Test how evented file checker handles forks

Pretty proud of this. We are testing distributed processes synchronized via pipes which makes it deterministic. Pretty cool.

We boot a listener in the parent process we then fork. Before we touch the file we verify the fork is booted using pipes. Then the parent process will touch the file while the fork waits on a pipe. Once the parent process signals that the file has been touched we continue inside of the fork.

1 files changed, 42 insertions, 1 deletions

diff --git a/activesupport/test/evented_file_update_checker_test.rb b/activesupport/test/evented_file_update_checker_test.rb
index ce2e05da2c..2cb2d8167f 100644
--- a/activesupport/test/evented_file_update_checker_test.rb
+++ b/activesupport/test/evented_file_update_checker_test.rb
@@ -12,7 +12,6 @@ class EventedFileUpdateCheckerTest < ActiveSupport::TestCase
 
   def new_checker(files = [], dirs = {}, &block)
     ActiveSupport::EventedFileUpdateChecker.new(files, dirs, &block).tap do |c|
-      c.updated?
       wait
     end
   end
@@ -35,6 +34,48 @@ class EventedFileUpdateCheckerTest < ActiveSupport::TestCase
     super
     wait
   end
+
+  test 'notifies forked processes' do
+    FileUtils.touch(tmpfiles)
+
+    checker = new_checker(tmpfiles) { }
+    assert !checker.updated?
+
+    # Pipes used for flow controll across fork.
+    boot_reader,  boot_writer  = IO.pipe
+    touch_reader, touch_writer = IO.pipe
+
+    pid = fork do
+      assert checker.updated?
+
+      # Clear previous check value.
+      checker.execute
+      assert !checker.updated?
+
+      # Fork is booted, ready for file to be touched
+      # notify parent process.
+      boot_writer.write("booted")
+
+      # Wait for parent process to signal that file
+      # has been touched.
+      IO.select([touch_reader])
+
+      assert checker.updated?
+    end
+
+    assert pid
+
+    # Wait for fork to be booted before touching files.
+    IO.select([boot_reader])
+    touch(tmpfiles)
+
+    # Notify fork that files have been touched.
+    touch_writer.write("touched")
+
+    assert checker.updated?
+
+    Process.wait(pid)
+  end
 end
 
 class EventedFileUpdateCheckerPathHelperTest < ActiveSupport::TestCase