SConstruct: automate choice of -j<n> (Spot got a new cpu )

SConstruct

@@ -674,6 +674,39 @@ SConsEnvironment.InstallPerm = InstallPerm
 # Your extra checks here
 env = conf.Finish()
 
+def get_cpu_count():
+    # priority: environ('NUM_CPU'), else try to read actual cpu count, else fallback
+    fallback = 4
+
+    if 'NUM_CPU' in os.environ:
+        return int(os.environ.get('NUM_CPU'))
+
+    # try multiprocessing.cpu_count() (Python 2.6+)
+    try:
+        import multiprocessing
+        return multiprocessing.cpu_count()
+    except (ImportError, NotImplementedError):
+        pass
+
+   # try psutil.cpu_count()
+    try:
+        import psutil
+        return psutil.cpu_count()
+    except (ImportError, AttributeError):
+        pass
+
+    # default value
+    return fallback
+
+
+# set number of parallel jobs during build
+# note: while not particularly intuitive or obvious from the documentation,
+# SetOption() will *not* over-ride commandline option passed by `scons -j<n>`
+# or `scons --jobs=<n>`
+SetOption('num_jobs', get_cpu_count())
+
+print "Running with --jobs=" + repr(GetOption('num_jobs'))
+
 library = SConscript('lib/SConscript')
 programs = SConscript('src/SConscript', exports='library')
 env.Default(library)

docs/install.rst

@@ -152,9 +152,9 @@ build the software from the potentially unstable ``develop`` branch:
    $ git clone -b develop https://github.com/sahib/rmlint.git 
    $ cd rmlint/
    $ scons config       # Look what features scons would compile
-   $ scons DEBUG=1 -j4  # Optional, build locally. 
+   $ scons DEBUG=1      # Optional, build locally.
    # Install (and build if necessary). For releases you can omit DEBUG=1
-   $ sudo scons DEBUG=1 -j4 --prefix=/usr install 
+   $ sudo scons DEBUG=1 --prefix=/usr install
 
 Done!
 

pkg/arch/PKGBUILD

@@ -25,7 +25,7 @@ pkgver() {
 
 build() {
     cd "${srcdir}/${pkgname}"
-    scons -j4 DEBUG=1 --prefix=${pkgdir}/usr --actual-prefix=/usr
+    scons DEBUG=1 --prefix=${pkgdir}/usr --actual-prefix=/usr
 }
 
 package() {

pkg/fedora/rmlint.spec

@@ -16,13 +16,13 @@ especially an extremely fast tool to remove duplicates from your filesystem.
 %prep 
 %autosetup -c rmlint-%{version}
 
-%build scons config; scons -j4 --prefix=%{buildroot}/usr --actual-prefix=/usr --libdir=lib64
+%build scons config; scons --prefix=%{buildroot}/usr --actual-prefix=/usr --libdir=lib64
 
 %install
 
 # Build rmlint, install it into BUILDROOT/<name>-<version>/,
 # but take care rmlint thinks it's installed to /usr (--actual_prefix)
-scons install -j4 --prefix=%{buildroot}/usr --actual-prefix=/usr --libdir=lib64
+scons install --prefix=%{buildroot}/usr --actual-prefix=/usr --libdir=lib64
 
 # Find all rmlint.mo files and put them in rmlint.lang
 %find_lang %{name}