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|
# frozen_string_literal: true
module Gitlab
module Database
module LoadBalancing
# A list of database hosts to use for connections.
class HostList
# hosts - The list of secondary hosts to add.
def initialize(hosts = [])
@hosts = hosts.shuffle
@index = 0
@mutex = Mutex.new
@hosts_gauge = Gitlab::Metrics.gauge(:db_load_balancing_hosts, 'Current number of load balancing hosts')
set_metrics!
end
def hosts
@mutex.synchronize { @hosts.dup }
end
def shuffle
@mutex.synchronize do
unsafe_shuffle
end
end
def length
@mutex.synchronize { @hosts.length }
end
def host_names_and_ports
@mutex.synchronize { @hosts.map { |host| [host.host, host.port] } }
end
def hosts=(hosts)
@mutex.synchronize do
::Gitlab::Database::LoadBalancing::Logger.info(
event: :host_list_update,
message: "Updating the host list for service discovery",
host_list_length: hosts.length,
old_host_list_length: @hosts.length
)
@hosts = hosts
unsafe_shuffle
end
set_metrics!
end
# Sets metrics before returning next host
def next
next_host.tap do |_|
set_metrics!
end
end
private
def unsafe_shuffle
@hosts = @hosts.shuffle
@index = 0
end
# Returns the next available host.
#
# Returns a Gitlab::Database::LoadBalancing::Host instance, or nil if no
# hosts were available.
def next_host
@mutex.synchronize do
break if @hosts.empty?
started_at = @index
loop do
host = @hosts[@index]
@index = (@index + 1) % @hosts.length
break host if host.online?
# Return nil once we have cycled through all hosts and none were
# available.
break if @index == started_at
end
end
end
def set_metrics!
@hosts_gauge.set({}, @hosts.length)
end
end
end
end
end
|
