w32: Fix regression caused by new g_poll implementation

diff --git a/util/oslib-win32.c b/util/oslib-win32.c
index 3077df3..d04dc8f 100644
--- a/util/oslib-win32.c
+++ b/util/oslib-win32.c
@@ -138,7 +138,7 @@  int inet_aton(const char *cp, struct in_addr *ia)
 {
     uint32_t addr = inet_addr(cp);
     if (addr == 0xffffffff) {
-	return 0;
+        return 0;
     }
     ia->s_addr = addr;
     return 1;
@@ -256,113 +256,186 @@  char *qemu_get_exec_dir(void)
 }
 
 /*
- * g_poll has a problem on Windows when using
- * timeouts < 10ms, in glib/gpoll.c:
+ * The original implementation of g_poll from glib has a problem on Windows
+ * when using timeouts < 10 ms.
  *
- * // If not, and we have a significant timeout, poll again with
- * // timeout then. Note that this will return indication for only
- * // one event, or only for messages. We ignore timeouts less than
- * // ten milliseconds as they are mostly pointless on Windows, the
- * // MsgWaitForMultipleObjectsEx() call will timeout right away
- * // anyway.
+ * Whenever g_poll is called with timeout < 10 ms, it does a quick poll instead
+ * of wait. This causes significant performance degradation of QEMU.
  *
- * if (retval == 0 && (timeout == INFINITE || timeout >= 10))
- *   retval = poll_rest (poll_msgs, handles, nhandles, fds, nfds, timeout);
- *
- * So whenever g_poll is called with timeout < 10ms it does
- * a quick poll instead of wait, this causes significant performance
- * degradation of QEMU, thus we should use WaitForMultipleObjectsEx
- * directly
+ * The following code is a copy of the original code from glib/gpoll.c
+ * (glib commit 20f4d1820b8d4d0fc4447188e33efffd6d4a88d8 from 2014-02-19).
+ * Some debug code was removed and the code was reformatted.
+ * All other code modifications are marked with 'QEMU'.
  */
-gint g_poll_fixed(GPollFD *fds, guint nfds, gint timeout)
+
+static int poll_rest(gboolean poll_msgs, HANDLE *handles, gint nhandles,
+                     GPollFD *fds, guint nfds, gint timeout)
 {
-    guint i;
-    HANDLE handles[MAXIMUM_WAIT_OBJECTS];
-    gint nhandles = 0;
-    int num_completed = 0;
+    DWORD ready;
+    GPollFD *f;
+    int recursed_result;
 
-    for (i = 0; i < nfds; i++) {
-        gint j;
+    if (poll_msgs) {
+        /* Wait for either messages or handles
+         * -> Use MsgWaitForMultipleObjectsEx
+         */
+        ready = MsgWaitForMultipleObjectsEx(nhandles, handles, timeout,
+                                            QS_ALLINPUT, MWMO_ALERTABLE);
 
-        if (fds[i].fd <= 0) {
-            continue;
+        if (ready == WAIT_FAILED) {
+            gchar *emsg = g_win32_error_message(GetLastError());
+            g_warning("MsgWaitForMultipleObjectsEx failed: %s", emsg);
+            g_free(emsg);
         }
-
-        /* don't add same handle several times
+    } else if (nhandles == 0) {
+        /* No handles to wait for, just the timeout */
+        if (timeout == INFINITE) {
+            ready = WAIT_FAILED;
+        } else {
+            SleepEx(timeout, TRUE);
+            ready = WAIT_TIMEOUT;
+        }
+    } else {
+        /* Wait for just handles
+         * -> Use WaitForMultipleObjectsEx
          */
-        for (j = 0; j < nhandles; j++) {
-            if (handles[j] == (HANDLE)fds[i].fd) {
-                break;
-            }
+        ready =
+            WaitForMultipleObjectsEx(nhandles, handles, FALSE, timeout, TRUE);
+        if (ready == WAIT_FAILED) {
+            gchar *emsg = g_win32_error_message(GetLastError());
+            g_warning("WaitForMultipleObjectsEx failed: %s", emsg);
+            g_free(emsg);
         }
+    }
 
-        if (j == nhandles) {
-            if (nhandles == MAXIMUM_WAIT_OBJECTS) {
-                fprintf(stderr, "Too many handles to wait for!\n");
-                break;
-            } else {
-                handles[nhandles++] = (HANDLE)fds[i].fd;
+    if (ready == WAIT_FAILED) {
+        return -1;
+    } else if (ready == WAIT_TIMEOUT || ready == WAIT_IO_COMPLETION) {
+        return 0;
+    } else if (poll_msgs && ready == WAIT_OBJECT_0 + nhandles) {
+        for (f = fds; f < &fds[nfds]; ++f) {
+            if (f->fd == G_WIN32_MSG_HANDLE && f->events & G_IO_IN) {
+                f->revents |= G_IO_IN;
             }
         }
-    }
 
-    for (i = 0; i < nfds; ++i) {
-        fds[i].revents = 0;
-    }
+        /* If we have a timeout, or no handles to poll, be satisfied
+         * with just noticing we have messages waiting.
+         */
+        if (timeout != 0 || nhandles == 0) {
+            return 1;
+        }
 
