No doubts that async/await pattern has significantly simplified working with asynchronous operations in C#. However, this simplification relates only to the situation when asynchronous operations are executed consequently. If we need to execute several asynchronous operations simultaneously (e.g. we need to call several micro-services) then we do not have many built-in capabilities and most probably Task.WhenAll will be used:

Task<SomeType1> someAsyncOp1 = SomeAsyncOperation1();
Task<SomeType2> someAsyncOp2 = SomeAsyncOperation2();
Task<SomeType3> someAsyncOp3 = SomeAsyncOperation3();
Task<SomeType4> someAsyncOp4 = SomeAsyncOperation4();
await Task.WhenAll(someAsyncOp1, someAsyncOp2, someAsyncOp4);
var result = new SomeContainer(
     someAsyncOp1.Result,someAsyncOp2.Result,someAsyncOp3.Result, someAsyncOp4.Result);

This is a working solution, but it is quite verbose and not very reliable (you can forget to add a new task to “WhenAll”). I would prefer something like that instead:

var result =  await 
    from r1 in SomeAsyncOperation1()
    from r2 in SomeAsyncOperation2()
    from r3 in SomeAsyncOperation3()
    from r4 in SomeAsyncOperation4()
    select new SomeContainer(r1, r2, r3, r4);

Further I will tell you what is necessary for this construction to work...

During code analysis, PVS-Studio analyzes the data flow and operates variable values. Values are taken from constants or derived from conditional expressions. We call them virtual values. Recently, we have refined them in order to work with multi-character constants and this has become the reason to create a new diagnostic rule.

Introduction

Multi-character-literals are implementation-defined, so different compilers can encode them in different ways. For example, GCC and Clang set a value, based on the order of the symbols in the literal, while MSVC moves them depending on the symbol's type (regular or escape).

When you run queries in ClickHouse, you might notice that the profiler often shows the LZ_decompress_fast function near the top. What is going on? This question had us wondering how to choose the best compression algorithm.

ClickHouse stores data in compressed form. When running queries, ClickHouse tries to do as little as possible, in order to conserve CPU resources. In many cases, all the potentially time-consuming computations are already well optimized, plus the user wrote a well thought-out query. Then all that's left to do is to perform decompression.



So why does LZ4 decompression becomes a bottleneck? LZ4 seems like an extremely light algorithm: the data decompression rate is usually from 1 to 3 GB/s per processor core, depending on the data. This is much faster than the typical disk subsystem. Moreover, we use all available CPU cores, and decompression scales linearly across all physical cores.

Once in a while, programmers who start getting acquainted with the PVS-Studio code analyzer ask me: «Is there a list of warnings that accurately indicate errors?» There is no such list because uninteresting (false) warnings in one project are very important and useful in another one. However, one can definitely start digging into the analyzer from the most exciting warnings. Let's take a closer look at this topic.

Every now and then we create our own problems with our own hands… with our vision of the world… with our inaction… with our laziness… and with our fears. As a result, it seems to become very convenient to swim in the public flow of sewage patterns… because it is warm and fun, and the rest does not matter – we can smell round. But after a fail comes the realization of the simple truth – instead of generating an endless stream of causes, self-pity and self-justification, it is enough just to do what you consider the most important for yourself. This will be the starting point for your new reality.

For me, the written below is just such a starting point. The way is expected to be lingering…

Nowadays security schema that lays on two tokens quite common. There are a lot of information about theme in the Internet. There are often only description what is Refresh and Access tokens and how to usem.

To understand concept behind tokens I would like to do one simple thought experiment.

We’re excited to announce starting today you can try the Windows Subsystem for Linux 2 by installing Windows build 18917 in the Insider Fast ring! In this blog post we’ll cover how to get started, the new wsl.exe commands, and some important tips. Full documentation about WSL 2 is available on our docs page.

