Thread vs Process

What is a Thread, really?

• Short answer:

  • Thread is a subset of a process

• Longer answer:

  • Thread is an independent set of values for CPU registers

• Detailed answer:

  • A thread is an execution context for CPU, which is all the information CPU needs to execute instructions. Essentially:

More about thread

Thread components:

• Program counter: keeps track of which instruc­tion to execute next
• Stack: which contains the execution history
• Registers: which hold its current working variables

Example:

A single thread could be displaying the current tab you’re in, and a different thread could be another tab.

What is a Process, really?

• Short answer:

  • Process is a running program

• Long answer:

  • The process model is based on two independent concepts: resource grouping and execution (thread)

More about process

Process components:

• stack: stores functional calls, local variables
• heap: memory that is dynamically allocated to a process during its execution
• text/code: code instructions
• data: static variables

Example:

When you double click on the Google Chrome icon on your computer, you start a process which will run the Google Chrome program

Thread vs Process

Essentially: Processes are used to group resources together; threads are the entities scheduled for execution on the CPU.

Comparsion Table

Resource Sharing Difference

• Processes have separate address spaces (indepedent)

• For multiple threads in the same process

  • Threads share same address space and code, data, heap segments
  • Threads DO NOT SHARE STACK