The early 1900s saw the popularisation of the automobile. Everyone was jumping on the proverbial bandwagon of this new transport technology. It was cool and exciting so people wanted to be part of it, even if they might not have had full technical understanding of the domain.
One of those movers was a company in the business of raising, selling, renting and feeding horses. The managers understood that horses were a dead-end business and that the future was in motorized vehicles. Thus they started putting a lot of money and effort into creating their own car.
Engineers were hired, meetings were had and factories were being prepped for production. After a few months of work the main obstacles were overcome and the plan to build and launch a car brand were looking good. That is when the CEO scheduled a surprise meeting with the chief engineer of the project.
"We had a top management meetin last week and what we came up with was spectacular! We are going to completely revolutionize the way people think about cars!"
"Really," said the surprised engineer.
"Yes! What is the most annoying thing about cars?" he asked and without giving the engineer a chance to reply continued "Running out of fuel. That never happens with horses, so this is really a step backwards."
The engineer felt like pointing out that there is such a thing as a horse that has run out of fuel. It's called a dead horse and the difference between that and a car was that adding fuel to a dead horse does not make it come back alive. But he chose not to mention this issue, but instead wanted to hear this new master plan.
"So what we are going to do - and this is going to be a world first - is to create a car that never runs out of fuel. We shall call it The Infinity Horse. Marketing department is already creating a campaign for this. I have seen some of the sketches and they are just out of this world!"
"Errrm, never runs out of fuel?" the engineer said with a puzzled look on his face.
"Never!"
"That's not really possible, how are you going to do that?"
"That's your job isn't it? Just make it happen, it can't be that hard."
A very unpleasant two weeks followed. The engineer did everything in his power to try to explain that the aim was impossible, which did not work, and trying to suggest alternative solutions, which did not work either. Nothing short of perfection was acceptable. As an example making the gas tank bigger was not an option because while it made the problem occur less often it was not enough.
"The Vision is The Infinity Horse. Unless we have this feature we have nothing," the CEO repeated every time issues were raised.
This drove our engineer to despair. He was being crushed between the unbreakable laws of physics and the immovable opinion of the CEO. Grasping at straws he started going through automotive parts catalogues. There he saw a new product: a warning light that activated when the car was running out of fuel. And then it came to him.
He took the warning light and modified it slightly. Instead of turning on a light it shut down the engine. This would fulfill the requirement. The car would never run out of fuel, because it could be easily proven that there was still gas in the tank. Said fuel could not be used for driving but it was there. The only thing this modification did was to reduce the maximum range making the car worse by every conceivable objective metric.
The CEO loved it. The Infinity Horse had been achieved and it was perfect! If this system caused people to get stranded, well, that's their own fault for not doing due diligence and adding enough fuel to the tank before embarking on their journey.
Monday, May 1, 2017
Sunday, April 16, 2017
Why don't you just rewrite it in X?
Whenever a new programming language becomes popular its fanpersons start evangelizing its virtues by going to existing projects and filing bug reports that look like this.
Hi, I noticed that this project is written in [programming language X]. You really should just rewrite it in [programming language Y] because it is better at [some feature Z]. Kthxbye!
When put like that this seems like a no-brainer. Being better at Z is good so surely everyone should just port their projects to Y.
Recently there has been movement to convert tooling used by various software projects in the Gnome stack from a mishmash of shell, Awk and Perl into Python 3. The main reasoning for this is that having only one "scripting" dependency to a modern, well maintained project makes it simple to compile applications using Gnome technologies on platforms such as Windows. Moving between projects also becomes easier.
One tool undergoing this transition is GTK-doc. which is a documentation generation tool written mostly in Perl. I have been working together with upstream to convert it to Python 3. This has been an educational experience in many ways. One of the first things learned is that converting between any two languages usually breaks down to three distinct phases.
A Perl to Python conversion is relatively straightforward in the case of gtk-doc. It mostly deals with regular expressions, arrays and dictionaries. All three of these behave pretty much the same in both languages so step one is mostly manual work. Step two consists of fixing all the bugs and behavioural changes introduced in phase one (many caused by typos and lapses of concentration during step one). This phase is basically debugging. The third step is then a question of converting regular expressions and global variables into objects and other sane and readable constructs.
