Fix error reporting on IOCP out of resources.

Here is my understanding of the history of this patch.

The patch that was applied to MongoDB's old vendored ASIO is
[0006-MONGO-Fix-IOCP-out-of-resource-handling.patch][1].

That patch is a solution to an [outstanding issue][2] in upstream ASIO,
both then and now.

The reason we applied the patch was because we thought that is might be
the solution to `BF-9006`. So, [SERVER-36885][3] was created to patch
ASIO.

But in `SERVER-36885`, its author says that likely the BF wasn't caused
by this ASIO issue, but instead was fixed by [SERVER-38789][4].

So, these changes probably address a genuine issue in ASIO, but possibly
not one that MongoDB has ever encountered.

[1]: https://github.com/mongodb/mongo/blob/4c38808c10021549e34e59b696e89b6541fae4c4/src/third_party/asio-master/patches/0006-MONGO-Fix-IOCP-out-of-resource-handling.patch
[2]: chriskohlhoff#312
[3]: https://jira.mongodb.org/browse/SERVER-36885
[4]: https://jira.mongodb.org/browse/SERVER-38789

Author: dgoffredo

asio/include/asio/detail/impl/win_iocp_io_context.ipp

@@ -308,7 +308,7 @@ void win_iocp_io_context::post_deferred_completion(win_iocp_operation* op)
   op->ready_ = 1;
 
   // Enqueue the operation on the I/O completion port.
-  if (!::PostQueuedCompletionStatus(iocp_.handle, 0, 0, op))
+  if (!::PostQueuedCompletionStatus(iocp_.handle, 0, op->completionKey(), op))
   {
     // Out of resources. Put on completed queue instead.
     mutex::scoped_lock lock(dispatch_mutex_);
@@ -328,7 +328,7 @@ void win_iocp_io_context::post_deferred_completions(
     op->ready_ = 1;
 
     // Enqueue the operation on the I/O completion port.
-    if (!::PostQueuedCompletionStatus(iocp_.handle, 0, 0, op))
+    if (!::PostQueuedCompletionStatus(iocp_.handle, 0, op->completionKey(), op))
     {
       // Out of resources. Put on completed queue instead.
       mutex::scoped_lock lock(dispatch_mutex_);
@@ -355,8 +355,9 @@ void win_iocp_io_context::on_pending(win_iocp_operation* op)
   if (::InterlockedCompareExchange(&op->ready_, 1, 0) == 1)
   {
     // Enqueue the operation on the I/O completion port.
+    op->completionKey() = overlapped_contains_result;
     if (!::PostQueuedCompletionStatus(iocp_.handle,
-          0, overlapped_contains_result, op))
+          0, op->completionKey(), op))
     {
       // Out of resources. Put on completed queue instead.
       mutex::scoped_lock lock(dispatch_mutex_);
@@ -379,8 +380,9 @@ void win_iocp_io_context::on_completion(win_iocp_operation* op,
   op->OffsetHigh = bytes_transferred;
 
   // Enqueue the operation on the I/O completion port.
+  op->completionKey() = overlapped_contains_result;
   if (!::PostQueuedCompletionStatus(iocp_.handle,
-        0, overlapped_contains_result, op))
+        0, op->completionKey(), op))
   {
     // Out of resources. Put on completed queue instead.
     mutex::scoped_lock lock(dispatch_mutex_);
@@ -401,8 +403,9 @@ void win_iocp_io_context::on_completion(win_iocp_operation* op,
   op->OffsetHigh = bytes_transferred;
 
   // Enqueue the operation on the I/O completion port.
+  op->completionKey() = overlapped_contains_result;
   if (!::PostQueuedCompletionStatus(iocp_.handle,
-        0, overlapped_contains_result, op))
+        0, op->completionKey(), op))
   {
     // Out of resources. Put on completed queue instead.
     mutex::scoped_lock lock(dispatch_mutex_);

asio/include/asio/detail/win_iocp_operation.hpp

@@ -59,6 +59,11 @@ class win_iocp_operation
     OffsetHigh = 0;
     hEvent = 0;
     ready_ = 0;
+    completionKey_ = 0;
+  }
+
+  ULONG_PTR& completionKey() {
+    return completionKey_;
   }
 
 protected:
@@ -68,7 +73,8 @@ class win_iocp_operation
 
   win_iocp_operation(func_type func)
     : next_(0),
-      func_(func)
+      func_(func),
+      completionKey_(0)
   {
     reset();
   }
@@ -84,6 +90,7 @@ class win_iocp_operation
   win_iocp_operation* next_;
   func_type func_;
   long ready_;
+  ULONG_PTR completionKey_;
 };
 
 } // namespace detail