processes
Summary
Process contexts
| Memory context | Hardware context | OS context |
|---|---|---|
| - code/machine code - data - stack - heap | - registers - program counter - return PC - stack pointer - frame pointer | - process properties - resources used - pid - process state |
Concept
Process abstraction
- dynamic abstraction for a executing programs
- stores information required to describe the running program
Memory regions
| Region | Contents |
|---|---|
| text | - instructions/code |
| data | - global variables - filled at compile time |
| stack | - local variables during function execution - allocated during call, deallocated on return |
| heap | - dynamic data - allocated at any point during runtime |
5 state process model
- create: spawn new process
- admit: process becomes ready to run
- switch(scheduled): process is selected to be run
- switch(release): process gives up CPU, either voluntarily or by scheduler
- event wait: process requests service that is unavailable or in progress, ie. I/O, user input, network request
- event occurs: request is fulfilled and process can continue
Queuing model
- global view from the OS’s perspective
- 1 CPU can only run <= 1 process at a time
Process control block(PCB)
- entry in the process table
- contains the whole context required to describe one process