When doing the conversion I have been mostly focusing on step one, while the gtk-doc maintainer has agreed to finalize the work with steps two and three. While converting the 6000+ lines file gtkdoc-mkdb, I did some measurements and it turns out that I could do the conversion at a peak rate of 500 lines an hour, meaning roughly 7 seconds per line of code.
This was achieved only on code that was easy to convert and was basically an exercise in Emacs fingering. Every now and then the code used "fancy" Perl features. Converting those parts was 10x, 100x, and sometimes up to 1000x slower. If the port had required architectural rework (which might happen when converting a lax language to one that has a lifetime checker in the compiler, for example) it would have slowed things down even more.
I don't know how much work steps 2 and 3 entail, but based on comments posted on certain IRC channels, it is probably quite a lot. Let's be generous and say overall these three items come to 250 lines of converted code per hour.
Now comes the truly sad part. This speed of conversion is not sustainable. Manually converting code from one format to another is the most boring, draining and soul-crushing work you can imagine. I could only do this for a maximum of a few hours per day and then I had to stop because all I could see was a flurry of dollar signs, semicolons and curly braces. Based on this we can estimate that a sustained rate of conversion one person can maintain is around 100 lines of code per hour (it is unlikely that this speed can be maintained if the project goes on for weeks but since there are no measurements let's ignore it for now).
The cURL project consists of roughly 100 thousand lines of C code according to Ohloh. If we assume that converting it to a some other language is just as easy as converting simple Perl to Python (which seems unlikely), the conversion would take 1000 person hours. At 8 hours per day that comes to around 5 months of full time work. Once that is done you get to port all the changes made in trunk since starting the conversion. Halting the entire project while converting it from one language to another is not an option.
This gives us a clear answer on why people don't just convert their projects from one language to another:
There is no such thing as "just rewrite it in X".
Hi, I noticed that this project is written in [programming language X]. You really should just rewrite it in [programming language Y] because it is better at [some feature Z]. Kthxbye!
When put like that this seems like a no-brainer. Being better at Z is good so surely everyone should just port their projects to Y.
Recently there has been movement to convert tooling used by various software projects in the Gnome stack from a mishmash of shell, Awk and Perl into Python 3. The main reasoning for this is that having only one "scripting" dependency to a modern, well maintained project makes it simple to compile applications using Gnome technologies on platforms such as Windows. Moving between projects also becomes easier.
One tool undergoing this transition is GTK-doc. which is a documentation generation tool written mostly in Perl. I have been working together with upstream to convert it to Python 3. This has been an educational experience in many ways. One of the first things learned is that converting between any two languages usually breaks down to three distinct phases.
- Manual syntax conversion
- Fixing bugs caused by conversion errors
- Converting code to idiomatic target language
A Perl to Python conversion is relatively straightforward in the case of gtk-doc. It mostly deals with regular expressions, arrays and dictionaries. All three of these behave pretty much the same in both languages so step one is mostly manual work. Step two consists of fixing all the bugs and behavioural changes introduced in phase one (many caused by typos and lapses of concentration during step one). This phase is basically debugging. The third step is then a question of converting regular expressions and global variables into objects and other sane and readable constructs.
When doing the conversion I have been mostly focusing on step one, while the gtk-doc maintainer has agreed to finalize the work with steps two and three. While converting the 6000+ lines file gtkdoc-mkdb, I did some measurements and it turns out that I could do the conversion at a peak rate of 500 lines an hour, meaning roughly 7 seconds per line of code.
This was achieved only on code that was easy to convert and was basically an exercise in Emacs fingering. Every now and then the code used "fancy" Perl features. Converting those parts was 10x, 100x, and sometimes up to 1000x slower. If the port had required architectural rework (which might happen when converting a lax language to one that has a lifetime checker in the compiler, for example) it would have slowed things down even more.
I don't know how much work steps 2 and 3 entail, but based on comments posted on certain IRC channels, it is probably quite a lot. Let's be generous and say overall these three items come to 250 lines of converted code per hour.
Now comes the truly sad part. This speed of conversion is not sustainable. Manually converting code from one format to another is the most boring, draining and soul-crushing work you can imagine. I could only do this for a maximum of a few hours per day and then I had to stop because all I could see was a flurry of dollar signs, semicolons and curly braces. Based on this we can estimate that a sustained rate of conversion one person can maintain is around 100 lines of code per hour (it is unlikely that this speed can be maintained if the project goes on for weeks but since there are no measurements let's ignore it for now).
