Process vs threads; importance in DS

Process and thread

• A process is a program in execution with its own address space (code, data, heap), resources (open files) and at least one thread of control.
• A thread is a lightweight unit of execution inside a process. It has its own program counter, registers and stack, but shares the address space, data and open files of its process.

Importance of threads in distributed systems

1. Multithreaded servers: a server handles many client requests at once. One dispatcher thread takes requests and worker threads process them, so a slow request (disk or network wait) does not block others. Example: a web server creates a thread per request, a file server serves many clients.
2. Hiding latency in clients: a web browser uses one thread to fetch the page while others fetch images and render, so the user is not blocked on network delay.
3. Overlap of computation and I/O, which improves performance and throughput, and makes use of multiprocessors.
4. Cheap communication and switching: shared memory between threads is more efficient than between processes.
5. Simpler program structure: blocking system calls (RPC, RMI) can be used in each thread while the program continues in others.
6. Better scalability as a server handles more clients per machine.