Tell about block and GCD
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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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