Question

Whenever I use just “make” to compile, my Makefile works fine. But when I use “make -j2”, I get the error that

mkdir: cannot create directory `objects': File exists
make: *** [objects/robot_driver_agent.o] Error 1

This is the Makefile –

INCLUDE = -I/usr/include/X11 -I/usr/local/include -I/usr/local/include/FL/images -I/usr/include/freetype2

CC=g++ 
CFLAGS=-w -D LINUX -O3 -fpermissive 
OBJDIR=objects
SRCDIR=src

LDFLAGS= -L/usr/X11R6/lib$(LIBSELECT) -lpthread -lfltk -lXext -lXft -lfontconfig -lXinerama -lpthread -ldl -lm -lX11

SOURCES_RAW= robot_driver_agent.cpp robot_driver_position.cpp robot_driver_priorityqueue.cpp main.cpp robot_driver_tree.cpp robot_driver_stack.cpp robot_driver_grid.cpp robot_driver_path.cpp grid_analyzer.cpp tcpserver.cpp tcpclient.cpp servercontrol.cpp clientcontrol.cpp robot.cpp udpserver.cpp udpclient.cpp owncontrol.cpp guiwindow.cpp rs232.cpp

TARGET:= go
TARGETD:= go_d

OBJECTS:=$(SOURCES_RAW:.cpp=.o)
OBJECTS:=$(patsubst %.o, $(OBJDIR)/%.o, $(OBJECTS))

SOURCES:=$(SOURCES_RAW)
SOURCES:=$(patsubst %.cpp, $(SRCDIR)/%.cpp, $(SOURCES))

all: $(TARGET)

$(TARGET): $(OBJECTS)
    $(CC) -w -D LINUX $(INCLUDE) $^ -o $@ $(LDFLAGS)

$(OBJDIR)/%.o: src/%.cpp
    test -d $(OBJDIR) || mkdir $(OBJDIR)
    $(CC) -g -c $< $(CFLAGS) -o $@ 

debug: $(TARGETD)

$(TARGETD): $(OBJECTS)
    $(CC) -w -D LINUX $(INCLUDE) $^ -o $@ $(LDFLAGS)

%.o: $(SRCDIR)/%.cpp
    $(CC) -c -g $< $(CFLAGS)-o $@



.PHONY : clean
clean:
    rm -f $(OBJDIR)/*.o
    rm -f $(TARGET) $(TARGETD)

Can anyone tell me why using both of the processors with -j2 makes this error appear and how to fix it? Thank you for any help.

Answer 1

Don’t create directories like that; it’s a race condition waiting to happen. Let Make handle the dependency resolution for you:

 $(OBJECTS): | $(OBJDIR)

 $(OBJDIR):
         mkdir $(OBJDIR)

This is taken directly from the order-only prerequisite example in the Make manual.