Concurrency Control

* In order to create concurrent execution context, and control how they operate within the library and application, three facilities need to be provided:
- Execution context: the state of a concurrent entity.
- Scheduling: to determine which execution context and/or CPU
- Synchronization: to cooperate between concurrent execution contexts

* Thread
- All threads in one process would share all the resources, like virtual address space, file descriptor/pointer, working directory, etc..
- A thread's registers, PC, stack and heap memory are private for the thread unless the thread communicates pointer to that memory to other threads.
- A thread is fully synchronous with itself unless some asynchronous events happen, like ISR.

* Thread Working Modes
- Pipeline
A task is broken into a series of suboperations, each of which is handled in series, but concurrently, by a different thread.
- Client/Server
Multiple clients contact with an independent server for each job anonymously (Multiple to one).
- Manager/worker
A single thread, the manager assigns work to other threads, the workers(One to multiple). Typically, the manager handles all input and parcels out work to the other tasks. At least two forms of the manager/worker model are common: static worker pool and dynamic worker pool.
- Work Crew
Multiple threads work together independently. A special form of manager/worker mode since the manager would join the workers after it creates workers.