When a process is created, it is assigned a unique PID

It is an independent unit for resource allocation in the system.

service operating system

The information required by the operating system to manage the process is in the PCB

The only sign that a process exists

Contains program instructions

Contains various data generated during operation

The most basic characteristics of the process

There are multiple process entities in the memory, executing concurrently

A process is a basic unit that can run independently, obtain resources independently, and receive scheduling independently.

Each process moves forward at an independent and unpredictable pace

The operating system must provide a process synchronization mechanism to solve asynchronous problems

Each process will be configured with a PCB, and the process composition structure is the same

Allocate system resources and initialize PCB

Already have running conditions, CPU is busy, waiting

Run on CPU

In some cases, after the time slice allocated to the process is used up, the process transitions from the running state back to the ready state.

Only one process is running on a single CPU at the same time

The process is waiting for an event to occur and cannot continue to execute. It actively applies for the CPU under system calls.

When the waiting event occurs, the blocking state returns to the ready state.

When the process ends, execute the exit system call to the CPU, and the system reclaims the memory space and PCB.

The pointer points to the compiled queue

Create index tables for processes in different states

Primitives implemented with on/off interrupts

A primitive is a special kind of program

Execution of primitives cannot be interrupted

Wait for something to happen

The event is over

selected by scheduler

Time slice ran out

ready

block

run

Different threads in the same process share system resources

Used in early operating systems, when "threads" were implemented by thread libraries

Threads are implemented by the operating system

A user-level thread maps to a kernel-level thread

advantage

shortcoming

Multiple user-level threads are mapped to one kernel-level thread, and only one kernel-level thread is allocated to a process.

advantage

shortcoming

compromise method

Based on data structures (low level)

Bucket-based sharing (advanced)

direct communication

Mailbox communication method