add job 12987
add job 12988
Wed Dec 19 22:20:59 CST 2018
del from 12987
Wed Dec 19 22:21:00 CST 2018
del from 12988
add job 12989
add job 12990
del from 12989
Wed Dec 19 22:21:01 CST 2018
add job 12991
Wed Dec 19 22:21:02 CST 2018
del from 12990
Wed Dec 19 22:21:03 CST 2018
del from 12991

add job 12987
add job 12988
Wed Dec 19 22:20:59 CST 2018
del from 12987
now the list is: 12988
Wed Dec 19 22:21:00 CST 2018
del from 12988
now the list is:
add job 12989
add job 12990
Wed Dec 19 22:21:01 CST 2018
add job 12991
Wed Dec 19 22:21:02 CST 2018
add job 12992
Wed Dec 19 22:21:03 CST 2018
add job 12993
Wed Dec 19 22:21:04 CST 2018
add job 12994
Wed Dec 19 22:21:05 CST 2018
add job 13091
Wed Dec 19 22:21:06 CST 2018
add job 13092
Wed Dec 19 22:21:07 CST 2018
Wed Dec 19 22:21:08 CST 2018

#include "apue.h"
#include <sys/wait.h>
#include <sys/signal.h>
#include <errno.h>

void printJobs();
void addJob(int);
void delJob();

void handler(int sig)
{
    sigset_t mask_all, pre_all;
    sigfillset(&mask_all); // fill all bits of the mask
    pid_t pid;
    while ((pid = waitpid(-1, NULL, 0)) > 0) {
        sigprocmask(SIG_BLOCK, &mask_all, &pre_all);
        printf("del from %dn", pid);
        delJob(pid);
        sigprocmask(SIG_UNBLOCK, &pre_all, NULL);
    }
    if (errno != ECHILD)
        printf("waitpid errorn");
}

int main(int argc, char **argv)
{
    pid_t pid;
    sigset_t mask_all, mask_one, pre_one;

    sigfillset(&mask_all);
    sigemptyset(&mask_one);
    sigaddset(&mask_one, SIGCHLD);
    signal(SIGCHLD, handler);
    for (int i = 0; i < 10; ++i) {
        sigprocmask(SIG_BLOCK, &mask_one, &pre_one); // block SIGCHLD
        if ((pid = fork()) == 0) {
            sigprocmask(SIG_SETMASK, &pre_one, NULL);
            sleep(1);
            execve("/bin/date", argv, NULL);
        }
        sigprocmask(SIG_BLOCK, &mask_all, NULL);     // block all sigals
        addJob(pid);
        sigprocmask(SIG_SETMASK, &pre_one, NULL); // unblock SIGCHLD
        sleep(1);
    }
    exit(0);
}

typedef struct Node {
    int val;
    struct Node *next;
} Node, *pNode;

pNode phead = NULL, ptail = NULL;

void printJobs()
{
    pNode pt = phead;
    while (pt) {
        printf("%d", pt->val);
        pt = pt->next;
    }
    printf("n");
}

void delJob(int pid)
{
    if (ptail) {
        pNode pt = phead, pre = NULL;
        while (pt && pt->val != pid) {
            pre = pt;
            pt = pt->next;
        }
        if (!pt) {
            printf("No job %dn", pid);
            return;
        }
        if (pt == phead) { // only have one node or empty
            phead = phead->next ? phead->next : NULL;
            free(pt);
            ptail = phead ? ptail : NULL;
        } else { // have more than one nodes
            printf("del %dn", pt->val);
            free(pt);
            pre->next = NULL;
            ptail = pt == ptail ? pre : ptail;
        }
        printf("now the list is: ");
        printJobs();
    } else {
        printf("No job %dn", pid);
    }
}

void addJob(int pid)
{
    printf("add job %dn", pid);
    pNode pt = malloc(sizeof(Node));
    pt->val = pid;
    pt->next = NULL;
    if (!phead) {
        phead = ptail = pt;
    } else {
        ptail->next = pt;
        ptail = pt;
    }
}