Detect number of CPU cores used for `make`

Alt. implementation of #401, #434

bin/ruby-build

@@ -96,6 +96,17 @@ file_is_not_empty() {
   fi
 }
 
+num_cpu_cores() {
+  local num=""
+  if [ "Darwin" = "$(uname -s)" ]; then
+    num="$(sysctl -n hw.ncpu 2>/dev/null || true)"
+  elif [ -r /proc/cpuinfo ]; then
+    num="$(grep -c ^processor /proc/cpuinfo)"
+    [ "$num" -gt 0 ] || num=""
+  fi
+  echo "${num:-2}"
+}
+
 install_package() {
   install_package_using "tarball" 1 "$@"
 }
@@ -374,7 +385,7 @@ build_package_standard() {
   if [ "${MAKEOPTS+defined}" ]; then
     MAKE_OPTS="$MAKEOPTS"
   elif [ -z "${MAKE_OPTS+defined}" ]; then
-    MAKE_OPTS="-j 2"
+    MAKE_OPTS="-j $(num_cpu_cores)"
   fi
 
   # Support YAML_CONFIGURE_OPTS, RUBY_CONFIGURE_OPTS, etc.

test/build.bats

@@ -3,6 +3,7 @@
 load test_helper
 export RUBY_BUILD_CACHE_PATH="$TMP/cache"
 export MAKE=make
+export MAKE_OPTS="-j 2"
 
 setup() {
   mkdir -p "$INSTALL_ROOT"
@@ -91,6 +92,51 @@ make -j 2
 OUT
 }
 
+@test "number of CPU cores defaults to 2" {
+  cached_tarball "ruby-2.0.0"
+
+  stub uname '-s : echo Darwin'
+  stub sysctl false
+  stub_make_install
+
+  export -n MAKE_OPTS
+  run_inline_definition <<DEF
+install_package "ruby-2.0.0" "http://ruby-lang.org/ruby/2.0/ruby-2.0.0.tar.gz"
+DEF
+  assert_success
+
+  unstub uname
+  unstub make
+
+  assert_build_log <<OUT
+ruby-2.0.0: --prefix=$INSTALL_ROOT
+make -j 2
+OUT
+}
+
+@test "number of CPU cores is detected on Mac" {
+  cached_tarball "ruby-2.0.0"
+
+  stub uname '-s : echo Darwin'
+  stub sysctl '-n hw.ncpu : echo 4'
+  stub_make_install
+
+  export -n MAKE_OPTS
+  run_inline_definition <<DEF
+install_package "ruby-2.0.0" "http://ruby-lang.org/ruby/2.0/ruby-2.0.0.tar.gz"
+DEF
+  assert_success
+
+  unstub uname
+  unstub sysctl
+  unstub make
+
+  assert_build_log <<OUT
+ruby-2.0.0: --prefix=$INSTALL_ROOT
+make -j 4
+OUT
+}
+
 @test "custom relative install destination" {
   export RUBY_BUILD_CACHE_PATH="$FIXTURE_ROOT"