Concurrency vs Parallelism From Stackoverflow
分类：stackoverflow读书笔记
stack overflow并发
Stackoverflow 精彩答案整理… 本人英语水平渣渣，翻译的主要目的自己整理加深理解。如果不幸误导您，，请见谅。如果您好心提醒我，可以直接底下留言。 原文链接
Concurrency is when two tasks can start, run, and complete in overlapping time periods. It doesn’t necessarily mean they’ll ever both be running at the same instant. Eg. multitasking on a single-core machine. 并发指的是两个任务可以在交错的期间内开始，运行，完成。并不一定意味着连个任务在同一个瞬间同时运行。例如单核机器上的多任务。
Parallelism is when tasks literally run at the same time, eg. on a multicore processor. 并行指的是多个任务按照字面意思同时运行。例如多核处理器上执行任务。
Quoting Sun’s Multithreaded Programming Guide: 引自 <<Sun’s Multithreaded Programming Guide>>
Concurrency: A condition that exists when at least two threads are making progress. A more generalized form of parallelism that can include time-slicing as a form of virtual parallelism. 并发：在如下条件下存在：至少两个线程在进行。更通用的并行模式中包含并发，把并发理解为带有时间间隔的虚拟并行。
Parallelism: A condition that arises when at least two threads are executing simultaneously. 并行：在这样的条件下出现：至少两个线程正在同时执行。
另一个比较形象的解释： Rob usually talks about Go and usually addresses the question of Concurrency vs Parallelism in a visual and intuitive explanation! Here is a short summary:
Task: Let’s burn a pile of obsolete language manuals! One at a time! 任务：烧掉一堆古老的语言参考手册。顺序执行：
Concurrency: There are many concurrently decompositions of the task! One example: 并发：任务分解，并发执行：
Parallelism: The previous configuration occurs in parallel if there are at least 2 gophers working at the same time or not. 至少要两只土拔鼠同时工作才能算的得上是并行。
Confusion exists because dictionary meanings of both these words are almost the same: 因为字典中把并发和并行解释的意思基本是相同的，所以有疑惑很正常。
Concurrent: existing, happening, or done at the same time(dictionary.com) Parallel: very similar and often happening at the same time(merriam webster). Yet the way they are used in computer science and programming are quite different. Here is my interpretation: 但是它们在CS中使用时有很大区别。这里是我的解释： Concurrency: Interruptability 并发：可中断。 Parallelism: Independentability 并行：无相互依赖关系。 篇幅有限，更多解释可以看原文，链接在最上面。
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