Application-level Concurrency (Concurrent Programming)
#1 Logic control flow:
is the sequence of Program Counter (PC) values (that corresponding exclusively to instructions contained in a program’s executable file or in shared objects linked into a program dynamically at run time).
Logical flows take many different forms in computer systems. Exception handlers, processes, signal handlers, threads, and Java processes are all examples of logical flows.
#2 Concurrent flow:
A logical flow whose execution overlaps in time with another flow is called a concurrent flow, and the 2 flows are said to run concurrently.
At the level of machine language or assembly language, control flow instructions usually work by altering the program counter. For some central processing units (CPUs), the only control flow instructions available are conditional or unconditional branch instructions, also termed jumps.
#3 Concurrency:
the general phenomenon of multiple flow executing concurrently is known as concurrency.
#4 Concurrent programs:
Applications that use application-level concurrency are known as concurrent programs.
#5 Mechanisms :
provided by OS for writing concurrent programs:
1) Logic control flows are modeled as processes.
2) Logic control flows are modeled as state machines.
3) Logic control flows are modeled as threads.