Breaking Bugs

79.904

-1 +1 +5

2-8-18-7

eaking
Bu

137.33

2-8-18-7

Big Sean

Not Big Sean

What is a bug?

A software bug is an error, flaw, failure, or fault in a computer program or system that produces an incorrect or unexpected result, or causes it to behave in unintended ways.

http://en.wikipedia.org/wiki/Software_bug

Bugs make users sad

Bugs make users angry

Why is it called a bug?

We all know the story about the moth right?

accually is Edison

The concept of errors in software dates back to Ada Lovelace notes on the analytical engine in 1843

Thomas Edison used the term 'bug' when referring to faults/difficulties in some of his inventions

It has been just so in all of my inventions. The first step is an intuition, and comes with a burst, then difficulties arise — this thing gives out and [it is] then that "Bugs" — as such little faults and difficulties are called — show themselves and months of intense watching, study and labor are requisite before commercial success or failure is certainly reached.

Thomas Edison 1878

Why do bugs occur?

Human error

                        
/* This is bad. Reaaly bad. It's a really, really bad hack.
 * If you're an employee of Intertrode Communication,
 * then I'm really, really sorry that you have to maintain
 * this. I was honestly planning on removing this tomorrow,
 * but I've been known to forget things like this. It happens.
 *
 * So here's the thing. I can't seem to figure out why the AccountId
 * variable isn't set. I've looked and looked, but I gotta leave now.
 * Anyway, I've found that I can just grab the AccountID from
 * the debugging logs. I suppose that to fix it, you'd
 * have to locate where it's clearing out the ID.
 *
 * Again, I'm sorry.
 */

http://www.badprogramming.com/code/Retrieving-an-accountId-in-the-log

Poor/misunderstood requirements

Unconsidered scenarios

Outside forces

                        
[GET] http://savewalterwhite.com?page=x'; DROP TABLE members; --

What kinds of bugs can we come across?

Arithmetic bugs

Logic bugs

Syntax bugs

Resource bugs

Multi-threading bugs

Interfacing bugs

Performance bugs

Teamworking bugs

Other bugs

Arithmetic bugs

Logic bugs

Syntax bugs

Resource bugs

Multi-threading bugs

Interfacing bugs

Performance bugs

Teamworking bugs

Other bugs

Division by zero

                        
        var deaAgents = ['Hank Schrader', 'Steven Gomez'];
        var methHeads = [];

        var agentsPerMethHead = deaAgents.length / methHeads.length

        alert(agentsPerMethHead); // Infinity

Arithmetic over/underflow (e.g. Y2K38)

                        
    var waltsBalance = 344324070495708573409874598734590728;

    alert(waltsBalance); // 3.4432407049570856e+35
    alert(parseInt(waltsBalance)); // 3

Loss of arithmetic precision

                        
                    var i = "010";

                    alert(parseInt(i)); // 8

Arithmetic bugs

Logic bugs

Syntax bugs

Resource bugs

Multi-threading bugs

Interfacing bugs

Performance bugs

Teamworking bugs

Other bugs

Infinite loops/recursion

                        
                while (true) {
                    alert('Better call Saul!');
                }

Off by one error

                        
var crew = ['Walter White', 'Jesse Pinkman', 'Skinny Pete', 'Badger'];

alert(crew[crew.length]); // undefined

Arithmetic bugs

Logic bugs

Syntax bugs

Resource bugs

Multi-threading bugs

Interfacing bugs

Performance bugs

Teamworking bugs

Other bugs

Assignment <> equality

                        
var crew = ['Walter White', 'Jesse Pinkman', 'Skinny Pete', 'Badger'];

for (var i = 0; i < crew.length; i++) {

    if (crew[i] = 'Walter White') {
        alert('I am the one who knocks');
    }
}

Arithmetic bugs

Logic bugs

Syntax bugs

Resource bugs

Multi-threading bugs

Interfacing bugs

Performance bugs

Teamworking bugs

Other bugs

Using an uninitialised variable

                        
        var k, i;

        for (i = 0; i < 10; i++) {
            k = k + 1;
        }

        alert(k); // NaN

Access violations

Segfaults, buffer overflow etc.

Null pointer dereference

                        
                public class CrystalMeth {

                    private float purity;

                    public float getPurity() {
                        return purity;
                    }
                }

                CrystalMeth product = null;
                product.getPurity() // NullPointerException

Resource leaks

Memory leaks etc.

Arithmetic bugs

Logic bugs

Syntax bugs

Resource bugs

Multi-threading bugs

Interfacing bugs

Performance bugs

Teamworking bugs

Other bugs

Deadlock (chicken or egg)

Two or more competing actions waiting for the other to finish.

Race condition

Assumption that one event or task finished before another begins.

Arithmetic bugs

Logic bugs

Syntax bugs

Resource bugs

Multi-threading bugs

Interfacing bugs

Performance bugs

Teamworking bugs

Other bugs

Incorrect API usage

Incorrect protocol implementation

Incorrect hardware handling

Incorrect assumptions of a particular platform

Arithmetic bugs

Logic bugs

Syntax bugs

Resource bugs

Multi-threading bugs

Interfacing bugs

Performance bugs

Teamworking bugs

Other bugs

High code complexity

Little to no caching

Inefficient disk/memory access

Arithmetic bugs

Logic bugs

Syntax bugs

Resource bugs

Multi-threading bugs

Interfacing bugs

Performance bugs

Teamworking bugs

Other bugs

Unpropagated updates

e.g. changing one instance of getQuality() to getPurity() but not others (DRY ftw!)

