Forking and waitpid()-ing for the -C/-c shell filters used to happen
directly in the multi-threaded tiling threads, which made fork() expensive
(full COW of the parent's address space) and unsafe (other threads could
hold libc/malloc locks at fork time). Now we pre-fork a small pool of
single-threaded worker processes once, before any tiling or reader threads
are spawned, and the tiling threads ask a worker to fork+exec the shell
child on their behalf, receiving the input/output pipe fds back via
SCM_RIGHTS. The fork() and waitpid() happen entirely inside the
single-threaded worker, where they are cheap and only block that worker.
Co-authored-by: Cursor <cursoragent@cursor.com>
* Progress on plumbing a string pool for full_keys through
* More plumbing for key_pool
* Don't keep features with identical locations as multiplier features
* Revert "Don't keep features with identical locations as multiplier features"
This reverts commit 413f0c8024.
* Adjust calculated maxzoom to account for duplicate feature locations
* Update changelog and version
* Add a test affected by the maxzoom change with duplicate locations
* Round the drop rate a little for cross-platform test consistency
