JVM crash on large polyfills

まず、TestH3Core.java の大きな polyfill ケースでクラッシュを再現し、次に関連する testPolyfill.c ケースおよび h3Api.polyfill 呼び出しと比較します。失敗が Java wrapper にあるのか core library にあるのかを特定し、大きなポリゴンのリグレッションテストによって修正の完了を確認します。

When the following is added to TestH3Core.java, the jvm crashes out on h3Api.polyfill before completing the tests. The polyfill works at resolution 9.

    @Test
    public void testPolyfillLarge() {
        List<Long> hexagons = h3.polyfill(
                ImmutableList.<GeoCoord>of(
                        new GeoCoord(41.5, -70.4),
                        new GeoCoord(41.5, -69.8),
                        new GeoCoord(42.1, -69.8),
                        new GeoCoord(42.1, -70.4)
                ), null,
                10
        );

        assertTrue(hexagons.size() > 1000);
    }

Is this an issue with the java wrapper, or is this impossible to do with the core library?

I don't know C but adding a similar test to h3 naively copying the existing styles to testPolyfill.c at level 11 still seems to work. If I increase the resolution up past 11 it eventually segfaults there too.

GeoCoord capeCodVerts[] = {
        {0.7243116395776468, -1.2287117934040082},  {0.7243116395776468, -1.218239817892042},
        {0.7347836150896128, -1.218239817892042}, {0.7347836150896128, -1.2287117934040082}};
Geofence capeCodGeofence;
GeoPolygon capeCodGeoPolygon;

capeCodGeofence.numVerts = 4;
capeCodGeofence.verts = capeCodVerts;
capeCodGeoPolygon.geofence = capeCodGeofence;
capeCodGeoPolygon.numHoles = 0;

TEST(polyfillLarge) {
    int numHexagons = H3_EXPORT(maxPolyfillSize)(&capeCodGeoPolygon, 12);
    H3Index* hexagons = calloc(numHexagons, sizeof(H3Index));

    H3_EXPORT(polyfill)(&capeCodGeoPolygon, 11, hexagons);
    int actualNumHexagons = 0;
    for (int i = 0; i < numHexagons; i++) {
        if (hexagons[i] != 0) {
            actualNumHexagons++;
        }
    }
    
    t_assert(actualNumHexagons > 10000, "got lots of hexagons");
    free(hexagons);
}