Class: Adocca::MemCache

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

Overview

A Ruby client library for memcached. Ripped from the gem.

Defined Under Namespace

Classes: ClientError, InternalError, MemCacheError, Server, ServerError

Constant Summary collapse

HOST_HASH =

a semi-unique id for this ruby instance

Array.new(32).collect do |e| (65 + rand(25)).chr end.join
DEFAULT_OPTIONS =

Default options for the cache object.

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

Default memcached port.

11211
DEFAULT_WEIGHT =

Default memcached server weight.

1
LIVELINESS_TIMEOUT =

The maximum amount of time we are willing to spend talking to servers before accepting that something horrible has happened.

5
ADD_NOTSTORED =

the response when the key is present

"NOT_STORED\r\n"
ADD_STORED =

the response when the key is NOT present

"STORED\r\n"
TRANS_EXPTIME =

lock expiry time

10
TRANS_MAX_TRIES = 
10

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(opts = {}) ⇒ MemCache

Valid options are:

:namespace
    If specified, all keys will have the given value prepended
    before accessing the cache.  Defaults to nil.

:readonly
    If this is set, any attempt to write to the cache will generate
    an exception.  Defaults to false.



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

def initialize(opts = {})
  opts = DEFAULT_OPTIONS.merge(opts)   
  @namespace = opts[:namespace]
  @readonly  = opts[:readonly]
  if ActionController::Base.allow_concurrency
    @mutex = Monitor.new
  else
    @mutex = NullMutex.new
  end
  @servers   = []
  @buckets   = []
end

Instance Attribute Details

#request_timeout ⇒ Object

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/am_memcache.rb', line 57

def request_timeout
  @request_timeout
end

Class Method Details

.log_error(e) ⇒ Object 



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# File 'lib/am_memcache.rb', line 82

def self.log_error(e)
  if defined?(RAILS_DEFAULT_LOGGER)
    RAILS_DEFAULT_LOGGER.error(e)
    RAILS_DEFAULT_LOGGER.error(PP.pp(e.backtrace, ""))
  else
    puts e
    pp e.backtrace
  end
end

Instance Method Details

#[](key) ⇒ Object

Shortcut to get a value from the cache.



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# File 'lib/am_memcache.rb', line 338

def [](key)
  self.get(key)
end

#[]=(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/am_memcache.rb', line 344

def []=(key, value)
  self.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/am_memcache.rb', line 99

def active?
  not @servers.empty?
end

#add(key, value, expiry = 0) ⇒ Object

Add an entry to the cache will return true if the entry didnt already exist



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# File 'lib/am_memcache.rb', line 204

def add(key, value, expiry = 0)
  cache_key = make_cache_key(key)
  marshaled_value = nil
  if Integer === value
    marshaled_value = value.to_s
  else
    marshaled_value = Marshal.dump(value)
  end
  send_command(cache_key, "add #{cache_key} 0 #{expiry} #{marshaled_value.size}\r\n" + marshaled_value) == ADD_STORED
end

#check(key) ⇒ Object

Method to check if a value is set, and NOT unmarshal, only return bool



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

def check(key)
  cache_key = make_cache_key(key)
  @mutex.synchronize do

    begin
      response, sock, server = sock_send_command(cache_key, "get #{cache_key}", true)
      
      return false if response =~ /^END/
      
      v, key, flags, bytes = response.split(/ /)
      value = sock.read(bytes.to_i)
      sock.timeout_gets(LIVELINESS_TIMEOUT)
      sock.timeout_gets(LIVELINESS_TIMEOUT)
    rescue Exception => err
      server.mark_dead(err.message) if server
      self.class.log_error(err)
      return false
    end
    
    true
  end
end

#dec(key, amount = 1) ⇒ Object

Increment an entry in the cache



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# File 'lib/am_memcache.rb', line 190

def dec(key, amount = 1)
  cache_key = make_cache_key(key)
  rval = send_command(cache_key, "decr #{cache_key} #{amount}")
  rval = rval.strip.to_i if rval =~ /^\d+/
  rval
end

#delete(key, expiry = 0) ⇒ Object

Remove an entry from the cache. return true if it is deleted



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# File 'lib/am_memcache.rb', line 229

def delete(key, expiry = 0)
  cache_key = make_cache_key(key)
  send_command(cache_key, "delete #{cache_key} #{expiry}")
end

