Chapter 5 (Concurrency) Flashcards
What does concurrent mean?
Happening at the same time
What kinds of systems does concurrency arise in?
Multiprogramming
Multiprocessing
Distributed processing
What’s the term for “Multiple processes on a uniprocessor system”?
Multiprogramming
What’s the term for multiple processes on a multiprocessor system?
Multiprocessing
What contexts does concurrency occur in?
Multiple applications
Structured applications
OS Structure
T/F The relative order of execution of concurrent processes is unpredictable
T
What is it called when the outcome of two processes accessing the same variable depends on their relative order of execution?
Race condition
When does a race condition occur?
When multiple processes or threads read and write data items so that the final results depends on the order of execution
What is the term for “A process competing for a resource never receives it due to scheduling of other processes”?
Starvation
If you have no mutual exclusion issue, can you have a deadlock?
Yes, a pair may be deadlocked waiting for the other to send a message
What are the three general approaches for achieving mutual exclusion?
Software
Hardware
Operating system or language
What is a coroutine?
Pass control back and forth
What are the problems with competition-style process interaction?
Mutual exclusion
Deadlock
Starvation
What are the problems with sharing-style process interaction?
Mutual exclusion
Deadlock
Starvation
Data coherence
What are the problems with communication-style process interaction?
Deadlock
Starvation
What are the problems with interrupt disabling?
Degraded multitasking performance
Doesn’t work on a multiprocessor system
What does interrupt disabling prevent?
Interleaving
What are the advantages of special machine instruction?
Works on uniprocessor or shared-memory multiprocessor
Simple and easy to verify
Permits multiple critical sections, each with its own variable
What are the disadvantages of special machine instruction?
Busy-waiting consumes processor time
Starvation possible since the process that runs next is arbitrary.
Deadlock
How is a deadlock possible when using special machine instructions?
p1 enters the critical section and is interrupted by a higher priority process p2. p2 cannot enter due to p1, and p1 will not be scheduled due to p2.
What is a strong semaphore?
Queue uses FIFO order and no starvation
What is a weak semaphore?
Queue has no ordering, could have starvation
T/F Binary semaphores are equally as powerful as a general semaphore
T
What happens when a counting semaphore is 0?
Blocking
What does a -5 semaphore value represent?
5 blocked threads
What does a semaphore value of 10 that has a wait/signal?
Lets a max of 10 threads pass
What does a counting semaphore value of 0 mean?
No processes waiting
What are the characteristics of a monitor?
Local data variables
Process enters monitor by invoking one of its procedures
Only one process may execute in the monitor at a time.
What are the two requirements for processes that interact?
Synchronization
Communication
T/F Message passing does not meet the requirements for processes that interact
F, messaging passing meets the requirements
T/F Message passing works in a distributed environment
T
What are the three combinations of message passing?>
Blocking send, blocking receive
Nonblocking send, blocking receive
Nonblocking send, nonblocking receive
What are the two types of message addressing?
Direct
Indirect
T/F Direct messaging allows for flexibility
F, Indirect
