vnc: threaded VNC server

Implement a threaded VNC server using the producer-consumer model.
The main thread will push encoding jobs (a list a rectangles to update)
in a queue, and the VNC worker thread will consume that queue and send
framebuffer updates to the output buffer.

The threaded VNC server can be enabled with ./configure --enable-vnc-thread.

If you don't want it, just use ./configure --disable-vnc-thread and a syncrhonous
queue of job will be used (which as exactly the same behavior as the old queue).
If you disable the VNC thread, all thread related code will not be built and there will
be no overhead.

Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

5 files changed, 663 insertions, 25 deletions

diff --git a/ui/vnc-jobs-async.c b/ui/vnc-jobs-async.c
new file mode 100644
index 0000000000..6e9cf08b69
--- /dev/null
+++ b/ui/vnc-jobs-async.c
@@ -0,0 +1,331 @@
+/*
+ * QEMU VNC display driver
+ *
+ * Copyright (C) 2006 Anthony Liguori <anthony@codemonkey.ws>
+ * Copyright (C) 2006 Fabrice Bellard
+ * Copyright (C) 2009 Red Hat, Inc
+ * Copyright (C) 2010 Corentin Chary <corentin.chary@gmail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+
+#include "vnc.h"
+#include "vnc-jobs.h"
+
+/*
+ * Locking:
+ *
+ * There is three levels of locking:
+ * - jobs queue lock: for each operation on the queue (push, pop, isEmpty?)
+ * - VncDisplay global lock: mainly used for framebuffer updates to avoid
+ *                      screen corruption if the framebuffer is updated
+ *			while the worker is doing something.
+ * - VncState::output lock: used to make sure the output buffer is not corrupted
+ * 		   	 if two threads try to write on it at the same time
+ *
+ * While the VNC worker thread is working, the VncDisplay global lock is hold
+ * to avoid screen corruptions (this does not block vnc_refresh() because it
+ * uses trylock()) but the output lock is not hold because the thread work on
+ * its own output buffer.
+ * When the encoding job is done, the worker thread will hold the output lock
+ * and copy its output buffer in vs->output.
+*/
+
+struct VncJobQueue {
+    QemuCond cond;
+    QemuMutex mutex;
+    QemuThread thread;
+    Buffer buffer;
+    bool exit;
+    QTAILQ_HEAD(, VncJob) jobs;
+};
+
+typedef struct VncJobQueue VncJobQueue;
+
+/*
+ * We use a single global queue, but most of the functions are
+ * already reetrant, so we can easilly add more than one encoding thread
+ */
+static VncJobQueue *queue;
+
+static void vnc_lock_queue(VncJobQueue *queue)
+{
+    qemu_mutex_lock(&queue->mutex);
+}
+
+static void vnc_unlock_queue(VncJobQueue *queue)
+{
+    qemu_mutex_unlock(&queue->mutex);
+}
+
+VncJob *vnc_job_new(VncState *vs)
+{
+    VncJob *job = qemu_mallocz(sizeof(VncJob));
+
+    job->vs = vs;
+    vnc_lock_queue(queue);
+    QLIST_INIT(&job->rectangles);
+    vnc_unlock_queue(queue);
+    return job;
+}
+
+int vnc_job_add_rect(VncJob *job, int x, int y, int w, int h)
+{
+    VncRectEntry *entry = qemu_mallocz(sizeof(VncRectEntry));
+
+    entry->rect.x = x;
+    entry->rect.y = y;
+    entry->rect.w = w;
+    entry->rect.h = h;
+
+    vnc_lock_queue(queue);
+    QLIST_INSERT_HEAD(&job->rectangles, entry, next);
+    vnc_unlock_queue(queue);
+    return 1;
+}
+
+void vnc_job_push(VncJob *job)
+{
+    vnc_lock_queue(queue);
+    if (queue->exit || QLIST_EMPTY(&job->rectangles)) {
+        qemu_free(job);
+    } else {
+        QTAILQ_INSERT_TAIL(&queue->jobs, job, next);
+        qemu_cond_broadcast(&queue->cond);
+    }
+    vnc_unlock_queue(queue);
+}
+
+static bool vnc_has_job_locked(VncState *vs)
+{
+    VncJob *job;
+
+    QTAILQ_FOREACH(job, &queue->jobs, next) {
+        if (job->vs == vs || !vs) {
+            return true;
+        }
+    }
+    return false;
+}
+
+bool vnc_has_job(VncState *vs)
+{
+    bool ret;
+
+    vnc_lock_queue(queue);
+    ret = vnc_has_job_locked(vs);
+    vnc_unlock_queue(queue);
+    return ret;
+}
+
+void vnc_jobs_clear(VncState *vs)
+{
+    VncJob *job, *tmp;
+
+    vnc_lock_queue(queue);
