Chapter 4 (Threads) Flashcards
What are the two main characteristics of a process?
Resource ownership
Scheduling/execution
T/F A processes main characteristics could be split apart and managed separately
T
What do we get if we split the two main characteristics of a process?
Process: owns resources
Thread: Executes
Refers to multiple threads of execution in a single process
Multithreading
What is a process called that is not multithreaded?
Single-threaded
How many threads does MS-DOS support?
1
T/F Traditional UNIX supports multiple user processes but only supports one thread per process
T
What modern OS’s support multiple threads per process?
Solaris and Windows
What does a process have in a multithreading context?
Virtual address space for the process image
Resource ownership
What does a thread have in a multithreading context?
Thread execution state
Thread context
Stack
Local variables
Shared access to memory and resources of its process
T/F In a multithreaded process model, each thread shares the user stack and kernel stack
F, they each have their own
What are some benefits of threads?
Faster to create
Faster to terminate
Faster to switch between
Communication between threads is more efficient
T/F Threads make program organization harder
F, they can make it easier
“word processor, thread to periodically save to disk” is an example of:
Asynchronous processing
overlapping activity is an example of:
Speed-up execution
Structuring a program logically into threads may aid with program design” is an example of:
Modularity
What states are associated with a thread?
Running
Ready
Blocked
T/F Suspending a process involves suspending all threads of the process since all threads share the same address space
T
T/F Termination of a process would terminate all threads within the process
T
What is a key benefit of threads?
Speed-up in execution through parallelism
T/F On a uniprocessor with multithreading, threads among the same process or differing processes are interleaved
T
What are the two ways to implement thread support in an OS?
User-level threads
Kernel-level threads
What are user-level threads?
Supports threading with the use of a thread library and the OS is not aware of the threads
What are kernel-level threads?
The OS supports threads itself
What are the advantages of user-level threads?
Thread switching does not involve the kernel (so it’s faster)
Scheduling can be application specific
Can run on any OS
What are the disadvantages of user-level threads?
Most system calls are blocking for processes (all threads within the process will be blocked)
The kernel can only assign processes to processors (two threads within the same process cannot run simultaneously on two processors)
What are the advantages of kernel-level threads?
The kernel can simultaneously schedule many threads of the same process on many processors
Blocking is done on a thread level, so one thread in a process can block while another runs
Kernel routines can be multithreaded
What are the disadvantages of the kernel level threads?
Thread switching within the same process requires a mode switch to the kernel, which may result in a significant slowdown
Amdahl’s law formula
1/(1-f)+(f/N)
T/F Typically, there is the same overhead cost as the number of processors involved increases
F, increased overhead
Can be made to run effectively on a multicore system
Database servers
What are some other examples of software that may benefit with multiple cores?
Multithreaded applications
Multiprocess applications
Java applications (JVM as well)
Multi-instance applications (running more than one instance in parallel)
