Process Termination or destroy a process

Processes may request their own termination by making the exit( ) system call, typically returning an int. This int is passed along to the parent if it is doing a wait( ), and is typically zero on successful completion and some non-zero code in the event of problems.

child code:

            int exitCode;
            exit( exitCode );  // return exitCode; has the same effect when executed from main( )

parent code:

            pid_t pid;
            int status
            pid = wait( &status ); 
            // pid indicates which child exited. exitCode in low-order bits of status
            // macros can test the high-order bits of status for why it stopped

Processes may also be terminated by the system for a variety of reasons, including:
- The inability of the system to deliver necessary system resources.
- In response to a KILL command, or other un handled process interrupt.
- A parent may kill its children if the task assigned to them is no longer needed.
- If the parent exits, the system may or may not allow the child to continue without a parent. ( On UNIX systems, orphaned processes are generally inherited by init, which then proceeds to kill them. The UNIX nohup command allows a child to continue executing after its parent has exited. )
When a process terminates, all of its system resources are freed up, open files flushed and closed, etc. The process termination status and execution times are returned to the parent if the parent is waiting for the child to terminate, or eventually returned to init if the process becomes an orphan. ( Processes which are trying to terminate but which cannot because their parent is not waiting for them are termed zombies. These are eventually inherited by init as orphans and killed off. Note that modern UNIX shells do not produce as many orphans and zombies as older systems used to. )

Comments

Thread

Thread What is Thread? A thread is a flow of execution through the process code, with its own program counter that keeps track of which instruction to execute next, system registers which hold its current working variables, and a stack which contains the execution history. A thread shares with its peer threads few information like code segment, data segment and open files. When one thread alters a code segment memory item, all other threads see that. A thread is also called a lightweight process . Threads provide a way to improve application performance through parallelism. Threads represent a software approach to improving performance of operating system by reducing the overhead thread is equivalent to a classical process. Each thread belongs to exactly one process and no thread can exist outside a process. Each thread represents a separate flow of control. Threads have been successfully used in implementing network servers and web server. They also provide a suitable foundation ...

Layered Operating System

Layered Operating System Layered Structure is a type of system structure in which the different services of the operating system are split into various layers, where each layer has a specific well-defined task to perform . It was created to improve the pre-existing structures like the Monolithic structure ( UNIX ) and the Simple structure ( MS-DOS ). Example – The Windows NT operating system uses this layered approach as a part of it . Design Analysis : The whole Operating System is separated into several layers ( from 0 to n ) as the diagram shows. Each of the layers must have its own specific function to perform. There are some rules in the implementation of the layers as follows. The outermost layer must be the User Interface layer. The innermost layer must be the Hardware layer. A particular layer can access all the layers present below it but it cannot access the layers present above it. That is layer n-1 can access all the layers from n-2 to 0 but it canno...

Multi Level Queue Scheduling (MLQ)

Multi Level Queue Scheduling (MLQ) · Multilevel queue scheduling classifies the processes according to their types for example, a multilevel queue scheduling algorithm makes a common. · In this scheduling ready queue is divided into various queue that are called sub queues. A subqueue is a distinct operational queue · The process are permanently assigned to subqueues, generally based on some property of the process such as memory size,priority or process type · Each subqueue has its process sucheduling algorithm. For example interactive process at the foreground may use round robin scheduling while batch jobs at the background may use the FCFS method · For example, consider a system with four different queues 1. ...

Classification of Operating System

Classification of operating systems The operating systems may be classified into different types depending upon the nature of interaction between the user and his/her program. The various types of operating system are : 1. single user operating system 2. Multi user operating system 3. Batch processing operating system 4. Multi programming operating system 5. Multi tasking operating system 6. Multiprocessing operating system 7. Time sharing operating system 8. Real time system Distributed system Multi threading operating system Single user operating system · ...

System structure operating architecture

System structure operating architecture An operating system is a construct that allows the user application programs to interact with the system hardware. Since the operating system is such a complex structure, it should be created with utmost care so it can be used and modified easily. An easy way to do this is to create the operating system in parts. Each of these parts should be well defined with clear inputs, outputs and functions. Simple Structure There are many operating systems that have a rather simple structure. These started as small systems and rapidly expanded much further than their scope. A common example of this is MS-DOS. It was designed simply for a niche amount for people. There was no indication that it would become so popular. An image to illustrate the structure of MS-DOS is as follows − It is better that operating systems have a modular structure, unlike MS-DOS. That would lead to greater control over the computer system and its various applications. T...

Easytolearn

Search This Blog