This document discusses shared memory and semaphores for inter-process communication. It describes:
1) Shared memory allows unrelated processes to access the same logical memory. Processes can create and attach to shared memory segments using system calls like shmget() and shmat().
2) Semaphores provide synchronization between processes. There are unnamed binary semaphores used for critical sections and named semaphores identified by name that can be accessed by multiple processes. Semaphore operations like sem_wait() and sem_post() are used for locking and unlocking.
A hash function usually means a function that compresses, meaning the output is shorter than the input
A hash function takes a group of characters (called a key) and maps it to a value of a certain length (called a hash value or hash).
The hash value is representative of the original string of characters, but is normally smaller than the original.
This term is also known as a hashing algorithm or message digest function.
Hash functions also called message digests or one-way encryption or hashing algorithm.
http://phpexecutor.com
A brief introduction to Process synchronization in Operating Systems with classical examples and solutions using semaphores. A good starting tutorial for beginners.
Basic Memory Management
Introduction
Logical and Physical address map
Memory allocation
Contiguous Memory allocation
Fixed and variable partition
Internal and External fragmentation and Compaction
Paging
Principle of operation
Page allocation
Hardware support for paging
Protection and sharing
Disadvantages of paging
Virtual Memory
Basics of Virtual Memory
Hardware and control structures
Locality of reference
Page fault
Working Set
Dirty page/Dirty bit
Demand paging
Page Replacement policies
Optimal (OPT)
First in First Out (FIFO)
Second Chance (SC)
Not recently used (NRU)
Least Recently used (LRU)
DSM system
Shared memory
On chip memory
Bus based multiprocessor
Working through cache
Write through cache
Write once protocol
Ring based multiprocessor
Protocol used
Similarities and differences b\w ring based and bus based
A hash function usually means a function that compresses, meaning the output is shorter than the input
A hash function takes a group of characters (called a key) and maps it to a value of a certain length (called a hash value or hash).
The hash value is representative of the original string of characters, but is normally smaller than the original.
This term is also known as a hashing algorithm or message digest function.
Hash functions also called message digests or one-way encryption or hashing algorithm.
http://phpexecutor.com
A brief introduction to Process synchronization in Operating Systems with classical examples and solutions using semaphores. A good starting tutorial for beginners.
Basic Memory Management
Introduction
Logical and Physical address map
Memory allocation
Contiguous Memory allocation
Fixed and variable partition
Internal and External fragmentation and Compaction
Paging
Principle of operation
Page allocation
Hardware support for paging
Protection and sharing
Disadvantages of paging
Virtual Memory
Basics of Virtual Memory
Hardware and control structures
Locality of reference
Page fault
Working Set
Dirty page/Dirty bit
Demand paging
Page Replacement policies
Optimal (OPT)
First in First Out (FIFO)
Second Chance (SC)
Not recently used (NRU)
Least Recently used (LRU)
DSM system
Shared memory
On chip memory
Bus based multiprocessor
Working through cache
Write through cache
Write once protocol
Ring based multiprocessor
Protocol used
Similarities and differences b\w ring based and bus based
We often need to store private data in programs, for example passwords, secret keys, and their derivatives, and we usually need to clear their traces in the memory after using them so that a potential intruder can't gain access to these data. In this article we will discuss why you can't clear private data using memset() function.
Overview
Assignment 1 : Hypothetical Machine Simulator
CSci 430: Introduction to Operating Systems Fall 2020
In this assignment you will be building an implementation of the hypothetical machine simulator like the one discussed in chapter 1 of our textbook and that you worked on for the first written assignment. The goal is to become better familiar with some fundamental hardware concepts that we rely on when building operating system components in this class. Another goal is to familiarize you with the structure of the assignments you need to complete for this class.
Questions
• What is the purpose of a standard fetch-execute cycle in a computing system?
• How does a computing system operate at the hardware level to translate and execute instructions? • How can test driven development help you to create and debug your code?
Objectives
Familiarize ourselves with test driven development and developing software to pass unit tests.
Become familiar with the class assignment structure of unit tests and system tests.
Refresh our understanding of basics of how computing systems operate at a hardware level, by studying in more
detail the Hypothetical Machine from our Stallings textbook, and implementing a working simulation of this hypothetical computing system.
