module Object::EM

Introduction

EventMachine provides a fast, lightweight framework for implementing Ruby programs that can use the network to communicate with other processes. Using EventMachine, Ruby programmers can easily connect to remote servers and act as servers themselves. EventMachine does not supplant the Ruby IP libraries. It does provide an alternate technique for those applications requiring better performance, scalability, and discipline over the behavior of network sockets, than is easily obtainable using the built-in libraries, especially in applications which are structurally well-suited for the event-driven programming model.

EventMachine provides a perpetual event-loop which your programs can start and stop. Within the event loop, TCP network connections are initiated and accepted, based on EventMachine methods called by your program. You also define callback methods which are called by EventMachine when events of interest occur within the event-loop.

User programs will be called back when the following events occur:

Usage example

Here’s a fully-functional echo server implemented in EventMachine:

require 'eventmachine'

module EchoServer
  def post_init
    puts "-- someone connected to the echo server!"
  end

  def receive_data data
    send_data ">>>you sent: #{data}"
    close_connection if data =~ %rquit/
  end

  def unbind
    puts "-- someone disconnected from the echo server!"
  end
end

EventMachine::run {
  EventMachine::start_server "127.0.0.1", 8081, EchoServer
}

What’s going on here? Well, we have defined the module EchoServer to implement the semantics of the echo protocol (more about that shortly). The last three lines invoke the event-machine itself, which runs forever unless one of your callbacks terminates it. The block that you supply to EventMachine.run contains code that runs immediately after the event machine is initialized and before it starts looping. This is the place to open up a TCP server by specifying the address and port it will listen on, together with the module that will process the data.

Our EchoServer is extremely simple as the echo protocol doesn’t require much work. Basically you want to send back to the remote peer whatever data it sends you. We’ll dress it up with a little extra text to make it interesting. Also, we’ll close the connection in case the received data contains the word “quit.”

So what about this module EchoServer? Well, whenever a network connection (either a client or a server) starts up, EventMachine instantiates an anonymous class, that your module has been mixed into. Exactly one of these class instances is created for each connection. Whenever an event occurs on a given connection, its corresponding object automatically calls specific instance methods which your module may redefine. The code in your module always runs in the context of a class instance, so you can create instance variables as you wish and they will be carried over to other callbacks made on that same connection.

Looking back up at EchoServer, you can see that we’ve defined the method receive_data which (big surprise) is called whenever data has been received from the remote end of the connection. Very simple. We get the data (a String object) and can do whatever we wish with it. In this case, we use the method send_data to return the received data to the caller, with some extra text added in. And if the user sends the word “quit,” we’ll close the connection with (naturally) close_connection. (Notice that closing the connection doesn’t terminate the processing loop, or change the fact that your echo server is still accepting connections!)

Questions and Futures

Would it be useful for EventMachine to incorporate the Observer pattern and make use of the corresponding Ruby observer package? Interesting thought.

Attributes

reactor_thread[R]

Exposed to allow joining on the thread, when run in a multithreaded environment. Performing other actions on the thread has undefined semantics.

threadpool_size[RW]

Size of the ::defer threadpool (defaults to 20)

Public Class Methods

Callback(object = nil, method = nil, &blk) click to toggle source

Utility method for coercing arguments to an object that responds to call Accepts an object and a method name to send to, or a block, or an object that responds to call.

cb = EM.Callback{ |msg| puts(msg) }
cb.call('hello world')

cb = EM.Callback(Object, :puts)
cb.call('hello world')

cb = EM.Callback(proc{ |msg| puts(msg) })
cb.call('hello world')
# File lib/em/callback.rb, line 15
def self.Callback(object = nil, method = nil, &blk)
  if object && method
    lambda { |*args| object.send method, *args }
  else
    if object.respond_to? :call
      object
    else 
      blk || raise(ArgumentError)
    end
  end
end
add_periodic_timer(*args, &block) click to toggle source

EventMachine#add_periodic_timer adds a periodic timer to the event loop. It takes the same parameters as the one-shot timer method, EventMachine#add_timer. This method schedules execution of the given block repeatedly, at intervals of time at least as great as the number of seconds given in the first parameter to the call.

Usage example

The following sample program will write a dollar-sign to stderr every five seconds. (Of course if the program defined network clients and/or servers, they would be doing their work while the periodic timer is counting off.)

EventMachine::run {
  EventMachine::add_periodic_timer( 5 ) { $stderr.write "$" }
}

Also see EventMachine::PeriodicTimer

# File lib/eventmachine.rb, line 400
def self.add_periodic_timer *args, &block
  interval = args.shift
  code = args.shift || block

  EventMachine::PeriodicTimer.new(interval, code)
end
add_timer(*args, &block) click to toggle source

EventMachine#add_timer adds a one-shot timer to the event loop. Call it with one or two parameters. The first parameters is a delay-time expressed in seconds (not milliseconds). The second parameter, if present, must be a proc object. If a proc object is not given, then you can also simply pass a block to the method call.

