Tell about block and GCD

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Tell about block and GCD..

Answer / babu

Block: Block objects are a C-level syntactic and runtime feature. Blocks are particularly useful as a callback because the block carries both the code to be executed on callback (on completion handler block) and the data needed during that execution.

GCD: GCD (Grand Central Dispatch) provides and manages FIFO queues to which your application can submit tasks in the form of block objects. Blocks submitted to dispatch queues are executed on a set of threads completely managed by the system. No guarantee is made as to the thread on which a task executes. GCD allows three kinds of queues:

Main: tasks execute serially on your application’s main thread

Concurrent: tasks are dequeued in FIFO order, but run concurrently and can finish in any order.

Serial: tasks execute one at a time in FIFO order

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