So we have this huge (is 11000 lines huge?) mainmodule.cpp source file in our project and every time I have to touch it I cringe.
As this file is so central and large, it keeps accumulating more and more code and I can't think of a good way to make it actually start to shrink.
The file is used and actively changed in several (> 10) maintenance versions of our product and so it is really hard to refactor it. If I were to "simply" split it up, say for a start, into 3 files, then merging back changes from maintenance versions will become a nightmare. And also if you split up a file with such a long and rich history, tracking and checking old changes in the SCC history suddenly becomes a lot harder.
The file basically contains the "main class" (main internal work dispatching and coordination) of our program, so every time a feature is added, it also affects this file and every time it grows. :-(
What would you do in this situation? Any ideas on how to move new features to a separate source file without messing up the SCC workflow?
(Note on the tools: We use C++ with Visual Studio; We use AccuRev as SCC but I think the type of SCC doesn't really matter here; We use Araxis Merge to do actual comparison and merging of files)
Merging will not be such a big nightmare as it will be when you'll get 30000 LOC file in the future. So:
Stop adding more code to that file.
Split it.
If you can't just stop coding during refactoring process, you could leave this big file as is for a while at least without adding more code to it: since it contains one "main class" you could inherit from it and keep inherited class(es) with overloaded functions in several new small and well designed files.
Find some code in the file which is relatively stable (not changing fast, and doesn't vary much between branches) and could stand as an independent unit. Move this into its own file, and for that matter into its own class, in all branches. Because it's stable, this won't cause (many) "awkward" merges that have to be applied to a different file from the one they were originally made on, when you merge the change from one branch to another. Repeat.
Find some code in the file which basically only applies to a small number of branches, and could stand alone. Doesn't matter whether it's changing fast or not, because of the small number of branches. Move this into its own classes and files. Repeat.
So, we've got rid of the code that's the same everywhere, and the code that's specific to certain branches.
This leaves you with a nucleus of badly-managed code - it's needed everywhere, but it's different in every branch (and/or it changes constantly so that some branches are running behind others), and yet it's in a single file that you're unsuccessfully trying to merge between branches. Stop doing that. Branch the file permanently, perhaps by renaming it in each branch. It's not "main" any more, it's "main for configuration X". OK, so you lose the ability to apply the same change to multiple branches by merging, but this is in any case the core of code where merging doesn't work very well. If you're having to manually manage the merges anyway to deal with conflicts, then it's no loss to manually apply them independently on each branch.
I think you're wrong to say that the kind of SCC doesn't matter, because for example git's merging abilities are probably better than the merge tool you're using. So the core problem, "merging is difficult" occurs at different times for different SCCs. However, you're unlikely to be able to change SCCs, so the issue is probably irrelevant.
It sounds to me like you're facing a number of code smells here. First of all the main class appears to violate the open/closed principle. It also sounds like it is handling too many responsibilities. Due to this I would assume the code to be more brittle than it needs to be.
While I can understand your concerns regarding traceability following a refactoring, I would expect that this class is rather hard to maintain and enhance and that any changes you do make are likely to cause side effects. I would assume that the cost of these outweighs the cost of refactoring the class.
In any case, since the code smells will only get worse with time, at least at some point the cost of these will outweigh the cost of refactoring. From your description I would assume that you're past the tipping point.
Refactoring this should be done in small steps. If possible add automated tests to verify current behavior before refactoring anything. Then pick out small areas of isolated functionality and extract these as types in order to delegate the responsibility.
In any case, it sounds like a major project, so good luck :)
The only solution I have ever imagined to such problems follows. The actual gain by the described method is progressiveness of the evolutions. No revolutions here, otherwise you'll be in trouble very fast.
Insert a new cpp class above the original main class. For now, it would basically redirect all calls to the current main class, but aim at making the API of this new class as clear and succinct as possible.
Once this has been done, you get the possibility to add new functionalities in new classes.
As for existing functionalities, you have to progressively move them in new classes as they become stable enough. You will lose SCC help for this piece of code, but there is not much that can be done about that. Just pick the right timing.
I know this is not perfect, though I hope it can help, and the process must be adapted to your needs!
Additional information
Note that Git is an SCC that can follow pieces of code from one file to another. I have heard good things about it, so it could help while you are progressively moving your work.
Git is constructed around the notion of blobs which, if I understand correctly, represent pieces of code files. Move these pieces around in different files and Git will find them, even if you modify them. Apart from the video from Linus Torvalds mentioned in comments below, I have not been able to find something clear about this.
Confucius say: "first step to getting out of hole is to stop digging hole."
Let me guess: Ten clients with divergent feature sets and a sales manager that promotes "customization"? I've worked on products like that before. We had essentially the same problem.
You recognize that having an enormous file is trouble, but even more trouble is ten versions that you have to keep "current". That's multiple maintenance. SCC can make that easier, but it can't make it right.
Before you try to break the file into parts, you need to bring the ten branches back in sync with each other so that you can see and shape all the code at once. You can do this one branch at a time, testing both branches against the same main code file. To enforce the custom behavior, you can use #ifdef and friends, but it's better as much as possible to use ordinary if/else against defined constants. This way, your compiler will verify all types and most probably eliminate "dead" object code anyway. (You may want to turn off the warning about dead code, though.)
