Download Process Management and Interprocess Communication in Operating Systems and more Slides Computer Science in PDF only on Docsity!
1
Chapter 3: Processes
- A primary task of an operating system is to
execute & manage processes
- Process management
- Issue with multiprogrammed systems, and multi- tasking systems
- May not be an issue with some systems (e.g., embedded systems– why?)
- Terms
- Process organization in memory
- Text section (program code)
- Data section: including stack & heap
- Process state
- Process context
- Process control block (PCB)
2
What is a process?
- More than a program
- A process is a program in execution (Ch 1, p.
- A program plus all the OS data structures
needed to run it
4
Process “State”
- As a process is running it changes state
- State: Indicates the current activity (or life
phase) of a process.
5
Diagram of Process State
(Figure 3.2, p. 101) Docsity.com
7
Process Control Block (PCB)
- Each process has a PCB
- Maintains context for the process when it’s not running
- Also stores other information for process
- Contents may vary by process type (e.g., threads, tasks)
- What is the context of a process?
- Context : When a process “looses” the CPU, what needs to be saved so that the process can be resumed later?
- Must save info including:
- CPU registers, memory management info
- Context is also referred to as “state”, which is confusing!
8
process context
In what address space are PCB’s stored?
What is this?
Also: Process priority
10
Switching Between Processes
(a) save context of current process
- Context of current process saved to PCB for that process
- Includes: (a) CPU register values: instruction counter, stack pointer, data registers, status register, and (b) memory management information
(b) load the context of the “next” process
- Context loaded from the PCB for the process
- Includes: (a) CPU register values: instruction counter, stack pointer, data registers, status register, and (b) memory management information
Linux process switch code (pp. 383-394, Linux scheduler, "The Linux Kernel Primer"; Handout) Docsity.com
11
Diagram Showing CPU Switch
From Process to Process (Fig 3.4)
right word?
right word?
How should we organize the
PCB’s for the processes?
- We have multiple PCB’s– need some kind
of data structure to organize them
- Typically, in a collection of queues
13
14
PCB Queues (Fig 3.6)
Note the names
Creating Processes (“Heavy
Weight Processes”)
- Terms
- Parent : Process that creates a new process
- Child : the new process that is created
- Processes have unique identifiers
- Often an integer value, process identifier (pid)
- Often, parent obtains child pid when creating a child
- With multiple processes
- Introduces coordination & synchronization issues
- E.g., how do processes share data?
- Different methods of starting a child process
- E.g.,
- Child runs a new program, or
- Child runs same program
- Make copy of all or parts of parents address space (e.g., UNIX)Docsity.com
17
Starting a Process on UNIX
int fork(); // returns child pid in parent
- Creates a new process, the child
- Child process gets a copy of parent address space
- fork() system call has unusual semantics
- fork() call returns twice!
- Once in address space of child process
- Function return value is 0 in child
- Once in address space of parent process
- Function return value is process ID of child in parent
19
Figure 3.11: Process creation
(One pattern of usage: exec is optional and waiting for child to die is optional)
20
#include <stdio.h> /* Example of creating a new process on UNIX (BSD; OS X) */ #include <sys/types.h> #include <unistd.h> #include <sys/wait.h>
int a = 1;
int main() { int status; int pid = fork(); if (-1 == pid) { printf("Eror calling fork\n"); } else if (0 == pid) { /* in child process / printf("Press enter to continue in child...\n"); fflush(stdout); getchar(); a = 10; // return from child, and terminate } else { / in parent process */ printf("Value of 'a' before waiting for child= %d\n", a); wait(&status); // status will have pid of child printf("Value of 'a' after waiting for child= %d\n", a); fflush(stdout); } }
OUTPUT: Value of 'a' before waiting for child= 1 Press enter to continue in child... Value of 'a' after waiting for child= 1
Docsity.com
