Performing a Multi Parameter Method in Background in ObjC

NSObject+Performer.h

//
//  NSObject+Performer.h
//  EurActiv
//
//  Created by Mathieu Godart on 21/01/11.
//  Copyright 2011 L'atelier du mobile. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface NSObject (Performer)

// Executed in background, this method will invoke the given invocation and release its arguments, if needed.
// Caution: all arguments must respond to release.
- (void)createPoolAndInvoke:(NSInvocation *)invocation;

// Invokes a method of the receiver on a new background thread, already populated with an NSAutoreleasePool.
// No need for the performed selector to handle the autorelease pool allocation. It also retains the argument
// objects until the call to aSelector.
// Throws an exception if the selector has an incorrect signature.
- (void)performSelectorInPooledBackground:(SEL)aSelector withObject:(id)arg1 withObject:(id)arg2 withObject:(id)arg3;

@end

NSObject+Performer.m

//
//  NSObject+Performer.m
//  EurActiv
//
//  Created by Mathieu Godart on 21/01/11.
//  Copyright 2011 L'atelier du mobile. All rights reserved.
//

#import "NSObject+Performer.h"


@implementation NSObject (Performer)


// Executed in background, this method will invoke the given invocation and release its arguments, if needed.
// Caution: all arguments must respond to release.
- (void)createPoolAndInvoke:(NSInvocation *)invocation {
    
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    
    if (![invocation.target respondsToSelector:invocation.selector]) {
        
        [NSException raise:@"Invalid target selector couple"
                    format:@"target %@ doesn't respond to %@",
         invocation.target, NSStringFromSelector(invocation.selector)];
    }

    [invocation invoke];
    [pool release];
    
    // After that the invocation will be released, and so will be its arguments.
}


// Invokes a method of the receiver on a new background thread, already populated with an NSAutoreleasePool.
// No need for the performed selector to handle the autorelease pool allocation. It also retains the argument
// objects until the call to aSelector.
// Throws an exception if the selector has an incorrect signature.
- (void)performSelectorInPooledBackground:(SEL)aSelector withObject:(id)arg1 withObject:(id)arg2 withObject:(id)arg3 {
    
    NSMethodSignature *sign = [self methodSignatureForSelector:aSelector];

    if (!sign) [NSException raise:@"Invalid selector signature" format:@"signature of %@ is invalid",
                NSStringFromSelector(aSelector)];
    
    NSInvocation* invocation = [NSInvocation invocationWithMethodSignature:sign];
    [invocation setTarget:self];
    [invocation setSelector:aSelector];

    if (sign.numberOfArguments > 2) [invocation setArgument:&arg1 atIndex:2];
    if (sign.numberOfArguments > 3) [invocation setArgument:&arg2 atIndex:3];
    if (sign.numberOfArguments > 4) [invocation setArgument:&arg3 atIndex:4];
    
    [invocation retainArguments];
    [self performSelectorInBackground:@selector(createPoolAndInvoke:) withObject:invocation];
}


@end