Allow restarting pool (#140)

* Allow restarting pool

The implementation of shutdown from
https://github.com/mperham/connection_pool/issues/27 does not actually
provide for a way for the pool to re-create connections, only render the
pool unusable. This implements such a behavior. A new method is added so
as to not change the existing behavior of `shutdown`.

Changes.md

@@ -3,6 +3,7 @@
 HEAD
 ------
 
+- Add `reload` to close all connections, recreating them afterwards [Andrew Marshall, #140]
 - Add `then` as a way to use a pool or a bare connection with the
   same code path [#138]
 

README.md

@@ -95,6 +95,22 @@ Shutting down a connection pool will block until all connections are checked in
 **Note that shutting down is completely optional**; Ruby's garbage collector will reclaim
 unreferenced pools under normal circumstances.
 
+## Reload
+
+You can reload a ConnectionPool instance in the case it is desired to close all
+connections to the pool and, unlike `shutdown`, afterwards recreate connections
+so the pool may continue to be used. Reloading may be useful after forking the
+process.
+
+```ruby
+cp = ConnectionPool.new { Redis.new }
+cp.reload { |conn| conn.quit }
+cp.with { |conn| conn.get('some-count') }
+```
+
+Like `shutdown`, this will block until all connections are checked in and
+closed.
+
 ## Current State
 
 There are several methods that return information about a pool.

lib/connection_pool.rb

@@ -95,10 +95,24 @@ class ConnectionPool
     nil
   end
 
+  ##
+  # Shuts down the ConnectionPool by passing each connection to +block+ and
+  # then removing it from the pool. Attempting to checkout a connection after
+  # shutdown will raise +ConnectionPool::PoolShuttingDownError+.
+
   def shutdown(&block)
     @available.shutdown(&block)
   end
 
+  ##
+  # Reloads the ConnectionPool by passing each connection to +block+ and then
+  # removing it the pool. Subsequent checkouts will create new connections as
+  # needed.
+
+  def reload(&block)
+    @available.shutdown(reload: true, &block)
+  end
+
   # Size of this connection pool
   attr_reader :size
 

lib/connection_pool/timed_stack.rb

@@ -81,10 +81,12 @@ class ConnectionPool::TimedStack
   end
 
   ##
-  # Shuts down the TimedStack which prevents connections from being checked
-  # out.  The +block+ is called once for each connection on the stack.
+  # Shuts down the TimedStack by passing each connection to +block+ and then
+  # removing it from the pool. Attempting to checkout a connection after
+  # shutdown will raise +ConnectionPool::PoolShuttingDownError+ unless
+  # +:reload+ is +true+.
 
-  def shutdown(&block)
+  def shutdown(reload: false, &block)
     raise ArgumentError, "shutdown must receive a block" unless block_given?
 
     @mutex.synchronize do
@@ -92,6 +94,7 @@ class ConnectionPool::TimedStack
       @resource.broadcast
 
       shutdown_connections
+      @shutdown_block = nil if reload
     end
   end
 
@@ -143,6 +146,7 @@ class ConnectionPool::TimedStack
       conn = fetch_connection(options)
       @shutdown_block.call(conn)
     end
+    @created = 0
   end
 
   ##

test/test_connection_pool_timed_stack.rb

@@ -102,6 +102,16 @@ class TestConnectionPoolTimedStack < Minitest::Test
     end
   end
 
+  def test_pop_shutdown_reload
+    stack = ConnectionPool::TimedStack.new(1) { Object.new }
+    object = stack.pop
+    stack.push(object)
+
+    stack.shutdown(reload: true) {}
+
+    refute_equal object, stack.pop
+  end
+
   def test_push
     stack = ConnectionPool::TimedStack.new(1) { Object.new }