# Processes Threads Handles

### Processes

* An instance of an executable
* Think of it as a container
* An application can have many processes i.e. your web browser
  * each tab you open will spawn a new processes
* A Process typically isnt aware of other processes on the machine
  * It believes it is the only process on the machine
* Each processes is started with a single thread, often called `primary thread` but can create additional threads from any of its threads

#### Three Types of Processes

* Application Processes
  * i.e chrome is an application process
  * Can be terminated by the user
* Background processes
  * Get started automatically
  * updating software
  * anti viruses
* Windows Processes
  * system level processes
  * automatically get launched at start up
    * device drivers
    * windows memory management

### Process Priority

* determines the amount of CPU time each processes will be allocated
* there are 6 different levels
  * Realtime
  * High
  * Above normal
  * Normal
  * Below normal
  * Low

#### Low

* only be given cpu time when there are no other higher priority processes running on the system

#### Normal

* by default normal is used for the creation of a processes
  * NORMAL\_PRIORITY\_CLASS

#### Realtime

* full access to the cpu
* very dangerous as this is higher than disk cache, mouse, keyboard
* will leave no cycles for anything else

### Threads

* a thread is the entity within a processes that can be scheduled for execution
* All threads of a process share its virtual address space and system resources
* Process can have many threads
  * also called multi threading

### Differences Processes and Threads

* processes use much more resources
* threads are lightweight
* processes are a team trying to complete a project
* thread is a single member of the team working on a part of a project
* processes are independent of each other
* threads are dependent on each other

### Handle

* Generic unit of identification
* pointer to our object
* many different types of handles
  * the most common one is handles to processes and handles to modules
* handles are system wide