Process
Today’s computer users rarely run just one program. From browsing in Chrome or gaming in CS:GO and streaming music on Spotify, multitasking is the norm. To support this, the system creates the illusion of multiple CPUs — a concept known as CPU virtualization. This is achieved through a technique called time-sharing, where the CPU rapidly switches between tasks to give each the appearance of running simultaneously. Each of these running programs is known as a process.
What is process?
A process is made up of the program code and the machine state necessary for execution — including the stack, heap, registers, and other essential componentss
Process API
The Process API provides essential functionality for managing processes, including:
- Creating a new process
- Terminating an existing process
- Waiting for a process to complete
- Suspending the current process
- Accessing metadata such as status and performance metrics
We’ll define Three simples state for each process.
- Running – Actively executing on the CPU
- Ready - Prepared to run, waiting to be scheduled by the CPU
- Blocked - Waiting for an external event or resource (e.g., I/O operation) before it can proceed
As explained above, the state of each process must be saved and restored when it is paused and resumed. The act of stopping one process, saving its state, and loading the state of another process to run on the CPU is known as a context switch.
More information of process state can be find here.
The operating system allows us to create and manage processes using the following system calls:
Fork: Creates a new process by duplicating the current one. more details
Wait: Delays the parent’s execution until the child process finishes or terminates.more details
Exec: Calling aother process from this process. (does no’t create new one but load the other process code into current process and run it). more details
Pipe: Create a queue, a uniderctional data channel to be used for interprocess. more details
Question
After reading these system calls, how can one create a simple prompt using fork() and wait()?
When one type > echo "Hello World" what happends?
Try to define which is the parent and which is the child. In addition, when running a CLI command, are we allowed to type a new command before the last one finishes?
When one type wc "Hello World" > example.txt what happends?
When wc is run unix stystem is looking for free file descriptor at 0.
When one type echo "Hello World" | wc what happends?
Try to think of the order of execution and which should wait to another.
Other importent syscall is kill, allowing to send signals to process.