这里有一些语义需要澄清:

并发或并行是资源争用的问题，而异步是关于控制流的问题。

不同的过程(或它们的组成操作)被称为异步的，当它们的处理顺序没有确定的实现时;换句话说，它们中的任何一个都有可能在任何给定的时间t被处理。根据定义，多个处理器(例如cpu或Persons)使多个处理器同时被处理成为可能;在单个处理器上，它们的处理是交错的(例如线程)。

当异步过程或操作共享资源时，它们被称为Concurrent;当没有资源共享(例如不同的处理器和存储)时，并行性是微不足道的保证;否则必须解决并发控制问题。

因此，异步过程或操作可以与其他过程或操作并行或并发地处理。

并发与并行: 并发在一个时间点上只能完成一个任务。例如:单CPU处理器 并行性在一个点上我们可以做多个任务。例如:双核或多核处理器

并发性意味着同时执行多个任务，但不一定是同时执行。当你必须执行多个任务，但你只有一个资源时，我们就会追求并发性。在单核环境中，并发是通过上下文切换实现的。

并行性就像同时执行多个任务，就像你可以一边唱歌一边洗澡。现在你在并行地做这些任务。

术语异步与线程执行有关。在异步模型中，当执行一个任务时，您可以切换到另一个任务，而无需等待前一个任务完成。

异步编程帮助我们实现并发性。多线程环境中的异步编程是实现并行的一种方法。

Concurrency Concurrency means that an application is making progress on more than one task at the same time (concurrently). Well, if the computer only has one CPU the application may not make progress on more than one task at exactly the same time, but more than one task is being processed at a time inside the application. It does not completely finish one task before it begins the next. Parallelism Parallelism means that an application splits its tasks up into smaller subtasks which can be processed in parallel, for instance on multiple CPUs at the exact same time. Concurrency vs. Parallelism In Detail As you can see, concurrency is related to how an application handles multiple tasks it works on. An application may process one task at at time (sequentially) or work on multiple tasks at the same time (concurrently). Parallelism on the other hand, is related to how an application handles each individual task. An application may process the task serially from start to end, or split the task up into subtasks which can be completed in parallel. As you can see, an application can be concurrent, but not parallel. This means that it processes more than one task at the same time, but the tasks are not broken down into subtasks. An application can also be parallel but not concurrent. This means that the application only works on one task at a time, and this task is broken down into subtasks which can be processed in parallel. Additionally, an application can be neither concurrent nor parallel. This means that it works on only one task at a time, and the task is never broken down into subtasks for parallel execution. Finally, an application can also be both concurrent and parallel, in that it both works on multiple tasks at the same time, and also breaks each task down into subtasks for parallel execution. However, some of the benefits of concurrency and parallelism may be lost in this scenario, as the CPUs in the computer are already kept reasonably busy with either concurrency or parallelism alone. Combining it may lead to only a small performance gain or even performance loss. Make sure you analyze and measure before you adopt a concurrent parallel model blindly.

从http://tutorials.jenkov.com/java-concurrency/concurrency-vs-parallelism.html

我用真实的场景来解释3个话题 假设你想去艾哈迈达巴德到孟买旅行，但你不知道怎么走，所以你决定使用地图应用程序(谷歌Maps)。

很正常但效率很低的一种方法是，你可以在开车前看完整的路径，然后你开始开车并到达目的地。

平行-你可以不断地驾驶和观察路径。 异步-你的朋友和你在车里，你给他你的手机打开地图应用程序，告诉他看地图和指导你。 同时行驶——你开了几公里，把车停在一边，看地图，找方向，然后继续开车。

每个人都很难将异步与并行或并发相关联，因为异步既不是并行的反义词，也不是并发的反义词。它是同步的反义词。它只是表示某些东西，在这个例子中是线程，是否会与其他东西同步，在这个例子中是另一个线程。