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Node.js异步处理CPU密集型任务

Node.js擅长数据密集型实时（data-intensive real-time）交互的应用场景。然而数据密集型实时应用程序并不是只有I/O密集型任务，当碰到CPU密集型任务时，比如要对数据加解密（node.bcrypt.js），数据压缩和解压（node-tar），或者要根据用户的身份对图片做些个性化处理，在这些场景下，主线程致力于做复杂的CPU计算，I/O请求队列中的任务就被阻塞。

Node.js主线程的event loop在处理所有的任务/事件时，都是沿着事件队列顺序执行的，所以在其中任何一个任务/事件本身没有完成之前，其它的回调、监听器、超时、nextTick()的函数都得不到运行的机会，因为被阻塞的event loop根本没机会处理它们，此时程序最好的情况是变慢，最糟的情况是停滞不动，像死掉一样。

一个可行的解决方案是新开进程，通过IPC通信，将CPU密集型任务交给子进程，子进程计算完毕后，再通过ipc消息通知主进程，并将结果返回给主进程。

和创建线程相比，开辟新进程的系统资源占用率大，进程间通信效率也不高。如果能不开新进程而是新开线程，将CPU耗时任务交给一个工作线程去做，然后主线程立即返回，处理其他的I/O请求，等到工作线程计算完毕后，通知主线程并将结果返回给主线程。那么在同时面对I/O密集型和CPU密集型服务的场景下，Node的主线程也会变得轻松，并能时刻保持高响应度。

Note: as @clibois mentioned below, due to the DRM Netflix uses, all decoding has to be done in CPU, making it somewhat choppy.

Note 2: Even the RPi 3 suffers from these CPU limitations. There is the potentially risky option of overclocking your RPi 3, but I haven't tried this.

If you manage to get smooth playback, please contact me, or post your solution here

UPDATE: I can no longer get this method to work. I have tried using Chromium v47, and v48, and both result in Netflix error "Oops, something went wrong" / C7053-1807, for which I can find no description online. If you manage to get things up and running, please contact me!

	/* A simple ADC example that checks the analog reading on ADC0 and turns
	* an LED on if the reading is higher than a threshold value and turns if
	* off if it is under that value. */
	#include <avr/io.h>
	#include <stdint.h>

	/* Which analog pin we want to read from. The pins are labeled "ADC0"
	* "ADC1" etc on the pinout in the data sheet. In this case ADC_PIN
	* being 0 means we want to use ADC0. On the ATmega328P this is also
	* the same as pin PC0 */

	//Origional code from http://www.ediy.com.my/index.php/blog/item/74-digispark-infrared-receiver
	//Modified by Daniel Splawski 02/11/2013

	//Uncomment DigiKeyboard statments for debugging
	//#include <DigiKeyboard.h>

	#include <SoftwareSerial.h>
	SoftwareSerial mySerial(0,1); // RX, TX

	int irPin = 2; //Sensor pin connect to digital pin2 (ATINY85 pin7)

	awk '
	BEGIN {
	buffer=""
	}
	{
	gsub(/<\/*trk>/,"",$0)
	gsub(/<\/*trkseg>/,"",$0)
	gsub(/<trkpt/,"<wpt", $0)
	gsub(/<\/trkpt>/,"<\/wpt>", $0)
	print

	echo "USAGE: rpi-netflix.sh workdirectory"
	echo "THIS ASSUMES YOU HAVE CHROMIUM!!!"
	echo "IF NOT, PRESS CTRL+C"
	sleep 5
	wget https://dl.google.com/dl/edgedl/chromeos/recovery/linux_recovery.sh
	echo "YOU MUST HAVE ENOUGH FREE SPACE!!!"
	echo "14\n" \| sudo WORKDIR=$1 ./linux_recovery.sh
	cd $1
	sudo apt-get install kpartx
	sudo kpartx -avs chromeos*.bin

	echo "USAGE: rpi-netflix.sh workdirectory"
	echo "THIS ASSUMES YOU HAVE CHROMIUM!!!"
	echo "IF NOT, PRESS CTRL+C"
	sleep 5
	wget https://dl.google.com/dl/edgedl/chromeos/recovery/linux_recovery.sh
	echo "YOU MUST HAVE ENOUGH FREE SPACE!!!"
	echo "14\n" \| sudo WORKDIR=$1 ./linux_recovery.sh
	cd $1
	sudo apt-get install kpartx
	sudo kpartx -avs chromeos*.bin

	//: Playground - noun: a place where people can play

	import UIKit

	// This is for dmoe, you can use a generice type to limit your observer to an UIViewController for common usage.
	protocol Notifiable {
	var name: Notification.Name { get }
	func observe(by observer: Any, withSelector selector: Selector, object: Any?)
	func post(object: Any? ,userInfo: [AnyHashable: Any]?)
	static func remove(observer: Any)

angp

Node.js异步处理CPU密集型任务

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