withContext

Calls the specified suspending block with a given coroutine context, suspends until it completes, and returns the result.

The resulting context for the block is derived by merging the current coroutineContext with the specified context using coroutineContext + context (see CoroutineContext.plus). This suspending function is cancellable. It immediately checks for cancellation of the resulting context and throws CancellationException if it is not active.

Calls to withContext whose context argument provides a CoroutineDispatcher that is different from the current one, by necessity, perform additional dispatches: the block can not be executed immediately and needs to be dispatched for execution on the passed CoroutineDispatcher, and then when the block completes, the execution has to shift back to the original dispatcher.

Note that the result of withContext invocation is dispatched into the original context in a cancellable way with a prompt cancellation guarantee, which means that if the original coroutineContext in which withContext was invoked is cancelled by the time its dispatcher starts to execute the code, it discards the result of withContext and throws CancellationException.

The cancellation behaviour described above is enabled if and only if the dispatcher is being changed. For example, when using withContext(NonCancellable) { ... } there is no change in dispatcher and this call will not be cancelled neither on entry to the block inside withContext nor on exit from it.