Class: MemCache

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

Overview

A Ruby client library for memcached.

This is intended to provide access to basic memcached functionality. It does not attempt to be complete implementation of the entire API, but it is approaching a complete implementation.

Defined Under Namespace

Classes: MemCacheError, Server

Constant Summary collapse

VERSION =

The version of MemCache you are using.

'1.5.0'
DEFAULT_OPTIONS =

Default options for the cache object.

{
  :namespace   => nil,
  :readonly    => false,
  :multithread => false,
}
DEFAULT_PORT =

Default memcached port.

11211
DEFAULT_WEIGHT =

Default memcached server weight.

1

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 exeception on cache writes when true.
[:multithread] Wraps cache access in a Mutex for thread safety.

Other options are ignored.


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# File 'lib/memcache.rb', line 100

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]
  @mutex       = Mutex.new if @multithread
  @buckets     = []
  self.servers = servers
end

Instance Attribute Details

#multithreadObject (readonly)

The multithread setting for this instance


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# File 'lib/memcache.rb', line 81

def multithread
  @multithread
end

#namespaceObject (readonly)

The namespace for this instance


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# File 'lib/memcache.rb', line 76

def namespace
  @namespace
end

#request_timeoutObject

The amount of time to wait for a response from a memcached server. If a response is not completed within this time, the connection to the server will be closed and an error will be raised.


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# File 'lib/memcache.rb', line 71

def request_timeout
  @request_timeout
end

#serversObject

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


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

def servers
  @servers
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 485

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 140

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 or MemCache#[]=.

Raises:


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# File 'lib/memcache.rb', line 324

def add(key, value, expiry = 0, raw = false)
  raise MemCacheError, "Update of readonly cache" if @readonly
  server, cache_key = request_setup key
  socket = server.socket

  value = Marshal.dump value unless raw
  command = "add #{cache_key} 0 #{expiry} #{value.size}\r\n#{value}\r\n"

  begin
    @mutex.lock if @multithread
    socket.write command
    socket.gets
  rescue SocketError, SystemCallError, IOError => err
    server.close
    raise MemCacheError, err.message
  ensure
    @mutex.unlock if @multithread
  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 536

def cache_decr(server, cache_key, amount)
  socket = server.socket
  socket.write "decr #{cache_key} #{amount}\r\n"
  text = socket.gets
  return nil if text == "NOT_FOUND\r\n"
  return text.to_i
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 548

def cache_get(server, cache_key)
  socket = server.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

  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

#cache_get_multi(server, cache_keys) ⇒ Object

Fetches cache_keys from server using a multi-get.

Raises:


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# File 'lib/memcache.rb', line 573

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

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

    unless keyline =~ /^VALUE (.+) (.+) (.+)/ 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}"
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 599

def cache_incr(server, cache_key, amount)
  socket = server.socket
  socket.write "incr #{cache_key} #{amount}\r\n"
  text = socket.gets
  return nil if text == "NOT_FOUND\r\n"
  return text.to_i
end

#decr(key, amount = 1) ⇒ Object

Deceremets 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 187

def decr(key, amount = 1)
  server, cache_key = request_setup key

  if @multithread then
    threadsafe_cache_decr server, cache_key, amount
  else
    cache_decr server, cache_key, amount
  end
rescue TypeError, SocketError, SystemCallError, IOError => err
  handle_error server, err
end

#delete(key, expiry = 0) ⇒ Object

Removes key from the cache in expiry seconds.


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# File 'lib/memcache.rb', line 347

def delete(key, expiry = 0)
  @mutex.lock if @multithread

  raise MemCacheError, "No active servers" unless active?
  cache_key = make_cache_key key
  server = get_server_for_key cache_key

  sock = server.socket
  raise MemCacheError, "No connection to server" if sock.nil?

  begin
    sock.write "delete #{cache_key} #{expiry}\r\n"
    sock.gets
  rescue SocketError, SystemCallError, IOError => err
    server.close
    raise MemCacheError, err.message
  end
ensure
  @mutex.unlock if @multithread
end

#flush_allObject

Flush the cache from all memcache servers.

Raises:


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# File 'lib/memcache.rb', line 371

def flush_all
  raise MemCacheError, 'No active servers' unless active?
  raise MemCacheError, "Update of readonly cache" if @readonly
  begin
    @mutex.lock if @multithread
    @servers.each do |server|
      begin
        sock = server.socket
        raise MemCacheError, "No connection to server" if sock.nil?
        sock.write "flush_all\r\n"
        result = sock.gets
        raise MemCacheError, $2.strip if result =~ /^(SERVER_)?ERROR(.*)/
      rescue SocketError, SystemCallError, IOError => err
        server.close
        raise MemCacheError, err.message
      end
    end
  ensure
    @mutex.unlock if @multithread
  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 203

def get(key, raw = false)
  server, cache_key = request_setup key

  value = if @multithread then
            threadsafe_cache_get server, cache_key
          else
            cache_get server, cache_key
          end

  return nil if value.nil?