+    QTAILQ_FOREACH_SAFE(job, &queue->jobs, next, tmp) {
+        if (job->vs == vs || !vs) {
+            QTAILQ_REMOVE(&queue->jobs, job, next);
+        }
+    }
+    vnc_unlock_queue(queue);
+}
+
+void vnc_jobs_join(VncState *vs)
+{
+    vnc_lock_queue(queue);
+    while (vnc_has_job_locked(vs)) {
+        qemu_cond_wait(&queue->cond, &queue->mutex);
+    }
+    vnc_unlock_queue(queue);
+}
+
+/*
+ * Copy data for local use
+ */
+static void vnc_async_encoding_start(VncState *orig, VncState *local)
+{
+    local->vnc_encoding = orig->vnc_encoding;
+    local->features = orig->features;
+    local->ds = orig->ds;
+    local->vd = orig->vd;
+    local->write_pixels = orig->write_pixels;
+    local->clientds = orig->clientds;
+    local->tight = orig->tight;
+    local->zlib = orig->zlib;
+    local->hextile = orig->hextile;
+    local->output =  queue->buffer;
+    local->csock = -1; /* Don't do any network work on this thread */
+
+    buffer_reset(&local->output);
+}
+
+static void vnc_async_encoding_end(VncState *orig, VncState *local)
+{
+    orig->tight = local->tight;
+    orig->zlib = local->zlib;
+    orig->hextile = local->hextile;
+}
+
+static int vnc_worker_thread_loop(VncJobQueue *queue)
+{
+    VncJob *job;
+    VncRectEntry *entry, *tmp;
+    VncState vs;
+    int n_rectangles;
+    int saved_offset;
+    bool flush;
+
+    vnc_lock_queue(queue);
+    while (QTAILQ_EMPTY(&queue->jobs) && !queue->exit) {
+        qemu_cond_wait(&queue->cond, &queue->mutex);
+    }
+    /* Here job can only be NULL if queue->exit is true */
+    job = QTAILQ_FIRST(&queue->jobs);
+    vnc_unlock_queue(queue);
+
+    if (queue->exit) {
+        return -1;
+    }
+
+    vnc_lock_output(job->vs);
+    if (job->vs->csock == -1 || job->vs->abort == true) {
+        goto disconnected;
+    }
+    vnc_unlock_output(job->vs);
+
+    /* Make a local copy of vs and switch output buffers */
+    vnc_async_encoding_start(job->vs, &vs);
+
+    /* Start sending rectangles */
+    n_rectangles = 0;
+    vnc_write_u8(&vs, VNC_MSG_SERVER_FRAMEBUFFER_UPDATE);
+    vnc_write_u8(&vs, 0);
+    saved_offset = vs.output.offset;
+    vnc_write_u16(&vs, 0);
+
+    vnc_lock_display(job->vs->vd);
+    QLIST_FOREACH_SAFE(entry, &job->rectangles, next, tmp) {
+        int n;
+
+        if (job->vs->csock == -1) {
+            vnc_unlock_display(job->vs->vd);
+            goto disconnected;
+        }
+
+        n = vnc_send_framebuffer_update(&vs, entry->rect.x, entry->rect.y,
+                                        entry->rect.w, entry->rect.h);
+
+        if (n >= 0) {
+            n_rectangles += n;
+        }
+        qemu_free(entry);
+    }
+    vnc_unlock_display(job->vs->vd);
+
+    /* Put n_rectangles at the beginning of the message */
+    vs.output.buffer[saved_offset] = (n_rectangles >> 8) & 0xFF;
+    vs.output.buffer[saved_offset + 1] = n_rectangles & 0xFF;
+
+    /* Switch back buffers */
+    vnc_lock_output(job->vs);
+    if (job->vs->csock == -1) {
+        goto disconnected;
+    }
+
+    vnc_write(job->vs, vs.output.buffer, vs.output.offset);
+
+disconnected:
+    /* Copy persistent encoding data */
+    vnc_async_encoding_end(job->vs, &vs);
+    flush = (job->vs->csock != -1 && job->vs->abort != true);
+    vnc_unlock_output(job->vs);
+
+    if (flush) {
+        vnc_flush(job->vs);
+    }
+
+    vnc_lock_queue(queue);
+    QTAILQ_REMOVE(&queue->jobs, job, next);
+    vnc_unlock_queue(queue);
+    qemu_cond_broadcast(&queue->cond);
+    qemu_free(job);
+    return 0;
+}
+
+static VncJobQueue *vnc_queue_init(void)
+{
+    VncJobQueue *queue = qemu_mallocz(sizeof(VncJobQueue));
+
+    qemu_cond_init(&queue->cond);
+    qemu_mutex_init(&queue->mutex);
+    QTAILQ_INIT(&queue->jobs);
+    return queue;
+}
+
+static void vnc_queue_clear(VncJobQueue *q)
+{
+    qemu_cond_destroy(&queue->cond);
+    qemu_mutex_destroy(&queue->mutex);
+    buffer_free(&queue->buffer);
+    qemu_free(q);
+    queue = NULL; /* Unset global queue */
+}
+
+static void *vnc_worker_thread(void *arg)
+{