Once there's only one version of that file shared implicitly by all branches, then it's rather easier to begin traditional refactoring methods.
The #ifdefs are primarily better for sections where the affected code only makes sense in the context of other per-branch customizations. One may argue that these also present an opportunity for the same branch-merging scheme, but don't go hog-wild. One colossal project at a time, please.
In the short run, the file will appear to grow. This is OK. What you're doing is bringing things together that need to be together. Afterwards, you'll begin to see areas that are clearly the same regardless of version; these can be left alone or refactored at will. Other areas will clearly differ depending on the version. You have a number of options in this case. One method is to delegate the differences to per-version strategy objects. Another is to derive client versions from a common abstract class. But none of these transformations are possible as long as you have ten "tips" of development in different branches.
I don't know if this solves your problem, but what I guess you want to do is migrate the content of the file to smaller files independent of each other (summed up).
What I also get is that you have about 10 different versions of the software floating around and you need to support them all without messing things up.
First of all there is just no way that this is easy and will solve itself in a few minutes of brainstorming. The functions linked in your file are all vital to your application, and simply cutting them of and migrating them to other files won't save your problem.
I think you only have these options:
Don't migrate and stay with what you have. Possibly quit your job and start working on serious software with good design in addition. Extreme programming is not always the best solution if you are working on a long time project with enough funds to survive a crash or two.
Work out a layout of how you would love your file to look once it's split up. Create the necessary files and integrate them in your application. Rename the functions or overload them to take an additional parameter (maybe just a simple boolean?).
Once you have to work on your code, migrate the functions you need to work on to the new file and map the function calls of the old functions to the new functions.
You should still have your main-file this way, and still be able to see the changes that were made to it, once it comes to a specific function you know exactly when it was outsourced and so on.
Try to convince your co-workers with some good cake that workflow is overrated and that you need to rewrite some parts of the application in order to do serious business.
Exactly this problem is handled in one of the chapters of the book "Working Effectively with Legacy Code" (http://www.amazon.com/Working-Effectively-Legacy-Michael-Feathers/dp/0131177052).
I think you would be best off creating a set of command classes that map to the API points of the mainmodule.cpp.
Once they are in place, you will need to refactor the existing code base to access these API points via the command classes, once that's done, you are free to refactor each command's implementation into a new class structure.
Of course, with a single class of 11 KLOC the code in there is probably highly coupled and brittle, but creating individual command classes will help much more than any other proxy/facade strategy.
I don't envy the task, but as time goes on this problem will only get worse if it's not tackled.
Update
I'd suggest that the Command pattern is preferable to a Facade.
Maintaining/organizing a lot of different Command classes over a (relatively) monolithic Facade is preferable. Mapping a single Facade onto a 11 KLOC file will probably need to be broken up into a few different groups itself.
Why bother trying to figure out these facade groups? With the Command pattern you will be able to group and organise these small classes organically, so you have a lot more flexibility.
Of course, both options are better than the single 11 KLOC and growing, file.
One important advice: Do not mix refactoring and bugfixes. What you want is a Version of your program that is identical to the previous version, except that the source code is differently.
One way could be to start splitting up the least big function/part into it's own file and then either include with a header (thus turning main.cpp into a list of #includes, which sounds a code smell in itself *I'm not a C++ Guru though), but at least it's now split into files).
You could then try to switch all maintenance releases over to the "new" main.cpp or whatever your structure is. Again: No other changes or Bugfixes because tracking those is confusing as hell.
Another thing: As much as you may desire making one big pass at refactoring the whole thing in one go, you might bite off more than you can chew. Maybe just pick one or two "parts", get them into all the releases, then add some more value for your customer (after all, Refactoring does not add direct value so it is a cost that has to be justified) and then pick another one or two parts.
Obviously that requires some discipline in the team to actually use the split files and not just add new stuff to the main.cpp all the time, but again, trying to do one massive refactor may not be the best course of action.
Rofl, this reminds me of my old job. It seems that, before I joined, everything was inside one huge file (also C++). Then they've split it up (at completely random points using includes) into about three (still huge files). The quality of this software was, as you might expect, horrible. The project totaled at about 40k LOC. (containing almost no comments but LOTS of duplicate code)
In the end I did a complete rewrite of the project. I started by redoing the worst part of the project from scratch. Of course I had in mind a possible (small) interface between this new part and the rest. Then I did insert this part into the old project. I didn't refactor the old code to create the interface necessary, but just replaced it. Then I took made small steps from there, rewriting the old code.
I have to say that this took about half a year and there was no development of the old code base beside bugfixes during that time.
edit:
The size stayed at about 40k LOC but the new application contained many more features and presumably less bugs in its initial version than the 8 year old software. One reason of the rewrite was also that we needed the new features and introducing them inside the old code was nearly impossible.
The software was for an embedded system, a label printer.
Another point that I should add is that in theory the project was C++. But it wasn't OO at all, it could have been C. The new version was object oriented.
