  not @servers.empty?
end

#add(key, value, expiry = 0, raw = false) ⇒ Object

Add key to the cache with value value that expires in expiry seconds, but only if key does not already exist in the cache. If raw is true, value will not be Marshalled.

Readers should call this method in the event of a cache miss, not MemCache#set.

Raises:



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# File 'lib/memcache.rb', line 413

def add(key, value, expiry = 0, raw = false)
  raise MemCacheError, "Update of readonly cache" if @readonly
  with_server(key) do |server, cache_key|
    value = Marshal.dump value unless raw
    logger.debug { "add #{key} to #{server}: #{value ? value.to_s.size : 'nil'}" } if logger
    command = "add #{cache_key} 0 #{expiry} #{value.to_s.size}#{noreply}\r\n#{value}\r\n"

    with_socket_management(server) do |socket|
      socket.write command
      break nil if @no_reply
      result = socket.gets
      raise_on_error_response! result
      result
    end
  end
end

#append(key, value) ⇒ Object

Append - ‘add this data to an existing key after existing data’ Please note the value is always passed to memcached as raw since it doesn’t make a lot of sense to concatenate marshalled data together.

Raises:



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# File 'lib/memcache.rb', line 455

def append(key, value)
  raise MemCacheError, "Update of readonly cache" if @readonly
  with_server(key) do |server, cache_key|
    logger.debug { "append #{key} to #{server}: #{value ? value.to_s.size : 'nil'}" } if logger
    command = "append #{cache_key} 0 0 #{value.to_s.size}#{noreply}\r\n#{value}\r\n"

    with_socket_management(server) do |socket|
      socket.write command
      break nil if @no_reply
      result = socket.gets
      raise_on_error_response! result
      result
    end
  end
end

#cache_decr(server, cache_key, amount) ⇒ Object

Performs a raw decr for cache_key from server. Returns nil if not found.



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# File 'lib/memcache.rb', line 682

def cache_decr(server, cache_key, amount)
  with_socket_management(server) do |socket|
    socket.write "decr #{cache_key} #{amount}#{noreply}\r\n"
    break nil if @no_reply
    text = socket.gets
    raise_on_error_response! text
    return nil if text == "NOT_FOUND\r\n"
    return text.to_i
  end
end

#cache_get(server, cache_key) ⇒ Object

Fetches the raw data for cache_key from server. Returns nil on cache miss.



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# File 'lib/memcache.rb', line 697

def cache_get(server, cache_key)
  with_socket_management(server) do |socket|
    socket.write "get #{cache_key}\r\n"
    keyline = socket.gets # "VALUE <key> <flags> <bytes>\r\n"

    if keyline.nil? then
      server.close
      raise MemCacheError, "lost connection to #{server.host}:#{server.port}"
    end

    raise_on_error_response! keyline
    return nil if keyline == "END\r\n"

    unless keyline =~ /(\d+)\r/ then
      server.close
      raise MemCacheError, "unexpected response #{keyline.inspect}"
    end
    value = socket.read $1.to_i
    socket.read 2 # "\r\n"
    socket.gets   # "END\r\n"
    return value
  end
end

#cache_get_multi(server, cache_keys) ⇒ Object

Fetches cache_keys from server using a multi-get.



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# File 'lib/memcache.rb', line 756

def cache_get_multi(server, cache_keys)
  with_socket_management(server) do |socket|
    values = {}
    socket.write "get #{cache_keys}\r\n"

    while keyline = socket.gets do
      return values if keyline == "END\r\n"
      raise_on_error_response! keyline

      unless keyline =~ /\AVALUE (.+) (.+) (.+)/ then
        server.close
        raise MemCacheError, "unexpected response #{keyline.inspect}"
      end

      key, data_length = $1, $3
      values[$1] = socket.read data_length.to_i
      socket.read(2) # "\r\n"
    end

    server.close
    raise MemCacheError, "lost connection to #{server.host}:#{server.port}" # TODO: retry here too
  end
end

#cache_incr(server, cache_key, amount) ⇒ Object

Performs a raw incr for cache_key from server. Returns nil if not found.



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# File 'lib/memcache.rb', line 784

def cache_incr(server, cache_key, amount)
  with_socket_management(server) do |socket|
    socket.write "incr #{cache_key} #{amount}#{noreply}\r\n"
    break nil if @no_reply
    text = socket.gets
    raise_on_error_response! text
    return nil if text == "NOT_FOUND\r\n"
    return text.to_i
  end
end

#cas(key, expiry = 0, raw = false) ⇒ Object

“cas” is a check and set operation which means “store this data but only if no one else has updated since I last fetched it.” This can be used as a form of optimistic locking.