+    VncJobQueue *queue = arg;
+
+    qemu_thread_self(&queue->thread);
+
+    while (!vnc_worker_thread_loop(queue)) ;
+    vnc_queue_clear(queue);
+    return NULL;
+}
+
+void vnc_start_worker_thread(void)
+{
+    VncJobQueue *q;
+
+    if (vnc_worker_thread_running())
+        return ;
+
+    q = vnc_queue_init();
+    qemu_thread_create(&q->thread, vnc_worker_thread, q);
+    queue = q; /* Set global queue */
+}
+
+bool vnc_worker_thread_running(void)
+{
+    return queue; /* Check global queue */
+}
+
+void vnc_stop_worker_thread(void)
+{
+    if (!vnc_worker_thread_running())
+        return ;
+
+    /* Remove all jobs and wake up the thread */
+    vnc_lock_queue(queue);
+    queue->exit = true;
+    vnc_unlock_queue(queue);
+    vnc_jobs_clear(NULL);
+    qemu_cond_broadcast(&queue->cond);
+}
diff --git a/ui/vnc-jobs-sync.c b/ui/vnc-jobs-sync.c
new file mode 100644
index 0000000000..49b77afcc9
--- /dev/null
+++ b/ui/vnc-jobs-sync.c
@@ -0,0 +1,73 @@
+/*
+ * QEMU VNC display driver
+ *
+ * Copyright (C) 2006 Anthony Liguori <anthony@codemonkey.ws>
+ * Copyright (C) 2006 Fabrice Bellard
+ * Copyright (C) 2009 Red Hat, Inc
+ * Copyright (C) 2010 Corentin Chary <corentin.chary@gmail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "vnc.h"
+#include "vnc-jobs.h"
+
+void vnc_jobs_clear(VncState *vs)
+{
+}
+
+void vnc_jobs_join(VncState *vs)
+{
+}
+
+VncJob *vnc_job_new(VncState *vs)
+{
+    vs->job.vs = vs;
+    vs->job.rectangles = 0;
+
+    vnc_write_u8(vs, VNC_MSG_SERVER_FRAMEBUFFER_UPDATE);
+    vnc_write_u8(vs, 0);
+    vs->job.saved_offset = vs->output.offset;
+    vnc_write_u16(vs, 0);
+    return &vs->job;
+}
+
+void vnc_job_push(VncJob *job)
+{
+    VncState *vs = job->vs;
+
+    vs->output.buffer[job->saved_offset] = (job->rectangles >> 8) & 0xFF;
+    vs->output.buffer[job->saved_offset + 1] = job->rectangles & 0xFF;
+    vnc_flush(job->vs);
+}
+
+int vnc_job_add_rect(VncJob *job, int x, int y, int w, int h)
+{
+    int n;
+
+    n = vnc_send_framebuffer_update(job->vs, x, y, w, h);
+    if (n >= 0)
+        job->rectangles += n;
+    return n;
+}
+
+bool vnc_has_job(VncState *vs)
+{
+    return false;
+}
diff --git a/ui/vnc-jobs.h b/ui/vnc-jobs.h
new file mode 100644
index 0000000000..b8dab8169f
--- /dev/null
+++ b/ui/vnc-jobs.h
@@ -0,0 +1,87 @@
+/*
+ * QEMU VNC display driver
+ *
+ * From libvncserver/rfb/rfbproto.h
+ * Copyright (C) 2005 Rohit Kumar, Johannes E. Schindelin
+ * Copyright (C) 2000-2002 Constantin Kaplinsky.  All Rights Reserved.
+ * Copyright (C) 2000 Tridia Corporation.  All Rights Reserved.
+ * Copyright (C) 1999 AT&T Laboratories Cambridge.  All Rights Reserved.
+ *
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef VNC_JOBS_H
+#define VNC_JOBS_H
+
+/* Jobs */
+VncJob *vnc_job_new(VncState *vs);
+int vnc_job_add_rect(VncJob *job, int x, int y, int w, int h);
+void vnc_job_push(VncJob *job);
+bool vnc_has_job(VncState *vs);
+void vnc_jobs_clear(VncState *vs);
+void vnc_jobs_join(VncState *vs);
+
+#ifdef CONFIG_VNC_THREAD
+
+void vnc_start_worker_thread(void);
+bool vnc_worker_thread_running(void);
+void vnc_stop_worker_thread(void);
+
+#endif /* CONFIG_VNC_THREAD */
+
+/* Locks */
+static inline int vnc_trylock_display(VncDisplay *vd)
+{
+#ifdef CONFIG_VNC_THREAD
+    return qemu_mutex_trylock(&vd->mutex);
+#else
+    return 0;
+#endif
+}
+
+static inline void vnc_lock_display(VncDisplay *vd)
+{
+#ifdef CONFIG_VNC_THREAD
+    qemu_mutex_lock(&vd->mutex);
+#endif
+}
+
+static inline void vnc_unlock_display(VncDisplay *vd)
+{
+#ifdef CONFIG_VNC_THREAD
+    qemu_mutex_unlock(&vd->mutex);
+#endif
+}
+
+static inline void vnc_lock_output(VncState *vs)
+{
+#ifdef CONFIG_VNC_THREAD
+    qemu_mutex_lock(&vs->output_mutex);
+#endif
+}
+
+static inline void vnc_unlock_output(VncState *vs)
+{
+#ifdef CONFIG_VNC_THREAD
+    qemu_mutex_unlock(&vs->output_mutex);
+#endif
+}
+
+#endif /* VNC_JOBS_H */
diff --git a/ui/vnc.c b/ui/vnc.c
index d0a4b75132..7330b2c889 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -25,6 +25,7 @@
  */
 