OK so for the most part rewriting API of production code is a bad idea as a start. Two things need to happen.
One, you need to actually have your team decide to do a code freeze on current production version of this file.
Two, you need to take this production version and create a branch that manages the builds using preprocessing directives to split up the big file. Splitting the compilation using JUST preprocessor directives (#ifdefs, #includes, #endifs) is easier than recoding the API. It's definitely easier for your SLAs and ongoing support.
Here you could simply cut out functions that relate to a particular subsystem within the class and put them in a file say mainloop_foostuff.cpp and include it in mainloop.cpp at the right location.
OR
A more time consuming but robust way would be to devise an internal dependencies structure with double-indirection in how things get included. This will allow you to split things up and still take care of co-dependencies. Note that this approach requires positional coding and therefore should be coupled with appropriate comments.
This approach would include components that get used based on which variant you are compiling.
The basic structure is that your mainclass.cpp will include a new file called MainClassComponents.cpp after a block of statements like the following:
#if VARIANT == 1
# define Uses_Component_1
# define Uses_Component_2
#elif VARIANT == 2
# define Uses_Component_1
# define Uses_Component_3
# define Uses_Component_6
...
#endif
#include "MainClassComponents.cpp"
The primary structure of the MainClassComponents.cpp file would be there to work out dependencies within the sub components like this:
#ifndef _MainClassComponents_cpp
#define _MainClassComponents_cpp
/* dependencies declarations */
#if defined(Activate_Component_1)
#define _REQUIRES_COMPONENT_1
#define _REQUIRES_COMPONENT_3 /* you also need component 3 for component 1 */
#endif
#if defined(Activate_Component_2)
#define _REQUIRES_COMPONENT_2
#define _REQUIRES_COMPONENT_15 /* you also need component 15 for this component */
#endif
/* later on in the header */
#ifdef _REQUIRES_COMPONENT_1
#include "component_1.cpp"
#endif
#ifdef _REQUIRES_COMPONENT_2
#include "component_2.cpp"
#endif
#ifdef _REQUIRES_COMPONENT_3
#include "component_3.cpp"
#endif
#endif /* _MainClassComponents_h */
And now for each component you create a component_xx.cpp file.
Of course i am using numbers but you should use something more logical based on your code.
Using preprocessor allows you to split things up without having to worry about API changes which is a nightmare in production.
Once you have production settled you can then actually work on redesign.
Well I understand your pain :) I've been in a few such projects as well and it's not pretty. There is no easy answer for this.
One approach that may work for you is to start adding safe guards in all functions, that is, checking arguments, pre/post-conditions in methods, then eventually adding unit tests all in order to capture the current functionality of the sources. Once you have this you are better equipped to re-factor the code because you will have asserts and errors popping up alerting you if you have forgotten something.
Sometimes though there are times when refactoring just may bring more pain than benefit. Then it may be better to just leave the original project and in a pseudo maintenance state and start from scratch and then incrementally adding the functionality from the beast.
You should not be concerned with reducing the file-size, but rather with reducing the class-size. It comes down to almost the same, but makes you look at the problem from a different angle (as #Brian Rasmussen suggests, your class seems to have to many responsibilities).
What you have is a classic example a known design antipattern called the blob. Take some time to read the article I point here, and maybe you may find something useful. Besides, if this project is as big as it looks, you should consider some design to prevent growing into code that you can't control.
This isn't an answer to the big problem, but a theoretical solution to a specific piece of it:
Figure out where you want to split the big file into subfiles. Put comments in some special format at each of those points.
Write a fairly trivial script that will break the file apart into subfiles at those points. (Perhaps the special comments have embedded filenames that the script can use as instructions for how to split it.) It should preserve the comments as part of the splitting.
Run the script. Delete the original file.
When you need to merge from a branch, first recreate the big file by concatenating the pieces back together, do the merge, and then re-split it.
Also, if you want to preserve the SCC file history, I expect the best way to do that is to tell your source control system that the individual piece files are copies of the original. Then it will preserve the history of the sections that were kept in that file, although of course it will also record that large parts were "deleted".
One way to split it without too much danger would be to take a historic look at all the line changes. Are there certain functions that are more stable than others? Hot spots of change if you will.
If a line hasn't been changed in a few years you can probably move it to another file without too much worry. I'd take a look at the source annotated with the last revision that touched a given line and see if there are any functions you could pull out.
Wow, sounds great. I think explaining to your boss, that you need a lot of time to refactor the beast is worth a try. If he doesn't agree, quitting is an option.
Anyway, what I suggest is basically throwing out all the implementation and regrouping it into new modules, let's call those "global services". The "main module" would only forward to those services and ANY new code you write will use them instead of the "main module". This should be feasible in a reasonable amount of time (because it's mostly copy and paste), you don't break existing code and you can do it one maintenance version at a time. And if you still have any time left, you can spend it refactoring all old depending modules to also use the global services.
Do not ever touch this file and the code again!
Treat is like something you are stuck with. Start writing adapters for the functionality encoded there.
Write new code in different units and talk only to adapters which encapsulate the functionality of the monster.
... if only one of the above is not possible, quit the job and get you a new one.