Works in block form like so:

cache.cas('some-key') do |value|
  value + 1
end

Returns: nil if the value was not found on the memcached server. STORED if the value was updated successfully EXISTS if the value was updated by someone else since last fetch

Raises:



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# File 'lib/memcache.rb', line 374

def cas(key, expiry=0, raw=false)
  raise MemCacheError, "Update of readonly cache" if @readonly
  raise MemCacheError, "A block is required" unless block_given?

  (value, token) = gets(key, raw)
  return nil unless value
  updated = yield value

  with_server(key) do |server, cache_key|
    logger.debug { "cas #{key} to #{server.inspect}: #{data.size}" } if logger

    value = Marshal.dump updated unless raw
    data = value.to_s
    command = "cas #{cache_key} 0 #{expiry} #{value.size} #{token}#{noreply}\r\n#{value}\r\n"

    with_socket_management(server) do |socket|
      socket.write command
      break nil if @no_reply
      result = socket.gets
      raise_on_error_response! result

      if result.nil?
        server.close
        raise MemCacheError, "lost connection to #{server.host}:#{server.port}"
      end

      result
    end
  end
end

#check_multithread_status! ⇒ Object 



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# File 'lib/memcache.rb', line 907

def check_multithread_status!
  return if @multithread

  if Thread.current[:memcache_client] != self.object_id
    raise MemCacheError, "      You are accessing this memcache-client instance from multiple threads but have not enabled multithread support.\n      Normally:  MemCache.new(['localhost:11211'], :multithread => true)\n      In Rails:  config.cache_store = [:mem_cache_store, 'localhost:11211', { :multithread => true }]\n    EOM\n  end\nend\n"

#create_continuum_for(servers) ⇒ Object 



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# File 'lib/memcache.rb', line 888

def create_continuum_for(servers)
  total_weight = servers.inject(0) { |memo, srv| memo + srv.weight }
  continuum = []

  servers.each do |server|
    entry_count_for(server, servers.size, total_weight).times do |idx|
      hash = Digest::SHA1.hexdigest("#{server.host}:#{server.port}:#{idx}")
      value = Integer("0x#{hash[0..7]}")
      continuum << Continuum::Entry.new(value, server)
    end
  end

  continuum.sort { |a, b| a.value <=> b.value }
end

#decr(key, amount = 1) ⇒ Object

Decrements the value for key by amount and returns the new value. key must already exist. If key is not an integer, it is assumed to be

  1. key can not be decremented below 0.



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# File 'lib/memcache.rb', line 211

def decr(key, amount = 1)
  raise MemCacheError, "Update of readonly cache" if @readonly
  with_server(key) do |server, cache_key|
    cache_decr server, cache_key, amount
  end
rescue TypeError => err
  handle_error nil, err
end

#delete(key, expiry = 0) ⇒ Object

Removes key from the cache in expiry seconds.

Raises:



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# File 'lib/memcache.rb', line 494

def delete(key, expiry = 0)
  raise MemCacheError, "Update of readonly cache" if @readonly
  with_server(key) do |server, cache_key|
    with_socket_management(server) do |socket|
      logger.debug { "delete #{cache_key} on #{server}" } if logger
      socket.write "delete #{cache_key} #{expiry}#{noreply}\r\n"
      break nil if @no_reply
      result = socket.gets
      raise_on_error_response! result
      result
    end
  end
end

#entry_count_for(server, total_servers, total_weight) ⇒ Object 



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# File 'lib/memcache.rb', line 903

def entry_count_for(server, total_servers, total_weight)
  ((total_servers * Continuum::POINTS_PER_SERVER * server.weight) / Float(total_weight)).floor
end

#fetch(key, expiry = 0, raw = false) ⇒ Object

Performs a get with the given key. If the value does not exist and a block was given, the block will be called and the result saved via add.

If you do not provide a block, using this method is the same as using get.



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# File 'lib/memcache.rb', line 244

def fetch(key, expiry = 0, raw = false)
  value = get(key, raw)

  if value.nil? && block_given?
    value = yield
    add(key, value, expiry, raw)
  end

  value
end

#flush_all(delay = 0) ⇒ Object

Flush the cache from all memcache servers. A non-zero value for delay will ensure that the flush is propogated slowly through your memcached server farm. The Nth server will be flushed N*delay seconds from now, asynchronously so this method returns quickly. This prevents a huge database spike due to a total flush all at once.

