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

geobuf.cpp

@@ -15,6 +15,7 @@
 #include "jsonpull/jsonpull.h"
 #include "text.hpp"
 #include "errors.hpp"
+#include "thread.hpp"
 
 #define POINT 0
 #define MULTIPOINT 1
@@ -379,12 +380,11 @@ void readFeature(protozero::pbf_reader &pbf, size_t dim, double e, std::vector<s
 		serial_feature sf;
 
 		sf.layer = layer;
-		sf.layername = layername;
 		sf.segment = sst->segment;
 		sf.has_id = has_id;
 		sf.id = 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[i].dv;
@@ -400,19 +400,17 @@ void readFeature(protozero::pbf_reader &pbf, size_t dim, double e, std::vector<s
 			if (o != NULL) {
 				json_object *min = json_hash_get(o, "minzoom");
 				if (min != NULL && (min->type == JSON_NUMBER)) {
-					sf.has_tippecanoe_minzoom = true;
 					sf.tippecanoe_minzoom = integer_zoom(sst->fname, milo::dtoa_milo(min->value.number.number));
 				}
 
 				json_object *max = json_hash_get(o, "maxzoom");
 				if (max != NULL && (max->type == JSON_NUMBER)) {
-					sf.has_tippecanoe_maxzoom = true;
 					sf.tippecanoe_maxzoom = integer_zoom(sst->fname, milo::dtoa_milo(max->value.number.number));
 				}
 
 				json_object *tlayer = json_hash_get(o, "layer");
 				if (tlayer != NULL && (tlayer->type == JSON_STRING)) {
-					sf.layername = tlayer->value.string.string;
+					layername = tlayer->value.string.string;
 				}
 			}
 
@@ -420,7 +418,7 @@ void readFeature(protozero::pbf_reader &pbf, size_t dim, double e, std::vector<s
 			json_end(jp);
 		}
 
-		serialize_feature(sst, sf);
+		serialize_feature(sst, sf, layername);
 	}
 }
 
@@ -465,7 +463,7 @@ void runQueue() {
 	}
 
 	for (size_t i = 0; i < CPUS; i++) {
-		if (pthread_create(&pthreads[i], NULL, run_parse_feature, &qra[i]) != 0) {
+		if (thread_create(&pthreads[i], NULL, run_parse_feature, &qra[i]) != 0) {
 			perror("pthread_create");
 			exit(EXIT_PTHREAD);
 		}
@@ -506,17 +504,16 @@ void outBareGeometry(drawvec const &dv, int type, struct serialization_state *ss
 	serial_feature sf;
 
 	sf.layer = layer;
-	sf.layername = layername;
 	sf.segment = sst->segment;
 	sf.has_id = false;
-	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;
 	sf.t = type;
 
-	serialize_feature(sst, sf);
+	serialize_feature(sst, sf, layername);
 }
 
 void readFeatureCollection(protozero::pbf_reader &pbf, size_t dim, double e, std::vector<std::string> &keys, std::vector<struct serialization_state> *sst, int layer, std::string layername) {