Merge JoinMarket-Org/joinmarket-clientserver#1177: Limit number of parallel builds during install to CPU core count

c0d6610df0 Limit number of parallel builds to CPU core count (Kristaps Kaupe)

Pull request description:

  I noticed too much parallel build processes for some time, but somehow missed that `export MAKEFLAGS='-j'` previously. If `-j` is given to `make` without any argument, it means unlimited job count. It may cause problems, especially on machines with limited available RAM amount (see https://github.com/JoinMarket-Org/joinmarket-clientserver/pull/1000#issuecomment-962425193, for example). And building in parallel with more jobs than CPU cores available does not make much sense.

Top commit has no ACKs.

Tree-SHA512: d59b0cc29d874aeb7079ef124de4bff9ca301995cc0c0a21cbcfebe56c84ca2f84a8196aceedfc763bf0fcc1216434b5f55fd3534d31fffd87bb74351d8024b6

install.sh

@@ -4,6 +4,10 @@ check_exists() {
     command -v "$1" > /dev/null
 }
 
+num_cores() {
+    python -c 'import multiprocessing as mp; print(mp.cpu_count())'
+}
+
 # This is needed for systems where GNU is not the default make, like FreeBSD.
 if check_exists gmake; then
     make=gmake
@@ -475,7 +479,7 @@ main ()
     export PKG_CONFIG_PATH="${jm_root}/lib/pkgconfig:${PKG_CONFIG_PATH}"
     export LD_LIBRARY_PATH="${jm_root}/lib:${LD_LIBRARY_PATH}"
     export C_INCLUDE_PATH="${jm_root}/include:${C_INCLUDE_PATH}"
-    export MAKEFLAGS='-j'
+    export MAKEFLAGS="-j $(num_cores)"
 
     # os check
     install_os="$( install_get_os )"