/* |
File: AdderOperation.m |
Abstract: Adds an array of numbers (very slowly) and returns the result. |
Version: 1.1 |
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*/ |
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#import "AdderOperation.h" |
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@interface AdderOperation () |
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// only accessed by the operation thread |
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@property (atomic, strong, readwrite) NSNumberFormatter * formatter; |
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// read/write versions of public properties |
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@property (atomic, assign, readwrite) NSInteger total; |
@property (atomic, copy, readwrite) NSString * formattedTotal; |
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@end |
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@implementation AdderOperation |
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- (instancetype)initWithNumbers:(NSArray *)numbers |
{ |
// can be called on any thread |
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// 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. |
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assert(numbers != nil); |
self = [super init]; |
if (self != nil) { |
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// 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. |
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if ( [[NSUserDefaults standardUserDefaults] boolForKey:@"retainNotCopy"] ) { |
self->_numbers = numbers; |
} else { |
self->_numbers = [numbers copy]; |
} |
assert(self->_numbers != nil); |
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// 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. |
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@synchronized ([AdderOperation class]) { |
static NSUInteger sSequenceNumber; |
self->_sequenceNumber = sSequenceNumber; |
sSequenceNumber += 1; |
} |
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self->_interNumberDelay = 1.0; |
} |
return self; |
} |
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- (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. |
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assert(NO); |
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assert(numbers != nil); |
self = [super init]; |
if (self != nil) { |
self->_numbers = [numbers copy]; |
assert(self->_numbers != nil); |
} |
return self; |
} |
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- (void)dealloc |
{ |
// can be called on any thread |
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// 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. |
} |
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- (void)main |
{ |
NSUInteger numberCount; |
NSUInteger numberIndex; |
NSTimeInterval localInterNumberDelay; |
NSInteger localTotal; |
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// This method is called by a thread that's set up for us by the NSOperationQueue. |
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assert( ! [NSThread isMainThread] ); |
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// 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. |
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localInterNumberDelay = self.interNumberDelay; |
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// 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. |
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self.formatter = [[NSNumberFormatter alloc] init]; |
assert(self.formatter != nil); |
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[self.formatter setNumberStyle:NSNumberFormatterDecimalStyle]; |
[self.formatter setUsesGroupingSeparator:YES]; |
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// Do the heavy lifting (-: |
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localTotal = 0; |
numberCount = [self.numbers count]; |
for (numberIndex = 0; numberIndex < numberCount; numberIndex++) { |
NSNumber * numberObj; |
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// Check for cancellation. |
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if ([self isCancelled]) { |
break; |
} |
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// Sleep for the inter-number delay. This makes it easier to |
// test cancellation and so on. |
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[NSThread sleepForTimeInterval:localInterNumberDelay]; |
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// Do the maths (but they said there'd be no maths!). |
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numberObj = self.numbers[numberIndex]; |
assert([numberObj isKindOfClass:[NSNumber class]]); |
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localTotal += [numberObj integerValue]; |
} |
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// 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). |
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self.total = localTotal; |
self.formattedTotal = [self.formatter stringFromNumber:@(localTotal)]; |
} |
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- (void)main2 |
{ |
NSUInteger numberCount; |
NSUInteger numberIndex; |
NSInteger total; |
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// 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. |
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assert(NO); |
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// This method is called by a thread that's set up for us by the NSOperationQueue. |
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assert( ! [NSThread isMainThread] ); |
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// Do the heavy lifting (-: |
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total = 0; |
numberCount = [self.numbers count]; |
for (numberIndex = 0; numberIndex < numberCount; numberIndex++) { |
NSNumber * numberObj; |
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// Check for cancellation. |
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if ([self isCancelled]) { |
break; |
} |
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// Sleep for a second. This makes it easier to test cancellation |
// and so on. |
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[NSThread sleepForTimeInterval:1.0]; |
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// Do the maths (but they said there'd be no maths!). |
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numberObj = self.numbers[numberIndex]; |
assert([numberObj isKindOfClass:[NSNumber class]]); |
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total += [numberObj integerValue]; |
} |
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// 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). |
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self.formattedTotal = [self.formatter stringFromNumber:@(total)]; |
} |
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@end |