In general, the productivity of coding superheroes is measured by the number of lines of code and the quality of the code they write. It means, when the developer churns out the output compared to input, they are declared as productive. Presently, every company wants a productive programmer to accelerate time-to-market and enrich mobile app user’s experience that helps them stand ahead of the competitors.

Alas! All the developers are not productive. Most of them, pull their hairs when the deadline is around the corner, when finding the source of bugs seems a hard nut to crack in, or when the client is complaining about the features not meeting the business needs. The reason behind for not performing to the peak efficiency is they work hard, but not smartly.

The developer’s productivity can be augmented when they work prudently, make the most out of the time, and incorporate the best practices.

Popularity of mobile applications continues to grow. So does OAuth 2.0 protocol on mobile apps. It's not enough to implement standard as is to make OAuth 2.0 protocol secure there. One needs to consider the specifics of mobile applications and apply some additional security mechanisms.

In this article, I want to share the concepts of mobile OAuth 2.0 attacks and security mechanisms used to prevent such issues. Described concepts are not new but there is a lack of the structured information on this topic. The main aim of the article is to fill this gap.

Alexandr Epaneshnikov, a 19-year-old Russian student who is legally blind, recently decided he wanted to be more independent by commuting on his own and relying less on his mom for rides to school. It meant taking a streetcar to a subway to his high school in Moscow, a 30-minute trip that Epaneshnikov assuredly navigates with a cane and Moovit, an urban mobility app optimized for screen readers.

Before reading this article, it is recommended to read the previous one: Audio over Bluetooth: most detailed information about profiles, codecs, and devices / по-русски

Some wireless headphone users note low sound quality and lack of high frequencies when using the standard Bluetooth SBC codec, which is supported by all headphones and other Bluetooth audio devices. A common recommendation to get better sound quality is to buy devices and headphones with aptX or LDAC codecs support. These codecs require licensing fees, that's why devices with them are more expensive.

It turns out that the low quality of SBC is caused by artificial limitations of all current Bluetooth stacks and headphones' configuration, and this limitation can be circumvented on any existing device with software modification only.

This week we issue a really huge selection of all the essential news you might have missed on Front-end development. Make sure to check the latest updates on CSS, HTML, and JavaScript.

From time to time, developers need to establish communication between several browser tabs to be able to send messages from one tab to another and receive responses. We have also faced this need at some point.

Some solutions already exist (like, for instance, BroadcastChannel API). However, its browser support leaves a lot to be desired, so we decided to use our own library. When the library was ready, that functionality was no longer required. Nevertheless, another task emerged: communication between an iframe and the main window.

On closer examination, it turned out that two-thirds of the library would not have to be changed — only some code refactoring was necessary. The library is a communication PROTOCOL that can work with text data. It can be applied in all cases in which text is transferred, such as iframes, window.open, worker, browser tabs or WebSocket.

How it works

Currently, the protocol has two functions: sending messages and subscription to events. Any message in the protocol is a data object. For us, the main field in that object is type, which tells us what kind of message it is. The type field is an enum with the following values:

According to Evans Data Corporation, there are 12 million developers in the world. About 350,000 of these software and mobile developers work and live in the UK including freelancers and IT employees.

How do you choose the best one among all this variety? The obvious answer — get going with a professional IT company. This will increase your chances to work with true professionals.

I’ve made my own research based on a variety of reliable resources like Google SERPs and user’s reviews, different independent media, including medium.com and aggregators, like businessofapps.com, Clutch, etc. and other independent sites. Based on the collected data, I’ve aggregated the total score for each of the 25 leaders, and here I represent a list of the winners: the top 5 software developers in the UK.

RUVDS and Habr continue the series of interviews with interesting people in IT field. Last time we talked to Richard «Levelord» Gray, level designer of popular games Duke Nukem, American McGee’s Alice, Heavy Metal F.A.K.K.2, SiN, Serious Sam, author of well-known «You’re not supposed to be here» phrase.

