[vlc-devel] [RFC] core: player: make the lock optionally reentrant

[Romain Vimont]

On Mon, May 13, 2019 at 04:25:46PM +0300, Rémi Denis-Courmont wrote:
> Hi,
> 
> I don't see the point in adding a parameter here. If you want to use libpulse-like semantics, just make the lock recursive.

The idea here is to use a recursive lock only for libvlc, and keep the
"normal" player lock otherwise.

> But in any case, this won't provide backward compatibility.

This will allow to call functions like libvlc_audio_get_track_count()
from a libvlc player callback like before.

> 
> Le 13 mai 2019 15:47:36 GMT+03:00, Romain Vimont <rom1v at videolabs.io> a écrit :
> >This will allow to implement the old libvlc API using the new player.
> >
> ><https://mailman.videolan.org/pipermail/vlc-devel/2019-May/124461.html>
> >---
> > include/vlc_player.h  | 25 ++++++++++++++++++++++++-
> > src/input/player.c    | 12 ++++++++----
> > src/playlist/player.c |  3 ++-
> > 3 files changed, 34 insertions(+), 6 deletions(-)
> >
> >diff --git a/include/vlc_player.h b/include/vlc_player.h
> >index 1aa5f8e687..d4c49fa89d 100644
> >--- a/include/vlc_player.h
> >+++ b/include/vlc_player.h
> >@@ -331,6 +331,29 @@ enum vlc_player_subtitle_sync
> >     VLC_PLAYER_SUBTITLE_SYNC_APPLY,
> > };
> > 
> >+/**
> >+ * Player lock type (normal or reentrant)
> >+ */
> >+enum vlc_player_lock_type
> >+{
> >+    /**
> >+     * Normal lock
> >+     *
> >+     * If the player is already locked, subsequent calls to
> >vlc_player_Lock()
> >+     * will deadlock.
> >+     */
> >+    VLC_PLAYER_LOCK_NORMAL,
> >+
> >+    /**
> >+     * Reentrant lock
> >+     *
> >+     * If the player is already locked, subsequent calls to
> >vlc_player_Lock()
> >+     * will still succeed. To unlock the player, one call to
> >+     * vlc_player_Unlock() per vlc_player_Lock() is necessary.
> >+     */
> >+    VLC_PLAYER_LOCK_REENTRANT,
> >+};
> >+
> > /** Player capability: can seek */
> > #define VLC_PLAYER_CAP_SEEK (1<<0)
> > /** Player capability: can pause */
> >@@ -1005,7 +1028,7 @@ vlc_player_title_list_GetAt(vlc_player_title_list
> >*titles, size_t idx);
> >* @return a pointer to a valid player instance or NULL in case of error
> >  */
> > VLC_API vlc_player_t *
> >-vlc_player_New(vlc_object_t *parent,
> >+vlc_player_New(vlc_object_t *parent, enum vlc_player_lock_type
> >lock_type,
> >                const struct vlc_player_media_provider *media_provider,
> >                void *media_provider_data);
> > 
> >diff --git a/src/input/player.c b/src/input/player.c
> >index da02375a66..e01701ba65 100644
> >--- a/src/input/player.c
> >+++ b/src/input/player.c
> >@@ -3367,9 +3367,13 @@ vlc_player_vout_Snapshot(vlc_player_t *player)
> > }
> > 
> > static void
> >-vlc_player_InitLocks(vlc_player_t *player)
> >+vlc_player_InitLocks(vlc_player_t *player, enum vlc_player_lock_type
> >lock_type)
> > {
> >-    vlc_mutex_init(&player->lock);
> >+    if (lock_type == VLC_PLAYER_LOCK_REENTRANT)
> >+        vlc_mutex_init_recursive(&player->lock);
> >+    else
> >+        vlc_mutex_init(&player->lock);
> >+
> >     vlc_mutex_init(&player->vout_listeners_lock);
> >     vlc_mutex_init(&player->aout_listeners_lock);
> >     vlc_cond_init(&player->start_delay_cond);
> >@@ -3426,7 +3430,7 @@ vlc_player_Delete(vlc_player_t *player)
> > }
> > 
> > vlc_player_t *
> >-vlc_player_New(vlc_object_t *parent,
> >+vlc_player_New(vlc_object_t *parent, enum vlc_player_lock_type
> >lock_type,
> >                const struct vlc_player_media_provider *media_provider,
> >                void *media_provider_data)
> > {
> >@@ -3514,7 +3518,7 @@ vlc_player_New(vlc_object_t *parent,
> >     }
> > 
> >     player->deleting = false;
> >-    vlc_player_InitLocks(player);
> >+    vlc_player_InitLocks(player, lock_type);
> > 
> >if (vlc_clone(&player->destructor.thread, vlc_player_destructor_Thread,
> >                   player, VLC_THREAD_PRIORITY_LOW) != 0)
> >diff --git a/src/playlist/player.c b/src/playlist/player.c
> >index bbdc39ba0e..8e3d94e2e8 100644
> >--- a/src/playlist/player.c
> >+++ b/src/playlist/player.c
> >@@ -123,7 +123,8 @@ static const struct vlc_player_cbs player_callbacks
> >= {
> > bool
> >vlc_playlist_PlayerInit(vlc_playlist_t *playlist, vlc_object_t *parent)
> > {
> >-    playlist->player = vlc_player_New(parent, &player_media_provider,
> >playlist);
> >+    playlist->player = vlc_player_New(parent, VLC_PLAYER_LOCK_NORMAL,
> >+                                      &player_media_provider,
> >playlist);
> >     if (unlikely(!playlist->player))
> >         return false;
> > 
> >-- 
> >2.20.1
> >
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> -- 
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