Re: [PATCH v3 1/3] util/main-loop: Fix maximum number of wait objects for win32

[Marc-André Lureau]

Hi

On Wed, Aug 24, 2022 at 12:52 PM Bin Meng <bmeng.cn@gmail.com> wrote:

From: Bin Meng <bin.meng@windriver.com>

The maximum number of wait objects for win32 should be
MAXIMUM_WAIT_OBJECTS, not MAXIMUM_WAIT_OBJECTS + 1.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
---

Changes in v3:
- move the check of adding the same HANDLE twice to a separete patch

Changes in v2:
- fix the logic in qemu_add_wait_object() to avoid adding
  the same HANDLE twice

 util/main-loop.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/util/main-loop.c b/util/main-loop.c
index f00a25451b..cb018dc33c 100644
--- a/util/main-loop.c
+++ b/util/main-loop.c
@@ -363,10 +363,10 @@ void qemu_del_polling_cb(PollingFunc *func, void *opaque)
 /* Wait objects support */
 typedef struct WaitObjects {
     int num;
-    int revents[MAXIMUM_WAIT_OBJECTS + 1];
-    HANDLE events[MAXIMUM_WAIT_OBJECTS + 1];
-    WaitObjectFunc *func[MAXIMUM_WAIT_OBJECTS + 1];
-    void *opaque[MAXIMUM_WAIT_OBJECTS + 1];
+    int revents[MAXIMUM_WAIT_OBJECTS];
+    HANDLE events[MAXIMUM_WAIT_OBJECTS];
+    WaitObjectFunc *func[MAXIMUM_WAIT_OBJECTS];
+    void *opaque[MAXIMUM_WAIT_OBJECTS];
 } WaitObjects;

 static WaitObjects wait_objects = {0};
@@ -395,6 +395,9 @@ void qemu_del_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque)
         if (w->events[i] == handle) {
             found = 1;
         }
+        if (i == MAXIMUM_WAIT_OBJECTS - 1) {
+            break;
+        }

hmm

 

         if (found) {
             w->events[i] = w->events[i + 1];
             w->func[i] = w->func[i + 1];

The way deletion works is by moving the i+1 element (which is always zeroed for i == MAXIMUM_WAIT_OBJECTS) to i.

After your patch, for i == MAXIMUM_WAIT_OBJECTS, we no longer clear the last value, and instead rely simply on updated w->num:

    if (found) {
        w->num--;
    }

 So your patch looks ok to me, but I prefer the current code.

Paolo, what do you say?