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Thread Affinity on OS X

My first experience in developing software to run on OS X has been a disappointing one. Previously, I have written software to run on Windows and Linux and in general I have found library or system API calls that provide me with the ability to access the services that I expect to be provided by the operating system. One such service is thread affinity - i.e. the ability to tie a particular thread to a given core. This is achieved using SetThreadAffinityMask() on Windows and sched_setaffinity() on Linux. However, I was very surprised to find that it does not appear to be possible to do this on OS X! 

OS X Leopard introduced a thread affinity API which provides the ability to provide affinity hints to the scheduler to improve data locality in caches. Unfortunately this API does not provide the ability to tie a thread to a core. This is a major gap, especially now that all new PCs and laptops are multi-core. 

So why do I want to be able to tie a thread to a core? I want to benchmark a piece of code and one of the data points of interest is to benchmark this code on a single core. With the current Mac OS X thread affinity API, this is not possible!

I'm finding it hard to believe that this service does not exist on OS X - I mean surely somebody must have wanted to run a single core benchmark on OS X running on a multi-core system. But after a couple of hours of googling and reading through the OS X APIs I have been unable to find out how to do this.

Coding The Architecture

I stumbled upon Coding the Architecture and found it to be a very refreshing and pragmatic view to software architecture and to the role of a software architect. I generally find that sites, blogs and articles on software architecture tend to focus on presenting a specific architectural process, modeling tool or on the latest trend in software architecture. Trying to find down to earth, practical advice on how to set oneself up for success as a software architect has proven difficult - until now. 

After browsing through some of the blog entries on the site and from one of its user groups, I am reminded of the resonant style of the Pragmatic Programmer book. It has the same practical and pragmatic feel. 

Some entries / articles that I found interesting:

• What is a Software Architect?
• Role profile for software architects
• Sharing Architectures
• Software Architecture Document Guidelines

ToDo Lists

Where would we be without ToDo lists? They have found their use in everything from keeping track of simple errands to keeping track of outstanding tasks in large scale projects. I find them an integral part of my day to day work and so over the years, I've tried out various ToDo list applications to try and find the one that the right fit for me.

I am constantly amazed by the vast number of different applications for managing ToDo lists that have emerged. They range from very simple single list tools, to complex tools that are more suited towards project management than they are for keeping track of what to get during the next visit to the shops.

ToDo list applications need to feel right when you are using them. I have all too often had the experience of trying out a particular ToDo list application only to find that it constrains my usage model in some way. I then spend a couple of days/weeks trying to adapt my usage model to the constraints and model offered by the application. I eventually get too frustrated and give up. I am convinced at this stage that different people are tuned to different ToDo list application features and that there is no one "ToDo list model" that fits all. In spite of this, I believe that I have found the magic ToDo list application that seems to fit most usage models - or at least it doesn't provide any constraints about how to manage your ToDo lists so you have the freedom to manage them whatever way you like.

After trying 20+ different applications over the past 10 or so years, I constantly return to Abstract Spoon's ToDoList application. This is without doubt one of the most flexible ToDo list managers out there and it acquires new features at a fast pace. This application really defines the meaning of feature rich. I have used it successfully for managing simple lists, project scheduling, time tracking, and SCRUM backlogs, burndown charts and even for online SCRUM boards. It is difficult to describe its feature list in a simple blog post so I encourage you to download it and give it a twirl.

The only downside that I have encountered with this particular application is that it is Windows specific. I'm sure that ports of this application to different OSes will occur with time but for the moment the cost of its excellent flexibility is only being able to use it on your Windows box(es).

Visual C++ 2008 Feature Pack Released

Previous posts have mentioned the Visual C++ 2008 feature pack which was available as a beta release. The full version has been released and is available for download. 

The previously reported bug with array::max_size() has now been fixed.

Some TR1 related resources from Microsoft:

• TR1 documentation
• Channel 9: Digging into TR1
• TR1 slide decks

C++ Lambda Functions

A previous post showed a code snippet for dumping the contents of an STL container using an ostream_iterator. Things have now gotten a little bit easier with the introduction of lambda functions into the upcoming C++0x standard. Lambda functions allow pieces of code to be passed around as if they were ordinary objects. Applying lambda functions for dumping the contents of an STL container gives:



vector<int> v(10);
generate(v.begin(), v.end(), rand);
for_each(v.begin(), v.end(), 
    [](int& x){ cout << x << " ";}); 

OK, so the syntax looks a bit strange at first, but it does add a powerful construct to the language.

Lambdas have only just been added to the C++0x standard and support for lambdas are not included in the beta version of the Visual Studio 2008 TR1 feature pack.

For more details and examples of lambda functions, check out Herb Sutter's recent trip report from the February/March ISO C++ standards meeting.

C++ TR1: stdint.h still missing from Visual Studio

stdint.h is a disappointing absence from both Visual Studio 2008 and the TR1 feature pack. This header was introduced in the C99 standard library to allow programmers to write more portable code by providing a set of typedefs that specify exact-width integer types, together with the defined minimum and maximum allowable values for each type. This standardized the approach for writing such things as uint32_t and should save countless hours of needless duplication for projects that like to define their own variants such as uint32, UINT32, u32, Xyz32U, etc.

Since the C++ standard was finalized in 1998, it missed this standard header by a year. In the latest update to the C++ standard (namely those extensions covered in TR1), support for this header has been added in the form of the cstdint header.

It is astonishing to find that a header that was standardized 9 years ago has still not made its way into Visual Studio 2008. Not even the recent feature pack beta which included support for most of the TR1 extensions, contained stdint.h! The lack of support for this header was logged as a bug with Microsoft way back in 2005 but is still in the "postponed" bucket.