  value = Marshal.load value unless raw

  return value
rescue TypeError, SocketError, SystemCallError, IOError => err
  handle_error server, 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 }

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# File 'lib/memcache.rb', line 237

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|
    keys = keys.join ' '
    values = if @multithread then
               threadsafe_cache_get_multi server, keys
             else
               cache_get_multi server, keys
             end
    values.each do |key, value|
      results[cache_keys[key]] = Marshal.load value
    end
  end

  return results
rescue TypeError, SocketError, SystemCallError, IOError => err
  handle_error server, err
end

#get_server_for_key(key) ⇒ 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 506

def get_server_for_key(key)
  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|
    server = @buckets[hkey % @buckets.nitems]
    return server if server.alive?
    hkey += hash_for "#{try}#{key}"
  end

  raise MemCacheError, "No servers available"
end

#handle_error(server, error) ⇒ Object

Handles error from server.


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# File 'lib/memcache.rb', line 610

def handle_error(server, error)
  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 528

def hash_for(key)
  (key.crc32_ITU_T >> 16) & 0x7fff
end

#incr(key, amount = 1) ⇒ Object

Increments the value for key by amount and retruns 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 276

def incr(key, amount = 1)
  server, cache_key = request_setup key

  if @multithread then
    threadsafe_cache_incr server, cache_key, amount
  else
    cache_incr server, cache_key, amount
  end
rescue TypeError, SocketError, SystemCallError, IOError => err
  handle_error server, err
end

#inspectObject

Returns a string representation of the cache object.


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# File 'lib/memcache.rb', line 132

def inspect
  "<MemCache: %d servers, %d buckets, ns: %p, ro: %p>" %
    [@servers.length, @buckets.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 495

def make_cache_key(key)
  if namespace.nil? then
    key
  else
    "#{@namespace}:#{key}"
  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 147

def readonly?
  @readonly
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 621

def request_setup(key)
  raise MemCacheError, 'No active servers' unless active?
  cache_key = make_cache_key key
  server = get_server_for_key cache_key
  raise MemCacheError, 'No connection to server' if server.socket.nil?
  return server, cache_key
end

#resetObject

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 398

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

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

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.

Raises:


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# File 'lib/memcache.rb', line 295

def set(key, value, expiry = 0, raw = false)
  raise MemCacheError, "Update of readonly cache" if @readonly
  server, cache_key = request_setup key
  socket = server.socket

  value = Marshal.dump value unless raw
  command = "set #{cache_key} 0 #{expiry} #{value.size}\r\n#{value}\r\n"

  begin
    @mutex.lock if @multithread
    socket.write command
    result = socket.gets
    raise MemCacheError, $1.strip if result =~ /^SERVER_ERROR (.*)/
  rescue SocketError, SystemCallError, IOError => err
    server.close
    raise MemCacheError, err.message
  ensure
    @mutex.unlock if @multithread
  end
end

#statsObject

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 434

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

  @servers.each do |server|
    sock = server.socket
    raise MemCacheError, "No connection to server" if sock.nil?

    value = nil
    begin
      sock.write "stats\r\n"
      stats = {}
      while line = sock.gets do
        break if line == "END\r\n"
        if line =~ /^STAT ([\w]+) ([\w\.\:]+)/ then
          name, value = $1, $2
          stats[name] = case name
                        when 'version'
                          value
                        when 'rusage_user', 'rusage_system' then
                          seconds, microseconds = value.split(/:/, 2)
                          microseconds ||= 0
                          Float(seconds) + (Float(microseconds) / 1_000_000)
                        else
                          if value =~ /^\d+$/ then
                            value.to_i
                          else
                            value
                          end
                        end
        end
      end
      server_stats["#{server.host}:#{server.port}"] = stats
    rescue SocketError, SystemCallError, IOError => err
      server.close
      raise MemCacheError, err.message
    end
  end

  server_stats
end

#threadsafe_cache_decr(server, cache_key, amount) ⇒ Object

:nodoc:


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

def threadsafe_cache_decr(server, cache_key, amount) # :nodoc:
  @mutex.lock
  cache_decr server, cache_key, amount
ensure
  @mutex.unlock
end

#threadsafe_cache_get(server, cache_key) ⇒ Object

:nodoc:


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# File 'lib/memcache.rb', line 636

def threadsafe_cache_get(server, cache_key) # :nodoc:
  @mutex.lock
  cache_get server, cache_key
ensure
  @mutex.unlock
end

#threadsafe_cache_get_multi(socket, cache_keys) ⇒ Object

:nodoc:


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# File 'lib/memcache.rb', line 643

def threadsafe_cache_get_multi(socket, cache_keys) # :nodoc:
  @mutex.lock
  cache_get_multi socket, cache_keys
ensure
  @mutex.unlock
end

#threadsafe_cache_incr(server, cache_key, amount) ⇒ Object

:nodoc:


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# File 'lib/memcache.rb', line 650

def threadsafe_cache_incr(server, cache_key, amount) # :nodoc:
  @mutex.lock
  cache_incr server, cache_key, amount
ensure
  @mutex.unlock
end