CODEWITHSUNDEEP
objective-ccocoadebuggingnslog
user1619911
user1619911

Reputation:

Conditional NSLog, Without decreasing Performance

bool kDebuggingEnabled = NO;
...
for(i=0; i<length; i++){
 ...
 if (kDebuggingEnabled) {
  NSLog (@"Value of variable # %i",$resultingOptions);
 }
}

whenever my app is live, my code checks the condition every time regarding NSLog. Is there any better way to improve performance of my code?

Upvotes: 2

Views: 1281

Answers (3)

Julien
Julien

Reputation: 3477

You have 3 choices:

1) if you want to enable/disable your logs at build time. The preprocessor solutions are the best:

// define MY_ENABLE_LOGS in your build settings for the debug configuration only, for example
#ifdef MY_ENABLE_LOGS
#define MYLog(...) NSLog(__VA_ARGS__)
#else
#define MyLog(...) do { } while(0)
#endif

2) if you want to be able to enable/disable logs at runtime (e.g. based on some hidden preferences), your solution is likely the best. You can try to hint the compiler to optimize things a bit, though:

// tell the compiler it's unlikely that kDebuggingEnabled will be true
#define MYLog(...) do { if (__builtin_expect(kDebuggingEnabled, 0)) { NSLog(__VA_ARGS__); } } while(0)

3) last option is a little bit more complicated but can provide richer info than just logs and only depends on the kind of logging you expect to provide. The idea is to use custom probes with dtrace (which can also be used within Instruments). This only works in OS X (not in iOS). See http://www.macresearch.org/tuning-cocoa-applications-using-dtrace-custom-static-probes-and-instruments for example.

Note that you can mix 1) and 2) depending on your needs. 3) is meant to be almost zero cost when probes are not traced and can provide much richer info than a simple log string.

One caveat with these solutions: the arguments of the logs won't be evaluated when MY_ENABLE_LOGS is not defined which might change your application behavior.

Upvotes: 2

mttrb
mttrb

Reputation: 8345

You could use preprocessor macros to turn logging on and off. A good example is the DLog macro from Marcus Zarra on the Cocoa is My Girlfriend blog.

#ifdef DEBUG
    #define DLog(...) NSLog(@"%s %@", __PRETTY_FUNCTION__, [NSString stringWithFormat:__VA_ARGS__])
#else
    #define DLog(...) do { } while (0)
#endif

You would place the above in your prefix.pch file and then simply replace NSLog statements with DLog statements. You also need to make sure that DEBUG is set in your debug build configuration.

Using preprocessor macros like this means that the logging code does not get compiled into your release build so there is no performance hit for the log statements.

The blog post also contains some other useful macros for handling assertions.

Upvotes: 5

Jack Lawrence
Jack Lawrence

Reputation: 10772

Use a preprocessor macro to check if you're building for debug:

#if DEBUG
// do stuff
#end

If the preprocessor (the thing that runs before the compiler) evaluates DEBUG to be true it'll keep the code there for the compiler to compile, but if DEBUG doesn't exist or is false, it'll erase that piece of code.

Upvotes: 1

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