X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/12b5d95d9d4f062539c3d7d7ac8dd5421dd6b6b0..b73985d8a0c9173aec57f6a81fe540b2813a5bff:/services/api/lib/eventbus.rb

diff --git a/services/api/lib/eventbus.rb b/services/api/lib/eventbus.rb
index 9bf95f5735..16bb030941 100644
--- a/services/api/lib/eventbus.rb
+++ b/services/api/lib/eventbus.rb
@@ -7,6 +7,8 @@ require 'oj'
 require 'faye/websocket'
 require 'record_filters'
 require 'load_param'
+require 'set'
+require 'thread'
 
 # Patch in user, last_log_id and filters fields into the Faye::Websocket class.
 module Faye
@@ -14,6 +16,29 @@ module Faye
     attr_accessor :user
     attr_accessor :last_log_id
     attr_accessor :filters
+    attr_accessor :sent_ids
+    attr_accessor :queue
+    attr_accessor :frame_mtx
+  end
+end
+
+module WebSocket
+  class Driver
+
+    class Server
+      alias_method :_write, :write
+
+      def write(data)
+        # Most of the sending activity will be from the thread set up in
+        # on_connect.  However, there is also some automatic activity in the
+        # form of ping/pong messages, so ensure that the write method used to
+        # send one complete message to the underlying socket can only be
+        # called by one thread at a time.
+        self.frame_mtx.synchronize do
+          _write(data)
+        end
+      end
+    end
   end
 end
 
@@ -50,6 +75,7 @@ class EventBus
     @channel = EventMachine::Channel.new
     @mtx = Mutex.new
     @bgthread = false
+    @connection_count = 0
   end
 
   # Push out any pending events to the connection +ws+
@@ -60,35 +86,27 @@ class EventBus
   #
   # It queries the database for log rows that are either
   #  a) greater than ws.last_log_id, which is the last log id which was a candidate to be sent out
-  #  b) if ws.last_log_id is nil, then it queries rows starting with notify_id
+  #  b) if ws.last_log_id is nil, then it queries the row notify_id
   #
-  # Regular Arvados permissions are applied using readable_by() and filters using record_filters()
-  # To avoid clogging up the database, queries are limited to batches of 100.  It will schedule a new
-  # push_events call if there are more log rows to send.
+  # Regular Arvados permissions are applied using readable_by() and filters using record_filters().
   def push_events ws, notify_id
     begin
-      if !notify_id.nil? and !ws.last_log_id.nil? and notify_id <= ws.last_log_id
-        # This notify is for a row we've handled already.
-        return
-      end
-
       # Must have at least one filter set up to receive events
       if ws.filters.length > 0
-        # Start with log rows readable by user, sorted in ascending order
-        logs = Log.readable_by(ws.user).order("id asc")
+        # Start with log rows readable by user
+        logs = Log.readable_by(ws.user)
 
         cond_id = nil
         cond_out = []
         param_out = []
 
-        if !ws.last_log_id.nil?
-          # Client is only interested in log rows that are newer than the
-          # last log row seen by the client.
+        if not ws.last_log_id.nil?
+          # We are catching up from some starting point.
           cond_id = "logs.id > ?"
           param_out << ws.last_log_id
-        elsif !notify_id.nil?
-          # No last log id, so look at rows starting with notify id
-          cond_id = "logs.id >= ?"
+        elsif not notify_id.nil?
+          # Get next row being notified.
+          cond_id = "logs.id = ?"
           param_out << notify_id
         else
           # No log id to start from, nothing to do, return
@@ -114,31 +132,28 @@ class EventBus
           logs = logs.where(cond_id, *param_out)
         end
 
