NSOperation, NSOperationQueue, Quality Of Service, GCD, Concurent, NSBlockOperation, NSInvocationOperation

1. NSOperation
Павел Альбицкий
p.albitsky@gmail.com

2. Classes
• NSOperationQueue
• NSOperation
– NSOperation subclass
– NSBlockOperation
– NSInvocationOperation

3. NSOperationQueue
NSOperation *networkingOperation = ...
NSOperation *resizingOperation = ...
resizingOperation addDependency:networkingOperation];
NSOperationQueue *operationQueue = [NSOperationQueue new];
[operationQueue addOperation:networkingOperation];
[operationQueue addOperation:resizingOperation];

4. NSBlockOperation

5. NSBlockOperation *block1 = [NSBlockOperation blockOperationWithBlock:^{
for (int i = 0; i < kIntervalCount; ++i) {
[NSThread sleepForTimeInterval:0.5];
NSLog(@"block1: %d, (%@)", i, [NSThread currentThread]);
}
}];
NSBlockOperation *block2 = [NSBlockOperation blockOperationWithBlock:^{
for (int i = 0; i < kIntervalCount; ++i) {
[NSThread sleepForTimeInterval:0.2];
NSLog(@"block2: %d, (%@)", i, [NSThread currentThread]);
}
}];
NSOperationQueue *queue = [NSOperationQueue new];
[queue addOperation:block1];
[queue addOperation:block2];
NSLog(@"Here we go!");
2016-02-28 19:14:53.027 Here we go!
2016-02-28 19:14:53.237 block2: 0, (<NSThread: 0x610000067440>{number = 2, name = (null)})
2016-02-28 19:14:53.437 block2: 1, (<NSThread: 0x610000067440>{number = 2, name = (null)})
2016-02-28 19:14:53.528 block1: 0, (<NSThread: 0x610000069f40>{number = 3, name = (null)})
2016-02-28 19:14:53.637 block2: 2, (<NSThread: 0x610000067440>{number = 2, name = (null)})
2016-02-28 19:14:53.838 block2: 3, (<NSThread: 0x610000067440>{number = 2, name = (null)})
2016-02-28 19:14:54.029 block1: 1, (<NSThread: 0x610000069f40>{number = 3, name = (null)})
2016-02-28 19:14:54.040 block2: 4, (<NSThread: 0x610000067440>{number = 2, name = (null)})
2016-02-28 19:14:54.530 block1: 2, (<NSThread: 0x610000069f40>{number = 3, name = (null)})
2016-02-28 19:14:55.030 block1: 3, (<NSThread: 0x610000069f40>{number = 3, name = (null)})
2016-02-28 19:14:55.532 block1: 4, (<NSThread: 0x610000069f40>{number = 3, name = (null)})

6. NSBlockOperation addExecutionBlock
NSBlockOperation *block1 = [NSBlockOperation blockOperationWithBlock:^{
for (int i = 0; i < kIntervalCount; ++i) {
[NSThread sleepForTimeInterval:0.5];
NSLog(@"block1_1: %d", i);
}
}];
[block1 addExecutionBlock:^{
for (int i = 0; i < kIntervalCount; ++i) {
[NSThread sleepForTimeInterval:0.5];
NSLog(@"block1_2: %d", i);
}
}];
NSBlockOperation *block2 = [NSBlockOperation blockOperationWithBlock:^{
for (int i = 0; i < kIntervalCount; ++i) {
[NSThread sleepForTimeInterval:0.2];
NSLog(@"block2: %d", i);
}
}];
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[queue addOperation:block1];
[queue addOperation:block2];
block2: 0
block2: 1
block1_2: 0
block1_1: 0
block2: 2
block2: 3
block1_2: 1
block1_1: 1
block2: 4
block1_2: 2
block1_1: 2
block1_1: 3
block1_2: 3
block1_1: 4
block1_2: 4

7. __block
int count1 = 7;
NSBlockOperation *block1 = [NSBlockOperation blockOperationWithBlock:^{
for (int i = 0; i < count1; ++i) {
[NSThread sleepForTimeInterval:0.5];
NSLog(@"block1: %d", i);
}
}];
__block int count2 = 3;
NSBlockOperation *block2 = [NSBlockOperation blockOperationWithBlock:^{
count2 = 7;
for (int i = 0; i < count2; ++i) {
[NSThread sleepForTimeInterval:0.2];
NSLog(@"block2: %d", i);
}
}];
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[queue addOperations:@[block1, block2] waitUntilFinished:YES];
NSLog(@"count2: %d", count2);
block2: 0
block2: 1
block1_1: 0
block2: 2
block2: 3
block1_1: 1
block2: 4
block2: 5
block2: 6
block1_1: 2
block1_1: 3
block1_1: 4
block1_1: 5
block1_1: 6
count2: 7