 #include "vnc.h"
+#include "vnc-jobs.h"
 #include "sysemu.h"
 #include "qemu_socket.h"
 #include "qemu-timer.h"
@@ -45,7 +46,6 @@
     } \
 }
 
-
 static VncDisplay *vnc_display; /* needed for info vnc */
 static DisplayChangeListener *dcl;
 
@@ -359,6 +359,7 @@ void do_info_vnc(Monitor *mon, QObject **ret_data)
 */
 
 static int vnc_update_client(VncState *vs, int has_dirty);
+static int vnc_update_client_sync(VncState *vs, int has_dirty);
 static void vnc_disconnect_start(VncState *vs);
 static void vnc_disconnect_finish(VncState *vs);
 static void vnc_init_timer(VncDisplay *vd);
@@ -502,19 +503,48 @@ static void vnc_desktop_resize(VncState *vs)
     }
     vs->client_width = ds_get_width(ds);
     vs->client_height = ds_get_height(ds);
+    vnc_lock_output(vs);
     vnc_write_u8(vs, VNC_MSG_SERVER_FRAMEBUFFER_UPDATE);
     vnc_write_u8(vs, 0);
     vnc_write_u16(vs, 1); /* number of rects */
     vnc_framebuffer_update(vs, 0, 0, vs->client_width, vs->client_height,
                            VNC_ENCODING_DESKTOPRESIZE);
+    vnc_unlock_output(vs);
     vnc_flush(vs);
 }
 
