module Mongo::BackgroundThread

The run!, running? and stop! methods used to be part of the public API in some of the classes which now include this module. Therefore these methods must be considered part of the driver’s public API for backwards compatibility reasons. However using these methods outside of the driver is deprecated.

@note Do not start or stop background threads in finalizers. See

https://jira.mongodb.org/browse/RUBY-2453 and
https://bugs.ruby-lang.org/issues/16288. When interpreter exits,
background threads are stopped first and finalizers are invoked next,
and MRI's internal data structures are basically corrupt at this point
if threads are being referenced. Prior to interpreter shutdown this
means threads cannot be stopped by objects going out of scope, but
most likely the threads hold references to said objects anyway if
work is being performed thus the objects wouldn't go out of scope in
the first place.

@api private

Public Instance Methods

run!() click to toggle source

Start the background thread.

If the thread is already running, this method does nothing.

@api public for backwards compatibility only

# File lib/mongo/background_thread.rb, line 46
def run!
  if @stop_requested && @thread
    wait_for_stop
    if @thread.alive?
      log_warn("Starting a new background thread in #{self}, but the previous background thread is still running")
      @thread = nil
    end
    @stop_requested = false
  end
  if running?
    @thread
  else
    start!
  end
end
running?() click to toggle source

@api public for backwards compatibility only

# File lib/mongo/background_thread.rb, line 63
def running?
  if @thread
    @thread.alive?
  else
    false
  end
end
stop!() click to toggle source

Stop the background thread and wait for to terminate for a reasonable amount of time.

@return [ true | false ] Whether the thread was terminated.

@api public for backwards compatibility only

# File lib/mongo/background_thread.rb, line 77
def stop!
  # If the thread was not started, there is nothing to stop.
  #
  # Classes including this module may want to perform additional
  # cleanup, which they can do by overriding this method.
  return true unless @thread

  # Background threads generally perform operations in a loop.
  # This flag is meant to be checked on each iteration of the
  # working loops and the thread should stop working when this flag
  # is set.
  @stop_requested = true

  # Besides setting the flag, a particular class may have additional
  # ways of signaling the background thread to either stop working or
  # wake up to check the stop flag, for example, setting a semaphore.
  # This can be accomplished by providing the pre_stop method.
  pre_stop

  # Now we have requested the graceful termination, and we could wait
  # for the thread to exit on its own accord. A future version of the
  # driver may allow a certain amount of time for the thread to quit.
  # For now, we additionally use the Ruby machinery to request the thread
  # be terminated, and do so immediately.
  #
  # Note that this may cause the background thread to terminate in
  # the middle of an operation.
  @thread.kill

  wait_for_stop
end

Private Instance Methods

do_work() click to toggle source

Override this method to do the work in the background thread.

# File lib/mongo/background_thread.rb, line 165
def do_work
end
pre_stop() click to toggle source

Override this method to perform additional signaling for the background thread to stop.

# File lib/mongo/background_thread.rb, line 170
def pre_stop
end
start!() click to toggle source
# File lib/mongo/background_thread.rb, line 111
def start!
  @thread = Thread.new do
    catch(:done) do
      until @stop_requested
        do_work
      end
    end
  end
end
wait_for_stop() click to toggle source

Waits for the thread to die, with a timeout.

Returns true if the thread died, false otherwise.

# File lib/mongo/background_thread.rb, line 124
def wait_for_stop
  # Wait for the thread to die. This is important in order to reliably
  # clean up resources like connections knowing that no background
  # thread will reconnect because it is still working.
  #
  # However, we do not want to wait indefinitely because in theory
  # a background thread could be performing, say, network I/O and if
  # the network is no longer available that could take a long time.
  start_time = Utils.monotonic_time
  ([0.1, 0.15] + [0.2] * 5 + [0.3] * 20).each do |interval|
    begin
      Timeout.timeout(interval) do
        @thread.join
      end
      break
    rescue ::Timeout::Error
    end
  end

  # Some driver objects can be reconnected, for backwards compatibiilty
  # reasons. Clear the thread instance variable to support this cleanly.
  if @thread.alive?
    log_warn("Failed to stop the background thread in #{self} in #{(Utils.monotonic_time - start_time).to_i} seconds: #{@thread.inspect} (thread status: #{@thread.status})")
    # On JRuby the thread may be stuck in aborting state
    # seemingly indefinitely. If the thread is aborting, consider it dead
    # for our purposes (we will create a new thread if needed, and
    # the background thread monitor will not detect the aborting thread
    # as being alive).
    if @thread.status == 'aborting'
      @thread = nil
      @stop_requested = false
    end
    false
  else
    @thread = nil
    @stop_requested = false
    true
  end
end