EventMachine#add_timer may be called from the block passed to EventMachine#run or from any callback method. It schedules execution of the proc or block passed to ::add_timer, after the passage of an interval of time equal to at least the number of seconds specified in the first parameter to the call.

EventMachine#add_timer is a non-blocking call. Callbacks can and will be called during the interval of time that the timer is in effect. There is no built-in limit to the number of timers that can be outstanding at any given time.

Usage example

This example shows how easy timers are to use. Observe that two timers are initiated simultaneously. Also, notice that the event loop will continue to run even after the second timer event is processed, since there was no call to EventMachine#stop_event_loop. There will be no activity, of course, since no network clients or servers are defined. Stop the program with Ctrl-C.

EventMachine::run {
  puts "Starting the run now: #{Time.now}"
  EventMachine::add_timer 5, proc { puts "Executing timer event: #{Time.now}" }
  EventMachine::add_timer( 10 ) { puts "Executing timer event: #{Time.now}" }
}

Also see EventMachine::Timer

# File lib/eventmachine.rb, line 370
def self.add_timer *args, &block
  interval = args.shift
  code = args.shift || block
  if code
    # check too many timers!
    s = add_oneshot_timer((interval.to_f * 1000).to_i)
    @timers[s] = code
    s
  end
end
attach(io, handler=nil, *args, &blk) click to toggle source

Attaches an IO object or file descriptor to the eventloop as a regular connection. The file descriptor will be set as non-blocking, and EventMachine will process receive_data and send_data events on it as it would for any other connection.

To watch a fd instead, use ::watch, which will not alter the state of the socket and fire notify_readable and notify_writable events instead.

# File lib/eventmachine.rb, line 778
def EventMachine::attach io, handler=nil, *args, &blk
  attach_io io, false, handler, *args, &blk
end
bind_connect(bind_addr, bind_port, server, port=nil, handler=nil, *args) { |c| ... } click to toggle source

::bind_connect is like ::connect, but allows for a local address/port to bind the connection to.

# File lib/eventmachine.rb, line 697
def self.bind_connect bind_addr, bind_port, server, port=nil, handler=nil, *args
  begin
    port = Integer(port)
  rescue ArgumentError, TypeError
    # there was no port, so server must be a unix domain socket
    # the port argument is actually the handler, and the handler is one of the args
    args.unshift handler if handler
    handler = port
    port = nil
  end if port

  klass = klass_from_handler(Connection, handler, *args)

  s = if port
        if bind_addr
          bind_connect_server bind_addr, bind_port.to_i, server, port
        else
          connect_server server, port
        end
      else
        connect_unix_server server
      end

  c = klass.new s, *args
  @conns[s] = c
  block_given? and yield c
  c
end
cancel_timer(timer_or_sig) click to toggle source

Cancel a timer using its signature. You can also use EventMachine::Timer#cancel

# File lib/eventmachine.rb, line 409
def self.cancel_timer timer_or_sig
  if timer_or_sig.respond_to? :cancel
    timer_or_sig.cancel
  else
    @timers[timer_or_sig] = false if @timers.has_key?(timer_or_sig)
  end
end
connect(server, port=nil, handler=nil, *args, &blk) click to toggle source

EventMachine#connect initiates a TCP connection to a remote server and sets up event-handling for the connection. You can call EventMachine#connect in the block supplied to EventMachine#run or in any callback method.

EventMachine#connect takes the IP address (or hostname) and port of the remote server you want to connect to. It also takes an optional handler Module which you must define, that contains the callbacks that will be invoked by the event loop on behalf of the connection.

See the description of EventMachine#start_server for a discussion of the handler Module. All of the details given in that description apply for connections created with EventMachine#connect.

Usage Example

Here’s a program which connects to a web server, sends a naive request, parses the HTTP header of the response, and then (antisocially) ends the event loop, which automatically drops the connection (and incidentally calls the connection’s unbind method).

module DumbHttpClient
  def post_init
    send_data "GET / HTTP/1.1\r\nHost: _\r\n\r\n"
    @data = ""
    @parsed = false
  end

  def receive_data data
    @data << data
    if !@parsed and @data =~ %r[\n][\r]*[\n]/
      @parsed = true
      puts "RECEIVED HTTP HEADER:"
      $`.each {|line| puts ">>> #{line}" }

      puts "Now we'll terminate the loop, which will also close the connection"
      EventMachine::stop_event_loop
    end
  end

  def unbind
    puts "A connection has terminated"
  end
end

EventMachine::run {
  EventMachine::connect "www.bayshorenetworks.com", 80, DumbHttpClient
}
puts "The event loop has ended"

There are times when it’s more convenient to define a protocol handler as a Class rather than a Module. Here’s how to do this:

class MyProtocolHandler < EventMachine::Connection
  def initialize *args
    super
    # whatever else you want to do here
  end

  #.......your other class code
end

If you do this, then an instance of your class will be instantiated to handle every network connection created by your code or accepted by servers that you create. If you redefine post_init in your protocol-handler class, your post_init method will be called inside the call to super that you will make in your initialize method (if you provide one).

