Tips:
- Some shared variables (jobs/susp) are modified within both signal handlers and the main routine, creating a concurrent situation that we need to handle correctly.
- Block signals before accessing shared data, and must restore the signal mask when finished, just like locking and unlocking a mutex.
- Do not wait a child process twice. Suspend in
waitfgand do all thewaitpids insigchld_handler. - Make sure to do error checking for all system calls.
To test all the cases, run the below command and compare the two output files.
make $(seq -s " " -f test%02g 1 16) > test.txt
make $(seq -s " " -f rtest%02g 1 16) > rtest.txt