discourse/lib/demon/email_sync.rb

# frozen_string_literal: true

require "demon/base"

class Demon::EmailSync < ::Demon::Base
  HEARTBEAT_KEY ||= "email_sync_heartbeat"
  HEARTBEAT_INTERVAL ||= 60.seconds

  def self.prefix
    "email_sync"
  end

  private

  def suppress_stdout
    false
  end

  def suppress_stderr
    false
  end

  def start_thread(db, group)
    Thread.new do
      RailsMultisite::ConnectionManagement.with_connection(db) do
        puts "[EmailSync] Thread started for group #{group.name} (id = #{group.id}) in db #{db}"
        begin
          obj = Imap::Sync.for_group(group)
        rescue Net::IMAP::NoResponseError => e
          group.update(imap_last_error: e.message)
          Thread.exit
        end

        @sync_lock.synchronize { @sync_data[db][group.id][:obj] = obj }

        status = nil
        idle = false

        while @running && group.reload.imap_mailbox_name.present? do
          puts "[EmailSync] Processing IMAP mailbox for group #{group.name} (id = #{group.id}) in db #{db}"
          status = obj.process(
            idle: obj.can_idle? && status && status[:remaining] == 0,
            old_emails_limit: status && status[:remaining] > 0 ? 0 : nil,
          )

          if !obj.can_idle? && status[:remaining] == 0
            puts "[EmailSync] Going to sleep for group #{group.name} (id = #{group.id}) in db #{db} to wait for new emails."

            # Thread goes into sleep for a bit so it is better to return any
            # connection back to the pool.
            ActiveRecord::Base.connection_handler.clear_active_connections!

            sleep SiteSetting.imap_polling_period_mins.minutes
          end
        end

        obj.disconnect!
      end
    end
  end

  def kill_threads
    # This is not really safe so the caller should ensure it happens in a
    # thread-safe context.
    # It should be safe when called from within a `trap` (there are no
    # synchronization primitives available anyway).
    @running = false

    @sync_data.each do |db, sync_data|
      sync_data.each do |_, data|
        data[:thread].kill
        data[:thread].join
        data[:obj]&.disconnect! rescue nil
      end
    end

    exit 0
  end

  def after_fork
    puts "[EmailSync] Loading EmailSync in process id #{Process.pid}"

    loop do
      break if Discourse.redis.set(HEARTBEAT_KEY, Time.now.to_i, ex: HEARTBEAT_INTERVAL, nx: true)
      sleep HEARTBEAT_INTERVAL
    end

    puts "[EmailSync] Starting EmailSync main thread"

    @running = true
    @sync_data = {}
    @sync_lock = Mutex.new

    trap('INT')  { kill_threads }
    trap('TERM') { kill_threads }
    trap('HUP')  { kill_threads }

    while @running
      Discourse.redis.set(HEARTBEAT_KEY, Time.now.to_i, ex: HEARTBEAT_INTERVAL)

      # Kill all threads for databases that no longer exist
      all_dbs = Set.new(RailsMultisite::ConnectionManagement.all_dbs)
      @sync_data.filter! do |db, sync_data|
        next true if all_dbs.include?(db)

        sync_data.each do |_, data|
          data[:thread].kill
          data[:thread].join
          data[:obj]&.disconnect!
        end

        false
      end

      RailsMultisite::ConnectionManagement.each_connection do |db|
        if SiteSetting.enable_imap
          groups = Group.where.not(imap_mailbox_name: '').map { |group| [group.id, group] }.to_h

          @sync_lock.synchronize do
            @sync_data[db] ||= {}

            # Kill threads for group's mailbox that are no longer synchronized.
            @sync_data[db].filter! do |group_id, data|
              next true if groups[group_id] && data[:thread]&.alive? && !data[:obj]&.disconnected?

              if !groups[group_id]
                puts("[EmailSync] Killing thread for group (id = #{group_id}) because mailbox is no longer synced")
              else
                puts("[EmailSync] Thread for group #{groups[group_id].name} (id = #{group_id}) is dead")
              end

              data[:thread].kill
              data[:thread].join
              data[:obj]&.disconnect!

              false
            end

            # Spawn new threads for groups that are now synchronized.
            groups.each do |group_id, group|
              if !@sync_data[db][group_id]
                puts("[EmailSync] Starting thread for group #{group.name} (id = #{group.id}) and mailbox #{group.imap_mailbox_name}")
                @sync_data[db][group_id] = {
                  thread: start_thread(db, group), obj: nil
                }
              end
            end
          end
        end
      end

      # Thread goes into sleep for a bit so it is better to return any
      # connection back to the pool.
      ActiveRecord::Base.connection_handler.clear_active_connections!

      sleep 5
    end

    @sync_lock.synchronize { kill_threads }
    Discourse.redis.del(HEARTBEAT_KEY)
    exit 0
  rescue => e
    STDERR.puts e.message
    STDERR.puts e.backtrace.join("\n")
    exit 1
  end
end