tclementdev

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

mdelete

func connection(connection: NSURLConnection, didReceiveAuthenticationChallenge challenge: NSURLAuthenticationChallenge) {
	if(challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodServerTrust) {
		var localTrust: Unmanaged<SecTrust>?
		let serverTrust = challenge.protectionSpace.serverTrust!
		let serverPublicKey = SecTrustCopyPublicKey(serverTrust).takeRetainedValue();
		let certificateData = NSData(contentsOfFile: NSBundle.mainBundle().pathForResource("pinning-certificate", ofType: "der")!)
		let localCertificate = SecCertificateCreateWithData(kCFAllocatorDefault, certificateData).takeRetainedValue();
		let policy = SecPolicyCreateBasicX509().takeRetainedValue()

		if SecTrustCreateWithCertificates(localCertificate, policy, &localTrust) == errSecSuccess {

parrots

@import WatchKit;

@interface CachingInterfaceController : WKInterfaceController

- (void)updateLabel:(WKInterfaceLabel *)label withString:(NSString *)string;
- (void)updateLabel:(WKInterfaceLabel *)label asHidden:(BOOL)hidden;
- (void)updateImage:(WKInterfaceImage *)image withImageNamed:(NSString *)imageName;
- (void)updateImage:(WKInterfaceImage *)image withBaseNameForAnimation:(NSString *)baseName withRange:(NSRange)range duration:(NSTimeInterval)duration repeatCount:(NSInteger)repeatCount;
- (NSString *)currentImageNameForImage:(WKInterfaceImage *)image;

steipete

// Taken from http://PSPDFKit.com. This snippet is under public domain.
#define UIKitVersionNumber_iOS_7_0 0xB57
BOOL PSPDFIsUIKitFlatMode(void) {
    static BOOL isUIKitFlatMode = NO;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        // We get the modern UIKit if system is running >= iOS 7 and we were linked with >= SDK 7.
        if (kCFCoreFoundationVersionNumber >= kCFCoreFoundationVersionNumber_iOS_7_0) {
            isUIKitFlatMode = (NSVersionOfLinkTimeLibrary("UIKit") >> 16) >= UIKitVersionNumber_iOS_7_0;
        }

steipete

// Taken from the commercial iOS PDF framework http://pspdfkit.com.
// Copyright (c) 2014 Peter Steinberger, PSPDFKit GmbH. All rights reserved.
// Licensed under MIT (http://opensource.org/licenses/MIT)
//
// You should only use this in debug builds. It doesn't use private API, but I wouldn't ship it.

// PLEASE DUPE rdar://27192338 (https://openradar.appspot.com/27192338) if you would like to see this in UIKit.

#import <objc/runtime.h>
#import <objc/message.h>