8. NSOperation start
NSBlockOperation *block1 = [[NSBlockOperation alloc] init];
[block1 addExecutionBlock:^{
for (int i = 0; i < kIntervalCount; ++i) {
[NSThread sleepForTimeInterval:0.5];
NSLog(@"block1: %d (%@)", i, [NSThread currentThread]);
}
}];
NSBlockOperation *block2 = [NSBlockOperation blockOperationWithBlock:^{
for (int i = 0; i < kIntervalCount; ++i) {
[NSThread sleepForTimeInterval:0.5];
NSLog(@"block2: %d (%@)", i, [NSThread currentThread]);
}
}];
[block1 start];
[block2 start];
NSLog(@“START");
block1: 0 (<NSThread: 0x600000061740>{number = 1, name = main})
block1: 1 (<NSThread: 0x600000061740>{number = 1, name = main})
block1: 2 (<NSThread: 0x600000061740>{number = 1, name = main})
block2: 0 (<NSThread: 0x600000061740>{number = 1, name = main})
block2: 1 (<NSThread: 0x600000061740>{number = 1, name = main})
block2: 2 (<NSThread: 0x600000061740>{number = 1, name = main})
START

9. NSInvocationOperation
- (void)runWithCount:(NSNumber *)count {
for (int i = 0; i < [count intValue]; ++i) {
[NSThread sleepForTimeInterval:0.5];
NSLog(@"operation: %d", i);
}
}
- (void)example5 {
NSInvocationOperation *invOp;
invOp = [[NSInvocationOperation alloc] initWithTarget:self
selector:@selector(runWithCount:)
object:@(3)];
[invOp start];
}

10. NSInvocationOperation result
- (NSNumber *)sum {
int result;
for (int i = 0; i < kIntervalCount; ++i) {
result += i;
NSLog(@"result: %d", result);
}
return @(result);
}
- (void)example6 {
NSInvocationOperation *invOp;
invOp = [[NSInvocationOperation alloc] initWithTarget:self
selector:@selector(sum)
object:nil];
[invOp start];
NSNumber *result = [invOp result];
}

11. NSOperation subclass

12. @interface CustomOperation : NSOperation
- (instancetype)initWithString:(NSString *)param;
@property(nonatomic, strong) NSString *param;
@end
@implementation CustomOperation
- (instancetype)initWithString:(NSString *)param {
self = [super init];
if (self) {
self.param = param;
}
return self;
}
- (void)main {
for (int i = 0; i < 5; ++i) {
[NSThread sleepForTimeInterval:.5];
NSLog(@"%@: %d", self.param, i);
}
}
@end

13. CustomOperation *op1 = [[CustomOperation alloc] initWithString:@"op1"];
CustomOperation *op2 = [[CustomOperation alloc] initWithString:@"op2"];
NSOperationQueue *queue = [NSOperationQueue new];
[queue addOperation:op2];
[queue addOperation:op1];
op1: 0
op2: 0
op2: 1
op1: 1
op1: 2
op2: 2
op2: 3
op1: 3
op1: 4
op2: 4
CustomOperation

14. Configuring for concurrent execution
@interface CustomOperation () {
BOOL executing;
BOOL finished;
}
- (void)completeOperation;
@end
@implementation CustomOperation
- (instancetype)initWithString:(NSString *)param {
self = [super init];
if (self) {
executing = NO;
finished = NO;
self.param = param;
}
return self;
}
- (BOOL)isConcurrent {
return YES;
}
- (BOOL)isExecuting {
return executing;
}
- (BOOL)isFinished {
return finished;
}
- (void)start {
if ([self isCancelled]) {
[self willChangeValueForKey:@"isFinished"];
finished = YES;
[self didChangeValueForKey:@"isFinished"];
return;
}
[self willChangeValueForKey:@"isExecuting"];
[NSThread detachNewThreadSelector:@selector(main)
toTarget:self
withObject:nil];
executing = YES;
[self didChangeValueForKey:@"isExecuting"];
}
- (void)main {
@try {
// Do some work
[self completeOperation];
}
@catch (NSException *exception) {}
}
- (void)completeOperation {
[self willChangeValueForKey:@"isFinished"];
[self willChangeValueForKey:@"isExecuting"];
executing = NO;
finished = YES;
[self didChangeValueForKey:@"isExecuting"];
[self didChangeValueForKey:@"isFinished"];
}

15. State
ready → executing → finished
• ready
The isReady property contains the value true when the operation is ready to
execute now or false if there are still unfinished operations on which it is
dependent.
• executing
The isExecuting property must report the value true if the operation is working
on its task or false if it is not.
• finished
The isFinished key path lets clients know that an operation finished its task
successfully or was cancelled and is exiting.
• cancelled
The isCancelled key path lets clients know that the cancellation of an
operation was requested.

