Process

A process is an independent program in execution with its own memory space. It is the smallest unit of work that can be scheduled by the operating system.

• Memory: Processes have separate memory spaces. Each process has its own address space, which means they do not share data directly. Inter-process communication (IPC) mechanisms are needed to share data between processes.
• Overhead: Creating and managing processes involves more overhead compared to threads due to the need for separate memory management.
• Isolation: Processes are isolated from each other, which enhances stability and security. If one process crashes, it does not affect others.
• Context Switching: Context switching between processes is generally more expensive as it involves switching memory maps and other resources.

#Use Cases

• Processes are preferred when tasks need to be isolated for security or stability reasons, or when tasks are highly independent and do not need to share data frequently.

#Anatomy of a Process

• PID (process id)
• PPID (parent process id)
• Environment
• CWD (Current Working Directory)
• UID (user id) and GID (group id)
• Priority and Scheduling
• File Descriptors
• Memory Management Information
• State (stage in the lifecycle)
• Signal Handling (the method of change of state of a process)

#Process Creation

• fork()
  • Creates a clone of the current process. Used a lot in concurrent programming. No parameters.
• exec()
  • Create completely different process. Needs a parameter of the program to run in the process.

#Process Hierarchy

#Init Process

First process and starts forking and exec-ing new processes.

Current substitute is systemd. Embedded uses busybox.

#Root Process

Same as init process. Usually PID 1.

Macos: kernel_task (0) launchd (1)

• Thread