-    if (timeout == -1) {
-        timeout = INFINITE;
-    }
+        /* If no timeout and handles to poll, recurse to poll them,
+         * too.
+         */
+        recursed_result = poll_rest(FALSE, handles, nhandles, fds, nfds, 0);
+        return (recursed_result == -1) ? -1 : 1 + recursed_result;
+    } else if (/* QEMU: removed the following unneeded statement which causes
+                * a compiler warning: ready >= WAIT_OBJECT_0 && */
+               ready < WAIT_OBJECT_0 + nhandles) {
+        for (f = fds; f < &fds[nfds]; ++f) {
+            if ((HANDLE) f->fd == handles[ready - WAIT_OBJECT_0]) {
+                f->revents = f->events;
+            }
+        }
 
-    if (nhandles == 0) {
-        if (timeout == INFINITE) {
-            return -1;
-        } else {
-            SleepEx(timeout, TRUE);
-            return 0;
+        /* If no timeout and polling several handles, recurse to poll
+         * the rest of them.
+         */
+        if (timeout == 0 && nhandles > 1) {
+            /* Remove the handle that fired */
+            int i;
+            if (ready < nhandles - 1) {
+                for (i = ready - WAIT_OBJECT_0 + 1; i < nhandles; i++) {
+                    handles[i-1] = handles[i];
+                }
+            }
+            nhandles--;
+            recursed_result = poll_rest(FALSE, handles, nhandles, fds, nfds, 0);
+            return (recursed_result == -1) ? -1 : 1 + recursed_result;
         }
+        return 1;
     }
 
-    while (1) {
-        DWORD res;
-        gint j;
-
-        res = WaitForMultipleObjectsEx(nhandles, handles, FALSE,
-            timeout, TRUE);
+    return 0;
+}
 
-        if (res == WAIT_FAILED) {
-            for (i = 0; i < nfds; ++i) {
-                fds[i].revents = 0;
+gint g_poll(GPollFD *fds, guint nfds, gint timeout)
+{
+    HANDLE handles[MAXIMUM_WAIT_OBJECTS];
+    gboolean poll_msgs = FALSE;
+    GPollFD *f;
+    gint nhandles = 0;
+    int retval;
+
+    for (f = fds; f < &fds[nfds]; ++f) {
+        if (f->fd == G_WIN32_MSG_HANDLE && (f->events & G_IO_IN)) {
+            poll_msgs = TRUE;
+        } else if (f->fd > 0) {
+            /* Don't add the same handle several times into the array, as
+             * docs say that is not allowed, even if it actually does seem
+             * to work.
+             */
+            gint i;
+
+            for (i = 0; i < nhandles; i++) {
+                if (handles[i] == (HANDLE) f->fd) {
+                    break;
+                }
             }
 
-            return -1;
-        } else if ((res == WAIT_TIMEOUT) || (res == WAIT_IO_COMPLETION) ||
-                   ((int)res < (int)WAIT_OBJECT_0) ||
-                   (res >= (WAIT_OBJECT_0 + nhandles))) {
-            break;
-        }
-
-        for (i = 0; i < nfds; ++i) {
-            if (handles[res - WAIT_OBJECT_0] == (HANDLE)fds[i].fd) {
-                fds[i].revents = fds[i].events;
+            if (i == nhandles) {
+                if (nhandles == MAXIMUM_WAIT_OBJECTS) {
+                    g_warning("Too many handles to wait for!\n");
+                    break;
+                } else {
+                    handles[nhandles++] = (HANDLE) f->fd;
+                }
             }
         }
+    }
 
-        ++num_completed;
+    for (f = fds; f < &fds[nfds]; ++f) {
+        f->revents = 0;
+    }
 
-        if (nhandles <= 1) {
-            break;
-        }
+    if (timeout == -1) {
+        timeout = INFINITE;
+    }
 
-        /* poll the rest of the handles
+    /* Polling for several things? */
+    if (nhandles > 1 || (nhandles > 0 && poll_msgs)) {
+        /* First check if one or several of them are immediately
+         * available
          */
-        for (j = res - WAIT_OBJECT_0 + 1; j < nhandles; j++) {
-            handles[j - 1] = handles[j];
+        retval = poll_rest(poll_msgs, handles, nhandles, fds, nfds, 0);
+
+        /* If not, and we have a significant timeout, poll again with
+         * timeout then. Note that this will return indication for only
+         * one event, or only for messages. We ignore timeouts less than
+         * ten milliseconds as they are mostly pointless on Windows, the
+         * MsgWaitForMultipleObjectsEx() call will timeout right away
+         * anyway.
+         *
+         * Modification for QEMU: replaced timeout >= 10 by timeout > 0.
+         */
+        if (retval == 0 && (timeout == INFINITE || timeout > 0)) {
+            retval = poll_rest(poll_msgs, handles, nhandles,
+                               fds, nfds, timeout);
         }
-        --nhandles;
+    } else {
+        /* Just polling for one thing, so no need to check first if
+         * available immediately
+         */
+        retval = poll_rest(poll_msgs, handles, nhandles, fds, nfds, timeout);
+    }
 
-        timeout = 0;
+    if (retval == -1) {
+        for (f = fds; f < &fds[nfds]; ++f) {
+            f->revents = 0;
+        }
     }
 
-    return num_completed;
+    return retval;
 }