Dataloader never exits Task.Supervisor spawned inside async_safely causing a memory leak

[samsondav]

We've been seeing ballooning memory usage on our production servers.

The memory is taken up by Task.Supervisor spawned here: https://github.com/absinthe-graphql/dataloader/blob/master/lib/dataloader.ex#L232. Each time that async_safely is run, a new supervisor is spawned which is never cleaned up.

For large queries, this supervisor can take up considerable memory (I’m not sure why, this may be another, different bug). In our case it takes 32MB per supervisor.

Certain queries can cause Absinthe.run to be called upwards of 30 times, which gives rather large memory requirements.