Today we welcome Randall Steward «Randy» Pitchford II, president, CEO and co-founder of Gearbox Software video game development company.

Randy started in 3D Realms where contributed to Duke Nukem 3D Atomic Edition and Shadow Warrior. Then he founded Gearbox Software and made Half-Life: Opposing Force, which won D.I.C.E in 2000. Other Gearbox titles include Half-Life: Blue Shift, Half-Life: Decay, Counter-Strike: Condition Zero, James Bond 007: Nightfire, Tony Hawk's Pro Skater 3, Halo: Combat Evolved and of course Borderlands.

The interview team also includes editor of Habr Nikolay Zemlyanskiy, Richard «Levelord» Gray, Randy’s wife Kristy Pitchford and Randy’s son Randy Jr.

In the previous articles we discussed PostgreSQL indexing engine and the interface of access methods, as well as hash indexes, B-trees, GiST, SP-GiST, GIN, RUM, and BRIN. But we still need to look at Bloom indexes.

Bloom

General concept

A classical Bloom filter is a data structure that enables us to quickly check membership of an element in a set. The filter is highly compact, but allows false positives: it can mistakenly consider an element to be a member of a set (false positive), but it is not permitted to consider an element of a set not to be a member (false negative).

The filter is an array of $$ bits (also called a signature) that is initially filled with zeros. $$ different hash functions are chosen that map any element of the set to $$ bits of the signature. To add an element to the set, we need to set each of these bits in the signature to one. Consequently, if all the bits corresponding to an element are set to one, the element can be a member of the set, but if at least one bit equals zero, the element is not in the set for sure.

In the case of a DBMS, we actually have $$ separate filters built for each index row. As a rule, several fields are included in the index, and it's values of these fields that compose the set of elements for each row.

By choosing the length of the signature $$, we can find a trade-off between the index size and the probability of false positives. The application area for Bloom index is large, considerably «wide» tables to be queried using filters on each of the fields. This access method, like BRIN, can be regarded as an accelerator of sequential scan: all the matches found by the index must be rechecked with the table, but there is a chance to avoid considering most of the rows at all.

It's not a secret that Microsoft has been working on the 8-th version of C# language for quite a while. The new language version (C# 8.0) is already available in the recent release of Visual Studio 2019, but it's still in beta. This new version is going to have a few features implemented in a somewhat non-obvious, or rather unexpected, way. Nullable Reference types are one of them. This feature is announced as a means to fight Null Reference Exceptions (NRE).

Today, even mobile application developing company has begun to consolidate ML related to other cutting edge technologies, for example, AI and predictive analysis. This is on the grounds that ML empowers mobile applications to learn, adjust, and improve after some time.

It’s an incredible accomplishment when you consider the way that changes requested an express order from designers for gadgets to execute a particular activity. At the point when this was the standard, software engineers needed to estimate and record for each conceivable situation (and this was a fantastic test).

Be that as it may, with ML in portable applications, we have removed the speculating game from the condition. It can likewise upgrade User Experience (UX) by understanding client conduct. So you can wager that ML in versatile won’t be restricted to voice associates and chatbots.

Specifics of QueryProvider

QueryProvider can’t deal with this:

var result = _context.Humans
                      .Select(x => $"Name: {x.Name}  Age: {x.Age}")
                      .Where(x => x != "")
                      .ToList();

It can’t deal with any sentence using an interpolated string, but it’ll easily deal with this:

var result = _context.Humans
                      .Select(x => "Name " +  x.Name + " Age " + x.Age)
                      .Where(x => x != "")
                      .ToList();

The most painful thing is to fix bugs after turning on ClientEvaluation (exception for client-side calculation), since all Automapper profiles should be strictly analyzed for interpolation. Let’s find out what’s what and propose our solution to the problem.

It is a new selection of tips and tricks about Python and programming from my Telegram-channel @pythonetc.

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