My sympathies - in my previous job I encountered a similar situation with a file that was several times larger than the one you have to deal with. Solution was:
Write code to exhaustively test the function in the program in question. Sounds like you won't already have this in hand...
Identify some code that can be abstracted out into a helper/utilities class. Need not be big, just something that is not truly part of your 'main' class.
Refactor the code identified in 2. into a separate class.
Rerun your tests to ensure nothing got broken.
When you have time, goto 2. and repeat as required to make the code manageable.
The classes you build in step 3. iterations will likely grow to absorb more code that is appropriate to their newly-clear function.
I could also add:
0: buy Michael Feathers' book on working with legacy code
Unfortunately this type of work is all too common, but my experience is that there is great value in being able to make working but horrid code incrementally less horrid while keeping it working.
Consider ways to rewrite the entire application in a more sensible way. Maybe rewrite a small section of it as a prototype to see if your idea is feasible.
If you've identified a workable solution, refactor the application accordingly.
If all attempts to produce a more rational architecture fail, then at least you know the solution is probably in redefining the program's functionality.
My 0.05 eurocents:
Re-design the whole mess, split it into subsystems taking into account the technical and business requirements (=many parallel maintenance tracks with potentially different codebase for each, there is obviously a need for high modifiability, etc.).
When splitting into subsystems, analyze the places which have most changed and separate those from the unchanging parts. This should show you the trouble-spots. Separate the most changing parts to their own modules (e.g. dll) in such a way that the module API can be kept intact and you don't need to break BC all the time. This way you can deploy different versions of the module for different maintenance branches, if needed, while having the core unchanged.
The redesign will likely need to be a separate project, trying to do it to a moving target will not work.
As for the source code history, my opinion: forget it for the new code. But keep the history somewhere so you can check it, if needed. I bet you won't need it that much after the beginning.
You most likely need to get management buy-in for this project. You can argue perhaps with faster development time, less bugs, easier maintaining and less overall chaos. Something along the lines of "Proactively enable the future-proofness and maintenance viability of our critical software assets" :)
This is how I'd start to tackle the problem at least.
Start by adding comments to it. With reference to where functions are called and if you can move things around. This can get things moving. You really need to assess how brittle the code base it. Then move common bits of functionality together. Small changes at a time.
Another book you may find interesting/helpful is Refactoring.
Something I find useful to do (and I'm doing it now although not at the scale you face), is to extract methods as classes (method object refactoring). The methods that differ across your different versions will become different classes which can be injected into a common base to provide the different behaviour you need.
I found this sentence to be the most interesting part of your post:
> The file is used and actively changed in several (> 10) maintenance versions of our product and so it is really hard to refactor it
First, I would recommend that you use a source control system for developing these 10 + maintenance versions that supports branching.
Second, I would create ten branches (one for each of your maintenance versions).
I can feel you cringing already! But either your source control isn't working for your situation because of a lack of features, or it's not being used correctly.
Now to the branch you work on - refactor it as you see fit, safe in the knowledge that you'll not upset the other nine branches of your product.
I would be a bit concerned that you have so much in your main() function.
In any projects I write, I would use main() only perform initialization of core objects - like a simulation or application object - these classes is where the real work should go on.
I would also initialize an application logging object in main for use globally throughout the program.
Finally, in main I also add leak detection code in preprocessor blocks that ensure it's only enabled in DEBUG builds. This is all I would add to main(). Main() should be short!
You say that
> The file basically contains the "main class" (main internal work dispatching and coordination) of our program
It sounds like these two tasks could be split into two separate objects - a co-ordinator and a work dispatcher.
When you split these up, you may mess up your "SCC workflow", but it sounds like adhering stringently to your SCC workflow is causing software maintenance problems. Ditch it, now and don't look back, because as soon as you fix it, you'll begin to sleep easy.
If you're not able to make the decision, fight tooth and nail with your manager for it - your application needs to be refactored - and badly by the sounds of it! Don't take no for an answer!
As you've described it, the main issue is diffing pre-split vs post-split, merging in bug fixes etc.. Tool around it. It won't take that long to hardcode a script in Perl, Ruby, etc. to rip out most of the noise from diffing pre-split against a concatenation of post-split. Do whatever's easiest in terms of handling noise:
remove certain lines pre/during concatenation (e.g. include guards)
remove other stuff from the diff output if necessary
You could even make it so whenever there's a checkin, the concatenation runs and you've got something prepared to diff against the single-file versions.
"The file basically contains the "main class" (main internal work dispatching and coordination) of our program, so every time a feature is added, it also affects this file and every time it grows."
If that big SWITCH (which I think there is) becomes the main maintenance problem, you could refactor it to use dictionary and the Command pattern and remove all switch logic from the existing code to the loader, which populates that map, i.e.:
// declaration
std::map<ID, ICommand*> dispatchTable;
...
// populating using some loader
dispatchTable[id] = concreteCommand;
...
// using
dispatchTable[id]->Execute();
I think the easiest way to track the history of source when splitting a file would be something like this:
Make copies of the original source code, using whatever history-preserving copy commands your SCM system provides. You'll probably need to submit at this point, but there's no need yet to tell your build system about the new files, so that should be ok.
