Explain the cleaner exception in the wait mechanics

1 files changed, 3 insertions, 0 deletions

diff --git a/DESIGN b/DESIGN
index d365fb5..eb8679e 100644
--- a/DESIGN
+++ b/DESIGN
@@ -46,6 +46,9 @@ every thread on every tick for the life of the process to catch something
 that happens once: at eight workers it doubled idle context switches, 255 to
 495 over thirty seconds.
 
+The cleaner is the exception, and waits on a pipe nobody reads. A poll
+timeout is an interval rather than a deadline, so no clock enters into it.
+
 Each binary is built in one compiler invocation. Without object files a build
 cannot link objects compiled with different FEATURES, which was a real
 failure mode. It costs incremental rebuilds, 0.075 seconds becoming 1.56.