memory doesn't free using features.geometry_mask function with fastapi about rasterio

[sgillies]

@aloi214 Thanks for the report! I have a few questions:

• Is fastapi required to produce the increasing memory? What do you see if you just loop over create_mask() without accumulating results?
• Are you aware that GDAL has a raster block cache? Sometimes this appears to be a leak to users. What do you see if you run your program with the environment variable set to GDAL_CACHEMAX=0?

[aloi214]

@sgillies Thanks for replying. As I know, usually the occupied memory after finishing each request should keep same after first request. And I run more test:

1. loop over create_mask() without append result into a list.
2. limit GDAL_CACHEMAX as

def create_mask(polyline):
    polyline = np.array(polyline)
    origin = polyline.min(axis=0)
    site_shape = (polyline.max(axis=0) - polyline.min(axis=0))[::-1].astype(int)
    shapely_geo = sg.Polygon(polyline-origin)
    with rasterio.Env(GDAL_CACHEMAX=0, CPL_VSIL_CURL_CACHE_SIZE=0, VSI_CACHE=False, VSI_CACHE_SIZE=0, aws_unsigned=True) as env:
        control_mask = features.geometry_mask([shapely_geo], out_shape=site_shape, transform=transform.IDENTITY, invert=False)
    return control_mask

3. Excute export GDAL_CACHEMAX=0 in command line to limit GDAL_CACHEMAX.

But the memory are keeping increase in all those cases. I'm not sure if I limit the GDAL_CACHEMAX successfully.