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tclementdev / libdispatch-efficiency-tips.md
Last active Nov 27, 2021
Making efficient use of the libdispatch (GCD)
View libdispatch-efficiency-tips.md

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

View EitherSequence.swift
////===--- EitherSequence.swift - A sequence type-erasing two sequences -----===//
////
//// This source file is part of the Swift.org open source project
////
//// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
//// Licensed under Apache License v2.0 with Runtime Library Exception
////
//// See https://swift.org/LICENSE.txt for license information
//// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
////
@airspeedswift
airspeedswift / OneSidedRanges.swift
Last active May 25, 2019
One-sided Range operators
View OneSidedRanges.swift
postfix operator ..< { }
prefix operator ..< { }
struct RangeStart<I: ForwardIndexType> { let start: I }
struct RangeEnd<I: ForwardIndexType> { let end: I }
postfix func ..<<I: ForwardIndexType>(lhs: I) -> RangeStart<I>
{ return RangeStart(start: lhs) }
prefix func ..<<I: ForwardIndexType>(rhs: I) -> RangeEnd<I>
View basicconstraints.swift
/*
ericasadun.com
Super-basic priority-less layout utilities
*/
#if os(iOS)
import UIKit
#else
View repmin.swift
// This accompanies http://chris.eidhof.nl/posts/repmin-in-swift.html
import UIKit
// Unfortunately, we need Box
public class Box<T> {
public let unbox: T
public init(_ value: T) { self.unbox = value }
}
@airspeedswift
airspeedswift / homogeneousnessedness.swift
Last active Aug 29, 2015
Swift-only homogeneousnessedness
View homogeneousnessedness.swift
extension SequenceType where Generator.Element: Equatable {
/// Checks every element in a sequence is equal to a given element
func all(element: Generator.Element) -> Bool {
return !contains { $0 != element }
}
/// Checks no element in a sequence is equal to a given element
func none(element: Generator.Element) -> Bool {
return !contains(element)
}