Test 3

Question 1

What is a Preprocessing Directive

Answer 1

Any code that begins with #
#include
#define
#ifdef - if defined
#ifndef - if not defined

Question 2

What is in a Header File

Answer 2

• constant definitions
• data type definitions
• function prototypes (but not function implementations)

Question 3

What are 4 Steps of the Compilation Process

Answer 3

1. Preprocessing
2. Assembly Code Creation
3. Machine Code Creation
4. Linking

Question 4

What are 2 Types of Linking

Answer 4

Static Linking: library code copied into executable
PROS: faster execution time
CONS: larger executable size
Dynamic Linking: library code is loaded at runtime
PROS: smaller executable size
CONS: slower execution time

Question 5

What is a Makefile

Answer 5

a text file that is used by the make command to automatically build executable programs and libraries from source code

Question 6

Makefiles: how do you declare a variable

Answer 6

• declare at the top of the file
• e.g. OBJ = linkExample1.o linkExample2.o
• use variable with $(OBJ)

Question 7

Makefiles: how do you clean?

Answer 7

clean:

rm -f *.o *~

Question 8

What is concurrent computing

Answer 8

a form of computing where several computations are executed at the same time

Question 9

What are the 3 main types of concurrent computing?

Answer 9

Multithreaded, multiple processors, and distributed systems

Question 10

What is a distributed system?

Answer 10

a large program that is executed over multiple physical host machines that communicate via internet or intranet

Question 11

What is a multi-process system?

Answer 11

a system running multiple processes/executables at the same time and they communicate with each other to accomplish a task

Question 12

What is a multi-threaded system?

Answer 12

a single process with multiple control flows where multiple tasks are performed by the same CPU but they take turn sharing the CPUs resources

Question 13

Name 3 common issues with concurrent computing

Answer 13

1. Shared Resources
2. Deadlocks
3. Race conditions

Question 14

In concurrent computing, what is the issue with shared resources? What are 2 methods for accessing shared variables?

Answer 14

Multiple threads or processes will likely need the same resources.

1. Mutex
2. Semaphore

Question 15

What is a Mutex?

Answer 15

MUTual EXclusion object
a program object created so multiple threads can take turns using it. only the thread that locked or acquired it can unlock it

Question 16

What is a Semaphore?

Answer 16

A variable used to control access to a common resource
It is a generalization of a Mutex
A thread waiting on a semaphore can be signalled by a different thread so that it can have access

Question 17

In concurrent computing, what are deadlocks?

Answer 17

a condition where multiple threads/processes are blocked and all waiting for a condition that will never occur
ALWAYS DUE TO IMPROPER MUTEX/SEMAPHORE HANDLING

Question 18

In concurrent computing, what are race conditions?

Answer 18

a timing problem in which the correctness of a program depends on one thread reaching a point in control flow before another thread ( the order things get processed is never guaranteed)

Question 19

What is process management?

Answer 19

allocating resources to processes, enabling processes to share and exchange info, protecting resources of each process from each other, and enabling syncing of processes

Question 20

What are two ways that process management can occur?

Answer 20

Shell commands (in the command line)
System calls (in a program)

Question 21

Name the 4 main system calls

Answer 21

FORK
EXEC
WAIT
SYSTEM

Question 22

How does FORK work?

Answer 22

It creates a new process with the current process as the parent of the new process

When using the fork() function as an R-Value, (int i = fork()) the it returns different values in the parent and child processes

In the parent process, Fork returns the PID of the child
In the child process, Fork returns 0

Question 23

How does EXEC work?

Answer 23

Allows the code to go off and run another program instead of this continuing with this one (and it uses the same process ID)

int execv(const char *path, char *const argv[]);
int execvp(const char *file, char *const argv[]);
int execl(const char *path, const char *arg, ....more args);
int execlp(const char *file, const char *arg, ... more args);

path = full path to the file
file = "./fileName"
v = arguments as an array
l = arguments as a list

Question 24

How does WAIT work?

Answer 24

wait(): allows us to put a delay in a parent program until ONE of it’s children returns
waitpid(childPID, &status, 0): allows parent to wait until a specific child is returned

Question 25

How does SYSTEM work?

Answer 25

allows us to run specified commands (or programs) as a shell command when called, the process blocks until the system call is done and then control returns to the program

Question 26

What is a signal?

Answer 26

An integer sent from one process to another

Question 27

What are the two user defined signals?