Delete code from these copies. That should not break the history for the lines you keep.
I think what I would do in this situation is bit the bullet and:
Figure out how I wanted to split the file up (based on the current development version)
Put an administrative lock on the file ("Nobody touch mainmodule.cpp after 5pm Friday!!!"
Spend your long weekend applying that change to the >10 maintenance versions (from oldest to newest), up to and including the current version.
Delete mainmodule.cpp from all supported versions of the software. It's a new Age - there is no more mainmodule.cpp.
Convince Management that you shouldn't be supporting more than one maintenance version of the software (at least without a big $$$ support contract). If each of your customers have their own unique version.... yeeeeeshhhh. I'd be adding compiler directives rather than trying to maintain 10+ forks.
Tracking old changes to the file is simply solved by your first check-in comment saying something like "split from mainmodule.cpp". If you need to go back to something recent, most people will remember the change, if it's 2 year from now, the comment will tell them where to look. Of course, how valuable will it be to go back more than 2 years to look at who changed the code and why?
Related
I am working on a motion control system, and will have at least 5 motors, each with parameters such as "gearbox ratio", "ticks per rev" "Kp", "Ki", "Kd", etc. that will be referenced upon construction of instances of the motors.
My question to StackOverflow is how should I organize these numbers? I know this is likely a preferential thing, but being new to coding I figure I could get some good opinions from you.
The three approaches I immediately see are as follows:
Write in the call to the constructor, either via variables or numbers-- PROS: limited coding, could be implemented in a way that it's easy to change, but possibly harder than #define's
Use #define's to accomplish similar to above -- PROS: least coding, easy to change (assuming you want to look at the source code)
Load a file (possibly named "motorparameters.txt") and load the parameters into an array and populate from that array. If I really wanted to I could add a GUI approach to changing this file rather than manual. -- PROS:easiest to change without diving into source code.
These parameters could change over time, and while there are other coders at the company, I would like to leave it in a way that's easy to configure. Do any of you see a particular benefit of #define vs. variables? I have a "constants.h" file already that I could easily add the #defines to, or I could add variables near the call to the constructor.
There's a principle know as YAGNI (You Ain't Gonna Need It) which says do the simplest thing first, then change it when (if) your requirements expand.
Sounds to me like the thing to do is:
Write a flexible motor class, that can handle any values (within reason), even though there are only 5 different sets of values you currently care about.
Define a component that returns the "right" values for the 5 motors in your system (or that constructs the 5 motors for your system using the "right values")
Initially implement that component to use some hard-coded values out of a header file
Retain the option to replace that component in future with an implementation of the same API, but that reads values out of a resource file, text file, XML file, GUI interaction with the user, off the internet, by making queries to the hardware to find out what motors it thinks it has, whatever.
I say this on the basis that you minimize expected effort by putting in a point of customizability where you suspect you'll want one (to prevent a lot of work when you change it later), but implement using the simplest thing that satisfies your current certain requirements.
Some people might say that it's not actually worth doing the typing (a) to define the component, better just to construct 5 motors in main() (b) to use constants from a header file, better just to type numeric literals in main(). The (b) people are widely despised as peddlers of "magic constants" (which doesn't mean they're necessarily wrong about relative total programming time by implementer and future maintainers, they just probably are) and the (a) people divide opinion. I tend to figure that defining this kind of thing takes a few minutes, so I don't really care whether it's worth it or not. Loading the values out of a file involves specifying a file format that I might regret as soon as I encounter a real reason to customize, so personally I can't be bothered with that until the requirement arises.
The general idea is to separate the portions of your code that will change from those that won't. The more likely something is to change, the more you need to make it easy to change.
If you're building a commercial app where hundreds or thousands of users will use many different motors, it might make sense to code up a UI and store the data in a config file.
If this is development code and these parameters are unlikely to change, then stuffing them into #defines in your constants.h file is probably the way to go.
Number 3 is a great option if you don't have security or IP concerns. Anytime you or someone else touches your code, you introduce the possibility of regressions. By keeping your parameters in a text file, not only are you making life easier on yourself, you're also reducing the scope of possible errors down the road.
I have a couple of libraries that were targetting multiple platforms, of which some realtime ones that did/do not have decent STL support, let alone tr1 or C++11. This means everything uses the library's own string/array/list/younameit classes. Now these platforms are getting abandoned in favour of 'pure' C++11 and STL (which I am very very glad for: the latest lib I did is the first one with the new standard and development time has shortened a lot, while code quality went up).
Now I want new projects to not depend on the custom string/array/... classes, and I'm planning to go for a step-by-step refactory: whenever I need some class, create a duplicate (well not a complete duplicate; still that hurts, but is there another option?) that uses STL instead. In the beginning that might mean a whole tree of classes might need changing at once. At the same time the original code should keep working for the next 4 years or so.
Practically the main question I'm facing now is: where do I put these new classes? For example
A\A.h depends on B\B.h and string.h
should become
a new A.h depending on a new B.h and <string>
Do I make a new class NewA and put in in A.h? Or make a class A in a new namespace and store it in A\newA.h? Or do I make a whole new subdirectory structure like new\A\A.h and new\B\b.h?