The cURL project consists of roughly 100 thousand lines of C code according to Ohloh. If we assume that converting it to a some other language is just as easy as converting simple Perl to Python (which seems unlikely), the conversion would take 1000 person hours. At 8 hours per day that comes to around 5 months of full time work. Once that is done you get to port all the changes made in trunk since starting the conversion. Halting the entire project while converting it from one language to another is not an option.
This gives us a clear answer on why people don't just convert their projects from one language to another:
There is no such thing as "just rewrite it in X".
Post scriptum
There are tools that automatically convert from one language to another. They can help, but only in step one. Steps two and three are still there, and could take more work than manually converted code because usually manual conversion produces more human-understandable code. Sadly Turing-completeness says that we can't have nice things.
Thursday, April 13, 2017
How Meson is tested
A build system is a very important part of the development workflow and people depend on it to work reliably. In order to achieve this we do a lot of testing on Meson. As this is mostly invisible to end users I thought I'd write some information about our testing setup and practices.
Perhaps the most unconventional thing is that Meson has no unit tests in the traditional sense of the word. The code consists of functions, classes and modules as you would expect but there are no test for these individual items. Instead all testing is done on full projects. The bulk of tests are what could traditionally be called integration tests. That is, we take an entire project that does one thing, such as compile and install a shared library, and then configures it, builds it, runs tests and runs install and checks that the output is correct.
There are also smaller scale tests which are called unit tests. They also configure a project but then inspect the result directly. As an example test might set up a project and build it, and then touch one file and verify that it triggers a rebuild. Some people might claim that these are not unit tests either or that they should instead be tested with mock classes and the like. This is a valid point to make, but this is the terminology we have converged unto.
Perhaps the most unconventional thing is that Meson has no unit tests in the traditional sense of the word. The code consists of functions, classes and modules as you would expect but there are no test for these individual items. Instead all testing is done on full projects. The bulk of tests are what could traditionally be called integration tests. That is, we take an entire project that does one thing, such as compile and install a shared library, and then configures it, builds it, runs tests and runs install and checks that the output is correct.
There are also smaller scale tests which are called unit tests. They also configure a project but then inspect the result directly. As an example test might set up a project and build it, and then touch one file and verify that it triggers a rebuild. Some people might claim that these are not unit tests either or that they should instead be tested with mock classes and the like. This is a valid point to make, but this is the terminology we have converged unto.
Enter The (Testing) Matrix
Our testing matrix is big. Really big. At its core are the three main supported platforms, Linux, Windows and OSX. We also support BSD's and the like but we currently don't have CI machines for them.
On Windows our Appveyor setup tests VS2010, 2015 and 2017 and in addition mingw and Cygwin. Apart from Cygwin these all are tested on both 32 and 64 bits variants. Visual studio is tested both with the Ninja and Visual Studio project generator backends.
OSX is the simplest, it is tested only with the Ninja backend using both regular and unity builds.
Linux tests do a lot more. In addition running the basic tests (both in unity and regular modes) it also runs the entire test suite in a cross compilation setup.
All of these tests are only for the core code. Meson supports a large amount of frameworks and libraries, such as GLib, Qt and Doxygen, and many programming languages. Every one of these has an associated test or, usually, several. This means that running the full test suite on Debian requires installing all of these:
- Boost
- D, Rust, Java, Fortran, C# and Swift compilers
- Qt 5, WxWidgets, GTK+ 3
- Valgrind
- GNUstep
- Protocol Buffers
- Cython
- GTest and GMock
And a bunch of other packages as well. The CI Docker image that has all of these installed takes 2 gigabytes of space. On many distros all dependencies are not available so packagers have to disable tests. Having a build dependency on all these packages sometimes yields interesting problems. As an example the Rust dependency means that Meson depends on LLVM. Every now and then it breaks on s390x meaning that Meson and every package that uses it to build get flagged for removal from Debian.
Every merge proposal to Meson master is run through all of these tests and is eligible for merging only if they all pass. There are no exceptions to this rule.
There are some downsides to this, the biggest being that every now and then Appveyor and/or Travis get clogged and getting the green light takes forever. We looked briefly into getting paid instances but for our usage the bill would be in the neighborhood of $300 per month. Given that you can buy your own hardware for that kind of money, this has not been seen as a worthwhile investment.
