Why fork() twice [duplicate]

by

All right, so now first of all: what is a zombie process?

It’s a process that is dead, but its parent was busy doing some other work, hence it could not collect the child’s exit status.

In some cases, the child runs for a very long time, the parent cannot wait for that long, and will continue with it’s work (note that the parent doesn’t die, but continues its remaining tasks but doesn’t care about the child).

In this way, a zombie process is created.

Now let’s get down to business. How does forking twice help here?

The important thing to note is that the grandchild does the work which the parent process wants its child to do.

Now the first time fork is called, the first child simply forks again and exits. This way, the parent doesn’t have to wait for a long time to collect the child’s exit status (since the child’s only job is to create another child and exit). So, the first child doesn’t become a zombie.

As for the grandchild, its parent has already died. Hence the grandchild will be adopted by the init process, which always collects the exit status of all its child processes. So, now the parent doesn’t have to wait for very long, and no zombie process will be created.

There are other ways to avoid a zombie process; this is just a common technique.

Hope this helps!

More Related Contents:

  1. what the output of this code and why?
  2. Debugging a linked-list
  3. printf anomaly after “fork()”
  4. How to use shared memory with Linux in C
  5. How to share memory between processes created by fork()?
  6. Differences between fork and exec
  7. How can one grab a stack trace in C?
  8. Working of fork() in linux gcc [duplicate]
  9. Grabbing output from exec
  10. How Can I debug a C program on Linux?
  11. Is it possible to “jump”/”skip” in GDB debugger?
  12. How to use POSIX semaphores on forked processes in C?
  13. Can popen() make bidirectional pipes like pipe() + fork()?
  14. Are file descriptors shared when fork()ing?
  15. How to solve “ptrace operation not permitted” when trying to attach GDB to a process?
  16. Cannot insert breakpoints. Addresses with low values
  17. fork() in c using printf [duplicate]
  18. How to make backtrace()/backtrace_symbols() print the function names?
  19. Multiple child process
  20. How to use execvp()
  21. How to make parent wait for all child processes to finish?
  22. Difference between “system” and “exec” in Linux?
  23. Why does forking my process cause the file to be read infinitely
  24. segfault only when NOT using debugger
  25. How do I debug the child process after fork() in gdb?
  26. C – Retrieving a child’s exit status that is larger than 8 bits
  27. What is the difference between fork and thread?
  28. Visually what happens to fork() in a For Loop
  29. addr2line on kernel module
  30. Why does malloc allocate a different number of bytes than requested?

Leave a Comment