[MESOS-10123] Windows overlapped IO discard handling can drop data.

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 1.10.0
• Component/s: libprocess
• Labels: windows
• Assignee: Benjamin Mahler
• Reporter: Benjamin Mahler
• Created: 21/Apr/20 17:07
• Updated: 24/Apr/20 22:10
• Resolved: 24/Apr/20 22:10

Description

When getting a discard request for an io operation on windows, a cancellation is requested [1] and when the io operation completes we check whether the future had a discard request to decide whether to discard it [2]:

template <typename T>
static void set_io_promise(Promise<T>* promise, const T& data, DWORD error)
{
  if (promise->future().hasDiscard()) {
    promise->discard();
  } else if (error == ERROR_SUCCESS) {
    promise->set(data);
  } else {
    promise->fail("IO failed with error code: " + WindowsError(error).message);
  }
}

However, it's possible the operation completed successfully, in which case we did not succeed at canceling it. We need to check for ERROR_OPERATION_ABORTED [3]:

template <typename T>
static void set_io_promise(Promise<T>* promise, const T& data, DWORD error)
{
  if (promise->future().hasDiscard() && error == ERROR_OPERATION_ABORTED) {
    promise->discard();
  } else if (error == ERROR_SUCCESS) {
    promise->set(data);
  } else {
    promise->fail("IO failed with error code: " + WindowsError(error).message);
  }
}

I don't think there are currently any major consequences to this issue, since most callers tend to be discarding only when they're essentially abandoning the entire process of reading or writing.

[1] https://github.com/apache/mesos/blob/1.9.0/3rdparty/libprocess/src/windows/libwinio.cpp#L448
[2] https://github.com/apache/mesos/blob/1.9.0/3rdparty/libprocess/src/windows/libwinio.cpp#L141-L151
[3] https://docs.microsoft.com/en-us/windows/win32/fileio/cancelioex-func