connection limiting

4 files changed, 220 insertions, 30 deletions

diff --git a/lib/net/ssh/multi/channel_proxy.rb b/lib/net/ssh/multi/channel_proxy.rb
index 99f7986..df5c04c 100644
--- a/lib/net/ssh/multi/channel_proxy.rb
+++ b/lib/net/ssh/multi/channel_proxy.rb
@@ -1,13 +1,32 @@
 module Net; module SSH; module Multi
+
+  # The ChannelProxy is a delegate class that represents a channel that has
+  # not yet been opened. It is only used when Net::SSH::Multi is running with
+  # with a concurrent connections limit (see Net::SSH::Multi::Session#concurrent_connections).
+  #
+  # You'll never need to instantiate one of these directly, and will probably
+  # (if all goes well!) never even notice when one of these is in use. Essentially,
+  # it is spawned by a Net::SSH::Multi::PendingConnection when the pending
+  # connection is asked to open a channel. Any actions performed on the
+  # channel proxy will then be recorded, until a real channel is set as the
+  # delegate (see #delegate_to). At that point, all recorded actions will be
+  # replayed on the channel, and any subsequent actions will be immediately
+  # delegated to the channel.
   class ChannelProxy
+    # This is the "on confirm" callback that gets called when the real channel
+    # is opened.
     attr_reader :on_confirm
 
+    # Instantiates a new channel proxy with the given +on_confirm+ callback.
     def initialize(&on_confirm)
       @on_confirm = on_confirm
       @recordings = []
       @channel = nil
     end
 
+    # Instructs the proxy to delegate all further actions to the given +channel+
+    # (which must be an instance of Net::SSH::Connection::Channel). All recorded
+    # actions are immediately replayed, in order, against the delegate channel.
     def delegate_to(channel)
       @channel = channel
       @recordings.each do |sym, args, block|
@@ -15,6 +34,10 @@ module Net; module SSH; module Multi
       end
     end
 
+    # If a channel delegate has been specified (see #delegate_to), the method
+    # will be immediately sent to the delegate. Otherwise, the call is added
+    # to the list of recorded method calls, to be played back when a delegate
+    # is specified.
     def method_missing(sym, *args, &block)
       if @channel
         @channel.__send__(sym, *args, &block)
@@ -23,4 +46,5 @@ module Net; module SSH; module Multi
       end
     end
   end
+
 end; end; end
\ No newline at end of file
diff --git a/lib/net/ssh/multi/pending_connection.rb b/lib/net/ssh/multi/pending_connection.rb
index fcebcba..6af0fac 100644
--- a/lib/net/ssh/multi/pending_connection.rb
+++ b/lib/net/ssh/multi/pending_connection.rb
@@ -1,7 +1,23 @@
 require 'net/ssh/multi/channel_proxy'
 
 module Net; module SSH; module Multi
+
+  # A PendingConnection instance mimics a Net::SSH::Connection::Session instance,
+  # without actually being an open connection to a server. It is used by
+  # Net::SSH::Multi::Session when a concurrent connection limit is in effect,
+  # so that a server can hang on to a "connection" that isn't really a connection.
+  #
+  # Any requests against this connection (like #open_channel or #send_global_request)
+  # are not actually sent, but are added to a list of recordings. When the real
+  # session is opened and replaces this pending connection, all recorded actions
+  # will be replayed against that session.
+  #
+  # You'll never need to initialize one of these directly, and (if all goes well!)
+  # should never even notice that one of these is in use. Net::SSH::Multi::Session
+  # will instantiate these as needed, and only when there is a concurrent
+  # connection limit.
   class PendingConnection
+    # Represents a #open_channel action.
     class ChannelOpenRecording #:nodoc:
       attr_reader :type, :extras, :channel
 
@@ -15,6 +31,7 @@ module Net; module SSH; module Multi
       end
     end
 
+    # Represents a #send_global_request action.
     class SendGlobalRequestRecording #:nodoc:
       attr_reader :type, :extra, :callback
 
@@ -27,51 +44,69 @@ module Net; module SSH; module Multi
       end
     end
 
+    # The Net::SSH::Multi::Server object that "owns" this pending connection.
     attr_reader :server
 
+    # Instantiates a new pending connection for the given Net::SSH::Multi::Server
+    # object.
     def initialize(server)
       @server = server
       @recordings = []
     end
 
