LU8 Thread Programming

Question 1

What is a thread?

Answer 1

The smallest unit of execution within a process.

Question 2

How do threads improve program performance?

Answer 2

perform multithreading

Question 3

What are multiple strands of execution in a single program called?

Answer 3

Threads

Question 4

When you invoke a program with threads, what does Linux create first?

Answer 4

A new process.

Question 5

Initially, how many threads does a Linux process have?

Answer 5

One

Question 6

True or False: A single process can have multiple threads executing different parts of the program at the same time.

Answer 6

True

Question 7

Compared to processes, what is one key advantage of using threads for concurrent execution?

Answer 7

• lightweight
• less overhead for creation/termination/context switching.

Question 8

What part of thread process do threads not share?

Answer 8

Stack Pointer and registers

Question 9

What part of process do threads share?

Answer 9

Code, Heap, Static Data

Question 10

What does stack pointer points to?

Answer 10

Points to the current stack where local variables, function parameters, and return addresses are stored.

Question 11

What are some of the disadvantages of processes vs threads

Answer 11

Processes:
* do not share resources very well
* context switching cost is very high

Question 12

If a crash happens on a thread, what can potentially happen?

Answer 12

Crash the entire process!

Question 13

What are three benefits of using threads?

Answer 13

• lightweight
• Takes less time to create/terminate/context switching
• inter-thread communication without invoking the kernel

Question 14

Under what criteria is a task suitable for threading?

Answer 14

• Has multiple parallel sub-tasks, blocking and long waits,
• use many CPU cycles
• needs to respond to asynchronous event

Question 15

Describe a scenario of when a thread can be use.

Answer 15

• Window manager
• multhreaded server
• spreadsheet
• etc.

Question 16

What library do you need to use if you want to code with threads?

Answer 16

libpthread for POSIX threads

POSIX: portable operating system interface

Question 17

What are the four major groups functions to handle the race condition in multithreading?

Answer 17

• Thread management (Creating, Detaching, Joining, Setting Attributes)
• Mutexes (Creating, Destroying, Locking, Unlocking)
• Condition variables (Creating, Destroying, Waiting, Signaling)
• Synchronization (Read/Write Locks, Barriers)

Question 18

What is the purpose of Thread management in threads?

Answer 18

Routines that work directly on threads - creating, detaching, joining, etc.

Question 19

What is the purpose of Mutexes in threads?

Answer 19

synchronization

ensure that only one thread can access a shared resource at any given time. This prevents race conditions and data corruption by enforcing mutual exclusion.

think of public restroom

Question 20

Name a few functions you can do with Mutex.

Answer 20

creating, destroying, locking and unlocking mutexes

Question 21

What is the purpose of Condition variables?

Answer 21

Routines that address communications between threads that share a mutex.

This group includes functions to create, destroy, wait and signal based upon specified variable values

Question 22

Is a routine to manage read/write lock a part of Synchronization thread?

Answer 22

Yes

Question 23

What API standard is POSIX threads a part of?

Answer 23

Standardized portable thread API

Question 24

What header file is needed for POSIX threads?

Answer 24

<pthread.h>
</pthread.h>

Question 25

How does the function `*thread_function (void *arg)` differ than the usual `*function_name()` ``` int pthread_create(pthread_t *thread, pthread_attr_t *attr, void *(*start_routine)(void *), void *arg); ```

Answer 25

pthread_t object that we can use to refer to the thread afterward-function to call and a parameter to pass to it

Question 26

What does the function res = pthread_join(a_thread, &thread_result) do?

Answer 26

1. This function will **wait** until the other thread terminates before it returns. 2. It then **return** the value 3. and **exits**.

Question 27

what does pthread_create argument thread do?

Answer 27

return the ID of the newly created thread

Question 28

What does pthread_create argument attr do?

Answer 28

An opaque attribute object that may be used to set thread attributes

Question 29

Where is the value stored?

Answer 29

start_routine

Question 30

Which value will the thread execute?

Answer 30

start_routine

Question 31

How do two threads synchronize and protect?

Answer 31

semaphores and mutexes

Question 32

What are some advantages of threads rather than new process?

Answer 32

faster communication

Question 33

How do we prevent race condition on a thread?

Answer 33

Mutexes

Question 34

Does a thread create additional thread?

Answer 34

Yes * concurrency/parallelism * asynchronous operations * responsiveness

Question 35

what does inter-process communication require

Answer 35

[ SPMs ] Requires specific mechanisms like: * signals * pipes * message queue * shared memory

Question 36

What does a semaphore act as around piece of code?

