Synchronization And Coordination

Front 1

Define Cooperating Process (or Thread).

Back 1

A process or thread that can affect or be affected by other processes executing in the system

Front 2

What can a 'Cooperating Process' do?

Back 2

1. Directly share data (threads)

2. Be allowed to share data through files (processes) or messages

Front 3

Why must access to share data be coordinated?

Back 3

Data inconsistency

Front 4

Define Race Condition.

Back 4

When several processes access and manipulate the same data concurrently and the outcome of the execution depends on the particular order in which the access takes place

Front 5

Is a 'Race Condition' desirable?

Back 5

No, we must ensure that coordinating processes
share data without interfering with each other

Front 6

What happens if two or more processes taking turns reading, modifying, and writing, however they do such out of order?

Back 6

The data will be inconsistent

Front 7

Define Critical Section.

Back 7

A segment of code, in a process, in which it
may be changing variables, tables, writing to
files, and other share dated

Front 8

How can data inconsistentcy be avoided?

Back 8

By carefully controlling which process enters
their critical section

Front 9

How do you control which process enters a 'Critcal Section'?

Back 9

Each process must request permission to enter its critical section, and no two process are allowed to execute in their critical section at the same time

Front 10

Define Bounded Waiting in terms of the 'critical section'?

Back 10

A critical section will usually terminate in fixed
time, and a thread, task or process will have to
wait a fixed time to enter it

Front 11

When does a process request permission to enter a 'critical section'?

Back 11

At the entry section

Front 12

What should a process do once it was completed its 'critical section'?

Back 12

Release control at the exit section.

Front 13

List the requirements of a 'Critical Section'.

Back 13

1. Mutual exclusion

2. Progress

3. Bounded waiting

Front 14

Define ' Mutual Exclusion' in terms of a 'Critical Section'.

Back 14

If one process is in its critical
section, then no other processes are in theirs

Front 15

Define 'Progress' in terms of a 'Critical Section'.

Back 15

If no process is in its critical section, only processes that aren't in their remainder section can request its critical section.

Front 16

Define 'Bounded Waiting' in terms of a 'Critical Section'.

Back 16

There exist a limit/bound on the number of other processes that may enter their critical section after an additional process has made a request and before that request is granted

Front 17

What tools does the 'POSIX' package include to coordinate synchronization?

Back 17

1. Mutex locks
2. Conditional variables
3. Read-write locks

Front 18

Define POSIX.

Back 18

'Portable Operating System Interface'

Defines the application programming interface (API), along with command line shellsand utility interfaces

Front 19

Defin Mutex Lock.

Back 19

A special variable that can be either
locked or unlocked

Front 20

What happens when a Mutex is 'locked'?

Back 20

It has a specific thread that holds or owns it

Front 21

What happens when a Mutex is 'unlocked or free'?

Back 21

It has no thread currently holding it

Front 22

What are in the queue of a 'Mutex'?

Back 22

Threads that are waiting to own it

Front 23

How is the order of in which threads own the 'Mutex' determined?

Back 23

The default thread scheduling policy, Often this is FCFS

Front 24

Why do programs use 'Mutex Locks'

Back 24

To preserve critical sections and to obtain exclusive access to resources

Front 25

How long are 'Mutex Locks' meant to be used for?

Back 25

Small periods of time

Front 26

What is the ideal use of 'Mutex Locks'?

Back 26

Making changes to data structures to help protect against inconsistent data

Front 27

What should you use to synchronize on events of indefinite durations?

Ex) Waiting for input

Back 27

A conditional Variable

Front 28

What is the data type of a 'Mutex Lock'?

Back 28

pthread_mutex_t mLock;

Front 29

What must be done inorder to create and initialize the 'Mutex Lock'?

Back 29

A user must create and initialize the mutex lock before using it

Front 30

What are the 2 option of initializing a 'Mutex Lock'?

Back 30

1. Static allocation
2. Dynamic allocation

Front 31

How would you statically allocate a 'Mutex Lock'?

Back 31

pthread_mutex_t mLock = PTHREAD_MUTEX_INITIALIZER;

Front 32

How would you dynamically allocate a 'Mutex Lock'?

Back 32

1. pthread_mutex_t mLock;

2. pthread_mutex_init(&mLock, NULL);

Front 33

Describe the difference of statically and dynamically allocating a 'Mutex Lock'?

Back 33

Dynamic allocation allows user to set the specific
attributes of mutex, while static is more efficient

Front 34

How would you destroy a 'Mutex Lock'?

Back 34

Using the destroy function

pthread_mutex_destroy(&mLock);

Front 35

How would you lock a 'Mutex Lock'?

Back 35

pthread_mutex_lock(&mLock);

Front 36

How would you unlock a 'Mutex Lock'?

