Helpers to emit asynchronous key press events (refs #3661)

We have the same bug in several outputs (SDL, AA, CACA), so lets make
the solution generic.
(cherry picked from commit cb72d26f0825b31fd10af18a03763b41067cfe37)

modules/video_output/keythread.c

+/*****************************************************************************
+ * keythread.c: Asynchronous threads to emit key events
+ *****************************************************************************
+ * Copyright (C) 2010 Rémi Denis-Courmont
+ *
+ * This program 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 program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ *****************************************************************************/
+
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <stdlib.h>
+
+#include <vlc_common.h>
+#include <assert.h>
+
+#include "keythread.h"
+
+struct key_thread
+{
+    vlc_object_t *libvlc;
+    int          value;
+    vlc_mutex_t  lock;
+    vlc_cond_t   wait;
+    vlc_thread_t thread;
+};
+
+static void *KeyThread (void *data)
+{
+    key_thread_t *keys = data;
+
+    mutex_cleanup_push (&keys->lock);
+    for (;;)
+    {
+        int value;
+
+        vlc_mutex_lock (&keys->lock);
+        /* Note: Key strokes may be lost. A chained list should be used. */
+        while (!(value = keys->value))
+            vlc_cond_wait (&keys->wait, &keys->lock);
+        keys->value = 0;
+        vlc_mutex_unlock (&keys->lock);
+
+        int canc = vlc_savecancel ();
+        var_SetInteger (keys->libvlc, "key-pressed", value);
+        vlc_restorecancel (canc);
+    }
+
+    vlc_cleanup_pop ();
+    assert (0);
+}
+
+
+#undef vlc_CreateKeyThread
+/**
+ * Create an asynchronous key event thread.
+ *
+ * Normally, key events are received by the interface thread (e.g. Qt4), or
+ * the window provider (e.g. XCB). However, some legacy video output plugins
+ * do not use window providers, neither do they run their own event threads.
+ * Instead, those lame video outputs insist on receiving key events from their
+ * Manage() function.
+ *
+ * Some key event handlers are quite slow so they should not be triggered from
+ * the video output thread. Worse yet, some handlers (such as snapshot) would
+ * deadlock if triggered from the video output thread.
+ */
+key_thread_t *vlc_CreateKeyThread (vlc_object_t *obj)
+{
+    key_thread_t *keys = malloc (sizeof (*keys));
+    if (unlikely(keys == NULL))
+        return NULL;
+
+    keys->libvlc = VLC_OBJECT(obj->p_libvlc);
+    keys->value = 0;
+    vlc_mutex_init (&keys->lock);
+    vlc_cond_init (&keys->wait);
+    if (vlc_clone (&keys->thread, KeyThread, keys, VLC_THREAD_PRIORITY_LOW))
+    {
+        vlc_cond_destroy (&keys->wait);
+        vlc_mutex_destroy (&keys->lock);
+        free (keys);
+        return NULL;
+    }
+    return keys;
+}
+
+void vlc_DestroyKeyThread (key_thread_t *keys)
+{
+    if (keys == NULL)
+        return;
+
+    vlc_cancel (keys->thread);
+    vlc_join(keys->thread, NULL);
+    vlc_cond_destroy(&keys->wait);
+    vlc_mutex_destroy(&keys->lock);
+    free (keys);
+}
+
+void vlc_EmitKey (key_thread_t *keys, int value)
+{
+    if (keys == NULL)
+        return;
+
+    vlc_mutex_lock(&keys->lock);
+    keys->value = value;
+    vlc_cond_signal(&keys->wait);
+    vlc_mutex_unlock(&keys->lock);
+}

modules/video_output/keythread.h

+/*****************************************************************************
+ * keythread.h:
+ *****************************************************************************
+ * Copyright (C) 2010 Rémi Denis-Courmont
+ *
+ * This program 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 program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ *****************************************************************************/
+
+typedef struct key_thread key_thread_t;
+
+key_thread_t *vlc_CreateKeyThread (vlc_object_t *obj);
+#define vlc_CreateKeyThread(o) vlc_CreateKeyThread(VLC_OBJECT(o))
+void vlc_DestroyKeyThread (key_thread_t *keys);
+void vlc_EmitKey (key_thread_t *keys, int value);