What multithreading issues have you encountered in your Flutter development experience?

Problems with updating the UI from background isolates, blocking the main thread (UI thread) with long operations, incorrect synchronization of access to shared data between isolates, memory leaks due to improper handling of ports and messages.

// Example of blocking the UI thread
void longRunningOperation() {
  // This long operation blocks the UI, making the app unresponsive
  for (int i = 0; i < 1000000000; i++) {
    // Perform some heavy work
  }
}

// Example of sending a message from a background isolate to update the UI
import 'dart:isolate';

void heavyTask(SendPort sendPort) {
  // Perform long work...
  String result = "Work completed!";
  sendPort.send(result); // Send result back to UI thread
}

// In the main thread
ReceivePort receivePort = ReceivePort();
Isolate.spawn(heavyTask, receivePort.sendPort);

receivePort.listen((message) {
  // Message received from background isolate, can update UI
  print("Received: $message");
});

To solve these problems, Isolate is actively used for performing heavy computations in the background without blocking the UI thread, as well as ReceivePort and SendPort for safe data exchange between isolates. Special attention is paid to serialization/deserialization of data when passing between isolates, since they do not share memory.