Introduction
In this assignment you will be implementing a simulation of the hypothetical machine architecture description given in our Stalling textbook chapter 01. The hypothetical machine described is simple, and is meant to illustrate the basics of a CPU hardware fetch/execute cycle for performing computation, and a basic machine instruction set with some examples processor-memory, data processing, and control type instructions. We will simplify the hypothetical machine architecture in some regards, but expand on it a bit in others for this assignment. You will be implementing the following list of opcodes for this simulation:
1
opcode mnemonic
0 NOOP / HALT
1 LOAD
2 STORE
3 JMP
4 SUB
5 ADD
description
Indicates system halt state
Load AC from memory
Store AC to memory
Perform unconditional jump to address Subtract memory reference from AC Add memory reference to AC
I have given you a large portion of the simulation structure for this first assignment, as the primary goal of the assignment is to become familiar with using system development tools, like make and the compiler and the unit test frameworks. For all assignments for this class, I will always give you a Makefile and a set of starting template files. The files given should build and run successfully, though they will be incomplete, and will not pass all (or any) of the defined unit and system tests you will be given. Your task for the assignments will always be to add code so that you can pass the unit and system tests to create a final working system, using the defined development system and Unix build tools.
All assignments will have 2 targets and files that define executables that are bu.
Program Assignment Process ManagementObjective This program a.docxwkyra78
Program Assignment : Process Management
Objective: This program assignment is given to the Operating Systems course to allow the students to figure out how a single process (parent process) creates a child process and how they work on Unix/Linux(/Mac OS X/Windows) environment. Additionally, student should combine the code for describing inter-process communication into this assignment. Both parent and child processes interact with each other through shared memory-based communication scheme or message passing scheme.
Environment: Unix/Linux environment (VM Linux or Triton Server, or Mac OS X), Windows platform
Language: C or C++, Java
Requirements:
i. You have wide range of choices for this assignment. First, design your program to explain the basic concept of the process management in Unix Kernel. This main idea will be evolved to show your understanding on inter-process communication, file processing, etc.
ii. Refer to the following system calls:
- fork(), getpid(), family of exec(), wait(), sleep() system calls for process management
- shmget(), shmat(), shmdt(), shmctl() for shared memory support or
- msgget(), msgsnd(), msgrcv(), msgctl(), etc. for message passing support
iii. The program should present that two different processes, both parent and child, execute as they are supposed to.
iv. The output should contain the screen capture of the execution procedure of the program.
v. Interaction between parent and child processes can be provided through inter-process communication schemes, such as shared-memory or message passing schemes.
vi. Result should be organized as a document which explains the overview of your program, code, execution results, and the conclusion including justification of your program, lessons you've learned, comments, etc.
Note:
i. In addition, please try to understand how the local and global variables work across the processes
ii. read() or write () functions are used to understand how they work on the different processes.
iii. For extra credit, you can also incorporate advanced features, like socket or thread functions, into your code.
Examples:
1. Process Creation and IPC with Shared Memory Scheme
=============================================================
#include <stdio.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
int main(){
pid_t pid;
int segment_id; //allocate the memory
char *shared_memory; //pointer to memory
const int size = 4096;
segment_id = shmget(IPC_PRIVATE, size, S_IRUSR | S_IWUSR);
shared_memory = (char *) shmat(segment_id, NULL, 0);
pid = fork();
if(pid < 0) { //error
fprintf(stderr, "Fork failed");
return 1;
}
else if(pid == 0){ //child process
char *child_shared_memory;
child_shared_memory = (char *) shmat(segment_id,NULL,0); //attach mem
sprintf(child_shared_memory, "Hello parent process!"); //write to the shared mem
shmdt(child_shared_memory);
}
else ...
Valgrind is a GPL'd system for debugging and profiling Linux programs. With Valgrind's tool suite you can automatically detect many memory management and threading bugs, avoiding hours of frustrating bug-hunting, making your programs more stable. You can also perform detailed profiling to help speed up your programs.
Macroeconomics- Movie Location
This will be used as part of your Personal Professional Portfolio once graded.
Objective:
Prepare a presentation or a paper using research, basic comparative analysis, data organization and application of economic information. You will make an informed assessment of an economic climate outside of the United States to accomplish an entertainment industry objective.
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Shared memory and semaphore? And how to use them? An explanation about those system calls.
1. Shared Memory
&
Semaphore
By
Venkata Durga Prasad. B
Email: venkata.prasad@vvdntech.in
2. Shared Memory
It allows two unrelated processes to access the same logical
memory.
Shared memory is a special range of addresses that is created
by IPC for one process and appears in the address space of
that process.
Other processes can then “attach” the same shared memory
segment into their own address space.
3. Creation:
shmget() is used to obtain access to a shared memory
segment.
int shmget(key_t key, size_t size, int shmflg);
The key argument is a access value associated with the
semaphore ID.
The size argument is the size in bytes of the requested shared
memory.
The shmflg argument specifies the initial access permissions
and creation control flags.
The flag uses IPC_CREAT | 0666 to set permission.
4. Creation:(Cont'd..)
On Success it returns the shared memory segment ID. On
failure, it returns -1
This call is also used to get the ID of an existing shared
segment.
5. Attachment:
To enable access to the shared memory, you must attach it to
the address space of a process.
void *shmat(int shm_id, const void *shm_addr, int shmflg);
shm_id is the shared memory ID returned by shmget().
