Zero Defects is Possible in Software

I make the claim in the title for two reasons. First, it sound's like an arrogant and unreasonable viewpoint. Which is more to draw you in than for any other reason.

More importantly my reason is that if you don't believe that you can write defect free code you will never be able to.

Let us start with understanding some ground rules of my claim.

• There is an implicit assumption that the computer you are running on is not subject to an out of spec environment, such as excessive heat or solar flares and that all the hardware is functioning properly.
• Second there is an assumption that the operating system is bug free with respect to the code you are writing.
• Further, it is assumed that the compiler you are using generated correct bug free code with respect to the software you are writing.

It is clear that in some cases the above may not be true. Which results in a quality ceiling that is potentially out of your control. However, given a take no prisoners approach to bug fixing at the level of the compiler and the OS, there is no reason that the second two conditions need to exist. Plus there are plenty of cases where as far as your software is concerned there are no bugs at those levels to deal with.

When you write code you will almost certainly introduce bugs. Occasionally, I write a small amount of code that is bug free. Just as you can type words that are spelled correctly that form grammatically correct sentences it is possible to write multiple lines of code that are bug free without modification.

Take this with an aggressive stance on bug fixing and testing and you should be able to write small  amounts of code that are bug free after only a few iterations.

An approach that I find that works is to fix every bug in code that I'm designing from scratch. The quicker I do this the faster the code becomes solid. It can be harder if you are a maintainer of code to do this as it means that you need to understand both what the code is doing and what the writer of the code intended. It is very difficult to determine intent if you don't have written requirements.

Written requirements are sometimes hard because they often change as you write code. This is due to the discovery process inherent in writing code to solve a problem that you don't fully understand at the start. It can be hard to develop the discipline to update requirements as they change over time. Creating a process with independent testing can help to make this happen. Even so some things will likely fall through the cracks.

The good news though is that even though not having a requirement makes determining the intent of the writer of the code hard to determine, it is often possible to determine based on how the code is used and using engineering judgment.

But, our goal is to leave the software we write in a bug free state when it is complete and for whatever reasons we move on to something new and leave the maintenance to someone else. If this happens the maintainers job is an easy one as they should never need to update the software because it just plain works.

More than likely if the software needs to be updated it would be to extend functionality which builds on the already solid core, which makes the maintainers job a lot easier.

At this point I imagine that you are probably still not convinced that it is possible to write bug free software.

If you can't believe that you can write bug free software you never will.

Unfortunately, I cannot lay claim to having zero defects in all the software I have written. But I can claim that some of the software I have written has zero defects and that over the years I have gotten better at writing software with zero defects.

Obviously, some things cannot be fixed quickly, or are inherited from the underlying system. While this is unfortunate, at the very least one can document that the defect exists so that a user of your software can make an informed decision about how to handle the problem.

This probably sounds overly idealistic. But there are things that over the years have led to countless problems in software.

In the end while I don't expect that you or I will deliver all software with zero defects. I do think that we can deliver some software with zero defects and for the software that has defects we can continue to fix the problems as they are discovered and with time iterate it to zero defects.

The problem with a less idealistic approach is that it leads inexorably to a point where you are spending all of your time fixing bugs in old code you wrote and not fixing bugs in new code. Bug debt or technical debt of this sort has a compounding effect which can only be corrected by either paying down the debt or by declaring technical bankruptcy and abandoning the debt laden code.

I hope that this inspires you to at least improve the quality of the code you write.

Technical Bankruptcy

Technical debt or bug debt is an insidious side effect of writing low quality code.

The technical debt that one engineer can accumulate in a career of programing can easily require 2 or more careers of other engineers to pay down.

A pay as you go policy says that you fix all bugs as they are discovered before writing new code. While this lowers your productivity initially. It helps you to develop better habits that introduce bugs at a lower rate. Plus it makes your software more appealing to customers.

