Give an example to show the advantages to using multithreaded Clients See page 142 of the core book (Tanebaum 2002).

See page of the core book (Tanebaum 2002). Compare the multithreaded file server based on dispatcher/worker model and a single threaded file server introduced during the lecture time; tell the advantages to using the multithreaded technique in server designing.

Explain what is so called stateless server, and stateful server? Give examples A stateless server does not keep information on the sate of its clients, and can change its own state without having to inform any client, e.g. A Web Server. A stateful server does maintain information on its clients, e.g. a file server that allows a client to keep a local copy of a file. See page 151 of the core book (Tanebaum 2002).

Explain what an object adapter is. Decisions on how to invoke an object are commonly referred to as activation policies. The mechanism to group objects per policy is sometimes called an Object Adaptor. The Object Adapter can also be thought of as the software implementing a specific activation policy. See page 154 of the core book (Tanebaum 2002).

For better understanding the code migration, a process is used to be modelled as a three segments model. What are these three segments? Code segment is the part that contains the set of instructions that make up the program that is being executed. Resource segment contains references to external resources needed by the process, such as file, printers, devices, other processes, and so on. Execution segment is used to store the current execution state of a process, consisting of private data, the stack, and the program counter.

For code migration in distributed system, explain what are the weak mobility model and the strong mobility model? What are the sender-initiated mobility and the receiver-initiated mobility? Weak mobility model: In this model, it is possible to transfer only the code segment, along with perhaps some initialization data. Feature: a transferred program is always started from its initial state, e.g. Java applets. Strong mobility model: Besides the code segment being transferred, the execution segment can be transferred as well. Feature: A running process can be stopped, subsequently moved to another machine, and then resume execution where it left off. In sender-initiated migration, migration is initiated at the machine where the code currently resides or is being executed. In receiver-initiated migration, the initiative for code migration is taken by the target machine

List all the alternatives for code migration.