1 files changed, 37 insertions, 6 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
index 7dd5169e43..36001efdd5 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
@@ -167,7 +167,6 @@ module ActiveRecord
         end
 
         private
-
           def internal_poll(timeout)
             no_wait_poll || (timeout && wait_poll(timeout))
           end
@@ -330,7 +329,6 @@ module ActiveRecord
           end
 
           private
-
             def spawn_thread(frequency)
               Thread.new(frequency) do |t|
                 loop do
@@ -359,7 +357,7 @@ module ActiveRecord
       include ConnectionAdapters::AbstractPool
 
       attr_accessor :automatic_reconnect, :checkout_timeout, :schema_cache
-      attr_reader :spec, :connections, :size, :reaper
+      attr_reader :spec, :size, :reaper
 
       # Creates a new ConnectionPool object. +spec+ is a ConnectionSpecification
       # object which describes database connection information (e.g. adapter,
@@ -428,7 +426,7 @@ module ActiveRecord
       # #connection can be called any number of times; the connection is
       # held in a cache keyed by a thread.
       def connection
-        @thread_cached_conns[connection_cache_key(@lock_thread || Thread.current)] ||= checkout
+        @thread_cached_conns[connection_cache_key(current_thread)] ||= checkout
       end
 
       # Returns true if there is an open connection being used for the current thread.
@@ -437,7 +435,7 @@ module ActiveRecord
       # #connection or #with_connection methods. Connections obtained through
       # #checkout will not be detected by #active_connection?
       def active_connection?
-        @thread_cached_conns[connection_cache_key(Thread.current)]
+        @thread_cached_conns[connection_cache_key(current_thread)]
       end
 
       # Signal that the thread is finished with the current connection.
@@ -472,6 +470,21 @@ module ActiveRecord
         synchronize { @connections.any? }
       end
 
+      # Returns an array containing the connections currently in the pool.
+      # Access to the array does not require synchronization on the pool because
+      # the array is newly created and not retained by the pool.
+      #
+      # However; this method bypasses the ConnectionPool's thread-safe connection
+      # access pattern. A returned connection may be owned by another thread,
+      # unowned, or by happen-stance owned by the calling thread.
+      #
+      # Calling methods on a connection without ownership is subject to the
+      # thread-safety guarantees of the underlying method. Many of the methods
+      # on connection adapter classes are inherently multi-thread unsafe.
+      def connections
+        synchronize { @connections.dup }
+      end
+
       # Disconnects all connections in the pool, and clears the pool.
       #
       # Raises:
@@ -717,6 +730,10 @@ module ActiveRecord
           thread
         end
 
+        def current_thread
+          @lock_thread || Thread.current
+        end
+
         # Take control of all existing connections so a "group" action such as
         # reload/disconnect can be performed safely. It is no longer enough to
         # wrap it in +synchronize+ because some pool's actions are allowed
@@ -986,15 +1003,30 @@ module ActiveRecord
         end
       end
 
+      attr_reader :prevent_writes
+
       def initialize
         # These caches are keyed by spec.name (ConnectionSpecification#name).
         @owner_to_pool = ConnectionHandler.create_owner_to_pool
+        @prevent_writes = false
 
         # Backup finalizer: if the forked child never needed a pool, the above
         # early discard has not occurred
         ObjectSpace.define_finalizer self, ConnectionHandler.unowned_pool_finalizer(@owner_to_pool)
       end
 
+      # Prevent writing to the database regardless of role.
+      #
+      # In some cases you may want to prevent writes to the database
+      # even if you are on a database that can write. `while_preventing_writes`
+      # will prevent writes to the database for the duration of the block.
+      def while_preventing_writes
+        original, @prevent_writes = @prevent_writes, true
+        yield
+      ensure
+        @prevent_writes = original
+      end
+
       def connection_pool_list
         owner_to_pool.values.compact
       end
@@ -1112,7 +1144,6 @@ module ActiveRecord
       end
 
       private
-
         def owner_to_pool
           @owner_to_pool[Process.pid]
         end