AlvinZhu gbammc

libdispatch efficiency tips

The libdispatch is one of the most misused API due to the way it was presented to us when it was introduced and for many years after that, and due to the confusing documentation and API. This page is a compilation of important things to know if you're going to use this library. Many references are available at the end of this document pointing to comments from Apple's very own libdispatch maintainer (Pierre Habouzit).

My take-aways are:

You should create very few, long-lived, well-defined queues. These queues should be seen as execution contexts in your program (gui, background work, ...) that benefit from executing in parallel. An important thing to note is that if these queues are all active at once, you will get as many threads running. In most apps, you probably do not need to create more than 3 or 4 queues.
Go serial first, and as you find performance bottle necks, measure why, and if concurrency helps, apply with care, always validating under system pressure. Reuse

The Problem

Standard practices say no non-root process gets to talk to the Internet on a port less than 1024. How, then, could I get Node talking on port 80 on EC2? (I wanted it to go as fast as possible and use the smallest possible share of my teeny tiny little micro-instance's resources, so proxying through nginx or Apache seemed suboptimal.)

The temptingly easy but ultimately wrong solution:

Alter the port the script talks to from 8000 to 80:

}).listen(80);

	/// Observes a run loop to detect any stalling or blocking that occurs.
	///
	/// This class is thread-safe.
	@interface GHRunLoopWatchdog : NSObject

	/// Initializes the receiver to watch the specified run loop, using a default
	/// stalling threshold.
	- (id)initWithRunLoop:(CFRunLoopRef)runLoop;

	/// Initializes the receiver to detect when the specified run loop blocks for

	<?xml version="1.0" encoding="UTF-8" standalone="no"?>
	<document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="6245" systemVersion="13E28" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" initialViewController="vXZ-lx-hvc">
	<dependencies>
	<plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="6238"/>
	<capability name="Aspect ratio constraints" minToolsVersion="5.1"/>
	</dependencies>
	<scenes>
	<!--View Controller-->
	<scene sceneID="ufC-wZ-h7g">
	<objects>

	@interface UIButton (VerticalLayout)

	- (void)centerVerticallyWithPadding:(float)padding;
	- (void)centerVertically;

	@end

	require 'sinatra' # gem install sinatra --no-rdoc --no-ri
	set :port, 3000
	set :environment, :production

	html = <<-EOT
	<html><head><style>
	#text{width:100%; font-size: 15px; padding: 5px; display: block;}
	</style></head><body>
	<input id="text" placeholder="Write then press Enter."/>
	<div id="chat"></div>