JS: Concurrancy and Event Loop-优快云博客

博客介绍了JavaScript基于事件循环的并发模型，事件循环会同步等待消息，且每条消息处理完才处理下一条，JavaScript不会阻塞，I/O通过事件和回调处理。还提到Node JS架构采用单线程事件循环，其认为I/O成本高，每个连接对应线程耗内存大，所有I/O是事件驱动且异步的。

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Event Loop

JavaScript has a concurrency model based on an "event loop". The event loop got its name because of how it's usually implemented, which usually resembles:

while (queue.waitForMessage()) {
  queue.processNextMessage();
}

queue.waitForMessage() waits synchronously for a message to arrive if there is none currently.

Each message is processed completely before any other message is processed.
setTimeout message: a minimum time and not a guaranteed time.
A web worker or a cross-origin iframe has its own stack, heap, and message queue.
A very interesting property of the event loop model is that JavaScript, unlike a lot of other languages, never blocks. Handling I/O is typically performed via events and callbacks

Node JS Architecture – Single Threaded Event Loop

The first basic thesis of node.js is that I/O is expensive.
The second basic thesis is that thread-per-connection is memory-expensive.
There is no way of making code run in parallel within a single request. However, all I/O is evented and asynchronous.