I know there are already a couple of similar questions, with great answers, but I'd like some more practical advice, not "read Working Effectively with Legacy Code". Though that is, with reason, a good answer, I'm more interested in what you practically did in a similar situation?
edit some clarification:
The majority of the current applications will also be ported to use STL in time as they will all run on the new platform (still in doubt about RTX or InTime, but one of those).
I do use a VCS, git, and pretty much everything that matters is covered by unit tests. Else this would be madness.
There's no real team and I'm on my own (unfortunately I cannot count my collegue as a team member when it comes to things like this, though being almost twice my age his programming level is less then half of mine, and I'm not even that skilled.
Don't duplicate classes. Let your old project run, and fork it somewhere. Of course, use unit testing and source control.
Then, I'd go for a depth-first approach, a bit at a time. Change one class at a time to adapt it to the new coding standards, and solve all compiler errors that result. This means in particular that for the class you are interested in, you first get rid of the old string.h, you change the interface and implementation (string/vector classes aren't that different from one another), and you build the project. Let compiler errors tell you where to go next.
Depending on the size of the project, you can begin with the least or most used class. Remove unused string/vector classes only after all the other classes have been converted.
This is likely to be a quite easy (albeit time consuming) operation (hence different from refactoring) and this can probably be handled quite well by multiple developers at a time, if you use a good version control system with good merge support and unit testing. Do use unit testing and version control. Really do.
Of course, you won't adapt your entire code to STL and C++0x, and you should strive first for the custom string/container classes, and add smart pointers where they belong. Your mid-term goal should be to remove every occurrence of delete in your whole code base.
If you've got a codebase which is a bit messy in respect to coding standards - a mix of different conventions from different people - is it reasonable to give one person the task of going through every file and bringing it up to meet standards?
As well as being tremendously dull, you're going to get a mass of changes in SVN (or whatever) which can make comparing versions harder. Is it sensible to set someone on the whole codebase, or is it considered stupid to touch a file only to make it meet standards? Should files be left alone until some 'real' change is needed, and then updated?
Tagged as C++ since I think different languages have different automated tools for this.
Should files be left alone until some 'real' change is needed, and then updated?
This is what I would do.
Even if it's primarily text layout changes, doing it by a manual process on a large scale risks breaking code that was working.
Treat it as a refactor and do it locally whenever code has to be touched for some other reason. Add tests if they're missing to improve your chances of not breaking the code.
If your code is already well covered by tests, you might get away with something global, but I still wouldn't advocate it.
I also think this is pretty much language-agnostic.
It also depends on what kind of changes you are planning to make in order to bring it up to your coding standard. Everyone's definition of coding standard is different.
More specifically:
Can your proposed changes be made to the project with 100% guarantee that the entire project will work identically the same as before? For example, changes that only affect comments, line breaks and whitespaces should be fine.
If you do not have 100% guarantee, then there is a risk that should not be taken unless it can be balanced with a benefit. For example, is there a need to gain a deeper understanding of the current code base in order to continue its development, or fix its bugs? Is the jumble of coding conventions preventing these initiatives? If so, evaluate the costs and benefits and decide whether a makeover is justified.
If you need to understand the current code base, here is a technique: tracing.
Make a copy of the code base. Note that tracing involves adding code, so it should not be performed on the production copy.
In the new copy, insert many fprintf (trace) statements into any functions considered critical. It may be possible to automate this.
Run the project with various inputs and collect those tracing results. This will help everyone understand the current project's design.
Another technique for understanding the current code base is to document the dependencies in the project.
Some kinds of dependencies (interface dependency, C++ include dependency, C++ typedef / identifier dependency) can be extracted by automated tools.
Run-time dependency can only be extracted through tracing, or by profiling tools.
I was thinking it's a task you might give a work-experience kid or put out onto RentaCoder
This depends mainly on the codebase's size.
I've seen three trainees given the task to go through a 2MLoC codebase (several thousand source files) in order to insert one new line into the standard disclaimer at the top of all the source files (with the line's content depending on the file's name and path). It took them several days. One of the three used most of that time to write a script that would do it and later only fixed the files where the script had failed to insert the line correctly, the other two just ploughed through the files. (The one who wrote the script later got a job at that company.)
The job of manually adapting all those files in that codebase to certain coding standards would probably have to be measured in man-years.
OTOH, if it's just a few dozen files, it's certainly doable.
Your codebase is very likely somewhere in between, so your best bet might be to set a "work-experience kid" to find out whether there's a tool that can do this to your satisfaction and, if so, make it work.
Should files be left alone until some 'real' change is needed, and then updated?
I'd strongly advice against this. If you do this, you will have "real" changes intermingled with whatever reformatting took place, making it nigh impossible to see the "real" changes in the diff.
You can address the formatting aspect of coding style fairly easily. There are a number of tools that can auto-format your code. I recommend hooking one of these up to your version control tool's "check in" feature. This way, people can use whatever format they want while editing their code, but when it gets checked in, it's reformatted to the official style.