#flush ⇒ Object

Flush cache



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# File 'lib/am_memcache.rb', line 268

def flush
  @mutex.synchronize do
    raise MemCacheError, "No active servers" unless self.active?
    @servers.each do |server|

      sock = server.socket
      unless sock.nil?
        begin
          sock.timeout_write("flush_all\r\n", LIVELINESS_TIMEOUT)
          sock.timeout_gets(LIVELINESS_TIMEOUT)
        rescue Exception => err
          server.mark_dead(err.message) if server
          self.class.log_error(err)
        end
      end
    end
  end
end

#get(key) ⇒ Object

get an entry from the cache



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# File 'lib/am_memcache.rb', line 136

def get(key)
  cache_key = make_cache_key(key)
  rval = nil
  @mutex.synchronize do
    begin
      response, sock, server = sock_send_command(cache_key, "get #{cache_key}", true)
      return :MemCache_no_such_entry if response =~ /^END/

      v, cache_key, flags, bytes = response.split(/ /)
      rval = sock.read(bytes.to_i)

      sock.timeout_gets(LIVELINESS_TIMEOUT)
      sock.timeout_gets(LIVELINESS_TIMEOUT)
    rescue Exception => err
      server.mark_dead(err.message) if server
      
      self.class.log_error(err)
      return :MemCache_no_such_entry
    end
  end

  if rval.strip.match(/\A\d+\z/)
    rval.strip.to_i
  else
    # Return the unmarshaled value.
    begin
      Marshal.load(rval)
    rescue ArgumentError, TypeError => err
      self.class.log_error(err)
      return :MemCache_no_such_entry
    end
  end
end

#get_server_for_key(key) ⇒ Object

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

Raises:



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# File 'lib/am_memcache.rb', line 592

def get_server_for_key(key)
  # Hash the value of the key to select the bucket.
  hkey = Integer("0x#{key}")
  
  # Fetch a server for the given key, retrying if that server is
  # offline.
  server = nil
  20.times do |tries|
    server = @buckets[(hkey + tries) % @buckets.nitems]
    break if server.alive?
  end

  raise MemCacheError, "No servers available" unless server
  server
end

#inc(key, amount = 1) ⇒ Object

Increment an entry in the cache



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# File 'lib/am_memcache.rb', line 180

def inc(key, amount = 1)
  cache_key = make_cache_key(key)
  rval = send_command(cache_key, "incr #{cache_key} #{amount}")
  rval = rval.strip.to_i if rval =~ /^\d+/
  rval
end

#inspect ⇒ Object

Return a string representation of the cache object.



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# File 'lib/am_memcache.rb', line 93

def inspect
  sprintf("<MemCache: %s servers, %s buckets, ns: %p, ro: %p>",
          @servers.nitems, @buckets.nitems, @namespace, @readonly)
end

#invalidate_namespace(ns) ⇒ Object

Invalidate a namespace in the cache.



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# File 'lib/am_memcache.rb', line 173

def invalidate_namespace(ns)
  inc(make_namespace_key(ns).last)
end

#lock(key, options = {}) ⇒ Object

Will create a reentrant lock on key, but waiting no more than timeout for the lock. Will sleep 1 second between each try.

Will return whether the locking was successful.



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# File 'lib/am_memcache.rb', line 297

def lock(key, options = {})
  timeout = options[:timeout] || 1 << 32
  expire = options[:expire] || 0
  cache_key = make_cache_key(key)
  start_at = Time.now
  we_locked_now = false
  we_locked_earlier = false
  ok_value = "#{HOST_HASH}:#{Thread.current.object_id}"
  while (!(we_locked_now = add(cache_key, ok_value, expire)) && 
         !(we_locked_earlier = (get(cache_key) == ok_value)) &&
         Time.now < start_at + timeout)
    sleep 1
  end
  return we_locked_now || we_locked_earlier
end

#make_cache_key(o) ⇒ Object

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



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# File 'lib/am_memcache.rb', line 575

def make_cache_key(o)
  if Array === o
    o = o.clone
    key = o.pop

    namespace_key = ""
    namespace_key << ":#{make_namespace_key(o).first}" unless o.empty?

    key = "#{@namespace}#{namespace_key}:#{key}"
    Digest::SHA1.hexdigest(key)
  else
    key = "#{@namespace}:#{o}"
    Digest::SHA1.hexdigest(key)
  end
end

