IOS Multithreading Knowledge Summary GCD Basics

Last Update:2015-09-19 Source: Internet

Author: User

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Basic concepts of the Process:1. Each process is an application, and there is a separate memory space, in general, a process exists in one application, but there are multiple processes. 2. Threads in the same process share in-memory resources in Memory. the basic concept of multi-threading:1. Each program has a main thread, which is created when the program starts (call the main function to Start)2. The main Thread's life cycle is bound to other applications, and when the program exits, the main thread stops. 3. Multithreading technology indicates that an application has multiple threads, and using multithreading can improve the efficiency of CPU usage and prevent thread blocking4. Any task that is likely to block the main thread does not execute in the main thread (for example, network Access) thread usage is not uncontrolled:the stack size of the main thread in 1.iOS is 1M2. Starting with a second thread is 512KB3. These values cannot be changed by the compiler switch or the thread API functiononly the main thread has the ability to directly modify the Ui. three types of multithreading technology for Ios:1.NSThread Each Nsthread object corresponds to one thread, lightweight. 2nsoperation/nsoperationqueue object-oriented Threading Technology. 3.gcd--grand Central Dispatch is a c-based framework that makes full use of multicore and is also an official recommended multithreaded technology by Apple. Comparison of three multithreading techniques:1.NSThread: pros: Nsthread is lighter than the other two and is easy to use. cons: you need to manage your Thread's lifecycle, thread synchronization, locking, sleep, and wake up. Thread synchronization has a certain overhead in locking data 2.NSOpertion: no need to care about thread management, data synchronization, You can focus on what you need to do. Nsopertion is Object-oriented. 3.GCD:GCD is a multi-core programming solution developed by Apple. Ios4.0+ can be used as an alternative to Nsthread,nsoperation's efficient and powerful technology, GCD is based on the C languageGCD is Apple's solution for multi-core parallel computingGCD will automatically take advantage of more CPU cores (such as dual-core, quad-core)GCD automatically manages the life cycle of threads (create threads, schedule tasks, Destroy Threads)programmers just need to tell gcd what tasks they want to perform, without having to write any thread management code there are two core concepts in Gcd:(1) task: What action to perform(2) queue: Storage Task queue: 1. Serial Queue: The task that is added to the queue is a single execution 2. Parallel (outgoing) queue: Tasks added to the queue are multiple simultaneous executions 3. Home Column: The tasks inside are performed on the main thread, which can be understood as the main queue is a serial queue 4. Global queue: parallel (outgoing) queue synchronous, asynchronous:1, synchronization: need to wait for the later task, will not open a new thread, will be directly using the current thread 2, async: do not need to wait for the later task, will open a new thread(1) perform the task Dispatch_sync (dispatch_queue_t queue, dispatch_block_t Block) in a synchronous manner;Parameter description:queue: queuesBlock: Task (2) Execute the task Dispatch_async asynchronously (dispatch_queue_t queue, dispatch_block_t block); 3. The difference between synchronous and asynchronousSynchronization: executing in the current threadAsync: executing in another threaddescription:The synchronization function does not have the ability to open threads, no matter what queue does not open the thread, the asynchronous function has the ability to open threads, open a few threads by the queue (the serial queue will only open a new thread, the concurrent queue will open multiple threads). Synchronization functions(1) Concurrent Queue: No thread(2) Serial Queue: No threadAsynchronous functions(1) Concurrent queue: can open n threads(2) serial queue: Open 1 threadsIn all functions, the names of functions, such as create\copy\new\retain, need to be release when the data is not Needed.the GCD data type does not need to be release in the Arc Environment. the data type of the CF (core Foundation) is still required for release in the Arc Environment. asynchronous functions have the ability to thread, but not necessarily the thread IOS Multithreading Knowledge Summary GCD Basics

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IOS Multithreading Knowledge Summary GCD Basics

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