Saturday, April 8, 2017
Meson project status update
The text below is a copy of this post to the Meson development mailing list.
have gone from "interesting but niche" to being seriously considered
for such core infrastructure projects as Mesa, Wayland, Xorg and even
systemd. I would like to thank everyone who has contributed in making
this possible. Thanks to all contributors, evangelists, those who have
converted their projects, or even proposed it. We would not be here
without you.
However having this much growth brings with it new problems. The main
one of these, as most of you have probably noticed, is the growth in
pull request backlog. I know there are MRs that have been waiting for
quite a while and that this is very frustrating to those people who
have filed them. My apologies to you, we are trying to make this
better.
The second issue is the perennial problem of documentation.
Interestingly these two issues are quite tied together in unexpected
ways.
One of the things which is taking a lot of time for me personally is
making sure that all the documentation is up to date after merge
requests are done. This is a major problem and is limiting the number
of changes that can go in.
We have examined various ways of solving this problem. We have a PoC
for moving all documentation away from the Github wiki and inside the
main repository. This way we can require that all merge requests come
with corresponding documentation changes. This would reduce the review
burden.
A preview of the site can be seen here: http://mesonbuild.com/
The downside of this approach is that we would lose the ability to do
in-browser wiki editing, and even typo fixes would need to go via pull
requests. This is unfortunate. There does not seem to be a solution
that would work for both use cases. Final decisions on this have not
been made, so if there are people who have good suggestions or prior
experience with this, please speak up.
There are many other ways to help, too. Thus far I have done a large
fraction of, well, everything, ranging from bug reports to review to
designing new features and helping people on the mailing list. All of
these activities are fun and interesting, but there is only so much
time and I feel I'm already spreading myself too thin. This causes
problems such as the above mentioned backlog of merge requests.
We already have a wonderful group of people doing great work on IRC
and elsewhere. Thank you all for your efforts. But the fact of the
matter is that if the project continues seeing more uptake, we are
going to need more helpers, especially reviewers. Currently this task
rests almost entirely on me and Nirbheek. Any help on this would be
greatly appreciated. Just going over the code and saying "based on a
cursory glance this seems ok" would be helpful.
The one elephant in the room is that currently only I have merge
access to master. This is an obvious bottleneck, but if we manage to
fix the other issues listed above it should not be a limiting issue.
Still, if usage and contributions keep growing, we might consider a
multi-maintainer mode. The project is now large enough that we can
have subsystem maintainers, much in the same way as in the Linux
kernel. Example of these could include Windows maintainer, Gnome tools
maintainer, Qt maintainer, Android maintainer, documentation
maintainer and so on. A different approach would be to just have more
people with commit access and allowing them to move around the code as
they have interest. If you have experience or knowledge on how to best
handle this, please let us know.
Thank you all, and keep on compiling!
Hello everyone
The last few weeks have been an amazing ride for the Meson project. Wehave gone from "interesting but niche" to being seriously considered
for such core infrastructure projects as Mesa, Wayland, Xorg and even
systemd. I would like to thank everyone who has contributed in making
this possible. Thanks to all contributors, evangelists, those who have
converted their projects, or even proposed it. We would not be here
without you.
However having this much growth brings with it new problems. The main
one of these, as most of you have probably noticed, is the growth in
pull request backlog. I know there are MRs that have been waiting for
quite a while and that this is very frustrating to those people who
have filed them. My apologies to you, we are trying to make this
better.
The second issue is the perennial problem of documentation.
Interestingly these two issues are quite tied together in unexpected
ways.
One of the things which is taking a lot of time for me personally is
making sure that all the documentation is up to date after merge
requests are done. This is a major problem and is limiting the number
of changes that can go in.
We have examined various ways of solving this problem. We have a PoC
for moving all documentation away from the Github wiki and inside the
main repository. This way we can require that all merge requests come
with corresponding documentation changes. This would reduce the review
burden.
A preview of the site can be seen here: http://mesonbuild.com/
The downside of this approach is that we would lose the ability to do
in-browser wiki editing, and even typo fixes would need to go via pull
requests. This is unfortunate. There does not seem to be a solution
that would work for both use cases. Final decisions on this have not
been made, so if there are people who have good suggestions or prior
experience with this, please speak up.
