Multi thread and Concurrency - Basic Understanding

 Multi thread - Why we need

1.  Responsiveness
2.  Performance

Multi thread, Synchronous and Asynchronous, one of the words you will here a lot.

let's take a simple example

In a supermarket people come and buy product and go to queue and purchase. In a simple scenario, there is one person who buys a large number of items and one with few items. If the customer with large items comes, other has to wait for a huge time. 

So can we reduce this ? IF yes --> How ?

In an application we have basically two parts. UI and backend

Looking at that point Responsiveness is more important to UI and Performance in backend. This is where threads become handy

Concurrency -  Multi tasking

• Achieved by multitasking between threads
• Concurrency == Multi tasking

Note: Even with one core we can achieve multitasking

One core -> multiple tasks concurrently

more cores -> multiple tasks parallelly

Performance Impact

• Completing a complex task much faster
• Finish more work in the same period of time
• For high scale services
• Fewer machines
• Less money spent on hardware
• More money save | money in pocket

Thread is a part of process and Process may have few components like

• Process Specific
• PID - process Id
• Mode
• Priority  etc
• Files
• Data (Heap)
• Code
• Thread (  there can be one or more threads)

each Thread will have

• Stack
• Instruction Pointer

Note: Thread will have its unique stack and Instruction pointer , but rest of the items are shared with in process context

Stack -> Region in memory, where local variables are stored, and passed in to functions

Instruction pointer -> Address of the next instruction to execute

Why we have its own stack and Instruction pointer ?

at given time each thread is executing different instructions in a different function 

Summary up to now

Why multi thread ?

Responsiveness achieved by concurrency

Performance achieved by parallelism

Thread

Stack

Instruction pointer

What thread share

files

heap(data)

code