Introduce ForkTracker.before_fork

Also add ForkTracker.unregister_before_fork and rename
ForkTracker.unregister to unregister_after_fork for consistency.

activesupport/lib/active_support/evented_file_update_checker.rb

@@ -99,7 +99,7 @@ def initialize(files, dirs)
       def finalizer
         proc do
           stop
-          ActiveSupport::ForkTracker.unregister(@after_fork)
+          ActiveSupport::ForkTracker.unregister_after_fork(@after_fork)
         end
       end
 

activesupport/lib/active_support/fork_tracker.rb

@@ -4,6 +4,7 @@ module ActiveSupport
   module ForkTracker # :nodoc:
     module CoreExt
       def _fork
+        ForkTracker.before_fork_callback
         pid = super
         if pid == 0
           ForkTracker.after_fork_callback
@@ -13,13 +14,18 @@ def _fork
     end
 
     @pid = Process.pid
-    @callbacks = []
+    @before_callbacks = []
+    @after_callbacks = []
 
     class << self
+      def before_fork_callback
+        @before_callbacks.each(&:call)
+      end
+
       def after_fork_callback
         new_pid = Process.pid
         if @pid != new_pid
-          @callbacks.each(&:call)
+          @after_callbacks.each(&:call)
           @pid = new_pid
         end
       end
@@ -28,13 +34,22 @@ def hook!
         ::Process.singleton_class.prepend(CoreExt)
       end
 
+      def before_fork(&block)
+        @before_callbacks << block
+        block
+      end
+
       def after_fork(&block)
-        @callbacks << block
+        @after_callbacks << block
         block
       end
 
-      def unregister(callback)
-        @callbacks.delete(callback)
+      def unregister_before_fork(callback)
+        @before_callbacks.delete(callback)
+      end
+
+      def unregister_after_fork(callback)
+        @after_callbacks.delete(callback)
       end
     end
   end

activesupport/test/fork_tracker_test.rb

@@ -7,16 +7,22 @@ def setup
     super
 
     @read, @write = IO.pipe
-    @called = false
+    @before_called = false
+    @after_called = false
 
-    @handler = ActiveSupport::ForkTracker.after_fork do
-      @called = true
+    @before_handler = ActiveSupport::ForkTracker.before_fork do
+      @before_called = true
+    end
+
+    @after_handler = ActiveSupport::ForkTracker.after_fork do
+      @after_called = true
       @write.write "forked"
     end
   end
 
   def teardown
-    ActiveSupport::ForkTracker.unregister(@handler)
+    ActiveSupport::ForkTracker.unregister_before_fork(@before_handler)
+    ActiveSupport::ForkTracker.unregister_after_fork(@after_handler)
 
     super
   end
@@ -35,7 +41,8 @@ def test_object_fork
     assert_equal "forked", @read.read
     @read.close
 
-    assert_not @called
+    assert @before_called
+    assert_not @after_called
   end
 
   def test_object_fork_without_block
@@ -44,7 +51,8 @@ def test_object_fork_without_block
       Process.waitpid(pid)
       assert_equal "forked", @read.read
       @read.close
-      assert_not @called
+      assert @before_called
+      assert_not @after_called
     else
       @read.close
       @write.close
@@ -64,7 +72,8 @@ def test_process_fork
     Process.waitpid(pid)
     assert_equal "forked", @read.read
     @read.close
-    assert_not @called
+    assert @before_called
+    assert_not @after_called
   end
 
   def test_process_fork_without_block
@@ -73,7 +82,8 @@ def test_process_fork_without_block
       Process.waitpid(pid)
       assert_equal "forked", @read.read
       @read.close
-      assert_not @called
+      assert @before_called
+      assert_not @after_called
     else
       @read.close
       @write.close
@@ -93,7 +103,8 @@ def test_kernel_fork
     Process.waitpid(pid)
     assert_equal "forked", @read.read
     @read.close
-    assert_not @called
+    assert @before_called
+    assert_not @after_called
   end
 
   def test_kernel_fork_without_block
@@ -102,7 +113,8 @@ def test_kernel_fork_without_block
       Process.waitpid(pid)
       assert_equal "forked", @read.read
       @read.close
-      assert_not @called
+      assert @before_called
+      assert_not @after_called
     else
       @read.close
       @write.close
@@ -132,18 +144,21 @@ def fark(&block)
     assert_equal "forked", @read.read
     @read.close
 
-    assert_not @called
+    assert @before_called
+    assert_not @after_called
   end
 
   def test_unregister_callback
-    ActiveSupport::ForkTracker.unregister(@handler)
+    ActiveSupport::ForkTracker.unregister_before_fork(@before_handler)
+    ActiveSupport::ForkTracker.unregister_after_fork(@after_handler)
 
     if pid = Process.fork
       @write.close
       Process.waitpid(pid)
       assert_equal "", @read.read
       @read.close
-      assert_not @called
+      assert_not @before_called
+      assert_not @after_called
     else
       @read.close
       @write.close