Use Ninja for speeding up build

.travis.yml

@@ -17,12 +17,12 @@ matrix:
       osx_image: xcode9.2
       env: TASK=test-mac
 before_install:
-  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then docker pull openjdk:8-jdk  ; fi
-  - if [[ "$TASK" == "test-fedora"     ]]; then docker pull fedora:27      ; fi
-  - if [[ "$TASK" == "test-ubuntu"     ]]; then docker pull ubuntu:16.04   ; fi
-  - if [[ "$TRAVIS_OS_NAME" == "osx"   ]]; then brew update                ; fi
-  - if [[ "$TRAVIS_OS_NAME" == "osx"   ]]; then rm '/usr/local/include/c++'; fi
-  - if [[ "$TRAVIS_OS_NAME" == "osx"   ]]; then brew install gcc@7 sbt     ; fi
+  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then docker pull openjdk:8-jdk   ; fi
+  - if [[ "$TASK" == "test-fedora"     ]]; then docker pull fedora:27       ; fi
+  - if [[ "$TASK" == "test-ubuntu"     ]]; then docker pull ubuntu:16.04    ; fi
+  - if [[ "$TRAVIS_OS_NAME" == "osx"   ]]; then brew update                 ; fi
+  - if [[ "$TRAVIS_OS_NAME" == "osx"   ]]; then rm '/usr/local/include/c++' ; fi
+  - if [[ "$TRAVIS_OS_NAME" == "osx"   ]]; then brew install gcc@7 ninja sbt; fi
 script:
   - make "$TASK"
 before_cache:

Dockerfile

@@ -1,11 +1,12 @@
 FROM openjdk:8-jdk
 
-RUN apt-get update && apt-get -y install cmake g++ libgomp1
+RUN apt-get update && apt-get -y install cmake g++ libgomp1 ninja-build
 
 ADD . /root
 WORKDIR /root
 
 RUN sed -i -e 's/    \${JAVA_JVM_LIBRARY}//' ./xgboost/CMakeLists.txt
+RUN sed -i -e 's/maybe_generator = ""/maybe_generator = " -GNinja"/' xgboost/jvm-packages/create_jni.py
 
 ENV CFLAGS -fvisibility=hidden -static-libgcc
 ENV CXXFLAGS -fvisibility=hidden -fvisibility-inlines-hidden -static-libgcc -static-libstdc++

Makefile

@@ -99,6 +99,7 @@ $(LIBXGBOOST4J_DYLIB):
 	cd xgboost/jvm-packages \
 	  && cat create_jni.py \
 	     | sed -e 's!CONFIG\["USE_OPENMP"\] = "OFF"!CONFIG["USE_OPENMP"] = "ON"!' \
+	     | sed -e 's!maybe_generator = ""!maybe_generator = " -GNinja"!' \
 	     | sed -e 's!join(args)!join(args + ["-DOpenMP_'$(LIBGOMP_A)'_LIBRARY='$(LIBGOMP_A)'"])!' \
 	     > create_jni.py~ \
 	  && CC=$(CC) CXX=$(CXX) CFLAGS=$(CFLAGS) CXXFLAGS=$(CXXFLAGS) \

README.md

@@ -10,6 +10,7 @@ XGBoost4J with cross-version suffix
 
 * macOS
 * Docker for Mac
+* Ninja
 * `g++-7` (installed by Homebrew, i.e. `brew install gcc`)
 
 ### How to Build and Test