+#ifdef CONFIG_VNC_THREAD
+static void vnc_abort_display_jobs(VncDisplay *vd)
+{
+    VncState *vs;
+
+    QTAILQ_FOREACH(vs, &vd->clients, next) {
+        vnc_lock_output(vs);
+        vs->abort = true;
+        vnc_unlock_output(vs);
+    }
+    QTAILQ_FOREACH(vs, &vd->clients, next) {
+        vnc_jobs_join(vs);
+    }
+    QTAILQ_FOREACH(vs, &vd->clients, next) {
+        vnc_lock_output(vs);
+        vs->abort = false;
+        vnc_unlock_output(vs);
+    }
+}
+#else
+static void vnc_abort_display_jobs(VncDisplay *vd)
+{
+}
+#endif
+
 static void vnc_dpy_resize(DisplayState *ds)
 {
     VncDisplay *vd = ds->opaque;
     VncState *vs;
 
+    vnc_abort_display_jobs(vd);
+
     /* server surface */
     if (!vd->server)
         vd->server = qemu_mallocz(sizeof(*vd->server));
@@ -642,7 +672,7 @@ int vnc_raw_send_framebuffer_update(VncState *vs, int x, int y, int w, int h)
     return 1;
 }
 
-static int send_framebuffer_update(VncState *vs, int x, int y, int w, int h)
+int vnc_send_framebuffer_update(VncState *vs, int x, int y, int w, int h)
 {
     int n = 0;
 
@@ -671,12 +701,14 @@ static int send_framebuffer_update(VncState *vs, int x, int y, int w, int h)
 static void vnc_copy(VncState *vs, int src_x, int src_y, int dst_x, int dst_y, int w, int h)
 {
     /* send bitblit op to the vnc client */
+    vnc_lock_output(vs);
     vnc_write_u8(vs, VNC_MSG_SERVER_FRAMEBUFFER_UPDATE);
     vnc_write_u8(vs, 0);
     vnc_write_u16(vs, 1); /* number of rects */
     vnc_framebuffer_update(vs, dst_x, dst_y, w, h, VNC_ENCODING_COPYRECT);
     vnc_write_u16(vs, src_x);
     vnc_write_u16(vs, src_y);
+    vnc_unlock_output(vs);
     vnc_flush(vs);
 }
 
@@ -693,7 +725,7 @@ static void vnc_dpy_copy(DisplayState *ds, int src_x, int src_y, int dst_x, int
     QTAILQ_FOREACH_SAFE(vs, &vd->clients, next, vn) {
         if (vnc_has_feature(vs, VNC_FEATURE_COPYRECT)) {
             vs->force_update = 1;
-            vnc_update_client(vs, 1);
+            vnc_update_client_sync(vs, 1);
             /* vs might be free()ed here */
         }
     }
@@ -813,15 +845,29 @@ static int find_and_clear_dirty_height(struct VncState *vs,
     return h;
 }
 
+#ifdef CONFIG_VNC_THREAD
+static int vnc_update_client_sync(VncState *vs, int has_dirty)
+{
+    int ret = vnc_update_client(vs, has_dirty);
+    vnc_jobs_join(vs);
+    return ret;
+}
+#else
+static int vnc_update_client_sync(VncState *vs, int has_dirty)
+{
+    return vnc_update_client(vs, has_dirty);
+}
+#endif
+
 static int vnc_update_client(VncState *vs, int has_dirty)
 {
     if (vs->need_update && vs->csock != -1) {
         VncDisplay *vd = vs->vd;
+        VncJob *job;
         int y;
-        int n_rectangles;
-        int saved_offset;
         int width, height;
-        int n;
+        int n = 0;
+
 
         if (vs->output.offset && !vs->audio_cap && !vs->force_update)
             /* kernel send buffers are full -> drop frames to throttle */
@@ -836,11 +882,7 @@ static int vnc_update_client(VncState *vs, int has_dirty)
          * happening in parallel don't disturb us, the next pass will
          * send them to the client.
          */
-        n_rectangles = 0;
-        vnc_write_u8(vs, VNC_MSG_SERVER_FRAMEBUFFER_UPDATE);
-        vnc_write_u8(vs, 0);
-        saved_offset = vs->output.offset;
-        vnc_write_u16(vs, 0);
+        job = vnc_job_new(vs);
 
