Task parallelism is a form of parallelization of computer code across multiple processor
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
Parallel computing is a form of computation in which many calculations are carried out simultaneously, operating on the principle that large problems can often be divided into smaller ones, which are then solved concurrently . There are several different forms of parallel computing: bit-level,...
environments. Task parallelism focuses on distributing execution processes (threads) across different parallel computing nodes. It contrasts to data parallelism
Data parallelism
Data parallelism is a form of parallelization of computing across multiple processors in parallel computing environments. Data parallelism focuses on distributing the data across different parallel computing nodes...
as another form of parallelism.
Description
In a multiprocessor system, task parallelism is achieved when each processor executes a different thread (or process) on the same or different data. The threads may execute the same or different code. In the general case, different execution threads communicate with one another as they work. Communication takes place usually to pass data from one thread to the next as part of a workflow
Workflow
A workflow consists of a sequence of connected steps. It is a depiction of a sequence of operations, declared as work of a person, a group of persons, an organization of staff, or one or more simple or complex mechanisms. Workflow may be seen as any abstraction of real work...
.
As a simple example, if we are running code on a 2-processor system (CPUs "a" & "b") in a parallel environment and we wish to do tasks "A" and "B" , it is possible to tell CPU "a" to do task "A" and CPU "b" to do task 'B" simultaneously, thereby reducing the run time of the execution. The tasks can be assigned using conditional statement
Conditional statement
In computer science, conditional statements, conditional expressions and conditional constructs are features of a programming language which perform different computations or actions depending on whether a programmer-specified boolean condition evaluates to true or false...
s as described below.
Task parallelism emphasizes the distributed (parallelized) nature of the processing (i.e. threads), as opposed to the data (data parallelism
Data parallelism
Data parallelism is a form of parallelization of computing across multiple processors in parallel computing environments. Data parallelism focuses on distributing the data across different parallel computing nodes...
). Most real programs fall somewhere on a continuum between Task parallelism and Data parallelism.
In computer science and numerical computation, pseudocode is a compact and informal high-level description of the operating principle of a computer program or other algorithm. It uses the structural conventions of a programming language, but is intended for human reading rather than machine reading...
below illustrates task parallelism:
program:
...
if CPU="a" then
do task "A"
else if CPU="b" then
do task "B"
end if
...
end program
The goal of the program is to do some net total task ("A+B"). If we write the code as above and launch it on a 2-processor system, then the runtime environment will execute it as follows.
In computing, SPMD is a technique employed to achieve parallelism; it is a subcategory of MIMD. Tasks are split up and run simultaneously on multiple processors with different input in order to obtain results faster. SPMD is the most common style of parallel programming...
system, both CPUs will execute the code.
In a parallel environment, both will have access to the same data.
The "if" clause differentiates between the CPU's. CPU "a" will read true on the "if" and CPU "b" will read true on the "else if", thus having their own task.
Now, both CPU's execute separate code blocks simultaneously, performing different tasks simultaneously.
Code executed by CPU "a":
program:
...
do task "A"
...
end program
Code executed by CPU "b":
program:
...
do task "B"
...
end program
This concept can now be generalized to any number of processors.
JVM Example
Similar to the previous example, Task Parallelism is also possible using the Java Virtual Machine JVM.
The code below illustrates task parallelism on the JVM using the commercial third-party Ateji PX extension.
Statements or blocks of statements can be composed in parallel using the || operator inside a parallel block, introduced with square brackets:
[
|| a++;
|| b++;
]
or in short form:
[ a++; || b++; ]
Each parallel statement within the composition is called a branch. We purposely avoid using the terms task or process which mean very different things in different contexts.
In electronics, a hardware description language or HDL is any language from a class of computer languages, specification languages, or modeling languages for formal description and design of electronic circuits, and most-commonly, digital logic...
In the semiconductor and electronic design industry, Verilog is a hardware description language used to model electronic systems. Verilog HDL, not to be confused with VHDL , is most commonly used in the design, verification, and implementation of digital logic chips at the register-transfer level...
and VHDL, which can also be considered as representing a "code static" software paradigm where the program has a static structure and the data is changing - as against a "data static" model where the data is not changing (or changing slowly) and the processing (applied methods) change (e.g. database search).
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