Process Concept - Operating Systems, Distributed Computation - Lecture Slides, Slides of Operating Systems

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PROCESSES

Process Concept Process Scheduling Operations on Processes Cooperating Processes Interprocess Communication Communication in Client-Server Systems

Process Concept

• An OS executes a variety of programs:
  • Batch system – jobs
  • Time-shared systems – user programs or tasks
• Terms job and process interchangeably.
• Process : a program in execution;
• A process includes:
  • Program counter
  • Stack
  • Data section
  • Code (“text”)
  • Registers
  • Heap

Diagram of Process State

Process Control Block (PCB)

• Information associated with each process.
• Process state
• Program counter
• CPU registers
• CPU scheduling information
• Memory-management information
• Accounting information
• I/O status information

PCB in Linux

struct task_struct {

pid_t pid; /* process identifier / long state; / state of the process / unsigned int time_slice; / scheduling info / struct task_struct * parent; / parent process / struct list_head children; / this process’s children */ struct files_struct files; / list of open files */ struct mm_struct mm; / address space of the process */

};

CPU Switch From Process to Process

Ready & Various I/O Device Queues

Process Scheduling

Addition of Medium Term Scheduling

Schedulers (Cont.)

• Short-term scheduler is invoked frequently (~100 ms)  (must be fast).
• Long-term scheduler is invoked infrequently (seconds, minutes)  (may be slow).

Context Switch

• When CPU switches to another process:
  • must save the state of the old process
  • load the saved state for the new process.
• Context-switch time is overhead ; the system does no useful work while switching.
• Time dependent on hardware support.

Process Creation

• Parent process create children processes, which, in turn create other processes, forming a tree of processes.
• 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. Docsity.com

Processes Tree on UNIX

Process Termination

• Process executes last statement and asks to end (exit). - Output data from child to parent (via wait). - Process’ resources are deallocated by operating system.