# frozen_string_literal: true
require 'thread'
module Puma
# Internal Docs for A simple thread pool management object.
#
# Each Puma "worker" has a thread pool to process requests.
#
# First a connection to a client is made in `Puma::Server`. It is wrapped in a
# `Puma::Client` instance and then passed to the `Puma::Reactor` to ensure
# the whole request is buffered into memory. Once the request is ready, it is passed into
# a thread pool via the `Puma::ThreadPool#<<` operator where it is stored in a `@todo` array.
#
# Each thread in the pool has an internal loop where it pulls a request from the `@todo` array
# and proceses it.
class ThreadPool
class ForceShutdown < RuntimeError
end
# How long, after raising the ForceShutdown of a thread during
# forced shutdown mode, to wait for the thread to try and finish
# up its work before leaving the thread to die on the vine.
SHUTDOWN_GRACE_TIME = 5 # seconds
# Maintain a minimum of +min+ and maximum of +max+ threads
# in the pool.
#
# The block passed is the work that will be performed in each
# thread.
#
def initialize(min, max, *extra, &block)
@not_empty = ConditionVariable.new
@not_full = ConditionVariable.new
@mutex = Mutex.new
@todo = []
@spawned = 0
@waiting = 0
@min = Integer(min)
@max = Integer(max)
@block = block
@extra = extra
@shutdown = false
@trim_requested = 0
@workers = []
@auto_trim = nil
@reaper = nil
@mutex.synchronize do
@min.times { spawn_thread }
end
@clean_thread_locals = false
end
attr_reader :spawned, :trim_requested, :waiting
attr_accessor :clean_thread_locals
def self.clean_thread_locals
Thread.current.keys.each do |key| # rubocop: disable Performance/HashEachMethods
Thread.current[key] = nil unless key == :__recursive_key__
end
end
# How many objects have yet to be processed by the pool?
#
def backlog
@mutex.synchronize { @todo.size }
end
def pool_capacity
waiting + (@max - spawned)
end
# :nodoc:
#
# Must be called with @mutex held!
#
def spawn_thread
@spawned += 1
th = Thread.new(@spawned) do |spawned|
Puma.set_thread_name 'threadpool %03i' % spawned
todo = @todo
block = @block
mutex = @mutex
not_empty = @not_empty
not_full = @not_full
extra = @extra.map { |i| i.new }
while true
work = nil
continue = true
mutex.synchronize do
while todo.empty?
if @trim_requested > 0
@trim_requested -= 1
continue = false
not_full.signal
break
end
if @shutdown
continue = false
break
end
@waiting += 1
not_full.signal
not_empty.wait mutex
@waiting -= 1
end
work = todo.shift if continue
end
break unless continue
if @clean_thread_locals
ThreadPool.clean_thread_locals
end
begin
block.call(work, *extra)
rescue Exception => e
STDERR.puts "Error reached top of thread-pool: #{e.message} (#{e.class})"
end
end
mutex.synchronize do
@spawned -= 1
@workers.delete th
end
end
@workers << th
th
end
private :spawn_thread
# Add +work+ to the todo list for a Thread to pickup and process.
def <<(work)
@mutex.synchronize do
if @shutdown
raise "Unable to add work while shutting down"
end
@todo << work
if @waiting < @todo.size and @spawned < @max
spawn_thread
end
@not_empty.signal
end
end
# This method is used by `Puma::Server` to let the server know when
# the thread pool can pull more requests from the socket and
# pass to the reactor.
#
# The general idea is that the thread pool can only work on a fixed
# number of requests at the same time. If it is already processing that
# number of requests then it is at capacity. If another Puma process has
# spare capacity, then the request can be left on the socket so the other
# worker can pick it up and process it.
#
# For example: if there are 5 threads, but only 4 working on
# requests, this method will not wait and the `Puma::Server`
# can pull a request right away.
#
# If there are 5 threads and all 5 of them are busy, then it will
# pause here, and wait until the `not_full` condition variable is
# signaled, usually this indicates that a request has been processed.
#
# It's important to note that even though the server might accept another
# request, it might not be added to the `@todo` array right away.
# For example if a slow client has only sent a header, but not a body
# then the `@todo` array would stay the same size as the reactor works
# to try to buffer the request. In that scenario the next call to this
# method would not block and another request would be added into the reactor
# by the server. This would continue until a fully bufferend request
# makes it through the reactor and can then be processed by the thread pool.
#
# Returns the current number of busy threads, or +nil+ if shutting down.
#
def wait_until_not_full
@mutex.synchronize do
while true
return if @shutdown
# If we can still spin up new threads and there
# is work queued that cannot be handled by waiting
# threads, then accept more work until we would
# spin up the max number of threads.
busy_threads = @spawned - @waiting + @todo.size
return busy_threads if @max > busy_threads
@not_full.wait @mutex
end
end
end
# If too many threads are in the pool, tell one to finish go ahead
# and exit. If +force+ is true, then a trim request is requested
# even if all threads are being utilized.
#
def trim(force=false)
@mutex.synchronize do
if (force or @waiting > 0) and @spawned - @trim_requested > @min
@trim_requested += 1
@not_empty.signal
end
end
end
# If there are dead threads in the pool make them go away while decreasing
# spawned counter so that new healthy threads could be created again.
def reap
@mutex.synchronize do
dead_workers = @workers.reject(&:alive?)
dead_workers.each do |worker|
worker.kill
@spawned -= 1
end
@workers.delete_if do |w|
dead_workers.include?(w)
end
end
end
class Automaton
def initialize(pool, timeout, thread_name, message)
@pool = pool
@timeout = timeout
@thread_name = thread_name
@message = message
@running = false
end
def start!
@running = true
@thread = Thread.new do
Puma.set_thread_name @thread_name
while @running
@pool.public_send(@message)
sleep @timeout
end
end
end
def stop
@running = false
@thread.wakeup
end
end
def auto_trim!(timeout=30)
@auto_trim = Automaton.new(self, timeout, "threadpool trimmer", :trim)
@auto_trim.start!
end
def auto_reap!(timeout=5)
@reaper = Automaton.new(self, timeout, "threadpool reaper", :reap)
@reaper.start!
end
# Tell all threads in the pool to exit and wait for them to finish.
#
def shutdown(timeout=-1)
threads = @mutex.synchronize do
@shutdown = true
@not_empty.broadcast
@not_full.broadcast
@auto_trim.stop if @auto_trim
@reaper.stop if @reaper
# dup workers so that we join them all safely
@workers.dup
end
if timeout == -1
# Wait for threads to finish without force shutdown.
threads.each(&:join)
else
# Wait for threads to finish after n attempts (+timeout+).
# If threads are still running, it will forcefully kill them.
timeout.times do
threads.delete_if do |t|
t.join 1
end
if threads.empty?
break
else
sleep 1
end
end
threads.each do |t|
t.raise ForceShutdown
end
threads.each do |t|
t.join SHUTDOWN_GRACE_TIME
end
end
@spawned = 0
@workers = []
end
end
end