multiprogramming system

Multi-programming is to load multiple programs into memory at the same time so that they can run concurrently. The operating system is also generated based on multiple channels, which improves resource utilization and system throughput.

process

definition

A process is an execution of a program. A
process is the running process of a process entity. It is an independent unit for the system to allocate and schedule resources.

After the thread is introduced, the thread becomes the basic unit of scheduling, and the process is still the basic unit of resource allocation.

Composition of Process Entities

Program: is a combination of a set of instructions

Process: It is an execution process of a program and an independent unit for resource allocation and scheduling by the system

Process entity: During one execution of the program, three parts, program block, data block, and program control block, will be generated in the memory. These three parts constitute the process entity, also known as the process image.

program block

Also commonly referred to as a code segment.
The code segment is the location of the program instructions of the process in memory, including the set of instructions that need to be executed;

data block

It is the location of the operation data of the process in memory, including the data set that needs to be operated

Program Control Block PCB

(Program Control Block, PCB)
contains the description information and control information of the process, and is the only sign of the existence of the process.

How the PCB is organized

link method
index method

process characteristics

state of the process

state

In addition, there are suspension states: ready suspension and blocking suspension

Process State Transitions

process control

Process control is mainly to realize the transition between process states

primitive language

Process control is generally implemented by primitives in the OS kernel

In order to ensure that the status of the PCB is consistent with the queue and other information, it is necessary to complete these modification operations in one go.

Process creation and termination

process switching

Process blocking and waking up

Process suspension and activation

process communication

Process communication refers to the exchange of information between processes

shared storage

pipe communication

messaging

CS system

Communication of processes between different computers of the primary user

socket
remote procedure call and remote method call

process synchronization

Process synchronization and mutual exclusion

The realization of process mutual exclusion is the realization of process synchronization in the same process first P and then V
, which is the first V and then P in two processes

access to critical resources

Hardware Implementation

interrupt mask method

TestAndSet command

Swap command

Semaphore mechanism

Classification

integer semaphore
record semaphore

Semaphore applications

Implement process mutual exclusion

Realize process synchronization

Realize the predecessor relationship of the process

Monitor mechanism

eg. synchronized

common problem

producer and consumer problem

The multi-producer and multi-consumer problem

When the capacity of the plate is 1, you don’t need to write mutex; when the capacity of the plate is greater than 1, you need mutex

smoker problem

reader and writer problem

dining philosophers problem

thread

Process is the basic unit of resource allocation, thread is the basic unit of scheduling
A process can have multiple threads

properties of threads

Implementation of threads

The Java language uses the many-to-many model

processor scheduling

When there are a bunch of tasks to be processed, but due to limited resources, these things cannot be processed at the same time. This requires determining some kind of rules to determine the order in which these tasks are processed, which is the problem of "scheduling" research.

Processor Scheduling Hierarchy

Advanced (Job) Scheduling

Advanced scheduling is mainly used in multi-batch-to-batch systems, while advanced scheduling is not set in time-sharing and real-time systems.

Intermediate (memory) scheduling

low-level (process) scheduling

Scheduling Guidelines

short turnaround time
short response time
High system throughput
High resource utilization
fair

process scheduling

Timing of process scheduling

kernel program critical section

Ordinary code (ordinary critical section) accesses ordinary critical resources (such as IO devices), and processor scheduling can be performed. Kernel
program (kernel program critical section) accesses kernel data structures (such as ready queue), and processor scheduling cannot be performed.