Make compilation on Raspberry Pi more user friendly (#11379)

sys/build.sh

@@ -1,11 +1,54 @@
 #!/bin/sh
 
+GetPlatform() {
+	# Get OS and platform to decide if we need to limit memory usage
+	# during the build
+	PLATFORM=$(uname -a)
+	case "$PLATFORM" in
+	"Linux raspberrypi"*) MAX_MEM_PER_JOB=300000;;
+	"Linux"*) MAX_MEM_PER_JOB=150000;;
+	*) MAX_MEM_PER_JOB=200000 # If platform is not Linux (fallback value)
+	esac
+}
+
+BuildJobsThrottler(){
+	echo "Building on Linux : computing number of allowed parallel jobs."
+	echo "Maximum allowed RAM memory per job is $MAX_MEM_PER_JOB kB."
+
+	# Get number of CPUs on this target
+	# getconf does not exit on Darwin. Use sysctl on Darwin machines.
+	CPU_N=$(getconf _NPROCESSORS_ONLN 2>/dev/null || sysctl -n hw.ncpu) 
+	printf "Number of CPUs is %s and "  "$CPU_N"
+
+	# Get remaining RAM that could be used for this build
+	FREE_RAM=$(grep MemAvailable /proc/meminfo | sed 's/[^0-9]//g')
+
+	DEFAULT_MAX_MEM_PER_JOB=200000
+	[ -z "${MAX_MEM_PER_JOB}" ] && MAX_MEM_PER_JOB="$DEFAULT_MAX_MEM_PER_JOB" # Defensive, prevent devision by 0
+	
+	# Assuming we may have many 300MB compilation jobs running in parallel
+	MEM_ALLOWED_JOBS=$((FREE_RAM / MAX_MEM_PER_JOB))
+	echo "current free RAM allows us to run $MEM_ALLOWED_JOBS jobs in parallel." 
+
+	# Set number of build jobs to be run in parallel as the minimum between $MEM_ALLOWED_JOBS and $CPU_N
+	MAKE_JOBS=$((MEM_ALLOWED_JOBS<CPU_N?MEM_ALLOWED_JOBS:CPU_N))
+	echo "So, the build will run on $MAKE_JOBS job(s)."
+}
+
+# Identify current platform
+GetPlatform
+
+# Define number of parallel jobs as function of resources and platform 
+BuildJobsThrottler
+
 if [ -z "${MAKE}" ]; then
 	MAKE=make
 	gmake --help >/dev/null 2>&1
 	[ $? = 0 ] && MAKE=gmake
 fi
+
 [ -z "${MAKE_JOBS}" ] && MAKE_JOBS=12
+
 [ -z "${CERTID}" ] && CERTID=org.radare.radare2
 
 # find root