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objective-cperformanceprofilingprofile
Plamen Terziev
Plamen Terziev

Reputation: 116

Custom performance profiler for Objective C

I want to create a simple to use and lightweight performance profile framework for Objective C. My goal is to measure the bottlenecks of my application.

Just to mention that I am not a beginner and I am aware of Instruments/Time Profiler. This is not what I am looking for. Time Profiler is a great tool but is too developer oriented. I want a framework that can collect performance data from a QA or pre production users and even incorporate in a real production environment to gather the real data.

The main part of this framework is the ability to measure how much time was spent in Objective C message (I am going to profile only Objective C messages).

The easiest way is to start timer in the beginning of a message and stop it at the end. It is the simplest way but its disadvantage is that it is to tedious and error prone - if any message has more than 1 return path then it will require to add the "stop timer" code before each return.

I am thinking of using method swizzling (just to note that I am aware that Apple are not happy with method swizzling but these profiled builds will be used internally only - will not be uploaded on the App Store).

My idea is to mark each message I want to profile and to generate automatically code for the method swizzling method (maybe using macros). When started, the application will swizzle the original selector with the generated one. The generated one will just start a timer, will call the original method and then will stop the timer. So in general the swizzled method will be just a wrapper of the original one.

One of the problems of the above idea is that I cannot think of an easy way how to automatically generate the methods to use for swizzling.

So I greatly will appreciate if anyone has any ideas how to automate the whole process. The perfect scenario is just to write one line of code anywhere mentioning the class and the selector I want to profile and the rest to be generated automatically.

Also will be very thankful if you have any other idea (beside method swizzling) of how to measure the performance.

Upvotes: 2

Views: 318

Answers (1)

Plamen Terziev
Plamen Terziev

Reputation: 116

I came up with a solution that works for me pretty well. First just to clarify that I was unable to find out an easy (and performance fast) way to automatically generate the appropriate swizzled methods for arbitrary selectors (i.e. with arbitrary arguments and return value) using only the selector name. So I had to add the arguments types and the return value for each selector, not only the selector name. In reality it should be relatively easy to create a small tool that would be able to parse all source files and detect automatically what are the arguments types and the returned value of the selector which we want to profile (and prepare the swizzled methods) but right now I don't need such an automated solution.

So right now my solution includes the above ideas for method swizzling, some C++ code and macros to automate and minimize some coding.

First here is the simple C++ class that measures time

class PerfTimer
{    
public:
    PerfTimer(PerfProfiledDataCounter* perfProfiledDataCounter);
    ~PerfTimer();

private:
    uint64_t _startTime;

    PerfProfiledDataCounter* _perfProfiledDataCounter;
};

I am using C++ to use that the destructor will be executed when object has exited the current scope. The idea is to create PerfTimer in the beginning of each swizzled method and it will take care of measuring the elapsed time for this method

The PerfProfiledDataCounter is a simple struct that counts the number of execution and the whole elapsed time (so it may find out what is the average time spent).

Also I am creating for each class I'd like profile, a category named "__Performance_Profiler_Category" and to conforms to "__Performance_Profiler_Marker" protocol. For easier creating I am using some macros that automatically create such categories. Also I have a set of macros that take selector name, return type and arguments type and create selectors for each selector name.

For all of the above tasks, I've created a set of macros to help me. Also I have a single file with .mm extension to register all classes and all selectors I'd like to profile. On app start, I am using the runtime to retrieve all classes that conforms to "__Performance_Profiler_Marker" protocol (i.e. the registered ones) and search for selectors that are marked for profiling (these selectors starts with predefined prefix). Note that this .mm file is the only file that needs .mm extension and there is no need to change file extension for each class I want to profile.

Afterwards the code swizzles the original selectors with the profiled ones. In each profiled one, I just create PerfTimer and call the swizzled method.

In brief that is my idea which turned out to work pretty smoothly.

Upvotes: 1

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