In general, I think it's best if you can do the big change all at once. In the past, we've done the following:
1. have a time dedicated to the reformatting when most people aren't working (e.g. at night or on the weekend
2. have a person check out as many files as possible at that time, reformat them, and check them in again
With a reformatting-only revision, you don't have to figure out what has changed in addition to the formatting.
I have three legacy applications that share a lot of source code and data. Multiple instances of each of these applications be executed by a user at any time, e.g. a dozen mixed application executions can be active at a time. These applications currently communicate through shared memory and messaging techniques so that they can maintain common cursor positioning, etc. The applications are written primarily in C++, use Qt and run in total to about 5 million lines of code. Only some of the existing code is threadsafe.
I want to consolidate these three executables into a single executable and use multi-threading functionality to allow multiple instance of each of the three functionality branches to execute at the same time. It has been suggested that I look into some of the features provided by Boost, e.g. shared pointers, and use OpenMP to orchestrate overall execution of the multiple threads.
Any comments on how to proceed will be appreciated, particularly references on the best way to tackle this kind of a refactoring problem.
My suggestion to you would be design the desired solution first (firstly assuming that the requirements are the same) and then build a phased migration path from the existing code base basing it on the requirements that third party functionality may introduce.
Refactoring should be one small step at a time - but knowing where you are going.
The Working Effectively with Legacy Code (Robert C. Martin Series) will be a good read I'd suggest.
Trust me (I've got the t shirts) don't attempt to refactor unless you know how to prove functionality - automated verification tests will be your saviour.
I don't think anyone will be able to give you an informed answer. There are too many things to take into considerations. Only after careful analysis of the processes involved and the code behind would anyone (you included) be able to provide you with a project path.
That said, there are however a few things you should take into consideration.
Your applications and the way they seem to communicate with each other seems to me an already sound solution. This is so, especially because you have 5 million lines of code to tackle with, if you choose to get into refactoring your current system. This is a strong deterrent. If there is a need to provide threading support in order to optimize current application messaging, I'd perhaps suggest you consider the possibility of introducing MT into the shared memory and messaging routines, instead of merging applications.
The act of merging your applications could be seen at first glance as the "simple" act of gluing your current code and removing the current routines responsible for memory sharing and messaging, replacing them with normal function calls to the glued objects. My gut tells me it will not be that simple. You have to consider that almost certainly your current backbone code was designed for the current messaging solution. Your current abstractions were thought of with this in mind. You will almost certainly find that you will also need to make significant changes to existing backbone code. And again here you will find that wall of 5 million lines a huge problem. Because changes will quickly propagate across your entire system and leave you with 5 million lines of code to handle and god knows how many new bugs.
I'd suggest 1 above. But it may be that you do need for some reason to consolidate your applications. That being so, I'd still suggest something else before you try 2. Create an interface application responsible for firing up, displaying and maintaining the current 3 applications. Your users will know no better if you do this right. You'll still be able to apply 1 to your current system and join your applications under a common interface, despite them being in fact separate entities.
"...about 5 million lines of code..." Hmm... It is hard to say for sure without knowing your system, but since it is a "legacy" system, you can probably gain a lot by removing code duplication. Check out Simian and CPD.
5 million lines is a lot ot code. Of course, you may need it, but my guess is that you don't.
You definitely need a good reason to change a change a code-base like that to be multi-threaded, especially in C++. Doing it without cleaning it up completely first is a recipe for disaster.
I have inherited a monster.
It is masquerading as a .NET 1.1 application processes text files that conform to Healthcare Claim Payment (ANSI 835) standards, but it's a monster. The information being processed relates to healthcare claims, EOBs, and reimbursements. These files consist of records that have an identifier in the first few positions and data fields formatted according to the specs for that type of record. Some record ids are Control Segment ids, which delimit groups of records relating to a particular type of transaction.
To process a file, my little monster reads the first record, determines the kind of transaction that is about to take place, then begins to process other records based on what kind of transaction it is currently processing. To do this, it uses a nested if. Since there are a number of record types, there are a number decisions that need to be made. Each decision involves some processing and 2-3 other decisions that need to be made based on previous decisions. That means the nested if has a lot of nests. That's where my problem lies.
This one nested if is 715 lines long. Yes, that's right. Seven-Hundred-And-Fif-Teen Lines. I'm no code analysis expert, so I downloaded a couple of freeware analysis tools and came up with a McCabe Cyclomatic Complexity rating of 49. They tell me that's a pretty high number. High as in pollen count in the Atlanta area where 100 is the standard for high and the news says "Today's pollen count is 1,523". This is one of the finest examples of the Arrow Anti-Pattern I have ever been priveleged to see. At its highest, the indentation goes 15 tabs deep.
My question is, what methods would you suggest to refactor or restructure such a thing?
I have spent some time searching for ideas, but nothing has given me a good foothold. For example, substituting a guard condition for a level is one method. I have only one of those. One nest down, fourteen to go.
Perhaps there is a design pattern that could be helpful. Would Chain of Command be a way to approach this? Keep in mind that it must stay in .NET 1.1.