Raises:



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# File 'lib/memcache.rb', line 517

def flush_all(delay=0)
  raise MemCacheError, 'No active servers' unless active?
  raise MemCacheError, "Update of readonly cache" if @readonly

  begin
    delay_time = 0
    @servers.each do |server|
      with_socket_management(server) do |socket|
        logger.debug { "flush_all #{delay_time} on #{server}" } if logger
        socket.write "flush_all #{delay_time}#{noreply}\r\n"
        break nil if @no_reply
        result = socket.gets
        raise_on_error_response! result
        result
      end
      delay_time += delay
    end
  rescue IndexError => err
    handle_error nil, err
  end
end

#get(key, raw = false) ⇒ Object Also known as: []

Retrieves key from memcache. If raw is false, the value will be unmarshalled.



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# File 'lib/memcache.rb', line 224

def get(key, raw = false)
  with_server(key) do |server, cache_key|
    logger.debug { "get #{key} from #{server.inspect}: #{value ? value.to_s.size : 'nil'}" } if logger
    value = cache_get server, cache_key
    return nil if value.nil?
    value = Marshal.load value unless raw
    return value
  end
rescue TypeError => err
  handle_error nil, err
end

#get_multi(*keys) ⇒ Object

Retrieves multiple values from memcached in parallel, if possible.

The memcached protocol supports the ability to retrieve multiple keys in a single request. Pass in an array of keys to this method and it will:

  1. map the key to the appropriate memcached server

  2. send a single request to each server that has one or more key values

Returns a hash of values.

cache["a"] = 1
cache["b"] = 2
cache.get_multi "a", "b" # => { "a" => 1, "b" => 2 }

Note that get_multi assumes the values are marshalled.



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# File 'lib/memcache.rb', line 273

def get_multi(*keys)
  raise MemCacheError, 'No active servers' unless active?

  keys.flatten!
  key_count = keys.length
  cache_keys = {}
  server_keys = Hash.new { |h,k| h[k] = [] }

  # map keys to servers
  keys.each do |key|
    server, cache_key = request_setup key
    cache_keys[cache_key] = key
    server_keys[server] << cache_key
  end

  results = {}

  server_keys.each do |server, keys_for_server|
    keys_for_server_str = keys_for_server.join ' '
    begin
      values = cache_get_multi server, keys_for_server_str
      values.each do |key, value|
        results[cache_keys[key]] = Marshal.load value
      end
    rescue IndexError => e
      # Ignore this server and try the others
      logger.warn { "Unable to retrieve #{keys_for_server.size} elements from #{server.inspect}: #{e.message}"} if logger
    end
  end

  return results
rescue TypeError => err
  handle_error nil, err
end

#get_server_for_key(key, options = {}) ⇒ Object

Pick a server to handle the request based on a hash of the key.

Raises:

  • (ArgumentError) 


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# File 'lib/memcache.rb', line 658

def get_server_for_key(key, options = {})
  raise ArgumentError, "illegal character in key #{key.inspect}" if
    key =~ /\s/
  raise ArgumentError, "key too long #{key.inspect}" if key.length > 250
  raise MemCacheError, "No servers available" if @servers.empty?
  return @servers.first if @servers.length == 1

  hkey = hash_for(key)

  20.times do |try|
    entryidx = Continuum.binary_search(@continuum, hkey)
    server = @continuum[entryidx].server
    return server if server.alive?
    break unless failover
    hkey = hash_for "#{try}#{key}"
  end
  
  raise MemCacheError, "No servers available"
end

#gets(key, raw = false) ⇒ Object 



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# File 'lib/memcache.rb', line 721

def gets(key, raw = false)
  with_server(key) do |server, cache_key|
    logger.debug { "gets #{key} from #{server.inspect}: #{value ? value.to_s.size : 'nil'}" } if logger
    result = with_socket_management(server) do |socket|
      socket.write "gets #{cache_key}\r\n"
      keyline = socket.gets # "VALUE <key> <flags> <bytes> <cas token>\r\n"

      if keyline.nil? then
        server.close
        raise MemCacheError, "lost connection to #{server.host}:#{server.port}"
      end

      raise_on_error_response! keyline
      return nil if keyline == "END\r\n"

      unless keyline =~ /(\d+) (\w+)\r/ then
        server.close
        raise MemCacheError, "unexpected response #{keyline.inspect}"
      end
      value = socket.read $1.to_i
      socket.read 2 # "\r\n"
      socket.gets   # "END\r\n"
      [value, $2]
    end
    result[0] = Marshal.load result[0] unless raw
    result
  end
rescue TypeError => err
  handle_error nil, err
end

#handle_error(server, error) ⇒ Object

Handles error from server.