# File lib/eventmachine.rb, line 691
def self.connect server, port=nil, handler=nil, *args, &blk
  bind_connect nil, nil, server, port, handler, *args, &blk
end
connect_unix_domain(socketname, *args, &blk) click to toggle source

Make a connection to a Unix-domain socket. This is not implemented on Windows platforms. The parameter socketname is a String which identifies the Unix-domain socket you want to connect to. socketname is the name of a file on your local system, and in most cases is a fully-qualified path name. Make sure that your process has enough local permissions to open the Unix-domain socket. See also the documentation for connect. This method behaves like connect in all respects except for the fact that it connects to a local Unix-domain socket rather than a TCP socket.

Note that this method is simply an alias for connect, which can connect to both TCP and Unix-domain sockets

# File lib/eventmachine.rb, line 845
def self.connect_unix_domain socketname, *args, &blk
  connect socketname, *args, &blk
end
connection_count() click to toggle source

Returns the total number of connections (file descriptors) currently held by the reactor. Note that a tick must pass after the ‘initiation’ of a connection for this number to increment. It’s usually accurate, but don’t rely on the exact precision of this number unless you really know EM internals.

For example, $count will be 0 in this case:

EM.run {
  EM.connect("rubyeventmachine.com", 80)
  $count = EM.connection_count
}

In this example, $count will be 1 since the connection has been established in the next loop of the reactor.

EM.run {
  EM.connect("rubyeventmachine.com", 80)
  EM.next_tick {
    $count = EM.connection_count
  }
}
# File lib/eventmachine.rb, line 974
def self.connection_count
  self.get_connection_count
end
defer(op = nil, callback = nil, &blk) click to toggle source

defer is for integrating blocking operations into EventMachine’s control flow. Call defer with one or two blocks, as shown below (the second block is optional):

operation = proc {
  # perform a long-running operation here, such as a database query.
  "result" # as usual, the last expression evaluated in the block will be the return value.
}
callback = proc {|result|
  # do something with result here, such as send it back to a network client.
}

EventMachine.defer( operation, callback )

The action of defer is to take the block specified in the first parameter (the “operation”) and schedule it for asynchronous execution on an internal thread pool maintained by EventMachine. When the operation completes, it will pass the result computed by the block (if any) back to the EventMachine reactor. Then, EventMachine calls the block specified in the second parameter to defer (the “callback”), as part of its normal, synchronous event handling loop. The result computed by the operation block is passed as a parameter to the callback. You may omit the callback parameter if you don’t need to execute any code after the operation completes.

Caveats

Note carefully that the code in your deferred operation will be executed on a separate thread from the main EventMachine processing and all other Ruby threads that may exist in your program. Also, multiple deferred operations may be running at once! Therefore, you are responsible for ensuring that your operation code is threadsafe. [Need more explanation and examples.] Don’t write a deferred operation that will block forever. If so, the current implementation will not detect the problem, and the thread will never be returned to the pool. EventMachine limits the number of threads in its pool, so if you do this enough times, your subsequent deferred operations won’t get a chance to run. [We might put in a timer to detect this problem.]

# File lib/eventmachine.rb, line 1043
def self.defer op = nil, callback = nil, &blk
  unless @threadpool
    require 'thread'
    @threadpool = []
    @threadqueue = ::Queue.new
    @resultqueue = ::Queue.new
    spawn_threadpool
  end

  @threadqueue << [op||blk,callback]
end
disable_proxy(from) click to toggle source

::disable_proxy takes just one argument, a Connection that has proxying enabled via enable_proxy. Calling this method will remove that functionality and your connection will begin receiving data via receive_data again.

# File lib/eventmachine.rb, line 1379
def self.disable_proxy(from)
  EM::stop_proxy(from.signature)
end
enable_proxy(from, to, bufsize=0) click to toggle source

::enable_proxy allows for direct writing of incoming data back out to another descriptor, at the C++ level in the reactor. This is especially useful for proxies where high performance is required. Propogating data from a server response all the way up to Ruby, and then back down to the reactor to be sent back to the client, is often unnecessary and incurs a significant performance decrease.

The two arguments are Connections, ‘from’ and ‘to’. ‘from’ is the connection whose inbound data you want relayed back out. ‘to’ is the connection to write it to.

Once you call this method, the ‘from’ connection will no longer get receive_data callbacks from the reactor, except in the case that ‘to’ connection has already closed when attempting to write to it. You can see in the example, that proxy_target_unbound will be called when this occurs. After that, further incoming data will be passed into receive_data as normal.

Note also that this feature supports different types of descriptors - TCP, UDP, and pipes. You can relay data from one kind to another.

