[gentoo-dev] [PATCH 14/15] scons-utils.eclass: Use nproc when --jobs is used without an argument

[Michał Górny]

Try to guess the number of processors when --jobs is passed without
an argument. We can't use a high number equivalent to GNU make behavior
(no limit) since SCons does not have an equivalent of --load-avg option.
Still, this is better than assuming some random, fixed number.
---
 eclass/scons-utils.eclass   | 30 ++++++++++++++++++++++++++++--
 eclass/tests/scons-utils.sh |  2 +-
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/eclass/scons-utils.eclass b/eclass/scons-utils.eclass
index 3185282..89618f9 100644
--- a/eclass/scons-utils.eclass
+++ b/eclass/scons-utils.eclass
@@ -149,6 +149,32 @@ escons() {
 	return ${ret}
 }
 
+# @FUNCTION: _scons_get_default_jobs
+# @INTERNAL
+# @DESCRIPTION:
+# Output the default number of jobs, used if -j is used without
+# argument. Tries to figure out the number of logical CPUs, falling
+# back to hardcoded constant.
+_scons_get_default_jobs() {
+	local nproc
+
+	if type -P nproc &>/dev/null; then
+		# GNU
+		nproc=$(nproc)
+	elif type -P python &>/dev/null; then
+		# fallback to python2.6+
+		# note: this may fail (raise NotImplementedError)
+		nproc=$(python -c 'import multiprocessing; print(multiprocessing.cpu_count());' 2>/dev/null)
+	fi
+
+	if [[ ${nproc} ]]; then
+		echo $(( nproc + 1 ))
+	else
+		# random default
+		echo 5
+	fi
+}
+
 # @FUNCTION: _scons_clean_makeopts
 # @INTERNAL
 # @USAGE: [makeflags] [...]
@@ -192,7 +218,7 @@ _scons_clean_makeopts() {
 					shift
 				else
 					# no value means no limit, let's pass a random int
-					new_makeopts+=( ${1}=5 )
+					new_makeopts+=( ${1}=$(_scons_get_default_jobs) )
 				fi
 				;;
 			# strip other long options
@@ -215,7 +241,7 @@ _scons_clean_makeopts() {
 								new_optstr+="j ${2}"
 								shift
 							else
-								new_optstr+="j 5"
+								new_optstr+="j $(_scons_get_default_jobs)"
 							fi
 							;;
 						# otherwise, everything after -j is treated as an arg
diff --git a/eclass/tests/scons-utils.sh b/eclass/tests/scons-utils.sh
index 6355c54..fcb5125 100755
--- a/eclass/tests/scons-utils.sh
+++ b/eclass/tests/scons-utils.sh
@@ -28,7 +28,7 @@ test-scons_clean_makeopts() {
 }
 
 # jobcount expected for non-specified state
-jc=5
+jc=$(_scons_get_default_jobs)
 # failed test counter
 failed=0
 
-- 
2.6.4