-        # Execute query and actually send the matching log rows
-        count = 0
-        limit = 10
-
-        logs.limit(limit).each do |l|
-          ws.send(l.as_api_response.to_json)
-          ws.last_log_id = l.id
-          count += 1
-        end
-
-        if count == limit
-          # Number of rows returned was capped by limit(), we need to schedule
-          # another query to get more logs (will start from last_log_id
-          # reported by current query)
-          EventMachine::next_tick do
-            push_events ws, nil
+        # Execute query and actually send the matching log rows. Load
+        # the full log records only when we're ready to send them,
+        # though: otherwise, (1) postgres has to build the whole
+        # result set and return it to us before we can send the first
+        # event, and (2) we store lots of records in memory while
+        # waiting to spool them out to the client. Both of these are
+        # troublesome when log records are large (e.g., a collection
+        # update contains both old and new manifest_text).
+        #
+        # Note: find_each implies order('id asc'), which is what we
+        # want.
+        logs.select('logs.id').find_each do |l|
+          if not ws.sent_ids.include?(l.id)
+            # only send if not a duplicate
+            ws.send(Log.find(l.id).as_api_response.to_json)
+          end
+          if not ws.last_log_id.nil?
+            # record ids only when sending "catchup" messages, not notifies
+            ws.sent_ids << l.id
           end
-        elsif !notify_id.nil? and (ws.last_log_id.nil? or notify_id > ws.last_log_id)
-          # Number of rows returned was less than cap, but the notify id is
-          # higher than the last id visible to the client, so update last_log_id
-          ws.last_log_id = notify_id
         end
-      elsif !notify_id.nil?
-        # No filters set up, so just record the sequence number
-        ws.last_log_id = notify_id
+        ws.last_log_id = nil
       end
     rescue ArgumentError => e
       # There was some kind of user error.
@@ -176,9 +191,12 @@ class EventBus
           # Set or reset the last_log_id.  The event bus only reports events
           # for rows that come after last_log_id.
           ws.last_log_id = p[:last_log_id].to_i
+          # Reset sent_ids for consistency
+          # (always re-deliver all matching messages following last_log_id)
+          ws.sent_ids = Set.new
         end
 
-        if ws.filters.length < MAX_FILTERS
+        if ws.filters.length < Rails.configuration.websocket_max_filters
           # Add a filter.  This gets the :filters field which is the same
           # format as used for regular index queries.
           ws.filters << filter
@@ -187,7 +205,7 @@ class EventBus
           # Send any pending events
           push_events ws, nil
         else
-          ws.send ({status: 403, message: "maximum of #{MAX_FILTERS} filters allowed per connection"}.to_json)
+          ws.send ({status: 403, message: "maximum of #{Rails.configuration.websocket_max_filters} filters allowed per connection"}.to_json)
         end
 
       elsif p[:method] == 'unsubscribe'
@@ -212,12 +230,14 @@ class EventBus
     end
   end
 
-  # Constant maximum number of filters, to avoid silly huge database queries.
-  MAX_FILTERS = 16
+  def overloaded?
+    @mtx.synchronize do
+      @connection_count >= Rails.configuration.websocket_max_connections
+    end
+  end
 
   # Called by RackSocket when a new websocket connection has been established.
   def on_connect ws
-
     # Disconnect if no valid API token.
     # current_user is included from CurrentApiClient
     if not current_user
@@ -230,22 +250,64 @@ class EventBus
     ws.user = current_user
     ws.filters = []
     ws.last_log_id = nil
+    ws.sent_ids = Set.new
+    ws.queue = Queue.new
+    ws.frame_mtx = Mutex.new
+
+    @mtx.synchronize do
+      @connection_count += 1
+    end
 
-    # Subscribe to internal postgres notifications through @channel.  This will
-    # call push_events when a notification comes through.
+    # Subscribe to internal postgres notifications through @channel and
+    # forward them to the thread associated with the connection.
     sub = @channel.subscribe do |msg|
-      push_events ws, msg
+      if ws.queue.length > Rails.configuration.websocket_max_notify_backlog
+        ws.send ({status: 500, message: 'Notify backlog too long'}.to_json)
+        ws.close
+        @channel.unsubscribe sub
+        ws.queue.clear
+      else
+        ws.queue << [:notify, msg]
+      end
     end
 
     # Set up callback for inbound message dispatch.
     ws.on :message do |event|
-      handle_message ws, event
+      ws.queue << [:message, event]
     end
 
     # Set up socket close callback
     ws.on :close do |event|
       @channel.unsubscribe sub
-      ws = nil
+      ws.queue.clear
+      ws.queue << [:close, nil]
+    end
+
+    # Spin off a new thread to handle sending events to the client.  We need a
+    # separate thread per connection so that a slow client doesn't interfere
+    # with other clients.
+    #
+    # We don't want the loop in the request thread because on a TERM signal,
+    # Puma waits for outstanding requests to complete, and long-lived websocket
+    # connections may not complete in a timely manner.
+    Thread.new do
+      # Loop and react to socket events.
+      begin
+        loop do
+          eventType, msg = ws.queue.pop
+          if eventType == :message
+            handle_message ws, msg
+          elsif eventType == :notify
+            push_events ws, msg
+          elsif eventType == :close
+            break
+          end
+        end
+      ensure
+        @mtx.synchronize do
+          @connection_count -= 1
+        end
+      end
     end
 
     # Start up thread to monitor the Postgres database, if none exists already.
@@ -281,8 +343,5 @@ class EventBus
       end
     end
 
-    # Since EventMachine is an asynchronous event based dispatcher, #on_connect
-    # does not block but instead returns immediately after having set up the
-    # websocket and notification channel callbacks.
   end
 end