Lectures

We break down the difference between suspension and thread blocking, why JVM file operations are most often blocking, and how this directly affects the choice of coroutine context: where to use Dispatchers.Default, and where to use Dispatchers.IO. Using examples with withContext, async, and the blocking Thread.sleep, we show how “accidental I/O on Default” can slow down CPU tasks, and how the discipline “I/O separately, CPU separately” simplifies architecture.

We break down how, in Kotlin coroutines, to properly separate blocking file I/O from CPU logic: where to put withContext( Dispatchers.IO), how to safely exit via return@withContext, why you need use { ... } to close resources, and why a “wide” IO context turns into a trash bin for responsibility. At the end: hands-on practice for the File Organizer utilities and a list of common mistakes.

We break down a practical pattern for concurrent processing of many files in Kotlin coroutines: how launch and async differ, how to batch-collect results with awaitAll(), why it’s dangerous to “start a thousand tasks at once”, how to limit concurrency with Dispatchers.IO.limitedParallelism(n), where the boundary between I/O and CPU lies, and how to integrate this into structured concurrency via coroutineScope.

We break down cooperative coroutine cancellation in long-running file operations: why blocking I/O “doesn’t hear” cancel(), why you need a chunk loop (read/write in chunks), where to place cancellation points via isActive and ensureActive(), how to work correctly with CancellationException (and not “silence” it in catch), and also how to cancel a task from the outside via cancelAndJoin().

We break down a practical strategy for reliable “publishing a result” when working with files: write to a draft ( .tmp/ .part), then atomically (as much as possible) “publish” via renameTo(), and in any case perform best-effort cleanup in finally. Using Kotlin and coroutines examples: try / finally, withContext( Dispatchers. IO), the deleteQuietly helper, safe report writing, and a wrapper for copying.