Example:

module ProxyConnection
  def initialize(client, request)
    @client, @request = client, request
  end

  def post_init
    EM::enable_proxy(self, @client)
  end

  def connection_completed
    send_data @request
  end

  def proxy_target_unbound
    close_connection
  end

  def unbind
    @client.close_connection_after_writing
  end
end

module ProxyServer
  def receive_data(data)
    (@buf ||= "") << data
    if @buf =~ %r\r\n\r\n/ # all http headers received
      EM.connect("10.0.0.15", 80, ProxyConnection, self, data)
    end
  end
end

EM.run {
  EM.start_server("127.0.0.1", 8080, ProxyServer)
}
# File lib/eventmachine.rb, line 1372
def self.enable_proxy(from, to, bufsize=0)
  EM::start_proxy(from.signature, to.signature, bufsize)
end
error_handler(cb = nil, &blk) click to toggle source

Catch-all for errors raised during event loop callbacks.

EM.error_handler{ |e|
  puts "Error raised during event loop: #{e.message}"
}
# File lib/eventmachine.rb, line 1312
def self.error_handler cb = nil, &blk
  if cb or blk
    @error_handler = cb || blk
  elsif instance_variable_defined? :@error_handler
    remove_instance_variable :@error_handler
  end
end
fork_reactor(&block) click to toggle source

::fork_reactor forks a new process and calls EM#run inside of it, passing your block.

# File lib/eventmachine.rb, line 322
def self.fork_reactor &block
  Kernel.fork do
    if self.reactor_running?
      self.stop_event_loop
      self.release_machine
      self.instance_variable_set( '@reactor_running', false )
    end
    self.run block
  end
end
get_max_timers() click to toggle source

Gets the current maximum number of allowed timers

# File lib/eventmachine.rb, line 950
def self.get_max_timers
  get_max_timer_count
end
heartbeat_interval() click to toggle source

Retrieve the heartbeat interval. This is how often EventMachine will check for dead connections that have had an InactivityTimeout set via EventMachine::Connection#set_comm_inactivity_timeout. Default is 2 seconds.

# File lib/eventmachine.rb, line 1386
def self.heartbeat_interval
  EM::get_heartbeat_interval
end
heartbeat_interval=(time) click to toggle source

Set the heartbeat interval. This is how often EventMachine will check for dead connections that have had an InactivityTimeout set via EventMachine::Connection#set_comm_inactivity_timeout. Takes a Numeric number of seconds. Default is 2.

# File lib/eventmachine.rb, line 1393
def self.heartbeat_interval= (time)
  EM::set_heartbeat_interval time.to_f
end
next_tick(pr=nil, &block) click to toggle source

Schedules a proc for execution immediately after the next “turn” through the reactor core. An advanced technique, this can be useful for improving memory management and/or application responsiveness, especially when scheduling large amounts of data for writing to a network connection. TODO, we need a FAQ entry on this subject.

next_tick takes either a single argument (which must be a Proc) or a block.

# File lib/eventmachine.rb, line 1092
def self.next_tick pr=nil, &block
  raise ArgumentError, "no proc or block given" unless ((pr && pr.respond_to?(:call)) or block)
  @next_tick_mutex.synchronize do
    (@next_tick_queue ||= []) << ( pr || block )
  end
  signal_loopbreak if reactor_running?
end
open_datagram_socket(address, port, handler=nil, *args) { |c| ... } click to toggle source

EventMachine#open_datagram_socket is for support of UDP-based protocols. Its usage is similar to that of EventMachine#start_server. It takes three parameters: an IP address (which must be valid on the machine which executes the method), a port number, and an optional Module name which will handle the data. This method will create a new UDP (datagram) socket and bind it to the address and port that you specify. The normal callbacks (see EventMachine#start_server) will be called as events of interest occur on the newly-created socket, but there are some differences in how they behave.

EventMachine::Connection#receive_data will be called when a datagram packet is received on the socket, but unlike TCP sockets, the message boundaries of the received data will be respected. In other words, if the remote peer sent you a datagram of a particular size, you may rely on EventMachine::Connection#receive_data to give you the exact data in the packet, with the original data length. Also observe that EventMachine::Connection#receive_data may be called with a zero-length data payload, since empty datagrams are permitted in UDP.

EventMachine::Connection#send_data is available with UDP packets as with TCP, but there is an important difference. Because UDP communications are connectionless, there is no implicit recipient for the packets you send. Ordinarily you must specify the recipient for each packet you send. However, EventMachine provides for the typical pattern of receiving a UDP datagram from a remote peer, performing some operation, and then sending one or more packets in response to the same remote peer. To support this model easily, just use EventMachine::Connection#send_data in the code that you supply for Connection:receive_data. EventMachine will provide an implicit return address for any messages sent to EventMachine::Connection#send_data within the context of a EventMachine::Connection#receive_data callback, and your response will automatically go to the correct remote peer. (TODO: Example-code needed!)

Observe that the port number that you supply to EventMachine#open_datagram_socket may be zero. In this case, EventMachine will create a UDP socket that is bound to an ephemeral (not well-known) port. This is not appropriate for servers that must publish a well-known port to which remote peers may send datagrams. But it can be useful for clients that send datagrams to other servers. If you do this, you will receive any responses from the remote servers through the normal EventMachine::Connection#receive_data callback. Observe that you will probably have issues with firewalls blocking the ephemeral port numbers, so this technique is most appropriate for LANs. (TODO: Need an example!)

