copies-rust: move CPU-heavy Rust processing into a child thread ? that runs in parallel with the parent thread fetching data. This can be disabled through a new config. CLI example: hg --config=devel.copy-tracing.multi-thread=no For now both threads use the GIL, later commits will reduce this. Differential Revision: https://phab.mercurial-scm.org/D9684

--- a/mercurial/configitems.py	Tue Jan 05 21:02:00 2021 +0100
+++ b/mercurial/configitems.py	Wed Jan 06 14:09:01 2021 +0100
@@ -700,6 +700,11 @@
 )
 coreconfigitem(
     b'devel',
+    b'copy-tracing.multi-thread',
+    default=True,
+)
+coreconfigitem(
+    b'devel',
     b'debug.extensions',
     default=False,
 )