CPU Abstraction: the Process
Mechanisms: low-level machinery
E.x. Time-sharing mechanism
"How"
Policies: algorithms for making some kind of decision within the OS
E.x. Scheduling policy
"Which"
Separating the two allows one easily to change policies without having to rethink the mechanism and thus is a form of modularity.
4.1 The Abstraction: A Process
The abstraction provided by the OS of a running program is something we will call a process.
What constitutes a process (its machine state)
Memory (address space): instructions, data (read, write)
Registers: program counter (PC), stack pointer, frame pointer
Persistent storage devices
4.2 Process API
Create, destroy, wait, miscellaneous control, status
4.3 Process Creation: A Little More Detail
Load the code and static data from disk into memory
Creating and initializing a stack
Doing other work as related to I/O setup
Start the program running at the entry point
4.4 Process States
Running: on a processor, executing instructions
Ready
Blocked
4.5 Data Structures
Process list
For each process
Registers (save and restore)
State of the process, ID
Parent process
Open files
Current directory
Process memory (start, size)
Bottom of the kernel stack
Trap frame for the current interrupt
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