         width = MIN(vd->server->width, vs->client_width);
         height = MIN(vd->server->height, vs->client_height);
@@ -857,25 +899,23 @@ static int vnc_update_client(VncState *vs, int has_dirty)
                 } else {
                     if (last_x != -1) {
                         int h = find_and_clear_dirty_height(vs, y, last_x, x);
-                        n = send_framebuffer_update(vs, last_x * 16, y,
-                                                    (x - last_x) * 16, h);
-                        n_rectangles += n;
+
+                        n += vnc_job_add_rect(job, last_x * 16, y,
+                                              (x - last_x) * 16, h);
                     }
                     last_x = -1;
                 }
             }
             if (last_x != -1) {
                 int h = find_and_clear_dirty_height(vs, y, last_x, x);
-                n = send_framebuffer_update(vs, last_x * 16, y,
-                                            (x - last_x) * 16, h);
-                n_rectangles += n;
+                n += vnc_job_add_rect(job, last_x * 16, y,
+                                      (x - last_x) * 16, h);
             }
         }
-        vs->output.buffer[saved_offset] = (n_rectangles >> 8) & 0xFF;
-        vs->output.buffer[saved_offset + 1] = n_rectangles & 0xFF;
-        vnc_flush(vs);
+
+        vnc_job_push(job);
         vs->force_update = 0;
-        return n_rectangles;
+        return n;
     }
 
     if (vs->csock == -1)
@@ -891,16 +931,20 @@ static void audio_capture_notify(void *opaque, audcnotification_e cmd)
 
     switch (cmd) {
     case AUD_CNOTIFY_DISABLE:
+        vnc_lock_output(vs);
         vnc_write_u8(vs, VNC_MSG_SERVER_QEMU);
         vnc_write_u8(vs, VNC_MSG_SERVER_QEMU_AUDIO);
         vnc_write_u16(vs, VNC_MSG_SERVER_QEMU_AUDIO_END);
+        vnc_unlock_output(vs);
         vnc_flush(vs);
         break;
 
     case AUD_CNOTIFY_ENABLE:
+        vnc_lock_output(vs);
         vnc_write_u8(vs, VNC_MSG_SERVER_QEMU);
         vnc_write_u8(vs, VNC_MSG_SERVER_QEMU_AUDIO);
         vnc_write_u16(vs, VNC_MSG_SERVER_QEMU_AUDIO_BEGIN);
+        vnc_unlock_output(vs);
         vnc_flush(vs);
         break;
     }
@@ -914,11 +958,13 @@ static void audio_capture(void *opaque, void *buf, int size)
 {
     VncState *vs = opaque;
 
+    vnc_lock_output(vs);
     vnc_write_u8(vs, VNC_MSG_SERVER_QEMU);
     vnc_write_u8(vs, VNC_MSG_SERVER_QEMU_AUDIO);
     vnc_write_u16(vs, VNC_MSG_SERVER_QEMU_AUDIO_DATA);
     vnc_write_u32(vs, size);
     vnc_write(vs, buf, size);
+    vnc_unlock_output(vs);
     vnc_flush(vs);
 }
 
@@ -960,6 +1006,9 @@ static void vnc_disconnect_start(VncState *vs)
 
 static void vnc_disconnect_finish(VncState *vs)
 {
+    vnc_jobs_join(vs); /* Wait encoding jobs */
+
+    vnc_lock_output(vs);
     vnc_qmp_event(vs, QEVENT_VNC_DISCONNECTED);
 
     buffer_free(&vs->input);
@@ -988,6 +1037,11 @@ static void vnc_disconnect_finish(VncState *vs)
     vnc_remove_timer(vs->vd);
     if (vs->vd->lock_key_sync)
         qemu_remove_led_event_handler(vs->led);
+    vnc_unlock_output(vs);
+
+#ifdef CONFIG_VNC_THREAD
+    qemu_mutex_destroy(&vs->output_mutex);
+#endif
     qemu_free(vs);
 }
 
@@ -1107,7 +1161,7 @@ static long vnc_client_write_plain(VncState *vs)
  * the client socket. Will delegate actual work according to whether
  * SASL SSF layers are enabled (thus requiring encryption calls)
  */
-void vnc_client_write(void *opaque)
+static void vnc_client_write_locked(void *opaque)
 {
     VncState *vs = opaque;
 
@@ -1121,6 +1175,19 @@ void vnc_client_write(void *opaque)
         vnc_client_write_plain(vs);
 }
 