All things being equal customers will pick the higher quality software over lower quality software. Which means higher sales. More sales may allow you to under cut your competition by dropping your price leading to more sales. Or you could say that our software is better so we charge more. This can also potentially have a positive impact on sales because people often do believe that higher prices correlate to better quality.

When you have more money coming in you can hire more and better engineers to write more high quality software.

If you go the other way and cut quality in an effort to reduce the time to market, which only really works when you are near the end of a development cycle. You negatively impact your income, assuming you have the competition of better software. In any case if you are the only producer of some software and it is profitable you will eventually find that someone will start competing based on quality.

At some point bad software can get so bad that one should consider declaring personal technical bankruptcy and move on. This may be a job change or if you are lucky only the cancellation of your project.

Unicode anyone?

As you may have guessed from my previous post I've been digging into Unicode. One may think it odd that I haven't done this sooner, but when working on legacy applications it is hard to justify supporting more modern things when you spend all your time trying to make legacy software better.

Fortunately, I'm now in a position of writing fresh new code that can be built on a strong basis. As I thought through many of the things I wanted to do I fairly quickly came to the conclusion that moving forward I needed to write things using Unicode.

Should be easy. Unicode has been around for 20 years now so, unlike the mere 3 years since adoption of C++ 11, everything should work and the skids should be smooth and well greased.

Of course not!

Windows seems to like UTF-16. That's fine. Other operating systems seem to like UTF-8 or UTF-16.

Out of the box on Mac and Ubuntu I can do something like the following:

    std::cout <<  u8"Α-Ωα-ω\n";

Of course on Windows not only is the u8" syntax not yet supported, but even if you get a std::string with a proper UTF-8 encoding that won't work either.

Turns out that I can set the cmd.exe console encoding to use UTF-8, and it works great if I use printf for my string, but std::cout doesn't work. To top things off Microsoft decided to explicitly disallow UTF-8 in their std::locale implementation. So I can't tell std::cout to send things to the console as UTF-8. Instead it appears that I will need to use printf or find another obscure way of outputting Unicode in my unit test console based application.

I'm not sure what this means, but it does give hope to those worried that the machines will take over. It will likely take them several decades to figure out the mess we have made with software.

g++ is dead

Lately I've been working on a project that involves using C++ to develop libraries for Windows, Mac, Ubuntu, iOS and Android, with an eye toward quality and portability.

Recently I decided that I needed to build a Unicode class to support a forward thinking basis for things. Of course C++ is generally not Unicode friendly, but it isn't all that unfriendly either. Especially with C++ 11.

So I dig in and start learning and coding and came up with a first pass of my class on Windows using Visual Studio 2013. So far so good.

Now let's go over to Ubuntu where where we have compilers like g++ 4.8 and Clang 3.3 that are reportedly more compliant than Visual Studio.

The first thing I notice is a missing include . The next thing I notice is that the API for std::basic_string that I was trying to emulate is well, just plain wrong! Not even close! 

I start digging and find that the GNU standard C++ library is about 6 sigmas off of supporting C++ 11. How can you claim your compiler is C++ 11 compliant but the library is not?

Fortunately, I eventually got to the point of using the new libc++ library which Apple switched to awhile ago and things work, in clang. But when I try to build for Android I can't get the experimental clang support to work. Probably because of 2 or 3 really important steps that I missed, but nonetheless I gave up.

Working through the problem I manged to hack around the deficiencies in the GNU standard library with regard to std::basic_string, but got nowhere with trying to get the codecvt stuff working. Turns out that the other option of using iconv isn't built into Android. I would have needed to jump through several major hoops to compile it and hook it in.

I eventually wrote my own conversion routines between UTF-8, UTF-16 and UTF-32.

So to the point of my post.

It is 2014. C++ 11 was ratified, in March of 2011 and formally adopted in August of 2011. So why, 3 years later, is the GNU library languishing? I would not have expected full support on day 1 or even 1 year after adoption, but 3 years? And the thing that is particularly annoying is that some of the stuff that isn't supported is trivial to correct.

