Hello friends i want to know What mechanisms does iOS provide to support multi-threading?

For the purpose of multithreading in IOS or OSX you use an async block called GCD(grandcentral dispatch). Basically what this does is allow you to run intensive task in the background without blocking the UI. If you want to use real threads in your application(i discourage this as GCD is adequate for most uses), you can use pthreads or any other c/c++ thread library.