+void vnc_client_write(void *opaque)
+{
+    VncState *vs = opaque;
+
+    vnc_lock_output(vs);
+    if (vs->output.offset) {
+        vnc_client_write_locked(opaque);
+    } else {
+        qemu_set_fd_handler2(vs->csock, NULL, vnc_client_read, NULL, vs);
+    }
+    vnc_unlock_output(vs);
+}
+
 void vnc_read_when(VncState *vs, VncReadEvent *func, size_t expecting)
 {
     vs->read_handler = func;
@@ -1272,8 +1339,11 @@ void vnc_write_u8(VncState *vs, uint8_t value)
 
 void vnc_flush(VncState *vs)
 {
-    if (vs->csock != -1 && vs->output.offset)
-        vnc_client_write(vs);
+    vnc_lock_output(vs);
+    if (vs->csock != -1 && vs->output.offset) {
+        vnc_client_write_locked(vs);
+    }
+    vnc_unlock_output(vs);
 }
 
 uint8_t read_u8(uint8_t *data, size_t offset)
@@ -1308,12 +1378,14 @@ static void check_pointer_type_change(Notifier *notifier)
     int absolute = kbd_mouse_is_absolute();
 
     if (vnc_has_feature(vs, VNC_FEATURE_POINTER_TYPE_CHANGE) && vs->absolute != absolute) {
+        vnc_lock_output(vs);
         vnc_write_u8(vs, VNC_MSG_SERVER_FRAMEBUFFER_UPDATE);
         vnc_write_u8(vs, 0);
         vnc_write_u16(vs, 1);
         vnc_framebuffer_update(vs, absolute, 0,
                                ds_get_width(vs->ds), ds_get_height(vs->ds),
                                VNC_ENCODING_POINTER_TYPE_CHANGE);
+        vnc_unlock_output(vs);
         vnc_flush(vs);
     }
     vs->absolute = absolute;
@@ -1617,21 +1689,25 @@ static void framebuffer_update_request(VncState *vs, int incremental,
 
 static void send_ext_key_event_ack(VncState *vs)
 {
+    vnc_lock_output(vs);
     vnc_write_u8(vs, VNC_MSG_SERVER_FRAMEBUFFER_UPDATE);
     vnc_write_u8(vs, 0);
     vnc_write_u16(vs, 1);
     vnc_framebuffer_update(vs, 0, 0, ds_get_width(vs->ds), ds_get_height(vs->ds),
                            VNC_ENCODING_EXT_KEY_EVENT);
+    vnc_unlock_output(vs);
     vnc_flush(vs);
 }
 
 static void send_ext_audio_ack(VncState *vs)
 {
+    vnc_lock_output(vs);
     vnc_write_u8(vs, VNC_MSG_SERVER_FRAMEBUFFER_UPDATE);
     vnc_write_u8(vs, 0);
     vnc_write_u16(vs, 1);
     vnc_framebuffer_update(vs, 0, 0, ds_get_width(vs->ds), ds_get_height(vs->ds),
                            VNC_ENCODING_AUDIO);
+    vnc_unlock_output(vs);
     vnc_flush(vs);
 }
 
@@ -1794,12 +1870,14 @@ static void vnc_colordepth(VncState *vs)
 {
     if (vnc_has_feature(vs, VNC_FEATURE_WMVI)) {
         /* Sending a WMVi message to notify the client*/
+        vnc_lock_output(vs);
         vnc_write_u8(vs, VNC_MSG_SERVER_FRAMEBUFFER_UPDATE);
         vnc_write_u8(vs, 0);
         vnc_write_u16(vs, 1); /* number of rects */
         vnc_framebuffer_update(vs, 0, 0, ds_get_width(vs->ds), 
                                ds_get_height(vs->ds), VNC_ENCODING_WMVi);
         pixel_format_message(vs);
+        vnc_unlock_output(vs);
         vnc_flush(vs);
     } else {
         set_pixel_conversion(vs);
@@ -2227,12 +2305,21 @@ static void vnc_refresh(void *opaque)
 
     vga_hw_update();
 
+    if (vnc_trylock_display(vd)) {
+        vd->timer_interval = VNC_REFRESH_INTERVAL_BASE;
+        qemu_mod_timer(vd->timer, qemu_get_clock(rt_clock) +
+                       vd->timer_interval);
+        return;
+    }
+
     has_dirty = vnc_refresh_server_surface(vd);
+    vnc_unlock_display(vd);
 
