[mesos] 01/06: Fixed discard race in libwinio io operations.

[bm...@apache.org]

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bmahler pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/mesos.git

commit 413981ad87da7c4f5f312e52a1f24f11cfe87fbd
Author: Benjamin Mahler <bm...@apache.org>
AuthorDate: Tue Apr 21 12:56:38 2020 -0400

    Fixed discard race in libwinio io operations.
    
    When getting a discard request for an io operation on windows,
    a cancellation is requested and when the io operation completes
    a check is performed to see if the future had a discard requested.
    However, it's possible that the operation completed successfully
    or had a failure and we should not be dropping that information
    from the caller.
    
    To correctly check whether the cancellation succeded, we need
    to check for ERROR_OPERATION_ABORTED.
    
    Review: https://reviews.apache.org/r/72404
---
 3rdparty/libprocess/src/windows/libwinio.cpp | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/3rdparty/libprocess/src/windows/libwinio.cpp b/3rdparty/libprocess/src/windows/libwinio.cpp
index 85ee7ea..453b9df 100644
--- a/3rdparty/libprocess/src/windows/libwinio.cpp
+++ b/3rdparty/libprocess/src/windows/libwinio.cpp
@@ -141,7 +141,11 @@ static_assert(
 template <typename T>
 static void set_io_promise(Promise<T>* promise, const T& data, DWORD error)
 {
-  if (promise->future().hasDiscard()) {
+  // If our discard induced CancelIoEx call succeeded, then we
+  // will see ERROR_OPERATION_ABORTED. Otherwise, the discard
+  // lost the race against the operation completing and we
+  // should just surface the result.
+  if (promise->future().hasDiscard() && error == ERROR_OPERATION_ABORTED) {
     promise->discard();
   } else if (error == ERROR_SUCCESS) {
     promise->set(data);