Scala Worker Actor 的设计注意事项

Question

今年秋天我参加了分布式系统课程，由于 Scala 演员在这个领域非常有用，所以我刚刚开始学习 Scala。从到目前为止我从文本“Scala 中的演员”中读到的有关演员的内容中，我有一个问题似乎并没有在文本中非常清楚地解决。

我目前正在一台具有多核处理器的机器上对我的程序进行建模，并在 Master-Workers 模型中使用基于事件的参与者。现在，以下两种设计选择中的哪一种会导致所有处理器内核得到最佳使用？

1) 将 Actor 的数量限制在一个固定的较小数量，而不管主 Actor 有多少工作，分配给工作 Actor（顺便说一下，有时可能相当大）

2) 生成与 Master Actor 需要完成的作业数量一样多的 Actor

哪些因素会影响我对上述两种选择的决定？

更新：我打印出我正在运行的 100 个工作角色的线程 ID，这是输出 -

No. of Processors-2
MainActor is on thread:Thread[ForkJoinPool-1-worker-0,5,main]
AccumulatorActor is on thread:Thread[ForkJoinPool-1-worker-1,5,main]

Worker Actor-1 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-4 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-5 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-6 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-7 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-8 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-9 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-10 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-3 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-12 running on thread:Thread[ForkJoinPool-1-worker-0,5,main] 
Worker Actor-13 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-14 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-15 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-2 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-16 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-11 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-17 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-18 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-19 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-20 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-21 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-22 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-23 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-24 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-25 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-26 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-28 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-29 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-27 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-30 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-31 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-33 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-32 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-34 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-35 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-36 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-38 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-39 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-40 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-41 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-42 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-43 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-44 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-45 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-46 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-47 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-48 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-51 running on thread:Thread[ForkJoinPool-1-worker-1,5,main]
Worker Actor-50 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-54 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-49 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-56 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-57 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-58 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-55 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-59 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-52 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-61 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-60 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-63 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-53 running on thread:Thread[ForkJoinPool-1-worker-1,5,main]
Worker Actor-65 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-66 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-68 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-64 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-62 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-70 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-69 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-67 running on thread:Thread[ForkJoinPool-1-worker-1,5,main]
Worker Actor-72 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-73 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-71 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-75 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-78 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-79 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-80 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-81 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-82 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-83 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-74 running on thread:Thread[ForkJoinPool-1-worker-1,5,main]
Worker Actor-84 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-85 running on thread:Thread[ForkJoinPool-1-worker-1,5,main]
Worker Actor-77 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-76 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-86 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-87 running on thread:Thread[ForkJoinPool-1-worker-1,5,main]
Worker Actor-88 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-89 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-91 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-92 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-94 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-95 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]
Worker Actor-96 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-90 running on thread:Thread[ForkJoinPool-1-worker-1,5,main]
Worker Actor-98 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-99 running on thread:Thread[ForkJoinPool-1-worker-1,5,main]
Worker Actor-100 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-93 running on thread:Thread[ForkJoinPool-1-worker-2,5,main]
Worker Actor-37 running on thread:Thread[ForkJoinPool-1-worker-0,5,main]
Worker Actor-97 running on thread:Thread[ForkJoinPool-1-worker-3,5,main]

从上面可以看出，ForkJoinPool 中有四个工作线程在运行，而我的机器上有 2 个 cpu 内核。我不确定为什么会这样，因为快速查看 ResizableThreadPoolScheduler 的来源让我相信最初池中的工作线程数等于 cpu 内核数，并且这些是动态增加的，以防任何参与者在池中的一个工作线程上被阻塞。我使用的所有演员都是基于事件的（反应）并且不执行任何阻塞操作。一个理想的场景是在 ForkJoinPool 中只有 2 个线程，并让它们在执行每个参与者工作的两个核心上并行运行。我对此的理解是正确的还是我在这里遗漏了什么？

Answer 1

您听起来好像在考虑演员，就好像他们是线程一样。拥有演员系统的部分目的是将您遇到的问题与演员本身分离。演员的制作成本很低，所以有几千个演员就可以了。拥有数千名演员并不意味着他们每个人都会尝试同时运行。

Scheduler 管理如何执行参与者请求。默认情况下，您将获得 ForkJoinScheduler 或（在特殊 JVM 上） ResizableThreadPoolScheduler

在这两种情况下，并行任务的数量都由ThreadPoolConfig 控制，默认为max(2*cores,4)。在这个类中，你还可以看到如何通过系统属性覆盖这些默认值：

• actors.enableForkJoin 允许您控制调度程序的选择
• actors.corePoolSize 设置初始“线程”池大小
• actors.maxPoolSize 设置最大尺寸

请注意，研究 Akka Actor 可能是一个更好的主意，因为它们可能会在某些时候使用 replace the original Scala actor implementation，提供更多功能并强制更清晰地遵守 Actor 模型（因为您只能获得 ActorRef 并且可以不再直接调用你的actor上的方法）。在 Akka 中，调度程序的等价物是 dispatchers。