/* |
File: AdderOperation.h |
Abstract: Adds an array of numbers (very slowly) and returns the result. |
Version: 1.1 |
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*/ |
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@import Foundation; |
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/* |
AdderOperation is an example of using NSOperation to do asynchronous processing |
in a sane fashion. It follows the thread confinement model. That is, you |
initialise the operation with an array of numbers to operate on, and it adds up |
those numbers and vends the result through read-only properties. |
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The data used by the operation are made thread safe in a number of different ways: |
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o Some properties (for example, numbers) are set up at initialisation time and |
can't be changed. These are immutable, thus can be safely shared between threads. |
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o Some properties must be set before the operation is queued and should be immutable |
after that. Again, these are thread safe because there's no possibility of two |
threads trying to mutate the same value at the same time. interNumberDelay |
is an example of this. |
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o Some properties are set by the operation but shouldn't be read by the client |
until the operation is finished. total and formattedTotal are examples of this. |
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o Some properties, like formatter, are private to the operation and are only ever |
accessed by the thread running the operation. |
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o Global data, like sSequenceNumber, is protected by a lock. |
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It's obvious that adding a few numbers is going to happen very quickly, so we |
artifically slow things down by sleeping for an extended period of time between |
additions. This delay is controlled by the interNumberDelay, which defaults to |
one second. |
*/ |
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@interface AdderOperation : NSOperation |
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- (instancetype)initWithNumbers:(NSArray *)numbers; |
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// set up by the init method that can't be changed |
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@property (atomic, copy, readonly ) NSArray * numbers; // of NSNumber |
@property (atomic, assign, readonly ) NSUInteger sequenceNumber; |
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// must be configured before the operation is started |
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@property (atomic, assign, readwrite) NSTimeInterval interNumberDelay; // defaults to 1.0 |
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// only meaningful after the operation is finished |
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@property (atomic, assign, readonly ) NSInteger total; |
@property (atomic, copy, readonly ) NSString * formattedTotal; |
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@end |