Operating System Lecture 7

Continued from Operating Systems Lecture 6

Process Creation

• Parent process create children processes, which, in turn create other processes, forming a tree of processes
• Generally, process identified and managed via a process identifier (pid)
• Resource sharing options
  • Parent and children share all resources
  • Children share subset of parent’s resources
  • Parent and child share no resources
• Execution options
  • Parent and children execute concurrently
  • Parent waits until children terminate
• Address space
  • Child duplicate of parent
  • Child has a program loaded into it
• UNIX examples The fork() System Call:
  • The fork() system call is used to create a new process, which is a child process.
    • The child process is an exact copy of the parent process, including its memory space, code, and resources.
    • After fork(), both the parent and child processes start executing independently from the same point in the code.
• The exec() System Call:
  • After a fork(), the child process can use the exec() system call to replace its current code and memory space with a completely new program.
    • This means the child process stops executing its original program and starts running the new program specified in the exec() call.
  • What Happens Internally:
    • The memory space of the calling process (in this case, the child process) is completely replaced by the new program.
    • This includes replacing the code, stack, heap, and data segments of the current process with those of the new program.
    • However, the process ID (PID) of the child process remains the same.
  • Parent process calls wait() waiting for the child to terminate

Process Termination

• Process executes last statement and then asks the operating system to delete it using the exit() system call.
  • Returns status data from child to parent (via wait())
  • Process’ resources are deallocated by operating system
• Parent may terminate the execution of children processes using the abort() system call. Some reasons for doing so:
  • Child has exceeded allocated resources
  • Task assigned to child is no longer required
  • The parent is exiting and the operating systems does not allow a child to continue if its parent terminates
• Some operating systems do not allow child to exist if its parent has terminated. If a process terminates, then all its children must also be terminated.
  • Cascading termination. All children, grandchildren, etc. are terminated.
  • The termination is initiated by the operating system.
• The parent process may wait for termination of a child process by using the wait() system call. The call returns status information and the pid of the terminated process.
  • pid = wait(&status)
• If no parent waiting (did not invoke wait()) process is a zombie
• If parent terminated without invoking wait(), process is an orphan

(Source: Dhruv Rathod)

References

Information

• date: 2025.01.30
• time: 09:04