Keep your iOS network activity indicator under control, in a *thread-safe* way. Also shows a useful means of debugging it by logging backtraces for on/off calls.

gistfile1.m

//
//  KBNetworkActivityIndicator.h
//  Kobov3
//
//  Created by Jim Dovey on 10-03-21.
//  Copyright 2010 Kobo Inc. All rights reserved.
//

#import <Foundation/Foundation.h>


@interface KBNetworkActivityIndicator : NSObject

// these implement a counting shim over the OS's toggle on/off value
+ (void) showNetworkActivityIndicator;
+ (void) hideNetworkActivityIndicator;

@end

//
//  KBNetworkActivityIndicator.m
//  Kobov3
//
//  Created by Jim Dovey on 10-03-21.
//  Copyright 2010 Kobo Inc. All rights reserved.
//

#import "KBNetworkActivityIndicator.h"
#import <libkern/OSAtomic.h>
#import "DebuggingAids.h"

#ifndef LOG_ACTIVITY_TOGGLE_STATS
# define LOG_ACTIVITY_TOGGLE_STATS 0
#endif

NSMutableSet * gNetworkActivityStacks = nil;

@interface KBNetworkActivityIndicatorCounter : NSObject
{
    volatile NSInteger _counter;
}

+ (KBNetworkActivityIndicatorCounter *) sharedCounter;

- (void) increment;
- (void) decrement;
- (void)toggleNetworkIndicator:(NSNumber *)on;

@end

#pragma mark -

@implementation KBNetworkActivityIndicator
#if LOG_ACTIVITY_TOGGLE_STATS
+ (void) initialize
{
	if ( self != [KBNetworkActivityIndicator class] )
		return;
	
	gNetworkActivityStacks = [[NSMutableSet alloc] initWithCapacity: 16];
}
#endif
+ (void) showNetworkActivityIndicator
{
#if LOG_ACTIVITY_TOGGLE_STATS
	@synchronized(gNetworkActivityStacks)
	{
		[gNetworkActivityStacks addObject: BacktraceString(3)];
	}
#endif
    [[KBNetworkActivityIndicatorCounter sharedCounter] increment];
}

+ (void) hideNetworkActivityIndicator
{
#if LOG_ACTIVITY_TOGGLE_STATS
	@synchronized(gNetworkActivityStacks)
	{
		[gNetworkActivityStacks removeObject: BacktraceString(3)];
	}
#endif
    [[KBNetworkActivityIndicatorCounter sharedCounter] decrement];
}

@end

#pragma mark -

@implementation KBNetworkActivityIndicatorCounter

+ (KBNetworkActivityIndicatorCounter *) sharedCounter
{
    static KBNetworkActivityIndicatorCounter *  volatile __singleton = nil;
    if ( __singleton == nil )
    {
        KBNetworkActivityIndicatorCounter * tmp = [[KBNetworkActivityIndicatorCounter alloc] init];
        if ( OSAtomicCompareAndSwapPtrBarrier(nil, tmp, (void * volatile *)&__singleton) == false )
            [tmp release];
    }
    
    return ( __singleton );
}

- (void) increment
{
    if ( OSAtomicIncrement32(&_counter) > 0 )
        [self performSelectorOnMainThread:@selector(toggleNetworkIndicator:) withObject:[NSNumber numberWithBool:YES] waitUntilDone:NO];
}

- (void) decrement
{
    if ( OSAtomicDecrement32(&_counter) <= 0 )
	{
        [self performSelectorOnMainThread:@selector(toggleNetworkIndicator:) withObject:[NSNumber numberWithBool:NO] waitUntilDone:NO];
#if LOG_ACTIVITY_TOGGLE_STATS
		@synchronized(gNetworkActivityStacks)
		{
			[gNetworkActivityStacks removeAllObjects];
		}
#endif
	}
}

- (void)toggleNetworkIndicator:(NSNumber *)on {
	[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:[on boolValue]];
}


@end