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# File 'lib/memcache.rb', line 859

def handle_error(server, error)
  raise error if error.is_a?(MemCacheError)
  server.close if server
  new_error = MemCacheError.new error.message
  new_error.set_backtrace error.backtrace
  raise new_error
end

#hash_for(key) ⇒ Object

Returns an interoperable hash value for key. (I think, docs are sketchy for down servers).



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# File 'lib/memcache.rb', line 651

def hash_for(key)
  Zlib.crc32(key)
end

#incr(key, amount = 1) ⇒ Object

Increments the value for key by amount and returns the new value. key must already exist. If key is not an integer, it is assumed to be 0.



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# File 'lib/memcache.rb', line 313

def incr(key, amount = 1)
  raise MemCacheError, "Update of readonly cache" if @readonly
  with_server(key) do |server, cache_key|
    cache_incr server, cache_key, amount
  end
rescue TypeError => err
  handle_error nil, err
end

#inspect ⇒ Object

Returns a string representation of the cache object.



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# File 'lib/memcache.rb', line 160

def inspect
  "<MemCache: %d servers, ns: %p, ro: %p>" %
    [@servers.length, @namespace, @readonly]
end

#make_cache_key(key) ⇒ Object

Create a key for the cache, incorporating the namespace qualifier if requested.



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# File 'lib/memcache.rb', line 639

def make_cache_key(key)
  if namespace.nil? then
    key
  else
    "#{@namespace}:#{key}"
  end
end

#noreply ⇒ Object 



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# File 'lib/memcache.rb', line 867

def noreply
  @no_reply ? ' noreply' : ''
end

#prepend(key, value) ⇒ Object

Prepend - ‘add this data to an existing key before existing data’ Please note the value is always passed to memcached as raw since it doesn’t make a lot of sense to concatenate marshalled data together.

Raises:



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# File 'lib/memcache.rb', line 475

def prepend(key, value)
  raise MemCacheError, "Update of readonly cache" if @readonly
  with_server(key) do |server, cache_key|
    logger.debug { "prepend #{key} to #{server}: #{value ? value.to_s.size : 'nil'}" } if logger
    command = "prepend #{cache_key} 0 0 #{value.to_s.size}#{noreply}\r\n#{value}\r\n"

    with_socket_management(server) do |socket|
      socket.write command
      break nil if @no_reply
      result = socket.gets
      raise_on_error_response! result
      result
    end
  end
end

#raise_on_error_response!(response) ⇒ Object 



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# File 'lib/memcache.rb', line 882

def raise_on_error_response!(response)
  if response =~ /\A(?:CLIENT_|SERVER_)?ERROR(.*)/
    raise MemCacheError, $1.strip
  end
end

#readonly? ⇒ Boolean

Returns whether or not the cache object was created read only.

Returns:

  • (Boolean) 


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# File 'lib/memcache.rb', line 175

def readonly?
  @readonly
end

#replace(key, value, expiry = 0, raw = false) ⇒ Object

Add key to the cache with value value that expires in expiry seconds, but only if key already exists in the cache. If raw is true, value will not be Marshalled.

Raises:



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# File 'lib/memcache.rb', line 434

def replace(key, value, expiry = 0, raw = false)
  raise MemCacheError, "Update of readonly cache" if @readonly
  with_server(key) do |server, cache_key|
    value = Marshal.dump value unless raw
    logger.debug { "replace #{key} to #{server}: #{value ? value.to_s.size : 'nil'}" } if logger
    command = "replace #{cache_key} 0 #{expiry} #{value.to_s.size}#{noreply}\r\n#{value}\r\n"

    with_socket_management(server) do |socket|
      socket.write command
      break nil if @no_reply
      result = socket.gets
      raise_on_error_response! result
      result
    end
  end
end

#request_setup(key) ⇒ Object

Performs setup for making a request with key from memcached. Returns the server to fetch the key from and the complete key to use.

Raises:



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# File 'lib/memcache.rb', line 875

def request_setup(key)
  raise MemCacheError, 'No active servers' unless active?
  cache_key = make_cache_key key
  server = get_server_for_key cache_key
  return server, cache_key
end

#reset ⇒ Object

Reset the connection to all memcache servers. This should be called if there is a problem with a cache lookup that might have left the connection in a corrupted state.



