aio: tweak walking in dispatch phase

Preparing for the following patch, use QLIST_FOREACH_SAFE and
modify the placement of walking_handlers increment/decrement.
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NFam Zheng <famz@redhat.com>
Message-id: 20170112180800.21085-7-pbonzini@redhat.com
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

aio-posix.c

@@ -369,19 +369,17 @@ bool aio_pending(AioContext *ctx)
 
 static bool aio_dispatch_handlers(AioContext *ctx)
 {
-    AioHandler *node;
+    AioHandler *node, *tmp;
     bool progress = false;
 
     /*
      * We have to walk very carefully in case aio_set_fd_handler is
      * called while we're walking.
      */
-    node = QLIST_FIRST(&ctx->aio_handlers);
-    while (node) {
-        AioHandler *tmp;
-        int revents;
+    ctx->walking_handlers++;
 
-        ctx->walking_handlers++;
+    QLIST_FOREACH_SAFE(node, &ctx->aio_handlers, node, tmp) {
+        int revents;
 
         revents = node->pfd.revents & node->pfd.events;
         node->pfd.revents = 0;
@@ -405,17 +403,17 @@ static bool aio_dispatch_handlers(AioContext *ctx)
             progress = true;
         }
 
-        tmp = node;
-        node = QLIST_NEXT(node, node);
-
-        ctx->walking_handlers--;
-
-        if (!ctx->walking_handlers && tmp->deleted) {
-            QLIST_REMOVE(tmp, node);
-            g_free(tmp);
+        if (node->deleted) {
+            ctx->walking_handlers--;
+            if (!ctx->walking_handlers) {
+                QLIST_REMOVE(node, node);
+                g_free(node);
+            }
+            ctx->walking_handlers++;
         }
     }
 
+    ctx->walking_handlers--;
     return progress;
 }
 

aio-win32.c

@@ -227,20 +227,18 @@ bool aio_pending(AioContext *ctx)
 
 static bool aio_dispatch_handlers(AioContext *ctx, HANDLE event)
 {
-    AioHandler *node;
+    AioHandler *node, *tmp;
     bool progress = false;
 
+    ctx->walking_handlers++;
+
     /*
      * We have to walk very carefully in case aio_set_fd_handler is
      * called while we're walking.
      */
-    node = QLIST_FIRST(&ctx->aio_handlers);
-    while (node) {
-        AioHandler *tmp;
+    QLIST_FOREACH_SAFE(node, &ctx->aio_handlers, node, tmp) {
         int revents = node->pfd.revents;
 
-        ctx->walking_handlers++;
-
         if (!node->deleted &&
             (revents || event_notifier_get_handle(node->e) == event) &&
             node->io_notify) {
@@ -275,17 +273,17 @@ static bool aio_dispatch_handlers(AioContext *ctx, HANDLE event)
             }
         }
 
-        tmp = node;
-        node = QLIST_NEXT(node, node);
-
-        ctx->walking_handlers--;
-
-        if (!ctx->walking_handlers && tmp->deleted) {
-            QLIST_REMOVE(tmp, node);
-            g_free(tmp);
+        if (node->deleted) {
+            ctx->walking_handlers--;
+            if (!ctx->walking_handlers) {
+                QLIST_REMOVE(node, node);
+                g_free(node);
+            }
+            ctx->walking_handlers++;
         }
     }
 
+    ctx->walking_handlers--;
     return progress;
 }