Process context and task structure

amardeepmr4

Process context:

Process is a active
entity, it needs certain resources- including CPU time, memory files and I/O devices to accomplish its task.

Each processor
stored sufficient information on it’s current operating state such
that when it is again scheduled to run on the processor it can resume
its operation from an identical position. This operational state
data is known as its context.

The context of a
process includes its address space, stack space, virtual address
space. Register set image(e.g., Program counter(PC), Stack
pointer(SP), Instruction register(IR), Program status word(PSW) and
other general processor registers), updating profiling or accounting
information, making a snapshot image of its associated kernel data
structures and updating the current state of the process(waiting,
ready, etc).

Task Structure:

It is C structure
and found in <linux/sched.h>.

This structure
contains all the necessary information for representing a process,
including the state of the process, scheduling and memory-management
information, list of open files and pointers to the process’s
parent and list of its children and siblings.

p { margin-bottom: 0.25cm; line-height: 115%; background: transparent }

sharavanraj209

06. 003.01. ASSIGNMENT

2. describe the process context and the associated task structure in detail .

Explanation: process context is its current state. We need to save the context of the current running process so it can be resumed after the interrupt is handle. Process context has four segment:-

1. STACK SEGMENT
2. LIBRARY SEGMENT
3.DATA SEGMENT
4.CODE SEGMENT

STACK SEGMENT : stack segment is used to store all local variables and for static allocation in a program. all function call’s result are store in stack segment but can’t estimate or predict exactly where a function call’s result will store. It totally depend on hardware architecture. Function call result are application binary interface (ABI) dependent. The values store in the stack are directly store in RAM. The access time for items in the stack is very fast. Stack has high address values.

LIBRARY SEGMENT : library segment has three part-

1. Dynamically linked library : The libraries are dynamically pulled it at run time using the link provided through the symbol table and executed as part of process.

2. Statically linked libraries : The libraries are linked statically means the link will load the libraries also with process at the time of loading the program.

3.Shared libraries: Rather than loading individual library function for every executing process we load only one instance of the libraries is loaded and shared by all executing process.

DATA SEGMENT: Data segment has three part-

1. HEAP:- Heap is the region where memory is dynamically allocated. Allocation of memory is done at run time and accessing the items present in a heap space is slower than stack space. The size of the heap is limited to the size of our virtual memory.

2. INITIALIZED DATA: All local and global variable (static variable,global variable,external variable,register variable,volatile,constant,macros,preprocessor directive,qualifiers,heap for dynamic memory allocation )are used by programmer is store in initialized data.

3. UNINITIALIZED DATA: Global and static variables that don’t have any explicit initialization in the program are stored in this data block. The kernel assign the data present in this segmented block to an arithmetic zero or null pointer starts executing. This block is also called BBS blocked,which is a block started by symbol.

4.CODE SEGMENT : Code segment has low address value. The function of program counter is done in this segment.

TASK STRUCTURE :-

For every process running ,the operating system maintain a task structure. Inside task structure operating system maintain information about executing process like pid,Ppid. Task structure has many executing process..

1. STATE: - process state of the program.

2.STACK:- Reference to stack segment it point to the begging of the stack.

3.PROCESS Id:- it is currently executing program id.

4. PROCESS PARENT Id:- By which the program that create your program.

5. REAL PARENT Id:- Real parent id is the current parent id.

6. PROGRAM COUNTER:- it tells which next statement is to be executed.

7. *mm:- this is the starting address of process context.

8. ACTIVE mm:- It is currently used address of process context.

9. tgid:- It is thread group id and stored in table.

10.comm:- It is the name of the program.

11. *files:- It tells which file is open.

12. *signals:- It tells which signal will be handle.

Process context and task structure

Howdy, Stranger!

Categories