Concurrency

Question 1

What mean “Program” term?

Answer 1

A program, or application, is a brand name. It’s a name that we use to refer to a software package. When we execute a program, the OS creates a process.

Question 2

What mean “Executable” term?

Answer 2

A file that can be loaded into memory and then run. Running an executable means creating a process and a thread for it, then changing the CPU’s instruction pointer to the first instruction of the executable.

Question 3

What mean “Task” term?

Answer 3

This chapter uses the term task in an abstract sense. Its meaning shifts as the level of abstraction changes:
a When discussing processes, a task is one of the process’s threads.
b When referring to a thread, a task might be a function call.
c When referring to an OS, a task might be a running program, which might
be comprised of multiple processes.

Question 4

What mean “Process” term?

Answer 4

Running programs execute as processes. A process has its own vir- tual address space, at least one thread, and lots of bookkeeping managed by the OS. File descriptors, environment variables, and scheduling priorities are managed per process. A process has a virtual address space, executable code, open handles to system objects, a security context, a unique process identi- fier, environment variables, a priority class, minimum and maximum working set sizes, and at least one thread of execution.

Each process is started with a single thread, often called the primary thread, but can create additional threads from any of its threads. Running pro- grams begin their life as a single process, but it isn’t uncommon to spawn subprocesses to do the work.

Question 5

What mean “Thread” term?

Answer 5

The thread metaphor is used to hint that multiple threads can work together as a whole.

Question 6

What mean “Thread of execution” term?

Answer 6

A sequence of CPU instructions that appear in serial. Multiple threads can run concurrently, but instructions within the sequence are intended to be executed one after another.

Question 7

What mean “Coroutine” term?

Answer 7

Also known as fibre, green thread, and lightweight thread, a corou- tine indicates tasks that switch within a thread. Switching between tasks becomes the responsibility of the program itself, rather than the OS. Two the- oretical concepts are important to distinguish:
a Concurrency, which is multiple tasks of any level of abstraction running at the same time
b Parallelism, which is multiple threads executing on multiple CPUs at the same time