Poor/out of date comments

A developer could develop according to incorrect or out of date comments in the code.

Poor documentation

Similar to above, if docs are out of date or incorrect, the developer may implement incorrectly also.

Merge problems

A bug could be introduced from a bad merger of code. Unresolved conflicts, aggressive SCM merging etc.

No standards

Walter does things using the x method, Jesse uses the y method. This crosshatch of standards results in a weak and impure product.

Arithmetic bugs

Logic bugs

Syntax bugs

Resource bugs

Multi-threading bugs

Interfacing bugs

Performance bugs

Teamworking bugs

Other bugs

Heisenbug

Heisenbug is a computer programming jargon term for a software bug that seems to disappear or alter its behavior when one attempts to study it.

http://en.wikipedia.org/wiki/Heisenbug

Often caused from debugging actually changing the program's operating environment

A Heisenbug is the kind of bug we don't want

Bohr bug

A repeatable bug; one that manifests reliably under a possibly unknown but well-defined set of conditions.

http://www.catb.org/jargon/html/B/Bohr-bug.html

The opposite of a Heisenbug

A Bohr bug is a bug that is easily repeatable

A Bohr bug is the kind of bug we want

B.A.D. - Broken As Designed

Said of a program that is bogus because of bad design and misfeatures rather than because of bugginess.

http://www.catb.org/jargon/html/B/BAD.html

Tree analogy

If a product, feature, architecture is poorly designed, you're gonna have a bad time

Schroedinbug

A design or implementation bug in a program that doesn't manifest until someone reading source or using the program in an unusual way notices that it never should have worked, at which point the program promptly stops working for everybody until fixed.

http://www.catb.org/jargon/html/S/schroedinbug.html

Fractal bug

A bug, after which its resolution is found, reveals additional self-similar bugs elsewhere in the code, after which they are fixed, likewise appear elsewhere still.

http://c2.com/cgi/wiki?FractalBug

Hindenbug

A bug with catastrophic behaviour

Not always a bug, can be from human error/mistake

Named after the Hindenburg disaster

P.E.B.K.A.C.

Problem Exists Between Keyboard And Chair

In other words a user error

Other terms exist such as 'ID10T' (I-D-ten-T), pilot error etc.

Display (IE) Bug

and many others...

Fencepost error

Aliasing bug

Stale pointer bug

Killer poke

Wrap around

Magic smoke

Black art

Cosmic rays

Memory smash

Bit rot

Voodoo programming

Dead chicken waving

Shared vocabulary

Do not underestimate this

Allows us to look at bugs at a higher level of abstraction

Allows us to look at common causes of certain kinds of bugs and thus common solutions

Can be domain specific

Prevention > Cure

What can we do to prevent bugs?

Write less code

Programming style

Defensive programming, coding standards, KISS, DRY etc.

Programming techniques

Can an exception be avoided? Is there a better alternative?

Take advantage of language features

Type hints, assertions, contracts etc.

Take advantage of IDE features

Linting, Inspections etc.

Short, concise user stories

Rather than a monolithic specification, which is hard to understand, let alone implement.

Be agile, iterate

Code Analysis

Continuous integration

Automated testing

Mess detection, complexity analysis, copy paste analysis etc.

Monitoring

Average response time, uptime, error logs etc.

Tools like New Relic etc.

Communication

Ensure code comments are concise

Keep on top of documentation

Knowledge sharing

Shared ownership of code

Education

Make things simple

Do everything you can to help the user

Ditch IE (< 8)

Usage of IE7 has dipped below 1%

Get supported browsers locked down early

Managing bugs

Bugs are inevitable and should never be ignored

Bugs should be categorised and prioritised

Note, the severity of a bug is not the same as it's importance for fixing. Consider triage.

Use a good bug tracking tool (e.g. not bugzilla)

Use a good debugging tool

Ensure all bugs are managed in one place

How bugs are reported is key

Have a good bug report template or similar

Example bug report

Not all bugs have to be fixed!

Some bugs may in fact be features!

A bug can be useful and something your users prefer (gmail's undo, lara croft)

Bugs can sometimes be deemed too low priority to spend time fixing

It is not economical to fix bugs of such low severity

There could be new work not yet released which inadvertently fixes the reported bug

PEBKAC

Be careful about rewarding bug fixes

Rewards for number of bugs fixed can promote fixes of simple bugs over important ones

Don't rank developers by bug count

Great way to reduce confidence, lack of volunteers for complex problems etc.

given enough eyeballs, all bugs are shallow

http://en.wikipedia.org/wiki/Linus%27s_Law

Benefits of open source

Do you really need to write that library or can you use that popular open source library with lots of eyeballs?

Why dropping your database on a production box isn't a big deal..

(although should be avoided at all costs of course!)

June 4 1996 - The European Space Agency's Ariane 5 Flight 501 was destroyed 40 seconds after takeoff

The US$1 billion prototype rocket self-destructed due to a bug in the on-board guidance software.

A bug in the code controlling the Therac-25 radiation therapy machine was directly responsible for at least five patient deaths in the 1980s when it administered excessive quantities of X-rays.

A Medtronic heart device was found vulnerable to remote attacks in March 2008

Smart ship USS Yorktown was left dead in the water in 1997 for nearly 3 hours after a divide by zero error

Y2K / Y2K38

After 03:14:07 UTC on 19 January 2038 - unix timestamp will 'wrap around' due to integer overflow

If you're storing timestamps in an integer field in your database you may want to consider updating

MySQL's UNIX_TIMESTAMP() function will return 0 after that date

Thanks!

@jenko