async_sender: factor out thread pool to a seprate class

.rubocop.yml

@@ -39,6 +39,7 @@ Style/SignalException:
 Naming/PredicateName:
   Exclude:
     - 'lib/airbrake-ruby/async_sender.rb'
+    - 'lib/airbrake-ruby/thread_pool.rb'
 
 Metrics/ClassLength:
   Max: 120

lib/airbrake-ruby.rb

@@ -12,6 +12,7 @@
 require 'airbrake-ruby/config'
 require 'airbrake-ruby/config/validator'
 require 'airbrake-ruby/promise'
+require 'airbrake-ruby/thread_pool'
 require 'airbrake-ruby/sync_sender'
 require 'airbrake-ruby/async_sender'
 require 'airbrake-ruby/response'

lib/airbrake-ruby/async_sender.rb

@@ -1,7 +1,5 @@
 module Airbrake
-  # Responsible for sending notices to Airbrake asynchronously. The class
-  # supports an unlimited number of worker threads and an unlimited queue size
-  # (both values are configurable).
+  # Responsible for sending notices to Airbrake asynchronously.
   #
   # @see SyncSender
   # @api private
@@ -15,25 +13,15 @@ class AsyncSender
       "and the following notice will not be delivered " \
       "Error: %<type>s - %<message>s\nBacktrace: %<backtrace>s\n".freeze
 
-    # @return [ThreadGroup] the list of workers
-    # @note This is exposed for eaiser unit testing
-    # @since v4.0.0
-    attr_reader :workers
-
-    # @return [Array<[Airbrake::Notice,Airbrake::Promise]>] the list of unsent
-    #   payload
-    # @note This is exposed for eaiser unit testing
-    # @since v4.0.0
-    attr_reader :unsent
-
     def initialize
       @config = Airbrake::Config.instance
-      @unsent = SizedQueue.new(Airbrake::Config.instance.queue_size)
-      @sender = SyncSender.new
-      @closed = false
-      @workers = ThreadGroup.new
-      @mutex = Mutex.new
-      @pid = nil
+
+      sender = SyncSender.new
+      @thread_pool = ThreadPool.new(
+        worker_size: @config.workers,
+        queue_size: @config.queue_size,
+        block: proc { |(notice, promise)| sender.send(notice, promise) }
+      )
     end
 
     # Asynchronously sends a notice to Airbrake.
@@ -42,101 +30,43 @@ def initialize
     #   library
     # @return [Airbrake::Promise]
     def send(notice, promise)
-      return will_not_deliver(notice, promise) if @unsent.size >= @unsent.max
-
-      @unsent << [notice, promise]
+      return will_not_deliver(notice, promise) unless @thread_pool << [notice, promise]
       promise
     end
 
-    # Closes the instance making it a no-op (it shut downs all worker
-    # threads). Before closing, waits on all unsent notices to be sent.
-    #
     # @return [void]
-    # @raise [Airbrake::Error] when invoked more than one time
     def close
-      threads = @mutex.synchronize do
-        raise Airbrake::Error, 'attempted to close already closed sender' if closed?
-
-        unless @unsent.empty?
-          msg = "#{LOG_LABEL} waiting to send #{@unsent.size} unsent notice(s)..."
-          logger.debug(msg + ' (Ctrl-C to abort)')
-        end
-
-        @config.workers.times { @unsent << [:stop, Airbrake::Promise.new] }
-        @closed = true
-        @workers.list.dup
-      end
-
-      threads.each(&:join)
-      logger.debug("#{LOG_LABEL} closed")
+      @thread_pool.close
     end
 
-    # Checks whether the sender is closed and thus usable.
     # @return [Boolean]
     def closed?
-      @closed
+      @thread_pool.closed?
     end
 
-    # Checks if an active sender has any workers. A sender doesn't have any
-    # workers only in two cases: when it was closed or when all workers
-    # crashed. An *active* sender doesn't have any workers only when something
-    # went wrong.
-    #
-    # Workers are expected to crash when you +fork+ the process the workers are
-    # living in. In this case we detect a +fork+ and try to revive them here.
-    #
-    # Another possible scenario that crashes workers is when you close the
-    # instance on +at_exit+, but some other +at_exit+ hook prevents the process
-    # from exiting.
-    #
-    # @return [Boolean] true if an instance wasn't closed, but has no workers
-    # @see https://goo.gl/oydz8h Example of at_exit that prevents exit
+    # @return [Boolean]
     def has_workers?
-      @mutex.synchronize do
-        return false if @closed
-
-        if @pid != Process.pid && @workers.list.empty?
-          @pid = Process.pid
-          spawn_workers
-        end
-
-        !@closed && @workers.list.any?
-      end
+      @thread_pool.has_workers?
     end
 
