chapter 4: Threads

Question 1

\_\_\_\_ is a thread library for Solaris that maps many user-level threads to one kernel thread.
A) Pthreads 
B) Green threads 
C) Sthreads 
D) Java threads

Answer 1

B- GREEN THREADS

Question 2

Pthreads refers to ____.
A) the POSTFIX standard.
B) an implementation for thread behavior.
C) a specification for thread behavior.
D) an API for process creation and synchronization

Answer 2

C- A SPECIFICATION FOR THREAD BEHAVIOR

Question 3

The \_\_\_\_ multithreading model multiplexes many user-level threads to a smaller or equal number of kernel threads.
A) many-to-one model 
B) one-to-one model 
C) many-to-many model
D) many-to-some model

Answer 3

C- MANY-TO-MANY MODEL

Question 4

Cancellation points are associated with \_\_\_\_ cancellation.
A) asynchronous 
B) deferred 
C) synchronous 
D) non-deferred

Answer 4

B- DEFERRED

Question 5

Which of the following would be an acceptable signal handling scheme for a multithreaded program?
A) Deliver the signal to the thread to which the signal applies.
B) Deliver the signal to every thread in the process.
C) Deliver the signal to only certain threads in the process.
D) All of the above

Answer 5

D- ALL OF THE ABOVE

Question 6

Signals can be emulated in windows through \_\_\_\_.
A) asynchronous procedure calls  
B) local procedure calls 
C) remote procedure
D) none of the above

Answer 6

A- ASYNCHRONOUS PROCEDURE CALLS

Question 7

Thread-specific data is data that ____.
A) is not associated with any process
B) has been modified by the thread but not yet updated to the parent process
C) is generated by the thread independent of the thread’s process
D) is copied and not shared with the parent process

Answer 7

D- IS COPIED AND NOT SHARED W/THE PARENT PROCESS

Question 8

LWP is ____.
A) short for lightweight processor
B) placed between system and kernel threads
C) placed between user and kernel threads
D) common in systems implementing one-to-one multithreading models

Answer 8

C- PLACED BETWEEN USER AND KERNEL THREADS (LIGHTWEIGHT PROCESS)

Question 9

Windows XP uses the \_\_\_\_.
A) one-to-one model 
B) many-to-one model 
C) one-to many-model
D) many-to-many model

Answer 9

A- ONE-TO-ONE MODEL

Question 10

In multithreaded programs, the kernel informs an application about certain events using a procedure known as a(n) \_\_\_\_.
A) signal 
B) upcall 
C) event handler 
D) pool

Answer 10

B- UPCALL

Question 11

Why should a web server not run as a single-threaded process?

Answer 11

For a web server that runs as a single-threaded process, only one client can be serviced at a time. This could result in potentially enormous wait times for a busy server.

Question 12

List the four major categories of the benefits of multithreaded programming. Briefly explain each

Answer 12

The benefits of multithreaded programming fall into the categories: responsiveness, resource sharing, economy, and utilization of multiprocessor architectures. Responsiveness means that a multithreaded program can allow a program to run even if part of it is blocked. Resource sharing occurs when an application has several different threads of activity within the same address space. Threads share the resources of the process to which they belong. As a result, it is more economical to create new threads than new processes. Finally, a single threaded process can only execute on one processor regardless of the number of processors actually present. Multiple threads can run on multiple processors, thereby increasing efficiency

Question 13

What are the two different ways in which a thread library could be implemented?

Answer 13

The first technique of implementing the library involves ensuring that all code and data structures for the library reside in user space with no kernel support. The other approach is to implement a kernel-level library supported directly by the operating system so that the code and data structures exist in kernel space

Question 14

Describe two techniques for creating Thread objects in Java

Answer 14

One approach is to create a new class that is derived from the Thread class and to override its run() method. An alternative – and more commonly used – technique is to define a class that implements the Runnable interface. When a class implements Runnable, it must define a run() method. The code implementing the run() method is what runs as a separate thread

Question 15

In Java, what two things does calling the start() method for a new Thread object accomplish?

Answer 15

Calling the start() method for a new Thread object first allocates memory and initializes a new thread in the JVM. Next, it calls the run() method, making the thread eligible to be run by the JVM. Note that the run() method is never called directly. Rather, the start() method is called, which then calls the run() method.

Question 16

Some UNIX systems have two versions of fork(). Describe the function of each version, as well as how to decide which version to use.

Answer 16

One version of fork() duplicates all threads and the other duplicates only the thread that invoked the fork() system call. Which of the two versions of fork() to use depends on the application. If exec() is called immediately after forking, then duplicating all threads is unnecessary, as the program specified in the parameters to exec() will replace the process. If, however, the separate process does not call exec() after forking, the separate process should duplicate all threads.

Question 17

How can deferred cancellation ensure that thread termination occurs in an orderly manner as compared to asynchronous cancellation?

Answer 17

In asynchronous cancellation, the thread is immediately cancelled in response to a cancellation request. There is no insurance that it did not quit in the middle of a data update or other potentially dangerous situation. In deferred cancellation, the thread polls whether or not it should terminate. This way, the thread can be made to cancel at a convenient time

Question 18

What is a thread pool and why is it used?

Answer 18

A thread pool is a collection of threads, created at process startup, that sit and wait for work to be allocated to them. This allows one to place a bound on the number of concurrent threads associated with a process and reduce the overhead of creating new threads and destroying them at termination

Question 19

In Windows XP, what are the general components of a thread?

Answer 19

he thread consists of a unique ID, a register set that represents the status of the processor, a user stack for user mode, a kernel stack for kernel mode, and a private storage area used by run-time libraries and dynamic link libraries.

Question 20

Describe the difference between the fork() and clone() Linux system calls.

Answer 20

The fork() system call is used to duplicate a process. The clone() system call behaves similarly except that, instead of creating a copy of the process, it creates a separate process that shares the address space of the calling process.

Question 21

T OR F:
 A traditional (or heavyweight) process has a single thread of control

Answer 21

TRUE

Question 22

T OR F:

A thread is composed of a thread ID, program counter, register set, and heap.

Answer 22

FALSE

Question 23

T OR F:

Virtually all contemporary operating systems support kernel threads.

Answer 23

TRUE

Question 24

T OR F:

Linux distinguishes between processes and threads

Answer 24

FALSE

Question 25

T OR F:

In Java, data shared between threads is simply declared globally

Answer 25

FALSE