NSObject+SPInvocationGrabbing.m

#import "NSObject+SPInvocationGrabbing.h"
#import <execinfo.h>

#pragma mark Invocation grabbing

@interface SPInvocationGrabber ()
@property (readwrite, retain, nonatomic) id object;
@property (readwrite, retain, nonatomic) NSInvocation *invocation;
@end

@implementation SPInvocationGrabber

@synthesize object = _object;
@synthesize invocation = _invocation;
@synthesize backgroundAfterForward, onMainAfterForward, waitUntilDone;

- (id)initWithObject:(id)obj
{
	return [self initWithObject:obj stacktraceSaving:NO];
}

- (id)initWithObject:(id)obj stacktraceSaving:(BOOL)saveStack
{
	if ((self = [super init]) != nil) {
		_object = [obj retain];
		if (saveStack) {
			[self saveBacktrace];
		}
	}
	return self;
}

- (void)dealloc
{
	free(frameStrings);
	[_object release];
	[_invocation release];
	[super dealloc];
}

- (void)runInBackground
{
	NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
	@try {
		[self invoke];
	}
	@finally {
		[pool drain];
	}
}


- (void)forwardInvocation:(NSInvocation *)anInvocation
{
	[anInvocation retainArguments];
	anInvocation.target = _object;
	self.invocation = anInvocation;

	if (backgroundAfterForward) {
		[NSThread detachNewThreadSelector:@selector(runInBackground) toTarget:self withObject:nil];
	} else if (onMainAfterForward) {
		[self performSelectorOnMainThread:@selector(invoke) withObject:nil waitUntilDone:waitUntilDone];
	}
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)inSelector
{
	NSMethodSignature *signature = [super methodSignatureForSelector:inSelector];
	if (signature == NULL) {
		signature = [_object methodSignatureForSelector:inSelector];
	}
    
	return signature;
}

- (void)invoke
{
	@try {
		[_invocation invoke];
	}
	@catch (NSException * e) {
		NSLog(@"SPInvocationGrabber's target raised %@:\n\t%@\nInvocation was originally scheduled at:", e.name, e);
		[self printBacktrace];
		printf("\n");
		[e raise];
	}

	self.invocation = nil;
	self.object = nil;
}

- (void)saveBacktrace
{
	void *backtraceFrames[128];
	frameCount = backtrace(&backtraceFrames[0], 128);
	frameStrings = backtrace_symbols(&backtraceFrames[0], frameCount);
}

- (void)printBacktrace
{
	for (int x = 3; x < frameCount; x++) {
		if (frameStrings[x] == NULL) {
			break;
		}
		printf("%s\n", frameStrings[x]);
	}
}

@end


@implementation NSObject (SPInvocationGrabbing)

- (id)grab
{
	return [[[SPInvocationGrabber alloc] initWithObject:self] autorelease];
}

- (id)invokeAfter:(NSTimeInterval)delta
{
	id grabber = [self grab];
	[NSTimer scheduledTimerWithTimeInterval:delta target:grabber selector:@selector(invoke) userInfo:nil repeats:NO];
	return grabber;
}

- (id)nextRunloop
{
	return [self invokeAfter:0];
}

- (id)inBackground
{
	SPInvocationGrabber *grabber = [self grab];
	grabber.backgroundAfterForward = YES;
	return grabber;
}

- (id)onMainAsync:(BOOL)async
{
	SPInvocationGrabber *grabber = [self grab];
	grabber.onMainAfterForward = YES;
	grabber.waitUntilDone = !async;
	return grabber;
}

@end