add Rscons.n_threads

spec/rscons_spec.rb

@@ -122,4 +122,70 @@ describe Rscons do
       end
     end
   end
+
+  describe ".determine_n_threads" do
+    context "when specified by environment variable" do
+      before(:each) do
+        expect(ENV).to receive(:[]).with("RSCONS_NTHREADS").and_return("3")
+      end
+      it "returns the user-specified number of threads to use" do
+        expect(Rscons.__send__(:determine_n_threads)).to eq(3)
+      end
+    end
+
+    context "when not specified by environment variable" do
+      before(:each) do
+        expect(ENV).to receive(:[]).with("RSCONS_NTHREADS").and_return(nil)
+      end
+
+      context "on Linux" do
+        before(:each) do
+          expect(RbConfig::CONFIG).to receive(:[]).with("host_os").and_return("linux")
+        end
+        it "returns the number of processors from /proc/cpuinfo" do
+          expect(File).to receive(:read).with("/proc/cpuinfo").and_return(<<EOF)
+processor : 0
+processor   : 1
+EOF
+          expect(Rscons.__send__(:determine_n_threads)).to eq(2)
+        end
+      end
+
+      context "on Windows" do
+        before(:each) do
+          expect(RbConfig::CONFIG).to receive(:[]).with("host_os").and_return("mingw")
+        end
+        it "returns the number of logical processors that wmic reports" do
+          expect(Rscons).to receive(:`).with("wmic cpu get NumberOfLogicalProcessors /value").and_return("NumberOfLogicalProcessors=7")
+          expect(Rscons.__send__(:determine_n_threads)).to eq(7)
+        end
+      end
+
+      context "on Darwin" do
+        before(:each) do
+          expect(RbConfig::CONFIG).to receive(:[]).with("host_os").and_return("darwin")
+        end
+        it "returns the number of threads that sysctl reports" do
+          expect(Rscons).to receive(:`).with("sysctl -n hw.ncpu").and_return("6")
+          expect(Rscons.__send__(:determine_n_threads)).to eq(6)
+        end
+      end
+
+      context "on an unknown platform" do
+        before(:each) do
+          expect(RbConfig::CONFIG).to receive(:[]).with("host_os").and_return("other")
+        end
+        it "returns 1" do
+          expect(Rscons.__send__(:determine_n_threads)).to eq(1)
+        end
+      end
+
+      context "when an error occurs" do
+        it "returns 1" do
+          expect(RbConfig::CONFIG).to receive(:[]).with("host_os").and_raise("foo")
+          expect(Rscons.__send__(:determine_n_threads)).to eq(1)
+        end
+      end
+    end
+  end
 end