Answer 27

10: SIGUSR1 12: SIGUSR2

Question 28

How do you install a signal handler?

Answer 28

signal (SIGUSR1/SIGUSR2,signalHandlerFunction); where signalHandlerFunction must take a single int parameter and return void -can use SIG_IGN (ignore signal), or SIG_DFL (use default handler)

Question 29

How do you send signals to other processes

Answer 29

kill(pid,SIGNALTOSEND); SIGNALTOSEND can be an integer or SIGUSR1, SIGUSR2, etc. Some examples of signals are: SIGINT-> signal interrupt (what happens when you press ctrl+C in terminal

Question 30

What is a socket?

Answer 30

An endpoint for sending or receiving data b/w processes

Question 31

How do two hosts communicate to each other through ports and IP addresses

Answer 31

Host 1 App unique port #transport LayerNetwork Layer -> IP Adress \/ NETWORK /\ IP Adress Network Layer Transport Layer unique port # App Host 2

Question 32

What is the transport layer?

Answer 32

A conceptual layer that indicates how indicates how exactly the data is transferred from source to destination (either TCP or UDP)

Question 33

What is the network layer?

Answer 33

provides the means of sending packets from a source host to a destination host

Question 34

What are the two main strategies for transfer layer

Answer 34

TCP: transmission control protocol UDP: User Datagram protocol

Question 35

What are the 3 types of sockets

Answer 35

Stream Sockets: (used for TCP) (think like a telephone call) - connection based, must have connection between sender and receiver before info is sent - must close connection when finished - used for reliable packet delivery Datagram Sockets: (used for UDP) (think like a text message) - data sent when ready - fastest packet delivery, but they can be corrupted Raw Sockets: -bypasses the transport layer completely

Question 36

What is the client server model

Answer 36

a commonly used architecture where one process acts as a server that received requests and clients and then performs the tasks accordingly

Question 37

What are the steps for setting up a client-server model with TCP protocol

Answer 37

#include int sockID = socket( (AF_INET/AR_LOCAL) ,SOCK_STREAM,IPPROTO_TCP) bind(sockID,

,); address is of type struct sockaddr we typecast to sockaddr from sockaddr_in (struct sockadd*) addr (# of pending req's that can be queued)); clientSock = accept(sockID, ,); int numBytesRecd = recv(clientSock, (space in memory), , 0); send (clientSock, buffer, bufferLength, 0 );

Question 38

What is the makefile structure

Answer 38

all: target1 target2 __TAB__| gcc -o programName target1.o target2.o target1: target1.c target1.h extraStuff.h __TAB__| gcc -c target1.c target2: target2.c target2.h extraStuff2.h __TAB__| gcc -c target2.c

Question 39

What are the steps for setting up a client server model with UDP protocol

Answer 39

serverSocket = socket(AF_INET,SOCK_STREAM,IPPROTO_UDP); select(,,, , ) numDescriptors = # of file descriptors/potential clients to accept readFDS/writeFDS = sets of file descriptors ready for reading and writing exceptFDS -> set to NULL timeout -> set to NULL for waiting indefinitely, {0,0} to not wait recvform(serverSocket, buffer, bufLen, 0, clientAddr*, clientAddrLength) sendTo(serverSocket, buffer, bufLen, 0, clientAddr*, clientAddrLength);

Question 40

What is a file descriptor? | What is the file descriptor set struct?

Answer 40

an integer ID (handle) used to access a file or other input/output resources (e.g. pipe or socket) struct fd_set can be used as follows: int socket fd_set readfds FD_ZERO(&readfds) FD_SET(socket,&readfds)

Question 41

What is a thread

Answer 41

a sequence of programmed instructions that can be managed independently by the OS it is faster to switch threads than to switch processes

Question 42

What are some unique properties of each thread? | What are some shared properties of threads from the same process?

Answer 42

UNIQUE: - thread ID - function call stack - program counter SHARED: - address space - data segment - code segment

Question 43

What are the thread functions and how do you use them?

Answer 43

pthread_create(pthread_t addr, NULL, functionPointer, functionParameter) pthread_exit(void *status) status variable allows the thread to return something pthread_join(pthread_t thread, void *status) waits until the specified thread ends

Question 44

How do you use semaphores?

Answer 44

#include sem_t semEx; sem_init(&semEx,0,1); volatile int count = 0; sem_wait(&semEx); //returns 0 if all goes well count++; sem_post(&semEx);//return 0 if good, increments the semaphore value