#make_namespace_key(ns, appendage = nil) ⇒ Object

Create a key for this namespace and return it along with the string you want to delete or incr to invalidate this specific namespace



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# File 'lib/am_memcache.rb', line 550

def make_namespace_key(ns, appendage = nil)
  # ensure that this is an Array
  ns = ns.to_a
  # get the first part of the Array
  next_part = ns.shift
  # create a unique namespace name of it
  next_part = [appendage, next_part].join(":") if appendage
  # create a unique memcache key of the namespace name
  next_key = "adocca:memcache:namespace:#{next_part}"
  # make sure it exists in memcache
  add(next_key, rand(1 << 31))
  # get its value in memcache
  salt = get(next_key)
  if ns.empty?
    # if this is the last part of the key return it + its secret salt along with itself (for invalidation purposes)
    ["#{next_part}:#{salt}", next_key]
  else
    # otherwise, fetch the rest along with the 
    last_part = make_namespace_key(ns, next_part)
    ["#{next_part}:#{salt}:#{last_part.first}", last_part.last]
  end
end

#readonly? ⇒ Boolean

Returns whether the cache was created read only.

Returns:

  • (Boolean) 


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# File 'lib/am_memcache.rb', line 104

def readonly?
  @readonly
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/am_memcache.rb', line 237

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

#send_command(key, command) ⇒ Object

Will send a command to the proper server for this key and return the response



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# File 'lib/am_memcache.rb', line 511

def send_command(key, command)
  sock_send_command(key, command)[0]
end

#servers=(servers) ⇒ Object

Set the servers that the requests will be distributed between. Entries can be either strings of the form “hostname:port” or “hostname:port:weight” or MemCache::Server objects.



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# File 'lib/am_memcache.rb', line 111

def servers=(servers)
  # Create the server objects.
  @servers = servers.collect do |server|
    case server
    when String
      host, port, weight = server.split(/:/, 3)
      port ||= DEFAULT_PORT
      weight ||= DEFAULT_WEIGHT
      Server::new(host, port, weight)
    when Server
      server
    else
      raise TypeError, "Cannot convert %s to MemCache::Server" %
        svr.class.name
    end
  end

  # Create an array of server buckets for weight selection of servers.
  @buckets = []
  @servers.each do |server|
    server.weight.times { @buckets.push(server) }
  end
end

#set(key, value, expiry = 0) ⇒ Object

Add an entry to the cache.



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# File 'lib/am_memcache.rb', line 216

def set(key, value, expiry = 0)
  cache_key = make_cache_key(key)
  marshaled_value = nil
  if Integer === value
    marshaled_value = value.to_s
  else
    marshaled_value = Marshal.dump(value)
  end
  send_command(cache_key, "set #{cache_key} 0 #{expiry} #{marshaled_value.size}\r\n" + marshaled_value)
end

#sock_send_command(key, command, squash_errors = false) ⇒ Object

Will send a command to the proper server for this key and return the response, socket and server



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# File 'lib/am_memcache.rb', line 519

def sock_send_command(key, command, squash_errors = false)
  @mutex.synchronize do
    server = nil
    begin
      raise MemCacheError, "No active servers" unless self.active?
      raise MemCacheError, "Update of readonly cache" if @readonly
      server = get_server_for_key(key)
      
      sock = server.socket
      raise MemCacheError, "No connection to server" if sock.nil?
      
      response = nil
      
      sock.timeout_write("#{command}\r\n", LIVELINESS_TIMEOUT)
      [sock.timeout_gets(LIVELINESS_TIMEOUT), sock, server]
                
    rescue Exception => err
      server.mark_dead(err.message) if server
      self.class.log_error(err)
      raise err unless squash_errors
      return err.message
    end
  end
end

#synchronize(key, &block) ⇒ Object

memcache-driven locking mechanism

Uses lock and unlock



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# File 'lib/am_memcache.rb', line 325

def synchronize(key, &block)
  if lock_success = lock(key, :expire => TRANS_EXPTIME, :timeout => TRANS_MAX_TRIES)
    begin
      yield
    ensure
      unlock(key)
    end
  else
    raise MemCacheError, "Couldn't obtain lock on #{key}"
  end
end

#unlock(key) ⇒ Object

Will release any lock on key.



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# File 'lib/am_memcache.rb', line 316

def unlock(key)
  self.delete(make_cache_key(key))
end