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>
* Improve maxzoom guessing for tightly-clustered point data sources
* Go back to the old distance estimate, since it is less mysterious
* Update changelog and version
* Add --maximum-zoom-at-least to specify a minimum maxzoom to guess
* Check whether the specified minimum maxzoom is out of range
* Rename the option to --smallest-maximum-zoom-guess
* Update tests, changelog, and version
* Handle points too when dropping or coalescing the "smallest" features.
* Add statistics of tile size reduction strategies to tileset metadata
* Update changelog and version
* Update documentation
* Change JSON objects to a union type to use less memory
* Stop storing the string representation of JSON numbers
* Restore the ability to create features with large integer attributes
* Make sure large-integer feature IDs still behave as before
* Add missing #include
* Don't preallocate as much space for arrays and objects
* Treat inability to check free disk space as a warning, not an error
* Update changelog and version