Answer 36

Act as gatekeepers

Question 37

What does mutex act as around piece of code?

Answer 37

Act as mutual exclusion device to protect sections of code

Question 38

A single thread can access _______ time?

Answer 38

Once at a time

Question 39

Is it better to protect sections of code via counting a semaphore?

Answer 39

No

Question 40

How do one obtain mutex lock?

Answer 40

pthread_mutex_lock

Question 41

A mutex will act like a _______

Answer 41

Lock

Question 42

Can mutex be an array?

Answer 42

Yes it refers to as multiple mutex objects that protect different resources.

Question 43

If there are several threads waiting, what will the program do?

Answer 43

One wins, the rest block, queue blocked thread

Question 44

True or False: When multiple threads are involved, it is typical to create and initialize a mutex variable.

Answer 44

True

Question 45

What is the command line compilation required to used pthread_mutex_unlock?

Answer 45

gcc -o helloWorld helloWorld.c -lpthread

Question 46

How do I unlock a mutex?

Answer 46

pthread_mutex_unlock

Question 47

What are the different Returns for Creating a Mutex

Answer 47

0 on success, Error number on failure

Question 48

EAGAIN mean?

Answer 48

The system lacked the necessary resources

Question 49

ENOMEM mean?

Answer 49

Insufficient memory

Question 50

EPERM mean?

Answer 50

Caller does not have privileges

Question 51

EBUSY mean?

Answer 51

An attempt to re-initialise a mutex

Question 52

EINVAL mean?

Answer 52

The value specified by attr is invalid

Question 53

Is creating new threads good?

Answer 53

Depends on the hardware

Question 54

What is the primary function of mutexes in multithreaded programming?

Answer 54

* To protect shared data * To prevent race conditions

Question 55

In multithreading, what does a 'race condition' refer to?

Answer 55

Unpredictable behavior due to threads accessing shared data concurrently.

Question 56

What can you pass to the parameters in pthread?

Answer 56

NULL or attribute object

Question 57

What is a signal interrupt?

Answer 57

Inter-thread communication

Question 58

Is TCP socket needed for internal processing?

Answer 58

No

Question 59

To fix the race condition with counter, should you lock and unlock

Answer 59

Yes

Question 60

If the mutex are never unlocked, is there an issue?

Answer 60

Yes (deadlock)

Question 61

What will happen if a mutex is destroyed before unlocked

Answer 61

Undefined outcome

Question 63

Multiple strands of execution in a single program is know as...

Answer 63

Threads

Question 64

When multiple threads access shared variables, it can result in...

Answer 64

Race conditions

Question 65

True or False: Thread is lighter than processes

Answer 65

True

Question 66

Are data and stack shared within threads?

Answer 66

Data is shared, but stack is not

Question 67

What is mutual exclusion mechanism?

Answer 67

Mutex

Question 68

What value should we pass through arg in pthread to ensure data

Answer 68

A reference

Question 69

Which operation should you use to unlock a mutex?

Answer 69

pthread_mutex_unlock

Question 70

True or False, shared memory has some type of mutex?

Answer 70

True

Question 71

If mutex is destroyed, do I have access?

Answer 71

No

Question 72

Does each thread have unique Stack and data?

Answer 72

Unique Stack

Question 73

What is one function to create threads?

Answer 73

pthread_create

Question 74

What is one function to create mutex lock?

Answer 74

pthread_mutex_init

Question 75

What do you need to do after the work with mutex is done?

Answer 75

Destroy the mutex object

Question 76

Threads communicates by...

Answer 76

Sharing Memory

Question 77

Each process has its own

Answer 77

Stack pointer (SP), and program counter (PC)

Question 78

True or False: Threads can be created with mutex attribute

Answer 78

True

Question 79

Explain the importance of synchronizing data access among threads in a single process.

Answer 79

To prevent **data corruption** and ensure **consistent** results.

Question 80

What is the benefit of inter-thread communication not invoking the kernel?

Answer 80

Increased performance due to lower overhead.

Question 81

Can threads exist without process

Answer 81

No

Question 82

True/False: All threads run the different program in the same process

Answer 82

False

Question 83

Mutex variable acts like a

Answer 83

Lock

Question 84

What are functions associated with thread

Answer 84

Creating, detaching, joining, set or query, thread attribute

Question 85

What is a mutex and when would you use one?

Answer 85

Used when multiple writes occur.

Question 86

Does process or threads requires more memory

Answer 86

Process

Question 87

Threads can _______ to create more threads

Answer 87

Fork/Lead

Question 88

Thread has its own stack pointer for ______

Answer 88

Local variable function