GeoTiffRasterSource should be thread-safe

[echeipesh]

When using GeoTiffRasterSource instance in multi-threaded context, either in spark multi-partition per executor or as part of async http4s application the following error is possible:

[info] java.lang.IllegalArgumentException
[info] at java.nio.Buffer.position(Buffer.java:244)
[info] at geotrellis.util.StreamingByteReader.ensureChunk(StreamingByteReader.scala:114)
[info] at geotrellis.util.StreamingByteReader.getBytes(StreamingByteReader.scala:118)
[info] at geotrellis.raster.io.geotiff.LazySegmentBytes.getBytes(LazySegmentBytes.scala:120)
[info] at geotrellis.raster.io.geotiff.LazySegmentBytes$$anonfun$readChunk$1.apply(LazySegmentBytes.scala:99)
[info] at geotrellis.raster.io.geotiff.LazySegmentBytes$$anonfun$readChunk$1.apply(LazySegmentBytes.scala:97)
[info] at scala.collection.immutable.List.map(List.scala:284)
[info] at geotrellis.raster.io.geotiff.LazySegmentBytes.readChunk(LazySegmentBytes.scala:97)
[info] at geotrellis.raster.io.geotiff.LazySegmentBytes$$anonfun$getSegments$1.apply(LazySegmentBytes.scala:115)
[info] at geotrellis.raster.io.geotiff.LazySegmentBytes$$anonfun$getSegments$1.apply(LazySegmentBytes.scala:115)
[info] at scala.collection.Iterator$$anon$12.nextCur(Iterator.scala:435)
[info] at scala.collection.Iterator$$anon$12.hasNext(Iterator.scala:441)
[info] at scala.collection.Iterator$$anon$13.hasNext(Iterator.scala:462)
[info] at scala.collection.Iterator$$anon$11.hasNext(Iterator.scala:409)
[info] at scala.collection.Iterator$$anon$12.hasNext(Iterator.scala:440)
[info] at scala.collection.Iterator$$anon$11.hasNext(Iterator.scala:409)
[info] at scala.collection.Iterator$$anon$11.hasNext(Iterator.scala:409)
[info] at geotrellis.contrib.vlm.geotiff.GeoTiffRasterSource.read(GeoTiffRasterSource.scala:58)
[info] at geotrellis.contrib.vlm.RasterSource$class.read(RasterSource.scala:163)
[info] at geotrellis.contrib.vlm.geotiff.GeoTiffRasterSource.read(GeoTiffRasterSource.scala:28)

This happens because underlying geotrellis.raster.io.geotiff.LazySegmentBytes nor GeoTiffTile which uses it is not thread safe. GeoTiffReader does not make promises about being thread safe, but RasterSource makes an implicit promise to be thread safe and thats a useful expectation.

For this issue I suggest:

• Use synchronize on GeoTiff[MultibandTile] contained by GeoTiffRasterSource to make all read methods thread-safe
• Update the documentation on RasterSource interface to state that thread-safe behavior is expected

[pomadchin]

The example of a possible fix + also an easy way to check it is a RasterSourceF usage: https://github.com/pomadchin/geotrellis-contrib/blob/feature/rs-effects-2/vlm/src/main/scala/geotrellis/contrib/vlm/effect2/geotiff/instances/GeoTiffMultibandReaderSync.scala#L32