+    # Instructs the pending session to replay all of its recordings against the
+    # given +session+, and to then replace itself with the given session.
     def replace_with(session)
       @recordings.each { |recording| recording.replay_on(session) }
       @server.replace_session(session)
     end
 
+    # Records that a channel open request has been made, and returns a new
+    # Net::SSH::Multi::ChannelProxy object to represent the (as yet unopened)
+    # channel.
     def open_channel(type="session", *extras, &on_confirm)
       channel = ChannelProxy.new(&on_confirm)
       @recordings << ChannelOpenRecording.new(type, extras, channel)
       return channel
     end
 
+    # Records that a global request has been made. The request is not actually
+    # sent, and won't be until #replace_with is called.
     def send_global_request(type, *extra, &callback)
       @recordings << SendGlobalRequestRecording.new(type, extra, callback)
       self
     end
 
+    # Always returns +true+, so that the pending connection looks active until
+    # it can be truly opened and replaced with a real connection.
     def busy?(include_invisible=false)
       true
     end
 
+    # Does nothing, except to make a pending connection quack like a real connection.
     def close
       self
     end
 
+    # Returns an empty array, since a pending connection cannot have any real channels.
     def channels
       []
     end
 
+    # Returns +true+, and does nothing else.
     def preprocess
       true
     end
 
+    # Returns +true+, and does nothing else.
     def postprocess(readers, writers)
       true
     end
 
+    # Returns an empty hash, since a pending connection has no real listeners.
     def listeners
       {}
     end
   end
+
 end; end; end
\ No newline at end of file
diff --git a/lib/net/ssh/multi/server.rb b/lib/net/ssh/multi/server.rb
index 65967ab..999e788 100644
--- a/lib/net/ssh/multi/server.rb
+++ b/lib/net/ssh/multi/server.rb
@@ -6,6 +6,9 @@ module Net; module SSH; module Multi
   # need to instantiate one of these directly: instead, you should use
   # Net::SSH::Multi::Session#use.
   class Server
+    # The Net::SSH::Multi::Session instance that manages this server instance.
+    attr_reader :master
+
     # The host name (or IP address) of the server to connect to.
     attr_reader :host
 
@@ -21,12 +24,14 @@ module Net; module SSH; module Multi
     attr_reader :gateway
 
     # Creates a new Server instance with the given connection information. The
-    # +options+ hash must conform to the options described for Net::SSH::start,
-    # with one addition:
+    # +master+ argument must be a reference to the Net::SSH::Multi::Session
+    # instance that will manage this server reference. The +options+ hash must
+    # conform to the options described for Net::SSH::start, with one addition:
     #
     # * :via => a Net::SSH::Gateway instance to use when establishing a
     #   connection to this server.
-    def initialize(host, user, options={})
+    def initialize(master, host, user, options={})
+      @master = master
       @host = host
       @user = user
       @options = options.dup
@@ -77,9 +82,9 @@ module Net; module SSH; module Multi
       @inspect ||= "#<%s:0x%x %s>" % [self.class.name, object_id, to_s]
     end
 