Thankfully, there are a number of implementations of stdint.h available, the most notable being Paul Hsieh's cross-platform free implementation and also a Microsoft compiler specific implementation. Simply place one of these implementations into the Visual Studio standard include paths and stdint.h support magically appears ... now why can't Microsoft do something like that!

C++ TR1: array VS 2008 Bug

Microsoft have recently released a Beta version of the Visual Studio 2008 Feature Pack which includes support for most of the C++ standard library extensions described in TR1. Alas, the beta sticker is appropriate as there are still some bugs to be ironed out.

The TR1 array container template provides functionality for implementing a fixed size array. This is a halfway point between plain old C style arrays and C++ STL vectors. The defining property of the array container is that its size is fixed. Consider and example of an array of 4 integers:

array<int,4> = { 0, 1, 2, 3 };

Since it adheres to the STL container rules, it must implement methods such as size(), and max_size(). For the array container, both of these should return the size of the array, which is fixed. In the above example, both should return 4. However, when using the VS 2008 TR1 implementation of array, a bug appears. The code:

#include <iostream>
#include <array>
using namespace std;
using namespace std::tr1;
int main()
{
    array<int, 4> arr = {1, 2, 3, 4};

    cout << "size: " << arr.size() << endl;
    cout << "max_size: " << arr.max_size() 
         << endl;
    return 0;
}

Produces the output:

size: 4
max_size: 1073741823

instead of:

size: 4
max_size: 4

If we take a look at the implementation of max_size() we can see the problem

size_type max_size() const
{    // return maximum possible length of sequence
    size_type _Count = (size_type)(-1) / sizeof(_Ty);

    return (0 < _Count ? _Count : 1);
}

Instead of simply retuning N (the size of the array), it performs the same computation as if this was a vector.

This issue has been logged as a bug with Microsoft and will hopefully be fixed before the "Gold" release of the feature pack.

C++ TR1

Effective C++, Third Edition summarizes TR1 this way:

TR1 ("Technical Report 1") is a specification for new functionality being added to C++'s standard library. This functionality takes the form of new class and function templates for things like hash tables, reference-counting smart pointers, regular expressions, and more. TR1 itself is just a document.

The TR1 draft does not contain any background information on the functionality it provides and doesn't contain any examples for how it should be used. For this sort of information refer to the proposal documents which were used to define the TR1 functionality. The relevant proposal documents are nicely catalogued by Scott Myers.

Microsoft have recently released a Beta version of the Visual Studio 2008 Feature Pack which includes support for most of the C++ standard library extensions described in TR1.

GCC v4.x also provides support for most of the extensions.

Over the next few weeks (more likely months) I plan on playing with the new TR1 features and I will add thoughts, learnings and code snippets to this blog.

Effective Concurrency ... so far

Following on from a previous post about The Pillars of Concurrency, here are links to the full set of Herb Sutters "Effective Concurrency" column topics (as of Feb 2008) ...

The Pillars of Concurrency
How Much Scalability Do You Have or Need?
Use Critical Sections (Preferably Locks) to Eliminate Races
Apply Critical Sections Consistently Avoid Calling Unknown Code While Inside a Critical Section
Use Lock Hierarchies to Avoid Deadlock
Break Amdahl's Law!
Going Superlinear

These are an excellent set of articles on the subject of concurrency and programming for multi-core that analyzes the many facets of the subject - from background theory, to locking and on to achieving scalability and performance.

Hiring Good Programmers

The company that I work for is currently embarking on a hiring spree. So I thought it would be a good idea to refresh my interviewing skills before I launch myself into the hiring process.

A recent Coding Horror entry highlights "The Years of experience myth" which is the inadequacy of trying to "match-- exactly and to the letter-- some highly specific laundry list of skills". Unfortunately when dealing with some recruitment agencies, I find this an all too common practice. Instead it is vital to remember that "... what software developers do best is learn. Employers should be loooking for passionate, driven, flexible self-educators who have a proven ability to code in whatever language -- and serving them up interesting projects they can engage with."

Joel Spolsky sums up the characteristics that employers should be looking for in future employees as "Smart and Gets Things Done".

So, now that we've figured out what to look for in a candidate, lets look at some resources that give tips for screening CVs, conducting phone screens or face to face interviews.

• The Guerilla Guide To Interviewing - Joel Spolsky gives practical and pragmatic advice on the whole process.
• Getting the Interview Phone Screen Right - because its very expensive to get it wrong.
• The Five Essential Phone-Screen Questions

And finally since the phone screen is probably the most important stage, it's worth highlighting the two common critical mistakes that an interviewer could make in the phone screen:

1. Don't let the candidate drive the interview. The interviewer should do most of the talking, guiding the conversation along until they're satisfied the candidate knows the answers to the questions (or has given up).
2. Watch out for one-trick ponies. Candidates who only know one particular language or programming environment, and protest complete ignorance of everything else, are a giant red warning flag.

» 10 techniques for gathering requirements | 10 Things | TechRepublic.com

A nice concise list of various ways to gather requirements:
» 10 techniques for gathering requirements 10 Things TechRepublic.com

When doing interviews of JAD sessions for the purposes of gathering requirements, try to ensure that you are in the same meeting room as the participants. This helps to build up a raport with the participants which generally leads to a more open dicussion which helps to produce better requirements.

Don't forget the 5 whys approach when gathering requirements. Often what a customer says he wants is different to what he needs. Dig into each requirement to fully understand why this is valuable to the customer and then ensure that the requirement is aimed at solving the root cause of the customers problem.