     private
 
-    def spawn_workers
-      @workers = ThreadGroup.new
-      @config.workers.times { @workers.add(spawn_worker) }
-      @workers.enclose
-    end
-
-    def spawn_worker
-      Thread.new do
-        while (message = @unsent.pop)
-          break if message.first == :stop
-          @sender.send(*message)
-        end
-      end
-    end
-
     def will_not_deliver(notice, promise)
       error = notice[:errors].first
 
       logger.error(
         format(
           WILL_NOT_DELIVER_MSG,
           log_label: LOG_LABEL,
-          capacity: @unsent.max,
+          capacity: @config.queue_size,
           type: error[:type],
           message: error[:message],
           backtrace: error[:backtrace].map do |line|
             "#{line[:file]}:#{line[:line]} in `#{line[:function]}'"
           end.join("\n")
         )
       )
-      promise.reject("AsyncSender has reached its capacity of #{@unsent.max}")
+      promise.reject("AsyncSender has reached its capacity of #{@config.queue_size}")
     end
   end
 end

lib/airbrake-ruby/thread_pool.rb

@@ -0,0 +1,128 @@
+module Airbrake
+  # ThreadPool implements a simple thread pool that can configure the number of
+  # worker threads and the size of the queue to process.
+  #
+  # @example
+  #   # Initialize a new thread pool with 5 workers and a queue size of 100. Set
+  #   # the block to be run concurrently.
+  #   thread_pool = ThreadPool.new(
+  #     worker_size: 5,
+  #     queue_size: 100,
+  #     block: proc { |message| print "ECHO: #{message}..."}
+  #   )
+  #
+  #   # Send work.
+  #   10.times { |i| thread_pool << i }
+  #   #=> ECHO: 0...ECHO: 1...ECHO: 2...
+  #
+  # @api private
+  # @since v4.6.1
+  class ThreadPool
+    include Loggable
+
+    # @return [ThreadGroup] the list of workers
+    # @note This is exposed for eaiser unit testing
+    attr_reader :workers
+
+    def initialize(worker_size:, queue_size:, block:)
+      @worker_size = worker_size
+      @queue_size = queue_size
+      @block = block
+
+      @queue = SizedQueue.new(queue_size)
+      @workers = ThreadGroup.new
+      @mutex = Mutex.new
+      @pid = nil
+      @closed = false
+
+      has_workers?
+    end
+
+    # Adds a new message to the thread pool. Rejects messages if the queue is at
+    # its capacity.
+    #
+    # @param [Object] message The message that gets passed to the block
+    # @return [Boolean] true if the message was successfully sent to the pool,
+    #   false if the queue is full
+    def <<(message)
+      return false if backlog >= @queue_size
+      @queue << message
+      true
+    end
+
+    # @return [Integer] how big the queue is at the moment
+    def backlog
+      @queue.size
+    end
+
+    # Checks if a thread pool has any workers. A thread pool doesn't have any
+    # workers only in two cases: when it was closed or when all workers
+    # crashed. An *active* thread pool doesn't have any workers only when
+    # something went wrong.
+    #
+    # Workers are expected to crash when you +fork+ the process the workers are
+    # living in. In this case we detect a +fork+ and try to revive them here.
+    #
+    # Another possible scenario that crashes workers is when you close the
+    # instance on +at_exit+, but some other +at_exit+ hook prevents the process
+    # from exiting.
+    #
+    # @return [Boolean] true if an instance wasn't closed, but has no workers
+    # @see https://goo.gl/oydz8h Example of at_exit that prevents exit
+    def has_workers?
+      @mutex.synchronize do
+        return false if @closed
+
+        if @pid != Process.pid && @workers.list.empty?
+          @pid = Process.pid
+          spawn_workers
+        end
+
+        !@closed && @workers.list.any?
+      end
+    end
+
+    # Closes the thread pool making it a no-op (it shut downs all worker
+    # threads). Before closing, waits on all unprocessed tasks to be processed.
+    #
+    # @return [void]
+    # @raise [Airbrake::Error] when invoked more than one time
+    def close
+      threads = @mutex.synchronize do
+        raise Airbrake::Error, 'this thread pool is closed already' if @closed
+
+        unless @queue.empty?
+          msg = "#{LOG_LABEL} waiting to process #{@queue.size} task(s)..."
+          logger.debug(msg + ' (Ctrl-C to abort)')
+        end
+
+        @worker_size.times { @queue << :stop }
+        @closed = true
+        @workers.list.dup
+      end
+
+      threads.each(&:join)
+      logger.debug("#{LOG_LABEL} thread pool closed")
+    end
+
+    def closed?
+      @closed
+    end
+
+    def spawn_workers
+      @worker_size.times { @workers.add(spawn_worker) }
+      @workers.enclose
+    end
+
+    private
+
+    def spawn_worker
+      Thread.new do
+        while (message = @queue.pop)
+          break if message == :stop
+          @block.call(message)
+        end
+      end
+    end
+  end
+end