Library reloading problems

[martinjankoehler]

@klayoutmatthias

With the library manager plugin we encounter problems with the File → Reload Cell Libraries menu action:
iic-jku/klayout-library-manager#41

Basically the issue is after a PCell is added into a library cell,
updating the outer top layout instantiating the libcell fails.

The main code was:

lib = pya.Library.library_by_name(lib_def.lib_name)
lib.layout().clear()
lib.layout().read(lib_def.lib_path)
lib.refresh()

I also tried this:

lib = pya.Library.library_by_name(LIB_NAME)
tmp = pya.Layout()
tmp.read(str(LIB_PATH))
lib.layout().assign(tmp)
lib.refresh()

I've attached a python macro that reproduces the issue:
library_reloading_issue1.py

[klayoutmatthias]

I created a simplified version of the script using Basic/TEXT instead of the S13G PCell:

library_reloading_issue1.py

My observation is: at the end the "top.gds" layout shows the TEXT PCell instead of the library's "subcell". Is that the effect it is supposed to demonstrate?

I guess there is a mixup of cell indexes here. The "top.gds" layout window is dirty and after reload everything is fine.

[klayoutmatthias]

Hi Martin,

I found the problem, but there is no simple workaround unfortunately. A cell mapping is required after the reload creates different cells and this does not happen currently.

A workaround was to re-register a library on refresh. I think that was the solution before the refresh method was added.

When the patch is in place, you should not change the library's layout directly. Instead, using "refresh" on the Library is enough. This will try reloading the library and do the mapping. For this, it will take a copy before reloading. That is essentially the same thing than re-registration.

However, you will also need to specify, how the reload is supposed to happen. A Library object is agnostic about how the layout is made. A Python-generated library needs to reimplement the "reload" method:

# ── 2. Register lib.gds as a KLayout library ─────────────────────────────────

# Unregister any stale copy from a previous run
existing = pya.Library.library_by_name(LIB_NAME)
if existing is not None:
    if hasattr(pya.Library, "unregister"):   # KLayout >= 0.30.5
        pya.Library.unregister(existing)
    else:
        existing.delete()
        
class MyLibLibrary(pya.Library):
  # ** It's important to override 'reload'. Only here you can safely modify the layout object **
  def reload(self):
    self.layout().clear()
    self.layout().read(LIB_PATH)
    return LIB_NAME

lib_obj = MyLibLibrary()
lib_obj.reload()
lib_obj.register(LIB_NAME)
print(f"Registered library '{LIB_NAME}'")

and later:

# ── 6. Switch active view to top.gds and reload MyLib ────────────────────────

mw.current_view_index = mw.index_of(top_cv.view())

lib = pya.Library.library_by_name(LIB_NAME)
lib.refresh()
print(f"Reloaded library '{LIB_NAME}' — top.gds should now show ntap1 inside subcell")

top_cv.view().add_missing_layers()
top_cv.view().zoom_fit()

print("Done.")

But remember that needs the mentioned patch first.

Matthias

[klayoutmatthias]

I have added a convenience method to simplify the registration of libraries from files: with Library#library_from_file you can directly create a library that is tied to a file:

# ── 2. Register lib.gds as a KLayout library ─────────────────────────────────

# Unregister any stale copy from a previous run
existing = pya.Library.library_by_name(LIB_NAME)
if existing is not None:
    if hasattr(pya.Library, "unregister"):   # KLayout >= 0.30.5
        pya.Library.unregister(existing)
    else:
        existing.delete()

# ** Using new convenience function **      
lib_obj = pya.Library.library_from_file(LIB_PATH, LIB_NAME)  
print(f"Registered library '{LIB_NAME}'")

The advantage is that you do not need to implement "reload". That is implied by the library object which is created (and registered) by library_from_file.

Matthias