My sense is that the ideas behind GNU and the "Free" software thing are fallacious, which I speculate is a major reason the Apple decided to ditch GNU and that we now see that a more open "open source" implementation in Clang and libc++ is now displacing GNU.

While I will likely continue to keep an eye on the GNU C++ compiler for awhile, it is now a distant #3 in my compiler recommendation list after Visual Studio and Clang. This leads me to the prediction that G++ will be a footnote in the history of C++ compilers. Although they could turn this around, but I'm not going to hold my breath.

Software Quality Ceiling

Over the past 3 years I have worked on a project porting a large legacy C++ code base so that it will run on Mac, Windows and in the future other platforms. In doing so we used a number of third party toolkits including Qt.

Portable libraries are nice to use when they work right. The problem is that sometimes you run up against quality issues with the libraries. Things that work right on one platform and not on another or things that simply don't work right on any platform.

Qt is a nice toolkit, but it has many issues. We worked closely with the support team at Digia to correct many issues, but with every software update a new set of problems are added. This means a long and laborious process of first creating a reproducible bit of code, reporting it, sometimes needing to convince the support people that it really is a bug, getting a patch, trying it out and often iterating several times until the patch is correct. Then we hope that the problem is corrected in the next update, which it often is, but about as often has new issues.

Of course Qt is not the only problem. Yesterday I was investigating the new threading library for C++ 11 in Visual Studio 2013. Everything was going along just fine as I was working on a simple ThreadPool class. It worked great except that it would hang when shutting down. I finally did a search and ran across the following http://connect.microsoft.com/VisualStudio/feedback/details/747145. A bug report against Visual Studio 2012. Marked Closed Deferred.

I'm able to workaround the problem by ensuring that my thread pool shuts down before returning from main, but now I'm faced with how to write a class that logically would be global that will correctly shutdown in Visual Studio. I have yet to test it on Mac or Ubuntu, but I'm fairly confident that I won't have the same problem there.

Over the years I have encountered numerous code generation problems with compilers. The good news is that I haven't run across anything recently. But in the back of my mind I continue to worry that one may show up. This is really bad because unless you actually run the code affected in the manner that would exhibit the bug you may never know you have this problem.

Then there are things like the openGL drivers for video cards. In some cases something works fine on one card but not on another. At that point you are faced with answering the question, did I do something wrong? Sometimes I did. In some cases the fact that it worked on one card was wrong. But in other cases I used the API correctly and there is a bug in the driver.

Then there is the unspecified behavior clause in languages. In C++ there are many places in the standard where the behavior is listed as unspecified or compiler dependent. In these cases I would prefer that it didn't compile or at the very least it should crash when I try to use it. In my recent porting project I ran across several cases where the compiler on the Mac crashed on badly written code, but on Windows it didn't. I was happy to find and fix those issues. But they should have not worked in the first place.

All of these issues result in a quality ceiling. My goal is to write code that is 100% bug free. Occasionally, I achieve that for simple cases. More often I have a few bugs that testing should eventually uncover. But if I'm working with tools, compilers, libraries, operating systems, etc. that are buggy I will always be faces with the fact that my software will be of a lower quality than I'm theoretically capable of writing.

As an industry we need to figure out how to break through the quality ceiling.

With that I close, because I have no answers.

Optimizing C++ Build Times

I've been fighting improving build times under C++ for years and over that time I've managed to put together a few good practices to help.

1) Use good header inclusion isolation.

Use forward declarations as much as possible.

Use the PIMPL idiom to provide better isolation.

Avoid include only libraries. Some are marginally OK, such as most of the STL. Others, especially certain boost libraries, can create enormous burdens. Wrap these using PIMPL or "has-a" instead of inheritance.

Use good encapsulation by splitting your classes into reasonably small DLLs. This reduces link times and helps enforce other good design practices.

In theory this should be all you need.

But there are some other things that work well.

2) Use IncrediBuild if you are building under Windows.

There are other distributed build systems as well, but at the moment I've not had any luck improving over local builds on today's multi-core hardware.

