Stop blocking ruby during long-running operations

test/test_helpers.rb

@@ -0,0 +1,27 @@
+require 'lxc'
+require 'test/unit/assertions'
+
+module TestHelpers
+  def assert_long_running_function_does_not_block_ruby(&block)
+    r, w = IO.pipe
+    begin
+      # Write something after a very short period, but only if Ruby isn't blocked!
+      t = Thread.new do
+        sleep(0.001)
+        # Sleep twice so that if the function is blocking and we wake up just
+        # after block.call(c) somehow, we will go back to sleep briefly and
+        # allow B to be written
+        sleep(0.001)
+        w.write('A')
+      end
+      # Call the function and see if Ruby gets blocked
+      block.call
+      w.write('B')
+      chars = r.read(2)
+      assert(chars == 'AB', "Expected thread to write before block finished, but it did not. Expected 'AB', got '#{chars}'")
+    ensure
+      r.close
+      w.close
+    end
+  end
+end