-    # Returns the Net::SSH session object for this server. If +ensure_open+
+    # Returns the Net::SSH session object for this server. If +require_session+
     # is false and the session has not previously been created, this will
-    # return +nil+. If +ensure_open+ is true, the session will be instantiated
+    # return +nil+. If +require_session+ is true, the session will be instantiated
     # if it has not already been instantiated, via the +gateway+ if one is
     # given, or directly (via Net::SSH::start) otherwise.
     #
@@ -94,9 +99,52 @@ module Net; module SSH; module Multi
     # (the Server instance that spawned them).
     #
     #   assert_equal server, server.session[:server]
-    def session(ensure_open=false)
-      return @session if @session || !ensure_open
-      @session ||= begin 
+    def session(require_session=false)
+      return @session if @session || !require_session
+      @session ||= master.next_session(self)
+    end
+
+    # Returns +true+ if the session has been opened, and the session is currently
+    # busy (as defined by Net::SSH::Connection::Session#busy?).
+    def busy?(include_invisible=false)
+      session && session.busy?(include_invisible)
+    end
+
+    # Closes this server's session. If the session has not yet been opened,
+    # this does nothing.
+    def close
+      session.close if session
+    ensure
+      master.server_closed(self) if session
+      @session = nil
+    end
+
+    public # but not published, e.g., these are used internally only...
+
+      # Indicate that the session currently in use by this server instance
+      # should be replaced by the given +session+ argument. This is used when
+      # a pending session has been "realized". Note that this does not
+      # actually replace the session--see #update_session! for that.
+      def replace_session(session) #:nodoc:
+        @ready_session = session
+      end
+
+      # If a new session has been made ready (see #replace_session), this
+      # will replace the current session with the "ready" session. This
+      # method is called from the event loop to ensure that sessions are
+      # swapped in at the appropriate point (instead of in the middle of an
+      # event poll).
+      def update_session! #:nodoc:
+        if @ready_session
+          @session, @ready_session = @ready_session, nil
+        end
+      end
+
+      # Returns a new session object based on this server's connection
+      # criteria. Note that this will not associate the session with the
+      # server, and should not be called directly; it is called internally
+      # from Net::SSH::Multi::Session when a new session is required.
+      def new_session #:nodoc:
         session = if gateway
           gateway.ssh(host, user, options)
         else
@@ -105,31 +153,16 @@ module Net; module SSH; module Multi
 
         session[:server] = self
         session
+      rescue Net::SSH::AuthenticationFailed => error
+        raise Net::SSH::AuthenticationFailed.new("#{error.message}@#{host}")
       end
-    rescue Net::SSH::AuthenticationFailed => error
-      raise Net::SSH::AuthenticationFailed.new("#{error.message}@#{host}")
-    end
-
-    # Returns +true+ if the session has been opened, and the session is currently
-    # busy (as defined by Net::SSH::Connection::Session#busy?).
-    def busy?(include_invisible=false)
-      session && session.busy?(include_invisible)
-    end
 
-    public # but not published, e.g., these are used internally only...
-    
       # Closes all open channels on this server's session. If the session has
       # not yet been opened, this does nothing.
       def close_channels #:nodoc:
         session.channels.each { |id, channel| channel.close } if session
       end
 
-      # Closes this server's session's transport layer. If the session has not
-      # yet been opened, this does nothing.
-      def close #:nodoc:
-        session.transport.close if session
-      end
-
       # Runs the session's preprocess action, if the session has been opened.
       def preprocess #:nodoc:
         session.preprocess if session
diff --git a/lib/net/ssh/multi/session.rb b/lib/net/ssh/multi/session.rb
index cffe972..99819e1 100644
--- a/lib/net/ssh/multi/session.rb
+++ b/lib/net/ssh/multi/session.rb
@@ -1,6 +1,8 @@
+require 'thread'
 require 'net/ssh/gateway'
 require 'net/ssh/multi/server'
 require 'net/ssh/multi/channel'
+require 'net/ssh/multi/pending_connection'
 
 module Net; module SSH; module Multi
   # Represents a collection of connections to various servers. It provides an
@@ -50,6 +52,13 @@ module Net; module SSH; module Multi
     # corresponding Net::SSH::Multi::Server definitions.
     attr_reader :groups
 
+    # The number of allowed concurrent connections. No more than this number
+    # of sessions will be open at any given time.
+    attr_accessor :concurrent_connections
+
+    # The number of connections that are currently open.
+    attr_reader :open_connections #:nodoc:
+
     # The list of "open" groups, which will receive subsequent server definitions.
     # See #use and #group.
     attr_reader :open_groups #:nodoc:
@@ -61,12 +70,30 @@ module Net; module SSH; module Multi
 
     # Creates a new Net::SSH::Multi::Session instance. Initially, it contains
     # no server definitions, no group definitions, and no default gateway.
-    def initialize
+    #
+    # You can set the #concurrent_connections property in the options. Setting
+    # it to +nil+ (the default) will cause Net::SSH::Multi to ignore any
+    # concurrent connection limit and allow all defined sessions to be open
+    # simultaneously. Setting it to an integer will cause Net::SSH::Multi to
+    # allow no more than that number of concurrently open sessions, opening
+    # subsequent sessions only when other sessions finish and close.
+    #
+    #   Net::SSH::Multi.start(:concurrent_connections => 10) do |session|
+    #     session.use ...
+    #   end
+    def initialize(options={})
       @servers = []
       @groups = {}
       @gateway = nil
       @active_groups = {}
       @open_groups = []
+      @connect_threads = []
+
+      @open_connections = 0
+      @pending_sessions = []
+      @session_mutex = Mutex.new
+
+      options.each { |opt, value| send("#{opt}=", value) }
     end
 
