并行编程和并行编程的区别是什么?我问了谷歌,但没有找到任何帮助我理解这种区别的东西。你能给我举个例子吗?

现在我找到了这个解释:http://www.linux-mag.com/id/7411 -但是“并发性是程序的属性”vs“并行执行是机器的属性”对我来说还不够-我仍然不能说什么是什么。


当前回答

我的理解是:

1)并发-使用共享资源串联运行 2)使用不同的资源并行运行

所以你可以让两件事情同时发生,即使它们在点(2)聚集在一起,或者两件事情在整个执行的操作中占用相同的储备(1)。

其他回答

并发编程是一个通用概念,即一个程序可以以未定义的完成顺序执行多个任务,并且这些任务可以同时执行,也可以不同时执行。

并行编程只是一种并发编程,其中这些任务运行在同时执行的线程上。

我真的不理解这里许多过于冗长的回答,这些回答似乎暗示并行编程和并行编程是不同的编程方法,它们并不重叠。

如果你在写一个并行程序,根据定义,你是在写一个并发程序的特殊情况。这些年来,术语似乎被不必要地混淆和复杂化了。

关于并发编程最好、最详细的报道之一是Joe Duffy所著的《Windows上的并发编程》一书。这本书定义了并发,然后继续解释各种操作系统资源,库等可用来编写“并行”程序,如。net中的任务并行库。

第5页:

并行性是使用并发性将操作分解为 粒度更细的组成部分,以便独立的部分可以运行 机器上的独立处理器"

同样,并行编程只是一种特殊类型的并发编程,其中多个线程/任务将同时运行。

PS 我一直不喜欢在编程中,并发和并行这两个词有如此多的含义。例:在编程之外的广阔世界里,“篮球比赛将并行进行”和“篮球比赛将并行进行”是完全相同的。

想象一下,在开发者大会上,他们在第一天宣传会议将“并行”运行,但第二天他们将“并发”运行,这是多么可笑的困惑。那会很搞笑的!

Concurrent programming regards operations that appear to overlap and is primarily concerned with the complexity that arises due to non-deterministic control flow. The quantitative costs associated with concurrent programs are typically both throughput and latency. Concurrent programs are often IO bound but not always, e.g. concurrent garbage collectors are entirely on-CPU. The pedagogical example of a concurrent program is a web crawler. This program initiates requests for web pages and accepts the responses concurrently as the results of the downloads become available, accumulating a set of pages that have already been visited. Control flow is non-deterministic because the responses are not necessarily received in the same order each time the program is run. This characteristic can make it very hard to debug concurrent programs. Some applications are fundamentally concurrent, e.g. web servers must handle client connections concurrently. Erlang, F# asynchronous workflows and Scala's Akka library are perhaps the most promising approaches to highly concurrent programming.

Multicore programming is a special case of parallel programming. Parallel programming concerns operations that are overlapped for the specific goal of improving throughput. The difficulties of concurrent programming are evaded by making control flow deterministic. Typically, programs spawn sets of child tasks that run in parallel and the parent task only continues once every subtask has finished. This makes parallel programs much easier to debug than concurrent programs. The hard part of parallel programming is performance optimization with respect to issues such as granularity and communication. The latter is still an issue in the context of multicores because there is a considerable cost associated with transferring data from one cache to another. Dense matrix-matrix multiply is a pedagogical example of parallel programming and it can be solved efficiently by using Straasen's divide-and-conquer algorithm and attacking the sub-problems in parallel. Cilk is perhaps the most promising approach for high-performance parallel programming on multicores and it has been adopted in both Intel's Threaded Building Blocks and Microsoft's Task Parallel Library (in .NET 4).

我的理解是:

1)并发-使用共享资源串联运行 2)使用不同的资源并行运行

所以你可以让两件事情同时发生,即使它们在点(2)聚集在一起,或者两件事情在整个执行的操作中占用相同的储备(1)。

如果你的程序使用线程(并发编程),它不一定会这样执行(并行执行),因为这取决于机器是否可以处理几个线程。

这是一个直观的例子。非线程机器上的线程:

        --  --  --
     /              \
>---- --  --  --  -- ---->>

螺纹机上的螺纹:

     ------
    /      \
>-------------->>

虚线表示执行的代码。正如您所看到的,它们都分开并分别执行,但是线程机器可以同时执行几个单独的部分。

我会试着用我自己的方式来解释它,它可能不是计算机术语,但它能给你一个大概的概念。

让我们以家务为例:洗碗,倒垃圾,修剪草坪等,我们有三个人(线程)A, B, C来做这些事情

并发: 三个人独立地开始不同的任务,例如,

A --> cleaning dishes
B --> taking out trash 
C --> mowing the lawn 

在这里,任务的顺序是不确定的,响应取决于工作量

并行: 在这里,如果我们想要提高吞吐量,我们可以分配多个人来完成一项任务,例如,清洁盘子,我们分配两个人,A擦洗盘子,B洗盘子,这可能会提高吞吐量。

洗碗:

A --> soaping the dishes
B --> washing the dishes

等等

希望这能给你一些启发!现在转到其他答案中解释的技术术语;)