If you wish to send datagrams to arbitrary remote peers (not necessarily ones that have sent data to which you are responding), then see EventMachine::Connection#send_datagram.

DO NOT call send_data from a datagram socket outside of a receive_data method. Use send_datagram. If you do use send_data outside of a receive_data method, you’ll get a confusing error because there is no “peer,” as send_data requires. (Inside of receive_data, send_data “fakes” the peer as described above.)

# File lib/eventmachine.rb, line 913
def self.open_datagram_socket address, port, handler=nil, *args
  klass = klass_from_handler(Connection, handler, *args)
  s = open_udp_socket address, port.to_i
  c = klass.new s, *args
  @conns[s] = c
  block_given? and yield c
  c
end
open_keyboard(handler=nil, *args) { |c| ... } click to toggle source

(Experimental)

# File lib/eventmachine.rb, line 1191
def self.open_keyboard handler=nil, *args
  klass = klass_from_handler(Connection, handler, *args)

  s = read_keyboard
  c = klass.new s, *args
  @conns[s] = c
  block_given? and yield c
  c
end
popen(cmd, handler=nil, *args) { |c| ... } click to toggle source

Run an external process. This does not currently work on Windows.

module RubyCounter
  def post_init
    # count up to 5
    send_data "5\n"
  end
  def receive_data data
    puts "ruby sent me: #{data}"
  end
  def unbind
    puts "ruby died with exit status: #{get_status.exitstatus}"
  end
end

EM.run{
  EM.popen("ruby -e' $stdout.sync = true; gets.to_i.times{ |i| puts i+1; sleep 1 } '", RubyCounter)
}

Also see EventMachine::DeferrableChildProcess and ::system

# File lib/eventmachine.rb, line 1161
def self.popen cmd, handler=nil, *args
  klass = klass_from_handler(Connection, handler, *args)
  w = Shellwords::shellwords( cmd )
  w.unshift( w.first ) if w.first
  s = invoke_popen( w )
  c = klass.new s, *args
  @conns[s] = c
  yield(c) if block_given?
  c
end
reactor_running?() click to toggle source

Tells you whether the EventMachine reactor loop is currently running. Returns true or false. Useful when writing libraries that want to run event-driven code, but may be running in programs that are already event-driven. In such cases, if EventMachine#reactor_running? returns false, your code can invoke EventMachine#run and run your application code inside the block passed to that method. If EventMachine#reactor_running? returns true, just execute your event-aware code.

This method is necessary because calling EventMachine#run inside of another call to EventMachine#run generates a fatal error.

# File lib/eventmachine.rb, line 1183
def self.reactor_running?
  (@reactor_running || false)
end
reactor_thread?() click to toggle source

Returns true if the calling thread is the same thread as the reactor.

# File lib/eventmachine.rb, line 301
def self.reactor_thread?
  Thread.current == @reactor_thread
end
run(blk=nil, tail=nil, &block) click to toggle source

::run initializes and runs an event loop. This method only returns if user-callback code calls stop_event_loop. Use the supplied block to define your clients and servers. The block is called by ::run immediately after initializing its internal event loop but before running the loop. Therefore this block is the right place to call ::start_server if you want to accept connections from remote clients.

For programs that are structured as servers, it’s usually appropriate to start an event loop by calling ::run, and let it run forever. It’s also possible to use ::run to make a single client-connection to a remote server, process the data flow from that single connection, and then call ::stop_event_loop to force ::run to return. Your program will then continue from the point immediately following the call to ::run.

You can of course do both client and servers simultaneously in the same program. One of the strengths of the event-driven programming model is that the handling of network events on many different connections will be interleaved, and scheduled according to the actual events themselves. This maximizes efficiency.

Server usage example

See ::start_server

Client usage example

See ::connect

# File lib/eventmachine.rb, line 236
def self.run blk=nil, tail=nil, &block
  @tails ||= []
  tail and @tails.unshift(tail)

  if reactor_running?
    (b = blk || block) and b.call # next_tick(b)
  else
    @conns = {}
    @acceptors = {}
    @timers = {}
    @wrapped_exception = nil
    @next_tick_queue ||= []
    begin
      @reactor_running = true
      initialize_event_machine
      (b = blk || block) and add_timer(0, b)
      if @next_tick_queue && !@next_tick_queue.empty?
        add_timer(0) { signal_loopbreak }
      end
      @reactor_thread = Thread.current
      run_machine
    ensure
      until @tails.empty?
        @tails.pop.call
      end

      begin
        release_machine
      ensure
        if @threadpool
          @threadpool.each { |t| t.exit }
          @threadpool.each do |t|
            next unless t.alive?
            # ruby 1.9 has no kill!
            t.respond_to?(:kill!) ? t.kill! : t.kill
          end
          @threadqueue = nil
          @resultqueue = nil
          @threadpool = nil
        end

        @next_tick_queue = nil
      end
      @reactor_running = false
      @reactor_thread = nil
    end

    raise @wrapped_exception if @wrapped_exception
  end
end
run_block(&block) click to toggle source

Sugars a common use case. Will pass the given block to run, but will terminate the reactor loop and exit the function as soon as the code in the block completes. (Normally, run keeps running indefinitely, even after the block supplied to it finishes running, until user code calls stop.)

