I have some directories which have source code. the source code in that directory are independent of each other. All are dependent on one single common/main directory.
In each directory there is one Makefile which will generate .so (dynamic lib file).


There is one main Makefile which will initiate or call make command in subdirectories.

Since it calls sequentially the time taken is more.

i want to call them simultaneously so the job (or compilation completes faster)


for example: current Makefile [Note : not exact makefile , just an example]

DIR1/make
DIR2/make

gcc *.c DIR1/xx.so DIR2/yy.so

if fork the make command like this.....

DIR1/make &
DIR2/make &

#i want to wait here for them to complete but dont know how

gcc *.c DIR1/xx.so DIR2/yy.so



..........
my question :

can any one tell me how can i wait for the process to complete when it is run in the background.

Or rather

How to know if the background process is finished

If your streams are really independent, you can have make run multiple forks with the -j parameter. It should split off concurrent processes and then wait at the bottom for the two dependencies to finish before running the final command.

eg:

$ make -j 4 all

Note that this may not in fact make things go any faster since most compiles are disk-bound, not CPU-bound; so having more processes means that more processes are sitting around waiting for disk i/o, and with the additional context switches the computer has to do it may result in a slower compile.

If you have a really large job to do (say for example the kernel) and you have a bunch of machines with identical OS installations, you might look into something like distcc which farms out gcc jobs to other computers.

Ya thats true i never thought of that