winio: Various fixes related to rebase and testdriver

1 files changed, 14 insertions, 6 deletions

diff --git a/rts/win32/AsyncWinIO.c b/rts/win32/AsyncWinIO.c
index 8a9a647160..70b4455c71 100644
--- a/rts/win32/AsyncWinIO.c
+++ b/rts/win32/AsyncWinIO.c
@@ -387,14 +387,22 @@ void registerAlertableWait (bool has_timeout, DWORD mssec, uint64_t num_req, boo
    finished overlapped entried belonging to the completed I/O requests.  The
    number of read entries will be returned in NUM.
 
-   NOTE: This function isn't thread safe, but is intended to be called only
-         when requested by the I/O manager via notifyScheduler.  In
-         that context it is thread safe as we're guaranteeing that the I/O
-         manager is blocked waiting for the read to happen followed by a
-         registerAlertableWait call.  */
+   We clear the outstanding request flag to prevent two threads from handling
+   the same payload early on.  Failing this the final safe guard is in
+   processCompletions.  */
 OVERLAPPED_ENTRY* getOverlappedEntries (uint32_t *num)
 {
-  *num = num_last_completed;
+  AcquireSRWLockExclusive (&lock);
+
+  if (outstanding_service_requests)
+    *num = num_last_completed;
+  else
+    *num = 0;
+
+  outstanding_service_requests = false;
+
+  ReleaseSRWLockExclusive (&lock);
+
   return entries;
 }