# File lib/eventmachine.rb, line 292
def self.run_block &block
  pr = proc {
    block.call
    EventMachine::stop
  }
  run(&pr)
end
schedule(*a, &b) click to toggle source

Runs the given callback on the reactor thread, or immediately if called from the reactor thread. Accepts the same arguments as EM::Callback

# File lib/eventmachine.rb, line 307
def self.schedule(*a, &b)
  cb = Callback(*a, &b)
  if reactor_running? && reactor_thread?
    cb.call
  else
    next_tick { cb.call }
  end
end
set_descriptor_table_size(n_descriptors=nil) click to toggle source

Sets the maximum number of file or socket descriptors that your process may open. You can pass this method an integer specifying the new size of the descriptor table. Returns the new descriptor-table size, which may be less than the number you requested. If you call this method with no arguments, it will simply return the current size of the descriptor table without attempting to change it.

The new limit on open descriptors ONLY applies to sockets and other descriptors that belong to EventMachine. It has NO EFFECT on the number of descriptors you can create in ordinary Ruby code.

Not available on all platforms. Increasing the number of descriptors beyond its default limit usually requires superuser privileges. (See set_effective_user for a way to drop superuser privileges while your program is running.)

# File lib/eventmachine.rb, line 1131
def self.set_descriptor_table_size n_descriptors=nil
  EventMachine::set_rlimit_nofile n_descriptors
end
set_effective_user(username) click to toggle source

A wrapper over the setuid system call. Particularly useful when opening a network server on a privileged port because you can use this call to drop privileges after opening the port. Also very useful after a call to set_descriptor_table_size, which generally requires that you start your process with root privileges.

This method has no effective implementation on Windows or in the pure-Ruby implementation of EventMachine. Call set_effective_user by passing it a string containing the effective name of the user whose privilege-level your process should attain. This method is intended for use in enforcing security requirements, consequently it will throw a fatal error and end your program if it fails.

# File lib/eventmachine.rb, line 1112
def self.set_effective_user username
  EventMachine::setuid_string username
end
set_max_timers(ct) click to toggle source

Sets the maximum number of timers and periodic timers that may be outstanding at any given time. You only need to call set_max_timers if you need more than the default number of timers, which on most platforms is 1000. Call this method before calling EventMachine#run.

# File lib/eventmachine.rb, line 944
def self.set_max_timers ct
  set_max_timer_count ct
end
set_quantum(mills) click to toggle source

For advanced users. This function sets the default timer granularity, which by default is slightly smaller than 100 milliseconds. Call this function to set a higher or lower granularity. The function affects the behavior of add_timer and add_periodic_timer. Most applications will not need to call this function.

The argument is a number of milliseconds. Avoid setting the quantum to very low values because that may reduce performance under some extreme conditions. We recommend that you not set a quantum lower than 10.

You may only call this function while an EventMachine loop is running (that is, after a call to EventMachine#run and before a subsequent call to EventMachine#stop).

# File lib/eventmachine.rb, line 935
def self.set_quantum mills
  set_timer_quantum mills.to_i
end
spawn(&block) click to toggle source

Spawn an erlang-style process

# File lib/em/spawnable.rb, line 72
def self.spawn &block
  s = SpawnedProcess.new
  s.set_receiver block
  s
end
start_server(server, port=nil, handler=nil, *args, &block) click to toggle source

::start_server initiates a TCP server (socket acceptor) on the specified IP address and port. The IP address must be valid on the machine where the program runs, and the process must be privileged enough to listen on the specified port (on Unix-like systems, superuser privileges are usually required to listen on any port lower than 1024). Only one listener may be running on any given address/port combination. ::start_server will fail if the given address and port are already listening on the machine, either because of a prior call to ::start_server or some unrelated process running on the machine. If ::start_server succeeds, the new network listener becomes active immediately and starts accepting connections from remote peers, and these connections generate callback events that are processed by the code specified in the handler parameter to start_server.

The optional handler which is passed to ::start_server is the key to EventMachine’s ability to handle particular network protocols. The handler parameter passed to ::start_server must be a Ruby Module that you must define. When the network server that is started by ::start_server accepts a new connection, it instantiates a new object of an anonymous class that is inherited from EventMachine::Connection, into which the methods from your handler have been mixed. Your handler module may redefine any of the methods in EventMachine::Connection in order to implement the specific behavior of the network protocol.

Callbacks invoked in response to network events always take place within the execution context of the object derived from EventMachine::Connection extended by your handler module. There is one object per connection, and all of the callbacks invoked for a particular connection take the form of instance methods called against the corresponding EventMachine::Connection object. Therefore, you are free to define whatever instance variables you wish, in order to contain the per-connection state required by the network protocol you are implementing.

