V3214. Unity Engine. Using Unity API in the background thread may result in an error.

The analyzer has detected that a property, method, or constructor is used after calling Awaitable.BackgroundThreadAsync. It may cause issues such as application hangs or throwing an exception when executed on a background thread. The Unity documentation states that all APIs that interact with the engine must be used exclusively on the main thread.

Look at the following example:

private async Awaitable LoadSceneAndDoHeavyComputation()
{
  await Awaitable.BackgroundThreadAsync();
  await SceneManager.LoadSceneAsync("MainScene");
  ....
}

public async Awaitable Update()
{
  if (....)
    await LoadSceneAndDoHeavyComputation(); 

  ....
}

When the LoadSceneAndDoHeavyComputation method is executed, the call to the Awaitable.BackgroundThreadAsync method switches the subsequent code execution within the same method to the background thread. This may cause issues when the SceneManager.LoadSceneAsync method is called later.

To avoid this, use the Awaitable.MainThreadAsync method to return to the main thread before calling the SceneManager.LoadSceneAsync method:

private async Awaitable LoadSceneAndDoHeavyComputation()
{
  await Awaitable.BackgroundThreadAsync();
  ....
  await Awaitable.MainThreadAsync();
  await SceneManager.LoadSceneAsync("MainScene");
}

Alternatively, execute SceneManager.LoadSceneAsync before switching to the background thread:

private async Awaitable LoadSceneAndDoHeavyComputation()
{
  await SceneManager.LoadSceneAsync("MainScene");
  await Awaitable.BackgroundThreadAsync();
  ....
}

This diagnostic is classified as:

CWE-691