Basic concepts of program, process, thread, coprocess, single thread and multi thread

One 、 Program

A program is a set of operable working steps designed to achieve a specific goal , For computers , A program is a set of ordered instructions that the system can recognize . The program can direct the computer to perform the actions we want it to do . The program is stored on disk , During execution, from disk to memory to register , Finally being CPU perform . A program is a language that communicates with a computer , Composed of specific syntax and keywords , From the entry point , The principle is from top to bottom , From left to right , Line by line .

Two 、 Processes and threads

1、 Definition

A process is a program with some independent functions. It is a running activity on a data set , A process is an independent unit of the system for resource allocation and scheduling .

A thread is an entity of a process , yes CPU Basic unit of dispatch and dispatch , It's a smaller, independent, basic unit than a process . The thread itself basically does not have system resources , Have only a few essential resources in operation ( Such as program counter , A set of registers and stacks ), But it can share all the resources owned by a process with other threads belonging to the same process .

2、 Relationship between them

One thread can create and undo another ; Multiple threads in the same process can execute concurrently .

Relative to the process , Thread is a concept closer to the body of execution , It can share data with other threads in the same process , But have your own stack space , Have a separate execution sequence .

3、 Difference between them

The main difference between processes and threads is that they are different ways of operating system resource management . The process has a separate address space , After a process crashes , No impact on other processes in protected mode , Threads are just different execution paths in a process . Threads have their own stack and local variables , But there is no separate address space between threads , If one thread dies, the whole process will die , So a multiprocess program is more robust than a multithreaded program , But when the process switches , High cost of resources , Less efficient . But for some concurrent operations that require simultaneous and shared variables , Only threads can be used , Can't use process .

3.1、 In short , A program has at least one process , A process has at least one thread .

3.2、 Thread partition scale is smaller than process , Make multithreaded programs have high concurrency .

3.3、 in addition , Processes have independent memory units during execution , Multiple threads share memory , Thus greatly improving the efficiency of the program .

3.4、 Threads are different from processes in execution . Each independent thread has an entry for the program to run 、 Exit of sequential execution sequence and program . But threads can't execute independently , Must exist in the application , Multiple thread execution control provided by the application .

3.5、 From a logical point of view , The meaning of multithreading is in an application , There are multiple execution parts that can be executed at the same time . But the operating system does not regard multiple threads as multiple independent applications , To achieve process scheduling and management and resource allocation . This is the important difference between processes and threads .

3、 ... and 、 coroutines

1、 Definition

Coroutine is a lightweight thread in user mode , The scheduling of the process is completely controlled by the user . A coroutine can have , The process is not managed by the operating system kernel , And it's completely controlled by the program . Instead of letting the operating system schedule , Why don't I do it myself , This is Xiecheng .

2、 Use scenarios of coroutine

Multiple coprocesses in a thread are executed serially , Can't use multi-core , therefore , obviously , Co process is not suitable for computing intensive scenarios . Coprocessor fit I/O Blocking type .

I/O Itself is blocking （ Compare with CPU For the world of time ）. For now , No matter what I/O How fast , It's no match for CPU The speed of , So a I/O Related procedures , When it's going on I/O In operation ,CPU It's actually free .

Let's assume this scenario , Here's the picture ：1 Threads have 5 individual I/O Things about （ Subroutines ） To deal with . If we absolutely serialize , So... Be one of them I/O Blocking time , other 4 individual I/O Can't be implemented , Because the program is absolutely serial ,5 individual I/O You have to queue up one by one for processing , When one I/O Blocking time , Other 4 One has to wait .

Four 、 Single thread and multi thread

1、 Single thread definition ：

Single thread ： A process has only one thread . Single thread in program execution , The program paths are arranged in a sequential order , The front has to be dealt with , Later will be implemented .

2、 Multithreading definition ： Multithreading refers to the program contains multiple execution flows , That is, you can run multiple different threads to perform different tasks in one program at the same time , That is to say, a single program is allowed to create multiple threads executing in parallel to complete their own tasks .

3、 Advantages and disadvantages of single thread ：

（1）、 Advantages of single threading ：

For single threads and many threads , System stability 、 It's very scalable 、 Rich software . More for point-to-point services .

（2） Single thread disadvantage ：
（1）、 When there are multiple processes , Now CPU No resources will be allocated to other processes , The processing time will be longer and slower .
（2）、 When the program is running, the window cannot be dragged , You must wait until the program is finished .

4、 Advantages and disadvantages of multithreading ：

advantage ：
Can improve CPU Utilization ratio . In multithreaded programs , When a thread has to wait ,CPU You can run other threads instead of waiting , This greatly improves the efficiency of the program .

shortcoming ：
（1）、 Threads are also programs , So threads need to take up memory , More threads occupy more memory ;
（2）、 Multithreading needs coordination and management , So we need to CPU Time tracking thread ;
（3）、 Access to shared resources between threads will affect each other , We must solve the problem of competing for shared resources ;
（4）、 Too many threads lead to too complex control , In the end, it may cause a lot of problems Bug