处理协程启动中的异常？

Question

For example, how do we handle exceptions in myHttpTask and myCpuTask ? and make sure we call result.error(exception) in the main thread?

// The scope for the UI thread
private val mainScope = CoroutineScope(Dispatchers.Main)

override fun onMethodCall(call: MethodCall, result: Result) {
  mainScope.launch {
    Log.e(TAG, "onMethodCall: I'm working in thread ${Thread.currentThread().name}")
    when (call.method) {
      "hello" -> {
        withContext(Dispatchers.IO) {
           // Run code on a IO thread (the amount of IO threads are 64 by default).
           myHttpTask()
        }
        withContext(Dispatchers.Default) {
           // Run code on a CPU thread (the amount equals the amount of CPU cores).
           myCpuTask()
        }

        // This will run on the main thread
        result.success("world")
      }
      else -> result.notImplemented()
    }
  }
}

Answer 1

Because coroutines allow to write a regular, sequential code for asynchronous operations, we can use the same techniques as for any other sequential code - try... catch . This is true as long as we only invoke suspend functions and we don't launch anything in the background using launch() , async() , etc.

For example in your case it could work like this:

override fun onMethodCall(call: MethodCall, result: Result) {
  mainScope.launch {
    Log.e(TAG, "onMethodCall: I'm working in thread ${Thread.currentThread().name}")
    when (call.method) {
      "hello" -> try {
        withContext(Dispatchers.IO) {
           // Run code on a IO thread (the amount of IO threads are 64 by default).
           myHttpTask()
        }
        withContext(Dispatchers.Default) {
           // Run code on a CPU thread (the amount equals the amount of CPU cores).
           myCpuTask()
        }

        // This will run on the main thread
        result.success("world")
      } catch (e: Throwable) {
        // Just an example, I don't know if such a method exists.
        result.failure("Error: $e")
      }
      else -> result.notImplemented()
    }
  }
}

While handling the exception, it will properly jump back to the main thread, as we would expect.