Where to catch exceptions when using Task.ContinueWith? - exception

Question

I would like to create an async method with Task that creates a file and immediately proceeds to executing next task which uploads created file to cloud.
Here is how this method looks:
public async TaskCreateAndUploadAsync()
{
await Task.Run(() =>
{
try
{
var _writeFile = new WriteFile(...);
_writeFile.DoWork();
}
catch (Exception e)
{
//Log..
}
}).ContinueWith((result) =>
{
if (!result.IsFaulted)
{
try
{
storage.UploadCreatedObject(...);
}
catch (Exception e)
{
//Log..
}
}
});
}
My question is: Is the way how I catch exceptions in each Task individually correct or I should use one try-catch block around whole "Task..Task.ContinueWith"?

Answer 1

Where to catch exceptions when using Task.ContinueWith?
The proper answer is "don't use ContinueWith". For asynchronous code, you can use await instead; for synchronous code like this, you can just use nothing:
public async TaskCreateAndUploadAsync()
{
await Task.Run(async () =>
{
try
{
var _writeFile = new WriteFile(...);
_writeFile.DoWork();
storage.UploadCreatedObject(...);
}
catch (Exception e)
{
//Log..
}
});
}
However, wrapping a method body in Task.Run like this is an antipattern; it's better to keep the method synchronous and have callers use Task.Run:
public void TaskCreateAndUpload()
{
try
{
var _writeFile = new WriteFile(...);
_writeFile.DoWork();
storage.UploadCreatedObject(...);
}
catch (Exception e)
{
//Log..
}
}
From your method names, it sounds like some of them should be asynchronous. I/O is inherently asynchronous. So, if you have truly asynchronous I/O (i.e., not using Task.Run for fake-asynchrony), then your resulting method may look like this:
public async Task TaskCreateAndUploadAsync()
{
try
{
var _writeFile = new WriteFile(...);
await _writeFile.DoWorkAsync();
await storage.UploadCreatedObjectAsync(...);
}
catch (Exception e)
{
//Log..
}
}
Note the use of await instead of ContiueWith in this last example.