NTBFifoOperationQueue.h

//
//  NTBFifoOperationQueue.h
//  Timeline
//
//  Created by Nigel Barber on 19/11/2013.
//  Copyright (c) 2013 Nigel Barber. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface NTBFifoOperationQueue : NSOperationQueue

@end

NTBFifoOperationQueue.m

//
//  NTBFifoOperationQueue.m
//  Timeline
//
//  Created by Nigel Barber on 19/11/2013.
//  Copyright (c) 2013 Nigel Barber. All rights reserved.
//

#import "NTBFifoOperationQueue.h"

@interface NTBFifoOperationQueue ()

@property( nonatomic, retain ) NSMutableArray *fifo;

@end


@implementation NTBFifoOperationQueue


-(id)init
{
    self = [ super init ];
    
    if( self )
    {
        self.fifo = [ NSMutableArray new ];
    }
    
    return self;
}






-(void)addOperation:(NSOperation *)operation
{
    NSMutableArray *fifo = self.fifo;
    
    void (^moveToQueue)(void) = ^void(void)
    {
        @synchronized( self )
        {
            if( fifo.count )
            {
                NSOperation *operationToQueue = fifo[ 0 ];
                [ super addOperation:operationToQueue ];
                
                [ fifo removeObjectAtIndex:0 ];
            }
        }
    };
    
    
    if( self.operationCount < self.maxConcurrentOperationCount )
    {
        [ super addOperation:operation ];
    }
    else
    {
        [ self.operations enumerateObjectsUsingBlock:^( NSOperation *operationToCancel, NSUInteger idx, BOOL *stop )
         {
             if( ! operationToCancel.isCancelled )
             {
                 [ operationToCancel setCompletionBlock:moveToQueue ];
                 
                 [ operationToCancel cancel ];
                 
                 *stop = YES;
             }
         }];
        
        @synchronized( self )
        {
            if( fifo.count >= self.maxConcurrentOperationCount )
            {
                [ fifo removeObjectAtIndex:0 ];
            }
            
            [ fifo addObject:operation ];
        }
    }
}


@end