AdderOperation.h

/*
    File:       AdderOperation.h
 
    Contains:   Adds an array of numbers (very slowly) and returns the result.
 
    Written by: DTS
 
    Copyright:  Copyright (c) 2010 Apple Inc. All Rights Reserved.
 
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*/
 
#import <Foundation/Foundation.h>
 
/*
    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.
    
    The data used by the operation are made thread safe in a number of different ways:
    
      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.
 
      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.
 
      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.
    
      o Some properties, like formatter, are private to the operation and are only ever 
        accessed by the thread running the operation.
        
      o Global data, like sSequenceNumber, is protected by a lock.
    
    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.
*/
 
@interface AdderOperation : NSOperation
{
    NSArray *           _numbers;
    NSUInteger          _sequenceNumber;
    NSTimeInterval      _interNumberDelay;
    NSInteger           _total;
    NSNumberFormatter * _formatter;
    NSString *          _formattedTotal;
}
 
- (id)initWithNumbers:(NSArray *)numbers;
 
// set up by the init method that can't be changed
 
@property (copy,   readonly ) NSArray *         numbers;                // of NSNumber
@property (assign, readonly ) NSUInteger        sequenceNumber;
 
// must be configured before the operation is started
 
@property (assign, readwrite) NSTimeInterval    interNumberDelay;       // defaults to 1.0
 
// only meaningful after the operation is finished
 
@property (assign, readonly ) NSInteger         total;
@property (copy,   readonly ) NSString *        formattedTotal;
 
@end