::start_server is often called inside the block passed to ::run, but it can be called from any EventMachine callback. ::start_server will fail unless the EventMachine event loop is currently running (which is why it’s often called in the block suppled to ::run).

You may call ::start_server any number of times to start up network listeners on different address/port combinations. The servers will all run simultaneously. More interestingly, each individual call to ::start_server can specify a different handler module and thus implement a different network protocol from all the others.

Usage example

Here is an example of a server that counts lines of input from the remote peer and sends back the total number of lines received, after each line. Try the example with more than one client connection opened via telnet, and you will see that the line count increments independently on each of the client connections. Also very important to note, is that the handler for the receive_data function, which our handler redefines, may not assume that the data it receives observes any kind of message boundaries. Also, to use this example, be sure to change the server and port parameters to the ::start_server call to values appropriate for your environment.

require 'rubygems'
require 'eventmachine'

module LineCounter
  MaxLinesPerConnection = 10

  def post_init
    puts "Received a new connection"
    @data_received = ""
    @line_count = 0
  end

  def receive_data data
    @data_received << data
    while @data_received.slice!( %r^[^\n]*[\n]/ )
      @line_count += 1
      send_data "received #{@line_count} lines so far\r\n"
      @line_count == MaxLinesPerConnection and close_connection_after_writing
    end
  end
end

EventMachine::run {
  host,port = "192.168.0.100", 8090
  EventMachine::start_server host, port, LineCounter
  puts "Now accepting connections on address #{host}, port #{port}..."
  EventMachine::add_periodic_timer( 10 ) { $stderr.write "*" }
}
# File lib/eventmachine.rb, line 558
def self.start_server server, port=nil, handler=nil, *args, &block
  begin
    port = Integer(port)
  rescue ArgumentError, TypeError
    # there was no port, so server must be a unix domain socket
    # the port argument is actually the handler, and the handler is one of the args
    args.unshift handler if handler
    handler = port
    port = nil
  end if port

  klass = klass_from_handler(Connection, handler, *args)

  s = if port
        start_tcp_server server, port
      else
        start_unix_server server
      end
  @acceptors[s] = [klass,args,block]
  s
end
start_unix_domain_server(filename, *args, &block) click to toggle source

Start a Unix-domain server

Note that this is an alias for ::start_server, which can be used to start both TCP and Unix-domain servers

# File lib/eventmachine.rb, line 594
def self.start_unix_domain_server filename, *args, &block
  start_server filename, *args, &block
end
stop_event_loop() click to toggle source

::stop_event_loop may called from within a callback method while EventMachine’s processing loop is running. It causes the processing loop to stop executing, which will cause all open connections and accepting servers to be run down and closed. Callbacks for connection-termination will be called as part of the processing of stop_event_loop. (There currently is no option to panic-stop the loop without closing connections.) When all of this processing is complete, the call to ::run which started the processing loop will return and program flow will resume from the statement following ::run call.

Usage example

require 'rubygems'
require 'eventmachine'

module Redmond
  def post_init
    puts "We're sending a dumb HTTP request to the remote peer."
    send_data "GET / HTTP/1.1\r\nHost: www.microsoft.com\r\n\r\n"
  end

  def receive_data data
    puts "We received #{data.length} bytes from the remote peer."
    puts "We're going to stop the event loop now."
    EventMachine::stop_event_loop
  end

  def unbind
    puts "A connection has terminated."
  end
end

puts "We're starting the event loop now."
EventMachine::run {
  EventMachine::connect "www.microsoft.com", 80, Redmond
}
puts "The event loop has stopped."

This program will produce approximately the following output:

We're starting the event loop now.
We're sending a dumb HTTP request to the remote peer.
We received 1440 bytes from the remote peer.
We're going to stop the event loop now.
A connection has terminated.
The event loop has stopped.
# File lib/eventmachine.rb, line 468
def self.stop_event_loop
  EventMachine::stop
end
stop_server(signature) click to toggle source

Stop a TCP server socket that was started with EventMachine#start_server.

# File lib/eventmachine.rb, line 586
def self.stop_server signature
  EventMachine::stop_tcp_server signature
end
system(cmd, *args, &cb) click to toggle source

::system is a simple wrapper for ::popen. It is similar to Kernel::system, but requires a single string argument for the command and performs no shell expansion.

The block or proc passed to ::system is called with two arguments: the output generated by the command, and a Process::Status that contains information about the command’s execution.

EM.run{
  EM.system('ls'){ |output,status| puts output if status.exitstatus == 0 }
}

You can also supply an additional proc to send some data to the process:

EM.run{
  EM.system('sh', proc{ |process|
    process.send_data("echo hello\n")
    process.send_data("exit\n")
  }, proc{ |out,status|
    puts(out)
  })
}

Like ::popen, ::system currently does not work on windows. It returns the pid of the spawned process.

