Operating Systems Chapter 3: Processes

Process Concept

• Operating systems execute various programs, categorized as batch systems for jobs and time-shared systems for user tasks.
• A process is a program in execution, progressing sequentially and comprising a program counter, stack, and data section.

Process State

• Process states include:
  • New: process being created.
  • Running: instructions are being executed.
  • Waiting: process waiting for an event or resources.
  • Ready: process waiting to be assigned to a CPU.
  • Terminated: process execution completed.

Process Control Block (PCB)

• PCB is a data structure representing a process in memory, storing various information including:
  • Current process state
  • Program counter
  • CPU registers
  • Scheduling information
  • Memory management data
  • Accounting info
  • I/O status data

Process Scheduling Queues

• Job queue: contains all processes in the system.
• Ready queue: contains processes ready for execution in main memory.
• Device queues: contains processes awaiting I/O devices.

Schedulers

• Long-term scheduler: selects processes for the ready queue from the job queue; invoked infrequently.
• Short-term scheduler: selects the next process to be executed; invoked very frequently.
• Medium-term scheduler (MTS): handles process swapping in and out of memory for better performance.

Context Switch

• A context switch occurs when the CPU switches to a different process, requiring the saving of the old process's state and loading of the new one.
• Context-switch time introduces overhead, as the system does not perform useful work during the switch.

Process Creation

• Parent processes create child processes, forming a process tree, with each child having one parent.
• Resources may be shared between processes, but address spaces are separate, preventing changes in one from affecting the other.
• UNIX example: fork system call creates a new process; exec replaces the child's memory with a new program.

Process Termination

• A process terminates when it executes its last statement and requests termination, leading to resource deallocation and removal from system lists.
• Parents may also terminate child processes under specific conditions, leading to cascading termination in some operating systems.

Cooperating Processes

• Independent processes operate without affecting each other, while cooperating processes can influence one another for purposes such as:
  • Information sharing
  • Speed-up in computation
  • Modularity
  • Convenience of programming

Producer-Consumer Problem

• Involves cooperating processes where a producer creates information consumed by a consumer.
• Unbounded-buffer: has no limit on buffer size, allowing producers to process without waiting.
• Bounded-buffer: has a fixed size, requiring producers to wait if the buffer is full.

Interprocess Communication (IPC)

• IPC mechanisms enable processes to communicate and synchronize actions, primarily through message passing.
• Operations include send(message) and receive(message) involving either fixed or variable length messages.
• Establishes communication links, which can be physical or logical.

Direct Communication

• Requires processes to name each other explicitly for message exchange:
  • send(P, message) sends a message to process P.
  • receive(Q, message) receives a message from process Q.

Indirect Communication

• Involves mailboxes (or ports) for message exchange, characterized by:
  • Unique identifiers for mailboxes.
  • Permitting communication only between processes sharing a mailbox.
  • Links may be unidirectional or bi-directional.

Buffering

• Message queuing can be implemented with:
  • Zero capacity: sender waits for receiver.
  • Bounded capacity: finite queue length; sender waits if full.
  • Unbounded capacity: infinite length; sender never waits.

Explore the key concepts of processes in operating systems through this quiz. You'll learn about process scheduling, interprocess communication, and the differences between batch and time-shared systems. Test your knowledge on the important aspects of processes and their management.