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Thread safety and #refresh_token #40

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@tristanm

I realise this is a generic question which could apply to many similar situations but I thought I'd bring it up in case anyone thinks it's useful to mention it in createsend-ruby's README.md.

In multi-threaded applications, it is possible to get into an unsafe situation when refreshing tokens, e.g.:

record = SomeModel.find(...)
cs = CreateSend::CreateSent.new(
    record.access_token,
    record.refresh_token
)

begin
  tries = 2
  cs.clients
rescue CreateSend::ExpiredOAuthToken => e
  access_token, expires_in, request_token = cs.refresh_token
  record.access_token = access_token
  record.request_token = request_token
  record.save
  retry if (trues -= 1).zero?
  raise e
end
  1. record.access_token expires
  2. Thread A encounters ExpiredOAuthToken
  3. Thread A calls #refresh_token
  4. Thread B encounters ExpiredOAuthToken
  5. Thread B calls #refresh_token but fails because record.refresh_token is now invalid
  6. Thread A persists new token
  7. Thread A continues

I'm assuming others have encountered this possibility. Anyone have any favoured suggestions for dealing with it?

I've created a question on SO too (modified the code to make it broader than createsend-ruby) if anyone would like some points!

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