There are many other ways to help, too. Thus far I have done a large
fraction of, well, everything, ranging from bug reports to review to
designing new features and helping people on the mailing list. All of
these activities are fun and interesting, but there is only so much
time and I feel I'm already spreading myself too thin. This causes
problems such as the above mentioned backlog of merge requests.
We already have a wonderful group of people doing great work on IRC
and elsewhere. Thank you all for your efforts. But the fact of the
matter is that if the project continues seeing more uptake, we are
going to need more helpers, especially reviewers. Currently this task
rests almost entirely on me and Nirbheek. Any help on this would be
greatly appreciated. Just going over the code and saying "based on a
cursory glance this seems ok" would be helpful.
The one elephant in the room is that currently only I have merge
access to master. This is an obvious bottleneck, but if we manage to
fix the other issues listed above it should not be a limiting issue.
Still, if usage and contributions keep growing, we might consider a
multi-maintainer mode. The project is now large enough that we can
have subsystem maintainers, much in the same way as in the Linux
kernel. Example of these could include Windows maintainer, Gnome tools
maintainer, Qt maintainer, Android maintainer, documentation
maintainer and so on. A different approach would be to just have more
people with commit access and allowing them to move around the code as
they have interest. If you have experience or knowledge on how to best
handle this, please let us know.
Thank you all, and keep on compiling!
Tuesday, April 4, 2017
Inspector Gadget as an allegory of software engineering profession in the modern age
Many people think that Inspector Gadget is a quirky 80s animation series about a bumbling, but well meaning cyborg police inspector fighting an evil organization called MAD. This is not true. In reality the show is an allegory about the day to day work life in a modern software development company. It tells this story with foresight and accuracy that rivals, and sometimes even exceeds, Silicon Valley and its ilk.
This may seem like a bold claim, but let's us examine a typical episode and we shall see how facts stand firmly by this assertion.
The supposed hero of this series is Inspector Gadget himself. At the beginning of every episode he is spending his free time and is then unexpectedly called into work. Some sort of disaster has struck and he is the only one who can fix it. The Inspector then says Don't worry, chief, I'm always on duty and heads off.
From this simple exchange we know that the Inspector is the hotshot rockstar developer. The Ninja! The Cowboy Coder! The man who has no concept of work-life balance! He drops whatever it is he is doing and goes off to solve the problem.
Once at work we quickly discover that he is more than a rockstar. He is, in fact, an incompetent fool who thinks he is the greatest thing ever. During the course of the entire show, Inspector Gadget does not manage to make a single thing better. All he does is run around from one place to another and try arbitrary things that are not in any way helpful or even rational. Examples include swinging a mallet around randomly (while breaking expensive pieces of arg), inflating his coat for no rhyme or reason (usually knocking innocent people over) or even helping the bad guys perpetrate their crimes because they just ask for his help.
At no point does anyone call Inspector Gadget out for clearly being a useless idiot who only does harm. The entire organisation would work more efficiently if he was kicked out. But yet he remains, having reached a high enough level on the police force's organisation chart that he can't be fired, or even challenged.
The second person in our group of people is not actually a person, but a dog. Brain is the pet of Inspector Gadget. Whenever the inspector heads off to solve a case, Brain is given the same task: follow Inspector Gadget around and fix everything he breaks.
Here we find the only major disparity between Inspector Gadget the series and real life. In the latter, the incompetent rockstar (also known as Senior Systems Architect) breaks so many things that it takes more than one person to fix them. In extreme cases the group can consists of every other developer in the company. Perhaps this is the reason why Brain is portrayed as a dog. He does not represent a single person, but all of them.
If ew observe how Brain fixes the Inspector's bumblings, a common pattern arises. He always has to fix things in a way that the Inspector does not notice anything. Presumably if he were to notice these fixes, he would go back and change things back the way he left them. That is, completely broken.
Brain never does anything else, his life is a continuous stream of fighting fires that should never have been set alight. An illuminating example of this is the "pineapple incident" in episode Volcano Island, between 13m 54s and 14m 45s.
The task of actually solving all problems is left to Penny, Gadget's niece. She does not fool around with pointless Rube Goldberg gadgets. She is highly competent and efficient in solving any problem. In an average episode Penny spends less than five minutes looking at the problem, finding the root cause, fixing it and wrapping everything up. She is a competent and smart person with solid engineering and problem solving skills. She single handedly thwarts MAD and is the main reason the entire world does not fall into anarchy.
