Revert "configure: bump min required glib version to 2.56"

This reverts commit b4c6036faa.

configure

@@ -3189,7 +3189,7 @@ fi
 ##########################################
 # glib support probe
 
-glib_req_ver=2.56
+glib_req_ver=2.48
 glib_modules=gthread-2.0
 if test "$modules" = yes; then
     glib_modules="$glib_modules gmodule-export-2.0"

include/glib-compat.h

@@ -19,12 +19,12 @@
 /* Ask for warnings for anything that was marked deprecated in
  * the defined version, or before. It is a candidate for rewrite.
  */
-#define GLIB_VERSION_MIN_REQUIRED GLIB_VERSION_2_56
+#define GLIB_VERSION_MIN_REQUIRED GLIB_VERSION_2_48
 
 /* Ask for warnings if code tries to use function that did not
  * exist in the defined version. These risk breaking builds
  */
-#define GLIB_VERSION_MAX_ALLOWED GLIB_VERSION_2_56
+#define GLIB_VERSION_MAX_ALLOWED GLIB_VERSION_2_48
 
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
@@ -68,6 +68,15 @@
  * without generating warnings.
  */
 
+#if defined(_WIN32) && !GLIB_CHECK_VERSION(2, 50, 0)
+/*
+ * g_poll has a problem on Windows when using
+ * timeouts < 10ms, so use wrapper.
+ */
+#define g_poll(fds, nfds, timeout) g_poll_fixed(fds, nfds, timeout)
+gint g_poll_fixed(GPollFD *fds, guint nfds, gint timeout);
+#endif
+
 #if defined(G_OS_UNIX)
 /*
  * Note: The fallback implementation is not MT-safe, and it returns a copy of

util/oslib-win32.c

@@ -362,6 +362,210 @@ const char *qemu_get_exec_dir(void)
     return exec_dir;
 }
 
+#if !GLIB_CHECK_VERSION(2, 50, 0)
+/*
+ * The original implementation of g_poll from glib has a problem on Windows
+ * when using timeouts < 10 ms.
+ *
+ * Whenever g_poll is called with timeout < 10 ms, it does a quick poll instead
+ * of wait. This causes significant performance degradation of QEMU.
+ *
+ * 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'.
+ */
+
+/*
+ * gpoll.c: poll(2) abstraction
+ * Copyright 1998 Owen Taylor
+ * Copyright 2008 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+static int poll_rest(gboolean poll_msgs, HANDLE *handles, gint nhandles,
+                     GPollFD *fds, guint nfds, gint timeout)
+{
+    DWORD ready;
+    GPollFD *f;
+    int recursed_result;
+
+    if (poll_msgs) {
+        /* Wait for either messages or handles
+         * -> Use MsgWaitForMultipleObjectsEx
+         */
+        ready = MsgWaitForMultipleObjectsEx(nhandles, handles, timeout,
+                                            QS_ALLINPUT, MWMO_ALERTABLE);
+
+        if (ready == WAIT_FAILED) {
+            gchar *emsg = g_win32_error_message(GetLastError());
+            g_warning("MsgWaitForMultipleObjectsEx failed: %s", emsg);
+            g_free(emsg);
+        }
+    } 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
+         */
+        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 (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;
+            }
+        }
+
+        /* 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 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 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;
+            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;
+    }
+
+    return 0;
+}
+
+gint g_poll_fixed(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;
+                }
+            }
+
+            if (i == nhandles) {
+                if (nhandles == MAXIMUM_WAIT_OBJECTS) {
+                    g_warning("Too many handles to wait for!\n");
+                    break;
+                } else {
+                    handles[nhandles++] = (HANDLE) f->fd;
+                }
+            }
+        }
+    }
+
+    for (f = fds; f < &fds[nfds]; ++f) {
+        f->revents = 0;
+    }
+
+    if (timeout == -1) {
+        timeout = INFINITE;
+    }
+
+    /* Polling for several things? */
+    if (nhandles > 1 || (nhandles > 0 && poll_msgs)) {
+        /* First check if one or several of them are immediately
+         * available
+         */
+        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);
+        }
+    } 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);
+    }
+
+    if (retval == -1) {
+        for (f = fds; f < &fds[nfds]; ++f) {
+            f->revents = 0;
+        }
+    }
+
+    return retval;
+}
+#endif
+
 int getpagesize(void)
 {
     SYSTEM_INFO system_info;