16. Cancelation
Once you add an operation to a queue, the operation is out
of your hands. The queue takes over and handles the
scheduling of that task. However, if you decide later that
you do not want to execute the operation after all—
because the user pressed a cancel button in a progress
panel or quit the application, for example—you can cancel
the operation to prevent it from consuming CPU time
needlessly.
• [NSOperation cancel]
• [NSOperationQueue cancellAllOperations]

17. NSOperationQueuePriority
typedef NS_ENUM(NSInteger, NSOperationQueuePriority) {
NSOperationQueuePriorityVeryLow = -8L,
NSOperationQueuePriorityLow = -4L,
NSOperationQueuePriorityNormal = 0,
NSOperationQueuePriorityHigh = 4,
NSOperationQueuePriorityVeryHigh = 8
};
NSOperation *op = ...
op.queuePriority = NSOperationQueuePriorityHigh;

18. NSQualityOfService
typedef NS_ENUM(NSInteger, NSQualityOfService) {
NSQualityOfServiceUserInteractive = 0x21,
NSQualityOfServiceUserInitiated = 0x19,
NSQualityOfServiceUtility = 0x11,
NSQualityOfServiceBackground = 0x09,
NSQualityOfServiceDefault = -1
} NS_ENUM_AVAILABLE(10_10, 8_0);
NSOperation *op = ...
op.qualityOfService = NSOperationQualityOfServiceUtility;
// threadPriority - deprecated

19. NSQualityOfService
• UserInteractive
Used for work directly involved in providing an interactive UI. For example,
processing control events or drawing to the screen.
• UserInitiated
Used for performing work that has been explicitly requested by the user, and for
which results must be immediately presented in order to allow for further user
interaction. For example, loading an email after a user has selected it in a message
list.
• Utility
Used for performing work which the user is unlikely to be immediately waiting for
the results. This work may have been requested by the user or initiated
automatically, and often operates at user-visible timescales using a non-modal
progress indicator. For example, periodic content updates or bulk file operations,
such as media import.
• Background
Used for work that is not user initiated or visible. In general, a user is unaware
that this work is even happening. For example, pre-fetching content, search
indexing, backups, or syncing of data with external systems.
• Default
Indicates no explicit quality of service information. Whenever possible, an
appropriate quality of service is determined from available sources.

20. completionBlock
CustomOperation *op = [[CustomOperation alloc] initWithString:@"op1"];
op.completionBlock = ^{
NSLog(@"completed: %@", [NSThread currentThread]);
};
[op start];
NSLog(@"isConcurrent: %d", op.isConcurrent);
isConcurrent: 1
op1: 0 (<NSThread: 0x608000068680>{number = 2, name = (null)})
op1: 1 (<NSThread: 0x608000068680>{number = 2, name = (null)})
op1: 2 (<NSThread: 0x608000068680>{number = 2, name = (null)})
op1: 3 (<NSThread: 0x608000068680>{number = 2, name = (null)})
op1: 4 (<NSThread: 0x608000068680>{number = 2, name = (null)})
completed: <NSThread: 0x618000076600>{number = 3, name = (null)}

21. NSOperationQueue
• Serial
queue.maxConcurrentOperationCount = 1;
• Concurrent
queue.maxConcurrentOperationCount = 6;
static const NSInteger
NSOperationQueueDefaultMaxConcurrentOperationCount = -1;

22. NSOperationQueue
@interface NSOperationQueue : NSObject
- (void)addOperation:(NSOperation *)op;
- (void)addOperations:(NSArray<NSOperation *> *)ops waitUntilFinished:(BOOL)wait;
- (void)addOperationWithBlock:(void (^)(void))block;
@property (readonly, copy) NSArray<__kindof NSOperation *> *operations;
@property (readonly) NSUInteger operationCount;
- (void)waitUntilAllOperationsAreFinished;
@property (getter=isSuspended) BOOL suspended;
@property (nullable, copy) NSString *name;
@property NSQualityOfService qualityOfService;
@end

23. KVO-Compliant Properties
• isCancelled - read-only
• isAsynchronous - read-only
• isExecuting - read-only
• isFinished - read-only
• isReady - read-only
• dependencies - read-only
• queuePriority - readable and writable
• completionBlock - readable and writable

24. NSOperation VS GCD
Grand Central Dispatch
• Delayed calls
• Performance
• Low-level
• Functional programming
NSOperation
• Dependency
• Priority queue and QoS
• Cancelation
• State
• Object oriented programming

25. Спасибо за внимание!
Павел Альбицкий
p.albitsky@gmail.com