Penny is never given any credit for this. In fact whenever she tries to talk some sense to the other characters, she is actively dismissed and belittled. Once the case is solved everyone goes to Inspector Gadget and congratulates him for doing a good job. The Inspector replies with something like I solved the case? I guess I did. Like any incompetent rockstar he is willing to take all the praise without doing any of the work.
In light of this it should be obvious why the character of Penny is a woman.
The final person in this gallery is Dr. Claw, the leader of MAD. During the course of the show he does only two things. One: he looks at live video streams on his computer while scratching a cat. Two: he complains that everything done by everyone else is wrong (while never doing anything himself).
There are two differing theories on what he is supposed to represent. The first claims that he represents the company founder/owner who struck gold but since then has lost grasp of the present and just lashes out to his underlings at random.
The other theory claims that the creators of the show were incredibly foresighted and created Dr Claw as a prototype of modern day internet trolls 25 years before they actually appeared.
This may seem like a bold claim, but let's us examine a typical episode and we shall see how facts stand firmly by this assertion.
The rockstar coder
From this simple exchange we know that the Inspector is the hotshot rockstar developer. The Ninja! The Cowboy Coder! The man who has no concept of work-life balance! He drops whatever it is he is doing and goes off to solve the problem.
Once at work we quickly discover that he is more than a rockstar. He is, in fact, an incompetent fool who thinks he is the greatest thing ever. During the course of the entire show, Inspector Gadget does not manage to make a single thing better. All he does is run around from one place to another and try arbitrary things that are not in any way helpful or even rational. Examples include swinging a mallet around randomly (while breaking expensive pieces of arg), inflating his coat for no rhyme or reason (usually knocking innocent people over) or even helping the bad guys perpetrate their crimes because they just ask for his help.
At no point does anyone call Inspector Gadget out for clearly being a useless idiot who only does harm. The entire organisation would work more efficiently if he was kicked out. But yet he remains, having reached a high enough level on the police force's organisation chart that he can't be fired, or even challenged.
The firefighter
Here we find the only major disparity between Inspector Gadget the series and real life. In the latter, the incompetent rockstar (also known as Senior Systems Architect) breaks so many things that it takes more than one person to fix them. In extreme cases the group can consists of every other developer in the company. Perhaps this is the reason why Brain is portrayed as a dog. He does not represent a single person, but all of them.
If ew observe how Brain fixes the Inspector's bumblings, a common pattern arises. He always has to fix things in a way that the Inspector does not notice anything. Presumably if he were to notice these fixes, he would go back and change things back the way he left them. That is, completely broken.
Brain never does anything else, his life is a continuous stream of fighting fires that should never have been set alight. An illuminating example of this is the "pineapple incident" in episode Volcano Island, between 13m 54s and 14m 45s.
The fixer
Penny is never given any credit for this. In fact whenever she tries to talk some sense to the other characters, she is actively dismissed and belittled. Once the case is solved everyone goes to Inspector Gadget and congratulates him for doing a good job. The Inspector replies with something like I solved the case? I guess I did. Like any incompetent rockstar he is willing to take all the praise without doing any of the work.
In light of this it should be obvious why the character of Penny is a woman.
The wild card
There are two differing theories on what he is supposed to represent. The first claims that he represents the company founder/owner who struck gold but since then has lost grasp of the present and just lashes out to his underlings at random.
The other theory claims that the creators of the show were incredibly foresighted and created Dr Claw as a prototype of modern day internet trolls 25 years before they actually appeared.
Sunday, March 26, 2017
Debian package dependency browser
The Debian package browser is great but it is somewhat limited. As an example even though you can get dependencies and build dependencies for any package but not reverse dependencies (i.e. list all packages that depend or build-depend on this package).
I wrote a simple program that downloads the package repository file, parses it and creates an SQLite DB with all the link information and a simple Flask web app to browse it. This is what it looks like when showing the information page on Flex.
