commit 6612b6ab8f07f10065cfc8ec0925addb910cecb8
Author: David Schwörer <schword2@mail.dcu.ie>
Date:   Mon Nov 25 13:44:23 2019 +0000

    Try to prevent race condition while building.
    
    This improves the current situation, as before it could happen that
    building failed, because the .a was not yet created. Now it waits for
    it to be created. Switching to atomic mv rather then to create it
    inplace, ensures that if the file is seen, it is valid.
    This does not address the case when the .a is recreated, and the
    dependend file is checked before whether the .a has changed.

diff --git a/make.config.in b/make.config.in
index df80ed2ad..a183cf2e8 100644
--- a/make.config.in
+++ b/make.config.in
@@ -242,11 +242,15 @@ endif
 
 ifeq ("$(TARGET)", "sub")
 LIB=$(MODULE_DIR)/$(SUB_NAME).a
-sub: makefile $(BOUT_CONFIG_FILE) $(BOUT_TOP)/include $(BOUT_TOP)/lib $(OBJ)
+sub:$(LIB)
+
+$(LIB): makefile $(BOUT_CONFIG_FILE) $(BOUT_TOP)/include $(BOUT_TOP)/lib $(OBJ)
 ifneq ("$(OBJ)foo", "foo")
 	@echo "  Adding $(OBJ) to $(LIB)"
-	@$(AR) $(ARFLAGS) $(LIB) $(OBJ)
-	@$(RANLIB) $(LIB)
+	@LIBT=$(LIB).$$$$.a && \
+		$(AR) $(ARFLAGS) $${LIBT} $(OBJ) && \
+		$(RANLIB) $${LIBT} && \
+		mv $${LIBT} $(LIB)
 endif
 endif
 
@@ -282,6 +286,7 @@ $(SUB_LIBS):$(DIRS__)
 
 $(SOURCEC): checklib
 $(SOURCEC:%.cxx=%.o): $(LIB)
+$(TARGET): | $(DIRS)
 $(TARGET): makefile $(BOUT_CONFIG_FILE) $(OBJ) $(SUB_LIBS)
 	@echo "  Linking" $(TARGET)
 	@$(LD) $(LDFLAGS) -o $(TARGET) $(OBJ) $(SUB_LIBS) $(BOUT_LIBS)