Thanks Sean! I can confirm the `rio hist` CLI is working well with Rasterio 1.1.1, py37. Thanks for keeping it afloat.

Pablo, I think your approach would make a great example and addition to the concurrency docs. Being able to do input, output and computation in parallel is a huge benefit. The locks seems effective at

An open Rasterio dataset object should not be passed between multiple processes or threads; the underlying GDALDataset is not thread safe. Additionally, the dataset's lifecycle should be made explicit

You can control the precision of the AAIGrid output using the GDAL creation options DECIMAL_PRECISION (or SIGNIFICANT_DIGITS). You can specify these as case-insensitive kwargs like `rasterio.open(...,