In addition you can do all sorts of analysis on the data. As an example here are the 20 packages that are depended on the most followed by the number of packages that depend on them:
libc6 19759
libstdc++6 6362
libgcc1 5814
libglib2.0-0 2906
python 2802
zlib1g 2620
libcairo2 1410
libgdk-pixbuf2.0-0 1385
libpango-1.0-0 1303
libpangocairo-1.0-0 1139
libqt5core5a 1122
libatk1.0-0 1075
libgtk2.0-0 1010
libxml2 979
libfreetype6 976
perl 880
libqt5gui5 845
libfontconfig1 834
python3 825
libqtcore4 810
And here is the same for build-dependencies:
debhelper 27189
cdbs 3130
dh-autoreconf 3098
dh-python 2959
pkg-config 2698
autotools-dev 2331
python-setuptools 2193
python-all 1888
cmake 1643
python3-setuptools 1539
dpkg-dev 1446
python3-all 1412
perl 1372
zlib1g-dev 1317
dh-buildinfo 1303
python 1302
libglib2.0-dev 1133
gem2deb 1104
default-jdk 1078
libx11-dev 973
The numbers are not exact because the parser is not perfect but as rough estimates these should be reliable. Just don't use them for anything requiring actual accuracy, ok?
The code is here. I probably won't work on it any more due to other obligations, but feel free to play around with it if you wish.
Thursday, March 16, 2017
Is static linking the solution to all of our problems?
Almost all programming languages designed in the last couple of years have a strong emphasis on static linking. Their approach to dependencies is to have them all in source which is compiled for each project separately. This provides many benefits, such as binaries that can be deployed everywhere and not needing to have or maintain a stable ABI in the language. Since everything is always recompiled and linked from scratch (apart from the standard library), ABI is not an issue.
The proponents of static linking often claim that shared libraries are unnecessary. Recompiling is fast and disks are big, thus it makes more sense to link statically than define and maintain ABI for shared libraries, which is a whole lot of ungrateful and hard work.
To see if this is the case, let's do an approximation experiment.
The proponents of static linking often claim that shared libraries are unnecessary. Recompiling is fast and disks are big, thus it makes more sense to link statically than define and maintain ABI for shared libraries, which is a whole lot of ungrateful and hard work.
To see if this is the case, let's do an approximation experiment.
Enter the Dost!
Let's assume a new programming language called Dost. This language is special in that it provides code that is just as performant as the equivalent C code and takes the same amount of space (which is no small feat). It has every functionality anyone would ever need, does not require a garbage collector and whose syntax is loved by all. The only thing it does not do is dynamic linking. Let us further imagine that, by magic, all open source projects in the world get rewritten in Dost overnight. How will this affect a typical Linux distro?
Take for example the executables in /usr/bin. They are all implemented in Dost, and thus are linked statically. They are probably a bit larger than their original C versions which were linked dynamically. But by how much? How would we find out?
Science to the rescue
Getting a rough ballpark estimate is simple. Running ldd /usr/bin/executable gives a list of all libraries the given executable links against. If it were linked statically, the executable would have a duplicate copy of all these libraries. Said in another way, each executable grows by the size of its dependencies. Then it is a matter of writing a script that goes through all the executables, looks up their dependencies, removes language standard libraries (libc, stdlibc++, a few others) and adds up how much extra space these duplicated libraries would take.
The script to do this can be downloaded from this Github repo. Feel free to run it on your own machines to verify the results.
Measurement results
Running that script on a Raspberry Pi with Rasbian used for running an IRC client and random compile tests says that statically linked binaries would take an extra 4 gigabytes of space.
Yes, really.
Four gigabytes is more space than many people have on their Raspi SD card. Wasting all that on duplicates of the exact same data does not seem like the best use of those bits. The original shared libraries take only about 5% of this, static linking expands them 20 fold. Running the measurement script on a VirtualBox Ubuntu install says that on that machine the duplicates would take over 10 gigabytes. You can fit an entire Ubuntu install in that space. Twice. Even if this were not in issue for disk space, it would be catastrophic for instruction caches.
A counterargument people often make is that static linking is more efficient than dynamic linking because the linker can throw away those parts of dependencies that are not used. If we assume that the linker did this perfectly, executables would need to use only 5% of the code in their dependencies for static linking to take less space than dynamic linking. This seems unlikely to be the case in practice.
In conclusion
Static linking is great for many use cases. These include embedded software, firmwares and end user applications. If your use case is running a single application in a container or VM, static linking is a great solution that simplifies deployment and increases performance.
On the other hand claiming that a systems programming language that does not provide a stable ABI and shared libraries can be used to build the entire userland of a Linux distribution is delusional.
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