Review Questions

Explain the motivation for threads.
Discuss the motivation for and difference between user-level and kernel-level threads.
Explain how the scheduler in a user-level threads package "multiplexes" user-level threads on top of kernel-level threads.
How many kernel-level threads should be used for a multi-threaded program? Should each user-level thread be mapped to a separate kernel-level thread? If not, why not?
Recall the classical definition of monitors (see Tannenbaum). Does the Java language (Pthreads library) support monitors? How is the support for condition variables in Java (Pthreads) different from condition variables in classical monitors?
Are monitors more "powerful" as a construct than semaphores? I.e., can you do accomplish some kind of synchronization using monitors that you cannot with semaphores? Are semaphores more powerful than monitors?
What is meant by a "race condition"? Explain what the implications of race conditions are for debugging concurrent applications.

What is meant by network transparency?
Discuss the pros and cons of the following statement: "One of the most important goals of distributed software is to provide network transparency".
Discuss how distributed systems provide fault-tolerance or enhanced availability. What are the costs associated with obtaining enhanced fault-tolerance?

Give examples of applications that fall into each of the six Gartner Group categories.
What is the motivation for multi-tier architectures? Discuss the pros and cons of multi-tier architectures.
What are the main costs associated with client-server systems? Are these costs reduced in any way in multi-tier architectures?
What is the motivation for thin clients? Do thin clients represent a move back towards centralized computing?

Discuss the pros and cons of stateless vs. stateful servers.
Is HTTP 1.0 stateful or stateless? How about HTTP 1.1?
Is TFTP stateless? If not, explain why not. Further, explain how would you redesign TFTP to make it stateless? Would there be any advantage to doing this?
Discuss the performance problems associated with HTTP 1.0. Are all these problems resolved in HTTP 1.1? Explain.
Discuss how and why cookies are used with HTTP.
Discuss why a sender can block while doing a "write" operation on a TCP socket.
Discuss why binary files can be transmitted without ASCII encoding for HTTP but need to be encoded into ASCII for email (SMTP).
How are threads useful for client-server applications? Discuss their use in both clients and servers.
What are the advantages and disadvantages of pre-allocating a pool of threads in a server instead of creating threads on demand?
What are the limitations of Java's socket API? i.e., are there tasks that you can do if you're using the UNIX/Solaris sockets API that you cannot do in Java?

What is meant by "at most once" and "at least once" RPC semantics? How can the underlying RPC protocol provide "at least once" semantics? How can it provide "at most once" semantics?
"It is impossible to implement exactly-once RPC semantics". Do you agree or disagree with this statement? If you disagree, explain how your RPC protocol would provide these semantics. If you agree, explain why you think it would be impossible to provide these semantics.
What are the implications of "at least once" semantics for the design of applications that use RPC.
Give an example of an RPC operation that is idempotent and another that is not idempotent.
In Java RMI, the remoteness of a remote object is (intentially) not transparent to the programmer. Briefly discuss the arguments for and against making the remoteness of an object visible to the programmer.
How can RMI be used to "pass behavior" from one system to another?
In RMI, how do you know if an object will be passed by reference or whether it will be passed by value?