# File lib/em/processes.rb, line 108
def EventMachine::system cmd, *args, &cb
  cb ||= args.pop if args.last.is_a? Proc
  init = args.pop if args.last.is_a? Proc

  # merge remaining arguments into the command
  cmd = ([cmd] + args.map{|a|a.to_s.dump}).join(' ')

  EM.get_subprocess_pid(EM.popen(cmd, SystemCmd, cb) do |c|
    init[c] if init
  end.signature)
end
watch(io, handler=nil, *args, &blk) click to toggle source

::watch registers a given file descriptor or IO object with the eventloop. The file descriptor will not be modified (it will remain blocking or non-blocking).

The eventloop can be used to process readable and writable events on the file descriptor, using EventMachine::Connection#notify_readable= and EventMachine::Connection#notify_writable=

EventMachine::Connection#notify_readable? and EventMachine::Connection#notify_writable? can be used to check what events are enabled on the connection.

To detach the file descriptor, use EventMachine::Connection#detach

Usage Example

module SimpleHttpClient
  def notify_readable
    header = @io.readline

    if header == "\r\n"
      # detach returns the file descriptor number (fd == @io.fileno)
      fd = detach
    end
  rescue EOFError
    detach
  end

  def unbind
    EM.next_tick do
      # socket is detached from the eventloop, but still open
      data = @io.read
    end
  end
end

EM.run{
  $sock = TCPSocket.new('site.com', 80)
  $sock.write("GET / HTTP/1.0\r\n\r\n")
  conn = EM.watch $sock, SimpleHttpClient
  conn.notify_readable = true
}
# File lib/eventmachine.rb, line 768
def EventMachine::watch io, handler=nil, *args, &blk
  attach_io io, true, handler, *args, &blk
end
watch_file(filename, handler=nil, *args) { |c| ... } click to toggle source

EventMachine’s file monitoring API. Currently supported are the following events on individual files, using inotify on Linux systems, and kqueue for OSX/BSD:

  • File modified (written to)

  • File moved/renamed

  • File deleted

::watch_file takes a filename and a handler Module containing your custom callback methods. This will setup the low level monitoring on the specified file, and create a new EventMachine::FileWatch object with your Module mixed in. FileWatch is a subclass of EM::Connection, so callbacks on this object work in the familiar way. The callbacks that will be fired by EventMachine are:

  • file_modified

  • file_moved

  • file_deleted

You can access the filename being monitored from within this object using EventMachine::FileWatch#path.

When a file is deleted, EventMachine::FileWatch#stop_watching will be called after your file_deleted callback, to clean up the underlying monitoring and remove EventMachine’s reference to the now-useless FileWatch. This will in turn call unbind, if you wish to use it.

The corresponding system-level Errno will be raised when attempting to monitor non-existent files, files with wrong permissions, or if an error occurs dealing with inotify/kqueue.

Usage example:

Make sure we have a file to monitor:
$ echo "bar" > %rtmp/foo

module Handler
  def file_modified
    puts "#{path} modified"
  end

  def file_moved
    puts "#{path} moved"
  end

  def file_deleted
    puts "#{path} deleted"
  end

  def unbind
    puts "#{path} monitoring ceased"
  end
end

EM.kqueue = true if EM.kqueue? # file watching requires kqueue on OSX

EM.run {
  EM.watch_file("/tmp/foo", Handler)
}

$ echo "baz" >> %rtmp/foo    =>    "/tmp/foo modified"
$ mv /tmp/foo %rtmp/of      =>    "/tmp/foo moved"
$ rm /tmp/oof               =>    "/tmp/foo deleted"
                            =>    "/tmp/foo monitoring ceased"

Note that we have not implemented the ability to pick up on the new filename after a rename. Calling path will always return the filename you originally used.

# File lib/eventmachine.rb, line 1263
def self.watch_file(filename, handler=nil, *args)
  klass = klass_from_handler(FileWatch, handler, *args)

  s = EM::watch_filename(filename)
  c = klass.new s, *args
  # we have to set the path like this because of how Connection.new works
  c.instance_variable_set("@path", filename)
  @conns[s] = c
  block_given? and yield c
  c
end
watch_process(pid, handler=nil, *args) { |c| ... } click to toggle source

EventMachine’s process monitoring API. Currently supported using kqueue for OSX/BSD.

Usage example:

module ProcessWatcher
  def process_exited
    put 'the forked child died!'
  end
end

pid = fork{ sleep }

EM.run{
  EM.watch_process(pid, ProcessWatcher)
  EM.add_timer(1){ Process.kill('TERM', pid) }
}
# File lib/eventmachine.rb, line 1292
def self.watch_process(pid, handler=nil, *args)
  pid = pid.to_i

  klass = klass_from_handler(ProcessWatch, handler, *args)

  s = EM::watch_pid(pid)
  c = klass.new s, *args
  # we have to set the path like this because of how Connection.new works
  c.instance_variable_set("@pid", pid)
  @conns[s] = c
  block_given? and yield c
  c
end