     QTAILQ_FOREACH_SAFE(vs, &vd->clients, next, vn) {
         rects += vnc_update_client(vs, has_dirty);
         /* vs might be free()ed here */
     }
+
     /* vd->timer could be NULL now if the last client disconnected,
      * in this case don't update the timer */
     if (vd->timer == NULL)
@@ -2291,6 +2378,10 @@ static void vnc_connect(VncDisplay *vd, int csock)
     vs->as.fmt = AUD_FMT_S16;
     vs->as.endianness = 0;
 
+#ifdef CONFIG_VNC_THREAD
+    qemu_mutex_init(&vs->output_mutex);
+#endif
+
     QTAILQ_INSERT_HEAD(&vd->clients, vs, next);
 
     vga_hw_update();
@@ -2348,6 +2439,11 @@ void vnc_display_init(DisplayState *ds)
     if (!vs->kbd_layout)
         exit(1);
 
+#ifdef CONFIG_VNC_THREAD
+    qemu_mutex_init(&vs->mutex);
+    vnc_start_worker_thread();
+#endif
+
     dcl->dpy_copy = vnc_dpy_copy;
     dcl->dpy_update = vnc_dpy_update;
     dcl->dpy_resize = vnc_dpy_resize;
diff --git a/ui/vnc.h b/ui/vnc.h
index 344a68644b..9619b247fb 100644
--- a/ui/vnc.h
+++ b/ui/vnc.h
@@ -29,6 +29,9 @@
 
 #include "qemu-common.h"
 #include "qemu-queue.h"
+#ifdef CONFIG_VNC_THREAD
+#include "qemu-thread.h"
+#endif
 #include "console.h"
 #include "monitor.h"
 #include "audio/audio.h"
@@ -59,6 +62,9 @@ typedef struct Buffer
 } Buffer;
 
 typedef struct VncState VncState;
+typedef struct VncJob VncJob;
+typedef struct VncRect VncRect;
+typedef struct VncRectEntry VncRectEntry;
 
 typedef int VncReadEvent(VncState *vs, uint8_t *data, size_t len);
 
@@ -101,6 +107,9 @@ struct VncDisplay
     DisplayState *ds;
     kbd_layout_t *kbd_layout;
     int lock_key_sync;
+#ifdef CONFIG_VNC_THREAD
+    QemuMutex mutex;
+#endif
 
     QEMUCursor *cursor;
     int cursor_msize;
@@ -152,6 +161,37 @@ typedef struct VncZlib {
     int level;
 } VncZlib;
 
+#ifdef CONFIG_VNC_THREAD
+struct VncRect
+{
+    int x;
+    int y;
+    int w;
+    int h;
+};
+
+struct VncRectEntry
+{
+    struct VncRect rect;
+    QLIST_ENTRY(VncRectEntry) next;
+};
+
+struct VncJob
+{
+    VncState *vs;
+
+    QLIST_HEAD(, VncRectEntry) rectangles;
+    QTAILQ_ENTRY(VncJob) next;
+};
+#else
+struct VncJob
+{
+    VncState *vs;
+    int rectangles;
+    size_t saved_offset;
+};
+#endif
+
 struct VncState
 {
     int csock;
@@ -199,7 +239,16 @@ struct VncState
     uint8_t modifiers_state[256];
     QEMUPutLEDEntry *led;
 
-    /* Encoding specific */
+    bool abort;
+#ifndef CONFIG_VNC_THREAD
+    VncJob job;
+#else
+    QemuMutex output_mutex;
+#endif
+
+    /* Encoding specific, if you add something here, don't forget to
+     *  update vnc_async_encoding_start()
+     */
     VncTight tight;
     VncZlib zlib;
     VncHextile hextile;
@@ -431,6 +480,8 @@ void vnc_framebuffer_update(VncState *vs, int x, int y, int w, int h,
 void vnc_convert_pixel(VncState *vs, uint8_t *buf, uint32_t v);
 
 /* Encodings */
+int vnc_send_framebuffer_update(VncState *vs, int x, int y, int w, int h);
+
 int vnc_raw_send_framebuffer_update(VncState *vs, int x, int y, int w, int h);
 
 int vnc_hextile_send_framebuffer_update(VncState *vs, int x,