Minor refactor on Thread pool (#1088)

* Move shutdown grace time constant to ThreadPool.
SHUTDOWN_GRACE_TIME is the only constant (from const.rb) used by
ThreadPool. It's better to move the constant than require all const.rb.
* Fix minor typo.

* Don't need to check if timeout is zero to immediately shutdown.
This removes the duplicated code and add test for forced shutdowns.

lib/puma/const.rb

@@ -113,11 +113,6 @@ module Const
     # sending data back
     WRITE_TIMEOUT = 10
 
-    # How long, after raising the ForceShutdown of a thread during
-    # forced shutdown mode, to wait for the thread to try and finish
-    # up it's work before leaving the thread to die on the vine.
-    SHUTDOWN_GRACE_TIME = 5 # seconds
-
     # The original URI requested by the client.
     REQUEST_URI= 'REQUEST_URI'.freeze
     REQUEST_PATH = 'REQUEST_PATH'.freeze

lib/puma/thread_pool.rb

@@ -4,10 +4,14 @@ module Puma
   # A simple thread pool management object.
   #
   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.
     #
@@ -259,18 +263,12 @@ def shutdown(timeout=-1)
         @workers.dup
       end
 
-      case timeout
-      when -1
+      if timeout == -1
+        # Wait for threads to finish without force shutdown.
         threads.each(&:join)
-      when 0
-        threads.each do |t|
-          t.raise ForceShutdown
-        end
-
-        threads.each do |t|
-          t.join Const::SHUTDOWN_GRACE_TIME
-        end
       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
@@ -288,7 +286,7 @@ def shutdown(timeout=-1)
         end
 
         threads.each do |t|
-          t.join Const::SHUTDOWN_GRACE_TIME
+          t.join SHUTDOWN_GRACE_TIME
         end
       end
 

test/test_thread_pool.rb

@@ -230,4 +230,21 @@ def test_auto_reap_dead_threads
 
     assert_equal 0, pool.spawned
   end
+
+  def test_force_shutdown_immediately
+    pool = new_pool(1, 1) {
+      begin
+        sleep 1
+      rescue Puma::ThreadPool::ForceShutdown
+      end
+    }
+
+    pool << 1
+
+    sleep 0.1
+
+    pool.shutdown(0)
+
+    assert_equal 0, pool.spawned
+  end
 end