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# File 'lib/memcache.rb', line 544

def reset
  @servers.each { |server| server.close }
end

#set(key, value, expiry = 0, raw = false) ⇒ Object

Raises:



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# File 'lib/memcache.rb', line 331

def set(key, value, expiry = 0, raw = false)
  raise MemCacheError, "Update of readonly cache" if @readonly
  with_server(key) do |server, cache_key|

    value = Marshal.dump value unless raw
    data = value.to_s
    logger.debug { "set #{key} to #{server.inspect}: #{data.size}" } if logger

    raise MemCacheError, "Value too large, memcached can only store 1MB of data per key" if data.size > ONE_MB

    command = "set #{cache_key} 0 #{expiry} #{data.size}#{noreply}\r\n#{data}\r\n"

    with_socket_management(server) do |socket|
      socket.write command
      break nil if @no_reply
      result = socket.gets
      raise_on_error_response! result

      if result.nil?
        server.close
        raise MemCacheError, "lost connection to #{server.host}:#{server.port}"
      end

      result
    end
  end
end

#stats ⇒ Object

Returns statistics for each memcached server. An explanation of the statistics can be found in the memcached docs:

code.sixapart.com/svn/memcached/trunk/server/doc/protocol.txt

Example:

>> pp CACHE.stats
{"localhost:11211"=>
  {"bytes"=>4718,
   "pid"=>20188,
   "connection_structures"=>4,
   "time"=>1162278121,
   "pointer_size"=>32,
   "limit_maxbytes"=>67108864,
   "cmd_get"=>14532,
   "version"=>"1.2.0",
   "bytes_written"=>432583,
   "cmd_set"=>32,
   "get_misses"=>0,
   "total_connections"=>19,
   "curr_connections"=>3,
   "curr_items"=>4,
   "uptime"=>1557,
   "get_hits"=>14532,
   "total_items"=>32,
   "rusage_system"=>0.313952,
   "rusage_user"=>0.119981,
   "bytes_read"=>190619}}
=> nil

Raises:



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# File 'lib/memcache.rb', line 580

def stats
  raise MemCacheError, "No active servers" unless active?
  server_stats = {}

  @servers.each do |server|
    next unless server.alive?

    with_socket_management(server) do |socket|
      value = nil
      socket.write "stats\r\n"
      stats = {}
      while line = socket.gets do
        raise_on_error_response! line
        break if line == "END\r\n"
        if line =~ /\ASTAT ([\S]+) ([\w\.\:]+)/ then
          name, value = $1, $2
          stats[name] = case name
                        when 'version'
                          value
                        when 'rusage_user', 'rusage_system' then
                          seconds, microseconds = value.split(/:/, 2)
                          microseconds ||= 0
                          Float(seconds) + (Float(microseconds) / 1_000_000)
                        else
                          if value =~ /\A\d+\Z/ then
                            value.to_i
                          else
                            value
                          end
                        end
        end
      end
      server_stats["#{server.host}:#{server.port}"] = stats
    end
  end

  raise MemCacheError, "No active servers" if server_stats.empty?
  server_stats
end

#with_server(key) ⇒ Object 



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# File 'lib/memcache.rb', line 840

def with_server(key)
  retried = false
  begin
    server, cache_key = request_setup(key)
    yield server, cache_key
  rescue IndexError => e
    logger.warn { "Server failed: #{e.class.name}: #{e.message}" } if logger
    if !retried && @servers.size > 1
      logger.info { "Connection to server #{server.inspect} DIED! Retrying operation..." } if logger
      retried = true
      retry
    end
    handle_error(nil, e)
  end
end

#with_socket_management(server, &block) ⇒ Object

Gets or creates a socket connected to the given server, and yields it to the block, wrapped in a mutex synchronization if @multithread is true.

If a socket error (SocketError, SystemCallError, IOError) or protocol error (MemCacheError) is raised by the block, closes the socket, attempts to connect again, and retries the block (once). If an error is again raised, reraises it as MemCacheError.

If unable to connect to the server (or if in the reconnect wait period), raises MemCacheError. Note that the socket connect code marks a server dead for a timeout period, so retrying does not apply to connection attempt failures (but does still apply to unexpectedly lost connections etc.).



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# File 'lib/memcache.rb', line 809

def with_socket_management(server, &block)
  check_multithread_status!

  @mutex.lock if @multithread
  retried = false

  begin
    socket = server.socket

    # Raise an IndexError to show this server is out of whack. If were inside
    # a with_server block, we'll catch it and attempt to restart the operation.

    raise IndexError, "No connection to server (#{server.status})" if socket.nil?

    block.call(socket)

  rescue SocketError, Timeout::Error => err
    logger.warn { "Socket failure: #{err.message}" } if logger
    server.mark_dead(err)
    handle_error(server, err)

  rescue MemCacheError, SystemCallError, IOError => err
    logger.warn { "Generic failure: #{err.class.name}: #{err.message}" } if logger
    handle_error(server, err) if retried || socket.nil?
    retried = true
    retry
  end
ensure
  @mutex.unlock if @multithread
end