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![Singleton
(for initialisation)
• dispatch_once
static MyObject *myObject = nil;
+(MyObject *)sharedInstance
{
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
if(!myObject){
myObject = [[myObject alloc] init];
}
return myObject;
}](https://image.slidesharecdn.com/gcdandconcurrencyprogramming-140110122735-phpapp02/75/Gcd-and-concurrency-programming-21-2048.jpg)
![Lockless Exclusion
• Serial queue are thread safe inside
-(void)accessSharedVariableAsync:(void(^)(id sharedVariable))block{
// myQueue must be a serial queue
dispatch_sync(myQueue, ^{
block([self sharedVariable]);
});
}](https://image.slidesharecdn.com/gcdandconcurrencyprogramming-140110122735-phpapp02/75/Gcd-and-concurrency-programming-22-2048.jpg)
![Singleton
(for initialisation)
• dispatch_once
static MyObject *myObject = nil;
+(MyObject *)sharedInstance
{
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
if(!myObject){
myObject = [[myObject alloc] init];
}
return myObject;
}](https://crownmelresort.com/image.slidesharecdn.com/gcdandconcurrencyprogramming-140110122735-phpapp02/75/Gcd-and-concurrency-programming-21-2048.jpg)
![Lockless Exclusion
• Serial queue are thread safe inside
-(void)accessSharedVariableAsync:(void(^)(id sharedVariable))block{
// myQueue must be a serial queue
dispatch_sync(myQueue, ^{
block([self sharedVariable]);
});
}](https://crownmelresort.com/image.slidesharecdn.com/gcdandconcurrencyprogramming-140110122735-phpapp02/75/Gcd-and-concurrency-programming-22-2048.jpg)
Uploaded byLi Lin
Gcd and concurrency programming
This document discusses concurrency programming and Grand Central Dispatch (GCD) in iOS. It covers threads and multi-threading, NSThread, NSObject, NSOperation, run loops, and GCD. GCD uses dispatch queues and blocks to simplify concurrent programming compared to directly using threads. It manages pools of threads to dispatch tasks asynchronously or synchronously. Serial dispatch queues are thread-safe. Common GCD functions include dispatch_async, dispatch_sync, dispatch_once, and dispatch_group_notify.
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Gcd and concurrency programming
- 1.
- 3. GCD • Sync vsAsync
- 4. Concurrency Programming • NSThread • NSObject •NSOperation • Run Loop • GCD
- 5. Thread • What isthread • What is multi-thread
- 6. Why Multithread ona Single Core? • Keep UI responsive.
- 7.
- 8. NSThread • Main threadand other threads • detachNewThreadSelector:toTarget:with Object: • Pro: light-weight (for code), directly control • Cons: Life cycle issue, race condition issue (lock, retain cycle)
- 9.
- 10. What to useThread? • Not in most cases
- 11.
- 12. NSOperation • Pros: • Adddependency • setMaxConcurrentOperationCount • re-use • Cancel, Suspend • Priority • suspend • compatible with KVO
- 13.
- 14. GCD • Less memorypenalty • Less configure • Less manage • Simplifies the code
- 15. GCD • GCD的核⼼心是dispatch queues •它管理pools of threads • 管理queues，⽽而⾮非直接管理threads It was first released with Mac OS X 10.6, and is also available with iOS 4 and above.
- 16. Thread pools • Threadpools. • Grab a thread from the pool and dispatch the task to it • Queue the task and wait for a thread to become available.
- 17. Blocks void (^aBlock)(int) =^(int z) {! ! NSLog(@“log”);! ! };! ! • Like a function pointer, except it also stores the context the block was created in. • Beware of retain cycles
- 18. GCD • Use queuesof blocks rather than threads
- 19. Dispatch Queue • MainQueue • Global Queue • Serial Queue
- 20. Dispatch async, sync •dispatch_async • dispatch_sync
- 21. Singleton (for initialisation) •dispatch_once static MyObject *myObject = nil; +(MyObject *)sharedInstance { static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ if(!myObject){ myObject = [[myObject alloc] init]; } return myObject; }
- 22. Lockless Exclusion • Serialqueue are thread safe inside -(void)accessSharedVariableAsync:(void(^)(id sharedVariable))block{ // myQueue must be a serial queue dispatch_sync(myQueue, ^{ block([self sharedVariable]); }); }
- 23.
- 24. Dispatch • dispatch_apply • dispatch_barrier_async •dispatch_source_create
- 25.
- 27.
- 28. Best Sources • HowTo Use NSOperations and NSOperationQueues http:// www.raywenderlich.com/19788/how-touse-nsoperations-and-nsoperationqueues
- 29. • NSOperation vsGrand Central Dispatch • http://stackoverflow.com/questions/10373331/ nsoperation-vs-grand-central-dispatch • Grand Central Dispatch Design Patterns by Robert Brown • http://www.slideshare.net/robby_brown/grandcentral-dispatch-design-patterns