Improve tiling speed (#195)

* Add a way to run tippecanoe single-threaded for profiling

* Do less work when the tilestats sample values list is already full

* Save a copy when retrieving the attribute key

* Fewer atomic operations

* Move string hashing from mbtiles to text

* Only do approximate attribute deduplication when writing tiles

* Feature dropping tests are sensitive to exact tile size

* All tile creators now create a string pool for the tile

* Features clipped away to nothing should not participate in that tile

* Revert "Only do approximate attribute deduplication when writing tiles"

This reverts commit c42b34b498.

* Also revert the related test changes

* Revert "Revert "Only do approximate attribute deduplication when writing tiles""

This reverts commit 18509876c3.

* Be more specific about the string hash function

* Use fnv1a instead of std::hash for everything

* Reduce the chance of hash collisions

* Stick a hash search on the front of the tree search in addpool

* Eliminate repeated hashing of the same string

* Switch instead of ifs in json parsing

* A few more cases to populate the hash in addpool

* Store the hash in the tree instead of recalculating

* Add explanatory comment for mysterious argument

* Fewer copies in attribute stringification

* Clean up ancient weirdness in JSON attribute stringification

* More serial_val cleanup

* Pass a serial_feature to rewrite instead of many broken-down arguments

* Get rid of the multiple geometries within `partial`

* Revert "Pass a serial_feature to rewrite instead of many broken-down arguments"

This reverts commit 6f4ab9b725.

* Goodbye, struct coalesce

* Revert "Features clipped away to nothing should not participate in that tile"

This reverts commit 124462fbdc.

* Migrating fields from partial to serial_feature

* Name reconciliation between serial_feature and partial

* Replace struct partial with an augmented serial_feature

* Fix some overzealous search-and-replace renaming

* Don't say struct so often

* Remove more of the former partial construction

* Commenting and cleaning up

* Trying again to avoid all these arguments to rewrite

* I swear I did this same thing before and it didn't work.

* More rewrite cleanup

* Exile --detect-shared-borders to its own file

* Add missing headers

* More commenting and cleanup

* More comments

* Sprinkle consts around

* Emplacing and std::moving

* More cleanup

* That shouldn't have worked after a std::move

* Don't need to allocate memory to compare keys

* Reduce use of the global string pool in tiling

* Another avoidable mvt_value construction

* Further reduction to explicit string pool passing

* These reverses are no longer optimizations

* These layernames can all be references

* Don't drag an unused layername string around with every feature

* Heed a compiler warning about potential buffer overflow

* Fix my confusion about which feature's string pool is relevant

* Avoid some unnecessary allocations in attribute accumulation

* Maybe faster serialization?

* Eliminate a comparison

* Do the same here

* Save a couple of allocations when parsing numbers in JSON

* Immediately assign features to layers instead of subdividing later

* Maintain tilestats for tippecanoe:retain_points_multiplier_sequence

* Crunch out more duplicate attribute values when writing out the tile

* Do tilestats for tippecanoe:retain_points_multiplier_first too

* Shell filters need to be real threads, even if nothing else does

* Simplify tippecanoe_minzoom/maxzoom representation

* Update version and changelog

flatgeobuf.cpp

@@ -7,6 +7,7 @@
 #include "milo/dtoa_milo.h"
 #include "main.hpp"
 #include "errors.hpp"
+#include "thread.hpp"
 
 static constexpr uint8_t magicbytes[8] = { 0x66, 0x67, 0x62, 0x03, 0x66, 0x67, 0x62, 0x01 };
 
@@ -131,7 +132,6 @@ void readFeature(const FlatGeobuf::Feature *feature, long long feature_sequence_
 	serial_feature sf;
 
 	sf.layer = layer;
-	sf.layername = layername;
 	sf.segment = sst->segment;
 	if (feature_sequence_id >= 0) {
 		sf.has_id = true;
@@ -139,8 +139,8 @@ void readFeature(const FlatGeobuf::Feature *feature, long long feature_sequence_
 		sf.has_id = false;
 	}
 	sf.id = feature_sequence_id;
-	sf.has_tippecanoe_minzoom = false;
-	sf.has_tippecanoe_maxzoom = false;
+	sf.tippecanoe_minzoom = -1;
+	sf.tippecanoe_maxzoom = -1;
 	sf.feature_minzoom = false;
 	sf.seq = (*sst->layer_seq);
 	sf.geometry = dv;
@@ -246,7 +246,7 @@ void readFeature(const FlatGeobuf::Feature *feature, long long feature_sequence_
 	sf.full_keys = full_keys;
 	sf.full_values = full_values;
 
-	serialize_feature(sst, sf);
+	serialize_feature(sst, sf, layername);
 }
 
 struct fgb_queued_feature {
@@ -303,7 +303,7 @@ void fgbRunQueue() {
 	}
 
 	for (size_t i = 0; i < CPUS; i++) {
-		if (pthread_create(&pthreads[i], NULL, fgb_run_parse_feature, &qra[i]) != 0) {
+		if (thread_create(&pthreads[i], NULL, fgb_run_parse_feature, &qra[i]) != 0) {
 			perror("pthread_create");
 			exit(EXIT_PTHREAD);
 		}