/*

     File: AdderOperation.m

 Abstract: Adds an array of numbers (very slowly) and returns the result.

  Version: 1.1

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#import "AdderOperation.h"

@interface AdderOperation ()

// only accessed by the operation thread

@property (atomic, strong, readwrite) NSNumberFormatter *   formatter;

// read/write versions of public properties

@property (atomic, assign, readwrite) NSInteger             total;

@property (atomic, copy,   readwrite) NSString *            formattedTotal;

@end

@implementation AdderOperation

- (instancetype)initWithNumbers:(NSArray *)numbers

{

    // can be called on any thread

    // An NSOperation's init method does not have to be thread safe; it's relatively 

    // easy to enforce the requirement that the init method is only called by the 

    // main thread, or just one single thread.  However, in this case it's easy to 

    // make the init method thread safe, so we do that.

    assert(numbers != nil);

    self = [super init];

    if (self != nil) {

        // Initialise our numbers property by taking a copy of the incoming 

        // numbers array.  Note that we use a copy here.  If you just retain 

        // the incoming value then the program will crash because our client 

        // passes us an NSMutableArray (which is type compatible with NSArray) 

        // and can then mutate it behind our back.

        if ( [[NSUserDefaults standardUserDefaults] boolForKey:@"retainNotCopy"] ) {

            self->_numbers = numbers;

        } else {

            self->_numbers = [numbers copy];

        }

        assert(self->_numbers != nil);

        // Set up our sequenceNumber property.  Note that, because we can be called 

        // from any thread, we have to use a lock to protect sSequenceNumber (that 

        // is, to guarantee that each operation gets a unique sequence number).  

        // In this case locking isn't a problem because we do very little within 

        // that lock; there's no possibility of deadlock, and the chances of lock 

        // contention are slight.

        @synchronized ([AdderOperation class]) {

            static NSUInteger sSequenceNumber;

            self->_sequenceNumber = sSequenceNumber;

            sSequenceNumber += 1;

        }

        self->_interNumberDelay = 1.0;

    }

    return self;

}

- (instancetype)initWithNumbers2:(NSArray *)numbers

{

    // IMPORTANT: This is method is not actually used.  It is here because it's a code 

    // snippet in the technote, and i wanted to make sure it compiles.

    assert(NO);

    assert(numbers != nil);

    self = [super init];

    if (self != nil) {

        self->_numbers = [numbers copy];

        assert(self->_numbers != nil);

    }

    return self;

}

- (void)dealloc

{

    // can be called on any thread

    // Note that we can safely release our properties here, even properties like 

    // formatter, which are meant to only be accessed by the operation's thread. 

    // That's because -retain and -release are always fully thread safe, even in 

    // situations where other methods on an object are not.

    // 

    // Of course, the actual work to release the objects is now done by ARC.

}

- (void)main

{

    NSUInteger      numberCount;

    NSUInteger      numberIndex;

    NSTimeInterval  localInterNumberDelay;

    NSInteger       localTotal;

    // This method is called by a thread that's set up for us by the NSOperationQueue.

    assert( ! [NSThread isMainThread] );

    // We latch interNumberDelay at this point so that, if the client changes 

    // it after they've queued the operation (something they shouldn't be doing, 

    // but hey, we're cautious), we always see a consistent value.

    localInterNumberDelay = self.interNumberDelay;

    // Set up the formatter.  This is a private property that's only accessed by 

    // the operation thread, so we don't have to worry about synchronising access to it.

    self.formatter = [[NSNumberFormatter alloc] init];

    assert(self.formatter != nil);

    [self.formatter setNumberStyle:NSNumberFormatterDecimalStyle];

    [self.formatter setUsesGroupingSeparator:YES];

    // Do the heavy lifting (-:

    localTotal = 0;

    numberCount = [self.numbers count];

    for (numberIndex = 0; numberIndex < numberCount; numberIndex++) {

        NSNumber *  numberObj;

        // Check for cancellation.

        if ([self isCancelled]) {

            break;

        }

        // Sleep for the inter-number delay.  This makes it easier to 

        // test cancellation and so on.

        [NSThread sleepForTimeInterval:localInterNumberDelay];

        // Do the maths (but they said there'd be no maths!).

        numberObj = self.numbers[numberIndex];

        assert([numberObj isKindOfClass:[NSNumber class]]);

        localTotal += [numberObj integerValue];

    }

    // Set our output properties base on the value we calculated.  Our client 

    // shouldn't look at these until -isFinished goes to YES (which happens when 

    // we return from this method).

    self.total = localTotal;

    self.formattedTotal = [self.formatter stringFromNumber:@(localTotal)];

}

- (void)main2

{

    NSUInteger      numberCount;

    NSUInteger      numberIndex;

    NSInteger       total;

    // IMPORTANT: This is method is not actually used.  It is here because it's a code 

    // snippet in the technote, and i wanted to make sure it compiles.

    assert(NO);

    // This method is called by a thread that's set up for us by the NSOperationQueue.

    assert( ! [NSThread isMainThread] );

    // Do the heavy lifting (-:

    total = 0;

    numberCount = [self.numbers count];

    for (numberIndex = 0; numberIndex < numberCount; numberIndex++) {

        NSNumber *  numberObj;

        // Check for cancellation.

        if ([self isCancelled]) {

            break;

        }

        // Sleep for a second.  This makes it easier to test cancellation 

        // and so on.

        [NSThread sleepForTimeInterval:1.0];

        // Do the maths (but they said there'd be no maths!).

        numberObj = self.numbers[numberIndex];

        assert([numberObj isKindOfClass:[NSNumber class]]);

        total += [numberObj integerValue];

    }

    // Set our output properties base on the value we calculated.  Our client 

    // shouldn't look at these until -isFinished goes to YES (which happens when 

    // we return from this method).

    self.formattedTotal = [self.formatter stringFromNumber:@(total)];

}

@end