3) Use multi-core machines.

The more cores the better.

4) Use SSD drives to eliminate disk bottlenecks.

Depending on the amount of code you are compiling you may not need an SSD drive. However, in my current project I've seen a 30% improvement in build times.

I also have found that when using IncrediBuild in combination with an SSD can really improve the throughput allowing you to use many more machines. I've recently done tests where I ran up to 100 agents seeing significant improvements between 50 and 100.

5) Figure out what the hardware bottlenecks really are.

Memory speed. This is still a potential bottleneck in today's hardware.

Memory amount. This is easy, if you are using more than about 3/4 of your memory typically while building, get more.

Disk speed. The disk cache can get into a swamped state where it takes as much as several minutes to finish writing all the cached data. This can lead to randomly long link or compilation times. Use SSD drives to take care of this.

Network speed. If you are using distributed builds then go to at least a gigabit network. Beyond that I'm unsure that there would be any gain. Below that it is clearly a bottleneck.

CPU speed. Faster is better unless the bottleneck is memory speed, disk speed, or network speed.

Number of cores. Since compilation can be highly parallel more is better, unless memory speed or disk speed is an issue. Usually more cores means faster memory so it is normally just disk speed that can slow you down.

6) Turn off active virus scanning.

This should be obvious, but every .obj, .dll, or .exe that you create would get scanned thus slowing your compilations considerably.

I find it amazing how often this is overlooked.

Does this work? Yes. I've taken a build that was pushing 15 minutes and reduced it to about 8 using the methods in 1). I've take a build that was pushing 10 minutes and dropped it to about 7 using and SSD drive. I further cut the same build down to about 4 minutes by taking the number of IncrediBuild clients from 20 to 100, 5 minutes for 50 clients.

Slow builds are productivity suckers. The slowest build I ever saw was 30 hours. I only did that once. At one point I worked on a project that went from 5 minutes to 1 1/2 hours in year.

Somewhere not far past 5 minutes will put you into a state where flow gets interrupted. If you find your flow getting interrupted often, you will be far less productive. Don't let that happen.

Ideally you should strive to keep your builds under 1 minute. I believe this is possible for typical builds with the right encapsulation of data regardless of the total size of your project. While an entire system built from scratch could still take days, your normal builds should not need to take long. If they do, you are wasting resources.

What is the Best Software Process?

In order to write good software you need some sort of process. As it turns out it doesn't really matter much which process you choose but there are a few key elements to a good process.

1) It must focus on your customer.

The first thing to get right is to solve the problem that is most needed by your customer. This can be a bit hard to determine because in most cases the customer will tell you what they think you can solve rather than what you can solve.

This means that sometimes they want you to do the impossible and you need to scale back their expectations or that they have already scaled back their expectations and what they really need to be solved is easy to do.

There is a real art in figuring this out but it is mostly about spending enough time understanding what it is that your customer does. This often means you need to learn something new outside the domain of computer science.

To me the chance to learn something new is the best part.

2) The process must be iterative.

No matter how you end up doing things there needs to be some iteration involved. This has led to many different process methodologies. All the best ones use some sort of iteration.

Basically this recognizes the fact that you can't create a great design without writing some code. Eventually you need to rewrite the code to deal with changes. Sometimes you get it right to start with, but usually that is for a trivial problem that you can already write the code for in your head.

3) The process should be collaborative.

Writing code by yourself is OK, but two heads are better than one. Code that is written by and maintained by multiple people will get better or worse over time depending on the team.

If it is getting worse then you have a problem with your team. Either you or your teammates need to learn to work better together. Almost always it is you that needs to improve. How can that be you ask?

Well what it boils down to is that most software engineers think their code is better than their colleagues. While that may be true in some cases it is almost always true that you can learn something from your teammates about writing better code.

Looking for that and adopting the best of others will make you a better engineer. When you get to this point then it is probably true that your teammates need to improve. They will be a lot more likely to adopt your good habits if you have first adopted theirs.

