runBlocking runs new coroutine and blocks current thread interruptibly until its completion. This function should not be used from coroutine. It is designed to bridge regular blocking code to libraries that are written in suspending style, to be used in main functions and in tests.

// line 1
runBlocking {
   // line 2
   launch(coroutineDispatcher) {
      // line 3
   }
   // line 4
}
// line 5
someFunction()

In case of using runBlocking lines of code will be executed in the next order:

line 1
line 2
line 4
line 3
line 5 // this line will be executed after coroutine is finished

Global scope is used to launch top-level coroutines which are operating on the whole application lifetime and are not cancelled prematurely. Another use of the global scope is operators running in Dispatchers.Unconfined, which don't have any job associated with them. Application code usually should use application-defined CoroutineScope, using async or launch on the instance of GlobalScope is highly discouraged.

// line 1
GlobalScope.launch(coroutineDispatcher) {
   // line 2
}
// line 3
someFunction()

In case of using GlobalScope.launch lines of code will be executed in the next order:

line 1
line 3
line 2

Thus runBlocking blocks current thread until its completion, GlobalScope.launch doesn't.