r.blend: Add nprocs parameter and use it for r.mapcalc (#6564)

The main step in r.blend is running r.mapcalc which is now multithreaded. The default number of threads is now whatever is available on the machine, so to limit that, r.blend needs nprocs which is passed to r.mapcalc (before that change, r.blend was not taking the advantage of multithreading in r.mapcalc).

Author: wenzeslaus

scripts/r.blend/r.blend.py

@@ -42,6 +42,8 @@
 # % key: c
 # % description: Combine resulting R,G,B layers into single output map
 # %end
+# %option G_OPT_M_NPROCS
+# %end
 
 import os
 import string
@@ -53,6 +55,7 @@ def main():
     second = options["second"]
     output = options["output"]
     percent = options["percent"]
+    nprocs = options["nprocs"]
 
     mapset = gs.gisenv()["MAPSET"]
 
@@ -80,7 +83,15 @@ def main():
     cmd = [template.substitute(ch=ch) for ch in ["r", "g", "b"]]
     cmd = ";".join(cmd)
 
-    gs.mapcalc(cmd, output=output, first=first, second=second, frac1=frac1, frac2=frac2)
+    gs.mapcalc(
+        cmd,
+        output=output,
+        first=first,
+        second=second,
+        frac1=frac1,
+        frac2=frac2,
+        nprocs=nprocs,
+    )
 
     for ch in ["r", "g", "b"]:
         map = "%s.%s" % (output, ch)

scripts/r.blend/tests/r_blend_test.py

@@ -0,0 +1,14 @@
+"""Test of r.blend"""
+
+import pytest
+
+from grass.tools import Tools
+
+
+@pytest.mark.parametrize("nprocs", [None, 0, 1, 2])
+def test_nprocs_accepted(xy_raster_dataset_session_mapset, nprocs):
+    """Check that the nprocs parameter is accepted"""
+    tools = Tools(session=xy_raster_dataset_session_mapset)
+    tools.r_mapcalc(expression="test_1 = 1")
+    tools.r_mapcalc(expression="test_2 = 2")
+    tools.r_blend(first="test_1", second="test_2", output="output", nprocs=nprocs)