JeOam

Author: https://www.cyanhall.com/

1. The Layer Tree

Core Animation's original name is Layer Kit

Core Animation is a compositing engine; its job is to compose different pieces of visual content on the screen, and to do so as fast as possible. The content in question is divided into individual layers stored in a hierarchy known as the layer tree. This tree forms the underpinning for all of UIKit, and for everything that you see on the screen in an iOS application.

In UIView, tasks such as rendering, layout and animation are all managed by a Core Animation class called CALayer. The only major feature of UIView that isn’t handled by CALayer is user interaction.

There are four hierarchies, each performing a different role:

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Apache Kafka is publish-subscribe messaging rethought as a distributed commit log.

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Project:

• project/: A directory named with the project's name which stores the actual Python package
  • __init__py
  • app.py
  • settings.py
  • urls.py
  • models/
    • __init__.py
    • baes.py
• handlers/

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#!/usr/bin/env python
# coding: utf-8

'''
Extract error log information from logfle

run:
$ python exlog.py file.log
Please enter an integer, last n (n > 1) day you want to extract:
Exactract finished.

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Keyboard Shortcuts	Descption
Cmd-/	Comment/uncomment
Cmd + Alt + L	Reformat code
Cmd-F	Find text
Cmd-Shift-F	Find text in files
Cmd-Plus	Expand code block
Cmd-Minus	Collapse code block
Cmd-B	Goto declaration of current variable
Cmd-U	Goto superclass

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NSZombieEnabled is an environment variable which controls whether the Foundation runtime will use zombies. When zombies are enabled, a deallocated object's class is dynamically changed to be _NSZombie, and by default, the memory region is never marked as free, although this can be controlled separately(so, remember to disable NSZombieEnabled for Archived Release Build).

The end result is that, with zombies enabled, messages to deallocated objects will no longer behave strangely or crash in difficult-to-understand ways, but will instead log a message and die in a predictable and debugger-breakpointable way. This is the tool to use when trying to track down over-releases and premature releases.

Zombies will take effect for all Objective-C objects that are deallocated through normal means, including most Cocoa classes as well as user-created classes. On 10.4 and earlier, a rather important exception to this is most/all TollFreeBridged classes, as they are deallocated using CoreFoundation which NSZombieEnab

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You use the CoreLocation framework to access location information about your user. You will need to instantiate a CLLocationManager object and call the asynchronous startUpdatingLocation message. You will get callbacks with the user's location via the CLLocationManagerDelegate that you supply.

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Add HeaderView in UICollectionView like UITableView's tableHeaderView:

{
    [self.collectionView registerNib:[UINib nibWithNibName:@"HeaderView" bundle:nil]
          forSupplementaryViewOfKind:UICollectionElementKindSectionHeader
                 withReuseIdentifier: @"HeaderView"];
}
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView   viewForSupplementaryElementOfKind:(NSString *)kind  atIndexPath:(NSIndexPath *)indexPath{
    if ([kind isEqualToString:UICollectionElementKindSectionHeader]){
        UICollectionReusableView *view = [collectionView dequeueReusableSupplementaryViewOfKind:kind   withReuseIdentifier:@"HeaderView" forIndexPath:indexPath];

JeOam

Except from Computer Systems: A Programmer's Perspective, Second Edition.

JeOam

#####What is Celery?
Celery is an asynchronous task queue. You can use it to execute tasks outside of the context of your application. The general idea is that any resource consuming tasks that your application may need to run can be offloaded to the task queue, leaving your application free to respond to client requests.

Celery has three core components:

• The Celery client. This is used to issue background jobs.
• The Celery workers. These are the processes that run the background jobs. Celery supports local and remote workers, so you can start with a single worker running on the same machine as your application server, and later add more workers as the needs of your application grow.
• The message broker. The client communicates with the the workers through a message queue, and Celery supports several ways to implement these queues. The most commonly used brokers are RabbitMQ and Redis.