Back 36

pthread_mutex_unlock(&mLock);

Front 37

How would you try lock a 'Mutex Lock'?

Back 37

pthread_mutex_trylock(&mLock);

Front 38

Describe unlocking and trylocking a 'Mutex Lock'.

Back 38

Unlocking and trylock return immediately or nonblocking.

Front 39

Describe locking a 'Mutex Lock'.

Back 39

Locking is a blocking function, cause any threads
in the mutex queue to be waiting

Front 40

When are 'Mutex Locks' useful?

Back 40

Locking a shared resource, modifying it, and
releasing it quickly

Front 41

Give an example of a poor situation of using a 'Mutex Lock'.

Back 41

x==y

because the time duration is undefined

Front 42

How would you create a conditional variable?

Back 42

pthread_con_t condV;

As with mutex locks, you must initialize conditional variables before using them

Front 43

What are the 2 options for intializing a conditional variable?

Back 43

1. Static allocation
2. Dynamic allocation

Front 44

How would you statically allocate a conditional variable?

Back 44

pthread_cond_t condV = PTHREAD_COND_INITIALIZER;

Front 45

How would you dynamically allocate a conditional variable?

Back 45

1. pthread_cond_t condV;
2. pthread_cond_init(&condV, NULL);

Front 46

How would you destroy a conditional variable?

Back 46

pthread_cond_destroy(&condV);

Front 47

Can a conditional variable be reinitialized once it has been destroyed?

Back 47

Yes, it can be reinitialized with pthread_cond_init

Front 48

What must be done first in order to use a conditional varible?

Back 48

A thread must acquire ownership of the mutex lock first

Front 49

After a thread has acquire ownership of a 'Mutex Lock', what is done next?

Back 49

The thread will then call the pthread_cond_wait() function

Front 50

What will happen when pthread_cond_wait() is called?

Back 50

The wait operation will cause the thread to release the mutex, and place the thread into the
conditional variable's queue

Front 51

How is calling pthread_cond_wait() considered efficient?

Back 51

This allows the thread to be “non-busy” waiting

Front 52

What happens when a thread returns successfully from pthread_cond_wait?

Back 52

It has acquired the mutex and can retest the predicate without explicitly reacquiring the mutex lock

Front 53

From the threads point of view, what happens when a thread returns successfully from pthread_cond_wait?

Back 53

It “believes” that it has maintained uninterrupted ownership of the mutex. It never realizes
that is has been blocked or waiting

Front 54

What happens when more than one thread is
waiting on the same condition, and one of the
threads modifies a value that is related to that
conditional?

Back 54

The thread needs to alert then other threads of
a possible change in the conditional

Front 55

How does a thread alert another thread of a possible change in the conditional?

Back 55

Signals

Front 56

What are the 2 options for alerting other threads of changes?

Back 56

1. pthread_cond_signal
2. pthread_cond_broadcast

Front 57

What does pthread_cond_signal do?

Back 57

Unblock at least one of the threads currently in the conditional variable's queue

Front 58

What will pthread_cond_broadcast do?

Back 58

Unblock all of the the threads currently in the conditional variable's queue

Front 59

What is one type of access that should be granted exclusively?

Back 59

Writing

Front 60

What is one type of access that should be shared?

Back 60

Reading

Front 61

What are 2 common methods of reader-writer synchronization?

Back 61

1. Reader synchronization

2. Writer synchronization

Front 62

What does 'Reader Synchronization' do?

Back 62

Give readers preference, and granting access to readers as long as a writer is currently writing

Front 63

What does 'Writer Synchronization' do?

Back 63

Give writers preference, delaying all readers until all waiting or active writers complete

Front 64

What does POSIX do?

Back 64

Allows the programmer to determine how/when a reader acquires a lock if writers are waiting

Front 65

What is the the data type for 'Read-Write Locks'?

Back 65

pthread_rwlock_t RWLOCK;

Front 66

What is done before a 'Read-Write Lock' (RW Lock) can be used?

Back 66

Initialized using the pthread_rwlock_init()
function

Front 67

How would you destroy a 'Read-Write Lock' (RW Lock)

Back 67

To destroy a RW lock use the pthread_rwlock_destroy function

Front 68

How would you acquire a read-write lock for reading?

Back 68

Use the pthread_rwlock_rdlock () function

Front 69

How would you acquire a read-write lock for writing?

Back 69

Use the pthread_rwlock_wrlock() function

Front 70

What do the pthread_rwlock_rdlock () function and the pthread_rwlock_wrlock() function have in common?

Back 70

Both functions will block until lock is available

Front 71

How would you unlock a Read-Write Lock?

Back 71

Use pthread_rwlock_unlock() function