     # At its simplest, this associates a named group with a server definition.
@@ -144,7 +171,7 @@ module Net; module SSH; module Multi
     #   session.use 'host2', 'user2', :via => nil
     #   session.use 'host3', 'user3', :via => Net::SSH::Gateway.new('gateway.host', 'user')
     def use(host, user, options={})
-      server = Server.new(host, user, {:via => default_gateway}.merge(options))
+      server = Server.new(self, host, user, {:via => default_gateway}.merge(options))
       exists = servers.index(server)
       if exists
         server = servers[exists]
@@ -313,6 +340,9 @@ module Net; module SSH; module Multi
     # whether #process returns +true+ (the block did not return +false+), or
     # +false+ (the block returned +false+).
     def process(wait=nil, &block)
+      realize_pending_connections!
+      wait = @connect_threads.any? ? 0 : wait
+
       return false unless preprocess(&block)
 
       readers = servers.map { |s| s.readers }.flatten
@@ -320,7 +350,11 @@ module Net; module SSH; module Multi
 
       readers, writers, = IO.select(readers, writers, nil, wait)
 
-      return postprocess(readers, writers)
+      if readers
+        return postprocess(readers, writers)
+      else
+        return true
+      end
     end
 
     # Sends a global request to all active sessions (see #active_sessions).
@@ -365,8 +399,8 @@ module Net; module SSH; module Multi
     def open_channel(type="session", *extra, &on_confirm)
       channels = active_sessions.map do |ssh|
         ssh.open_channel(type, *extra) do |c|
-          c[:server] = ssh[:server]
-          c[:host] = ssh[:server].host
+          c[:server] = c.connection[:server]
+          c[:host] = c.connection[:server].host
           on_confirm[c] if on_confirm
         end
       end
@@ -448,5 +482,69 @@ module Net; module SSH; module Multi
       servers.each { |server| server.postprocess(readers, writers) }
       true
     end
+
+    # Takes the #concurrent_connections property into account, and tries to
+    # return a new session for the given server. If the concurrent connections
+    # limit has been reached, then a Net::SSH::Multi::PendingConnection instance
+    # will be returned instead, which will be realized into an actual session
+    # as soon as a slot opens up.
+    #
+    # If +force+ is true, the concurrent_connections check is skipped and a real
+    # connection is always returned.
+    def next_session(server, force=false) #:nodoc:
+      @session_mutex.synchronize do
+        if !force && concurrent_connections && concurrent_connections <= open_connections
+          connection = PendingConnection.new(server)
+          @pending_sessions << connection
+          return connection
+        end
+
+        @open_connections += 1
+      end
+
+      begin
+        server.new_session
+      rescue Exception => e
+        @session_mutex.synchronize { @open_connections -= 1 }
+        raise
+      end
+    end
+
+    # Tells the session that the given server has closed its connection. The
+    # session indicates that a new connection slot is available, which may be
+    # filled by the next pending connection on the next event loop iteration.
+    def server_closed(server) #:nodoc:
+      @session_mutex.synchronize do
+        unless @pending_sessions.delete(server.session)
+          @open_connections -= 1
+        end
+      end
+    end
+
+    # Invoked by the event loop. If there is a concurrent_connections limit in
+    # effect, this will close any non-busy sessions and try to open as many
+    # new sessions as it can. It does this in threads, so that existing processing
+    # can continue.
+    #
+    # If there is no concurrent_connections limit in effect, then this method
+    # does nothing.
+    def realize_pending_connections! #:nodoc:
+      return unless concurrent_connections
+
+      servers.each do |s|
+        s.close if !s.busy?(true)
+        s.update_session!
+      end
+
+      @connect_threads.delete_if { |t| !t.alive? }
+
+      count = concurrent_connections ? (concurrent_connections - open_connections) : @pending_sessions.length
+      count.times do
+        session = @pending_sessions.pop or break
+        @connect_threads << Thread.new do
+          session.replace_with(next_session(session.server, true))
+        end
+      end
+    end
   end
 end; end; end
\ No newline at end of file