Thanks for any and all ideas.
I just had some legacy code at work this week that was similar (although not as dire) as what you are describing.
There is no one thing that will get you out of this. The state machine might be the final form your code takes, but thats not going to help you get there, nor should you decide on such a solution before untangling the mess you already have.
First step I would take is to write a test for the existing code. This test isn't to show that the code is correct but to make sure you have not broken something when you start refactoring. Get a big wad of data to process, feed it to the monster, and get the output. That's your litmus test. if you can do this with a code coverage tool you will see what you test does not cover. If you can, construct some artificial records that will also exercise this code, and repeat. Once you feel you have done what you can with this task, the output data becomes your expected result for your test.
Refactoring should not change the behavior of the code. Remember that. This is why you have known input and known output data sets to validate you are not going to break things. This is your safety net.
Now Refactor!
A couple things I did that i found useful:
Invert if statements
A huge problem I had was just reading the code when I couldn't find the corresponding else statement, I noticed that a lot of the blocks looked like this
if (someCondition)
{
100+ lines of code
{
...
}
}
else
{
simple statement here
}
By inverting the if I could see the simple case and then move onto the more complex block knowing what the other one already did. not a huge change, but helped me in understanding.
Extract Method
I used this a lot.Take some complex multi line block, grok it and shove it aside in it's own method. this allowed me to more easily see where there was code duplication.
Now, hopefully, you haven't broken your code (test still passes right?), and you have more readable and better understood procedural code. Look it's already improved! But that test you wrote earlier isn't really good enough... it only tells you that you a duplicating the functionality (bugs and all) of the original code, and thats only the line you had coverage on as I'm sure you would find blocks of code that you can't figure out how to hit or just cannot ever hit (I've seen both in my work).
Now the big changes where all the big name patterns come into play is when you start looking at how you can refactor this in a proper OO fashion. There is more than one way to skin this cat, and it will involve multiple patterns. Not knowing details about the format of these files you're parsing I can only toss around some helpful suggestions that may or may not be the best solutions.
Refactoring to Patterns is a great book to assist in explainging patterns that are helpful in these situations.
You're trying to eat an elephant, and there's no other way to do it but one bite at a time. Good luck.
A state machine seems like the logical place to start, and using WF if you can swing it (sounds like you can't).
You can still implement one without WF, you just have to do it yourself. However, thinking of it like a state machine from the start will probably give you a better implementation then creating a procedural monster that checks internal state on every action.
Diagram out your states, what causes a transition. The actual code to process a record should be factored out, and called when the state executes (if that particular state requires it).
So State1's execute calls your "read a record", then based on that record transitions to another state.
The next state may read multiple records and call record processing instructions, then transition back to State1.
One thing I do in these cases is to use the 'Composed Method' pattern. See Jeremy Miller's Blog Post on this subject. The basic idea is to use the refactoring tools in your IDE to extract small meaningful methods. Once you've done that, you may be able to further refactor and extract meaningful classes.
I would start with uninhibited use of Extract Method. If you don't have it in your current Visual Studio IDE, you can either get a 3rd-party addin, or load your project in a newer VS. (It'll try to upgrade your project, but you will carefully ignore those changes instead of checking them in.)
You said that you have code indented 15 levels. Start about 1/2-way out, and Extract Method. If you can come up with a good name, use it, but if you can't, extract anyway. Split in half again. You're not going for the ideal structure here; you're trying to break the code in to pieces that will fit in your brain. My brain is not very big, so I'd keep breaking & breaking until it doesn't hurt any more.
As you go, look for any new long methods that seem to be different than the rest; make these in to new classes. Just use a simple class that has only one method for now. Heck, making the method static is fine. Not because you think they're good classes, but because you are so desperate for some organization.
Check in often as you go, so you can checkpoint your work, understand the history later, be ready to do some "real work" without needing to merge, and save your teammates the hassle of hard merging.
Eventually you'll need to go back and make sure the method names are good, that the set of methods you've created make sense, clean up the new classes, etc.
If you have a highly reliable Extract Method tool, you can get away without good automated tests. (I'd trust VS in this, for example.) Otherwise, make sure you're not breaking things, or you'll end up worse than you started: with a program that doesn't work at all.
A pairing partner would be helpful here.
Judging by the description, a state machine might be the best way to deal with it. Have an enum variable to store the current state, and implement the processing as a loop over the records, with a switch or if statements to select the action to take based on the current state and the input data. You can also easily dispatch the work to separate functions based on the state using function pointers, too, if it's getting too bulky.
There was a pretty good blog post about it at Coding Horror. I've only come across this anti-pattern once, and I pretty much just followed his steps.
Sometimes I combine the state pattern with a stack.
It works well for hierarchical structures; a parent element knows what state to push onto the stack to handle a child element, but a child doesn't have to know anything about its parent. In other words, the child doesn't know what the next state is, it simply signals that it is "complete" and gets popped off the stack. This helps to decouple the states from each other by keeping dependencies uni-directional.
It works great for processing XML with a SAX parser (the content handler just pushes and pops states to change its behavior as elements are entered and exited). EDI should lend itself to this approach too.