The second parameter, shm_addr, is the address at which the
shared memory is to be attached to the current process.
The third parameter, shmflg, is a bitwise flag.
SHM_RDONLY, which makes the attached memory read-only.
6. Attachment:(cont'd...)
On success shmat() returns a pointer to the first byte of shared
memory.
On failure, it returns -1.
7. Detachment:
The shmdt function detaches the shared memory from the
current process. It takes a pointer to the address returned by
shmat.
Int shmdt(shm_ptr);
On success shmdt() returns 0,
On error -1 is returned.
8. Controlling:
shmctl() performs the control operation specified by cmd on
the shared memory segment whose identifier is given in shmid.
int shmctl(int shmid, int cmd, struct shmid_ds *buf);
The first parameter, shm_id, is the identifier returned from
shmget.
The second parameter, command, is the action to take. It can
take three values.
9. Controlling:(cont'd...)
IPC_STAT Sets the data in the shmid_ds structure to reflect
the values associated with the shared memory.
IPC_SET Sets the values associated with the shared memory
to those provided in the shmid_ds data structure, if the process
has permission to do so.
IPC_RMID Deletes the shared memory segment.
The third parameter, buf, is a pointer to the structure containing
the modes and permissions for the shared memory.
On success, it returns 0, on failure, –1.
10. NOTE:
If you did not remove your shared memory segments they
will be in the system forever. This will degrade the system
performance.
Use the ipcs command to check if you have shared
memory segments left in the system.
Use the ipcrm command to remove your shared memory
segments.
11. Semaphore
A semaphore is a special type of variable that can be
incremented or decremented,
But crucial access to the variable is guaranteed to be atomic,
even in a multi- threaded program.
12. Types of semaphore:
There are two types of semaphores. They are
Unnamed semaphore
Named semaphore
13. 1.unnamed semaphore:
The semaphore is placed in a region of memory that is shared
between multiple threads.
This semaphore also termed as binary semaphore.
a binary semaphore that takes only values 0 or 1.
Binary semaphores are used to protect a piece of code so that
only one thread of execution can run it at any one time.
14. Initialization:
sem_init() initializes the unnamed semaphore at the address
pointed to by sem. The value argument specifies the initial
value for the semaphore.
int sem_init(sem_t *sem, int pshared, unsigned int value);
The pshared parameter controls the type of semaphore.
If the value of pshared is 0, the semaphore is local to the
current process.
Otherwise, the semaphore may be shared between
processes.
15. Controlling:
int sem_wait(sem_t *sem);
sem_wait() decrements (locks) the semaphore pointed to by
sem.
If the semaphore's value is greater than zero, then the
decrement proceeds, and the function returns, immediately.
If the semaphore currently has the value zero, then the call
blocks until either it becomes possible to perform the
decrement.
On success it returns 0, and on failure -1.
16. Controlling:(cont'd...)
int sem_post(sem_t * sem);
sem_post() increments (unlocks) the semaphore pointed to
by sem.
If the semaphore's value consequently becomes greater than
zero,
Then another process or thread blocked in a sem_wait call will
be woken up and proceed to lock the semaphore.
On success it returns 0, and on failure -1.
17. Destroy( ):
int sem_destroy(sem_t *sem);
sem_destroy() destroys the unnamed semaphore at the
address pointed to by sem.
Only a semaphore that has been initialized by sem_init should
be destroyed using sem_destroy().
Destroying a semaphore that other processes or threads are
currently blocked on (in sem_wait) produces undefined
behavior.
sem_destroy() returns 0 on success, on error, -1 is returned.
18. 2.Named semaphore:
A named semaphore is identified by a name of the form
/some-name, consisting of an initial slash, followed by one or
more characters, none of which are slashes.
Two processes can operate on the same named semaphore by
passing the same name to sem_open.
19. Creation:
sem_t *sem_open(const char *name, int oflag, mode_t mode,
unsigned int value);
sem_open() creates a new POSIX semaphore or opens an
existing semaphore.
The semaphore is identified by name.
The oflag argument specifies flags that control the operation of
the call.
If O_CREAT is specified in oflag, then the semaphore is
created if it does not already exist.
20. Creation:(cont'd...)
The mode argument specifies the permissions to be placed on
the new semaphore.
The value argument specifies the initial value for the new
semaphore.
If O_CREAT is specified, and a semaphore with the given
name already exists, then mode and value are ignored.
On success, sem_open() returns the address of the new
semaphore.
On error, sem_open() returns SEM_FAILED.
21. Destroy:
int sem_unlink(const char *name);
sem_unlink() removes the named semaphore referred to
by name.
On success sem_unlink() returns 0.
On error, -1 is returned.
22. NOTE:
Programs using the POSIX semaphores API must be compiled
with cc -lrt to link against the real-time library.
Otherwise compile with cc -pthread.