Terminating background process on next foreground process - c

Question

I'm having trouble looping through my shell and terminating a background process. I can't figure out the proper usage of waitpid after looking at a few questions like this for hours, so I'll describe my problem.
I need to run a sleep command for a few seconds, save that pid, run an ls command and keep my shell running while the sleep runs in the background. The next foreground process that executes, (ls) afterwards will clean up the background process after executing. So I wrote something like this
while(1) {
//Prompt user input
//Get input from user
//Parse & tokenize
//Determine if this process is to run in the background
if((strcmp(symbols[0], "&") == 0) || (strcmp(symbols[0], "&\n") == 0)) {
backgroundFlag = true;
} else {
backgroundFlag = false;
foregroundFlag = true;
}
pid_t childPid = fork();
if(backgroundFlag == true && childPid != 0) {
backgroundPid = childPid;
}
//Determine the process
if(childPid == 0) {
//Run in the background
if(backgroundFlag == true) {
printf(">>>IN CHILD(background): backgroundPid = %d\n", getpid());
backgroundPid = getpid();
} else {
foregroundFlag = true;
//debug
printf("\n>>>IN CHILD: pid = %d\n", getpid());
}
//Save this for child pid
childPid = getpid();
//Execute the command
execvp(command1[0], args1-1);
} else {
printf("\n>>>In Parent: pid = %d\n", getpid());
//this is the parent
if(backgroundFlag == false && backgroundPid == 0) {
wait(NULL);
foregroundFlag = false;
printf("\n...Child reaped: pid = %d\n", childPid);
} else if (backgroundFlag == true && backgroundPid > 0) {
pid_t return_pid = waitpid(backgroundPid, 0, WNOHANG);
if(return_pid == backgroundPid) {
printf("\n...background child reaped: pid = %d\n", backgroundPid);
backgroundPid = 0;
}
}
}
}
but the shell just runs the process, hangs and never gives me a reaped message. In that case when I hit enter, it will restart the parent to the top of the loop, but never reap the background process. What exactly am I doing wrong? I tried looping with backgroundPid and -1, WNOHANG, and a few other flags, but I just keep getting the same thing - either it will run and hang never prompting again for input until hitting ENTER, or it will run first and not allow any other foreground processes to go.
Either way it never reaps the background.
This is what i get as result of doing sleep(3) & (it's a custom sleep that echoes), then ls before completion, then ls again
progShell> ./customecho testing &
COMMAND #1: ./customecho
...The above command will be executed in background
>>>In Parent: pid = 7774
Freeing input...
backgroundPid - 7793
looping...
>>>IN CHILD(background): backgroundPid = 7793
progShell> ls
COMMAND #1: ls
>>>In Parent: pid = 7774
Freeing input...
backgroundPid - 7793
looping...
progShell>
>>>IN CHILD: pid = 7794
Makefile progShell progShell.c customecho.c customecho
customecho PID=7793: testing
Then only after hitting ENTER do i get this...
no termination...
Freeing input...
backgroundPid - 7793
looping...
Edit: played around for a while, and managed to fix a bit of the code -
while(1) {
//Determine if this process is to run in the background
if((strcmp(symbols[0], "&") == 0) || (strcmp(symbols[0], "&\n") == 0)) {
backgroundFlag = true;
backgroundFinishedFlag = false;
} else {
backgroundFlag = false;
foregroundFlag = true;
}
printf("Background finished: %d\n", backgroundFinishedFlag);
printf("Background flag: %d\n", backgroundFlag);
//Create a new process
pid_t childPid = fork();
//Determine if this process is to run in the background, and assign appropriately per process.
if(backgroundFlag == true && childPid == 0) {
backgroundPid = getpid();
printf("Background process (PID=%d)\n", backgroundPid);
} else if(backgroundFlag == true) {
backgroundPid = childPid;
}
//Determine the process we are in - this is child
if(childPid == 0) {
//debug
//Run in the background
if(backgroundFlag == true) {
printf(">>>IN CHILD(background): backgroundPid = %d\n", getpid());
} else {
//Run in the foreground
printf("\n>>>IN CHILD: pid = %d\n", getpid());
}
//Save this for child pid
childPid = getpid();
//Execute the command
execvp(command1[0], args1-1);
} else {
//this is the parent
//debug
printf("\n>>>In Parent: pid = %d\n", getpid());
printf("\t this parent's child is - %d and background id is %d\n", childPid, backgroundPid);
//There is a foreground process - execute it first.
if(foregroundFlag) {
waitpid(childPid, NULL, 0);
foregroundFlag = false;
printf("\n...Child reaped: pid = %d\n", childPid);
}
//Determine if there is a background process to be reaped
if(backgroundFinishedFlag == false && backgroundPid > 0 && (waitpid(backgroundPid, NULL, WNOHANG) > 0)) {
printf("\nTerminating background process now!\n");
backgroundFinishedFlag = true;
backgroundPid = 0;
}
}
}
It terminates child in background upon completion of next foreground process...
Just one problem is, when the background process is finished, I would like it to prompt for input again - is there any signal catch I can use to do this? Ex... after the sleep prints, it overwrites the "shellProg> " prompt looking like input and leaves a blank space to use for input.
shellProg> sne PID=9886: testing
(i hit enter or any input here otherwise no prompt)
Freeing input...
backgroundPid - 9886
looping...
shellProg>