4) The process must include testing.

This is obvious, but there are some good and bad ways of testing. While you should test your own code it should always be tested by someone else. Testing should be independent and done by a team that doesn't also do development.

The testing team should develop somewhat of an adversarial role with respect to the code. However, it should be more of a friendly rivalry. The goal of the developer is zero bugs. The goal of the tester is to find many bugs.

Failure to achieve either of these should be a sign that the respective team has room to improve.

5) The process should include documentation.

The first documentation should be written by the software engineer. It should be written, no videos, and it should clearly state what the feature should do (requirements) and how it works (specification).

Each of these can be used to produce other documents, a test plan, user documentation, etc.

6) There needs to be accountability.

This can come in many forms. For example source control maintains a record of who did what and when, a bug tracking database records defect and is used to assign them to the appropriate party, a schedule gives management, marketing, and other stakeholders a prediction as to when they can expect delivery so that they can plan accordingly.

7) Return on Investment Must be Estimated.

Technically this goes under accountability, but it is so often ignored that I call it out specifically.

Software that costs more to develop than it saves should never be started. For example if it takes $100,000 to automate a shipping process where the savings is only $20,000 over the next 5 years then there is probably better things to do.

Not only is this a losing proposition, it is likely that the project will get canceled making it an even bigger waste of money and time. It will also piss off the engineers that work on it.

If you are an engineer starting work on a project like this then make sure management knows it is a waste of resources. If they don't listen, move on. You don't need the aggravation, and there are plenty of software development shops around that do work on profitable projects.

On the other hand if adding a feature for $100,000 will add $1,000,000 a year in revenue then it is most likely a good thing to work on.

Spend your development resources where they will make you the most money. It's good business and it's good for the team.

8) Focus on the End Game.

Often from the time of feature completeness to release can take several weeks. Often one thing, such as finishing documentation, web site, marketing materials, etc. can end up taking a surprisingly long time. These needs can often push back the date of feature completeness by a month or two for a given release date.

Gantt charts are very helpful in planning your end game to ensure that everything that has dependencies on the software being complete are done.

9) Use Technology Only When Appropriate.

There are some technologies that are pretty much a given. For example you need a compiler.

Other things should be a given such as using source control and a bug tracking database.

Then there are technologies that may or may not be helpful. Most things can be done manually. Such as managing requirements, specifications, etc. Tools exist to do these things, but are not necessary to write software. Use them only if they really help you.

If they are black holes where information is poured but never used then get rid of them as they are just taking up time.

10) The Process Must be Simple.

If you can't explain it in 10 minutes to your mother and have her understand it, then it's too complicated.

A complicated process will fail. It won't get buy in from your team. It will be interpreted differently by different team members. It can take a long time to be fully adopted.

11) Use Iteration to Improve the Process

With each release you can sit down and examine your process. Figure out what worked well and what didn't work so well. Focus on the areas that didn't work well and figure out how to make them work better.

One thing that happens frequently over time is that as things improve you hit a release where a the quality slips. This tends to come from complacency. You have to keep working to improve.

One way to deal with this is to keep raising the bar. Recognize that you can always improve some part of the process as there is not a perfect process.

12) Adapt Process to Your Needs.

Don't just adopt a process. No process is perfect and every team has slightly different needs.

For example, a young inexperienced team can greatly benefit from pairs programming while a highly seasoned team would only be slowed by pairs programming. Some would argue that point with me, but 30 years of development experience tells me otherwise.

Adapt process ideas to your team needs. Don't just blindly adopt a process as it won't work if you and your team don't understand why you are doing things in a particular way.

Conclusion

With a little effort you can write good software. With a lot more effort you may be able to write slightly better software. But if it doesn't make your company money, it's a bad process.

The traveling salesman problem is a great example of a problem where achieving the perfect solution can take so much compute time that the salesman could have gone with a quick less than optimal solution and be back from his trip before the computation of the perfect solution is finished.

Don't let your process become such a large cost that you can't get the job done.