[vlc-devel] [PATCH 10/10] vout: control: replace the custom hold/release/wait by a vlc_sem_t

[Steve Lhomme]

The goal is to protect the access to the command array.

We still allow pushing commands from the thread holding the command array, to
avoid a deadlock if the same thread tries to request this resource twice.
---
 src/video_output/control.c | 28 ++++++++--------------------
 src/video_output/control.h |  4 +---
 2 files changed, 9 insertions(+), 23 deletions(-)

diff --git a/src/video_output/control.c b/src/video_output/control.c
index 52960d66591..da08d362164 100644
--- a/src/video_output/control.c
+++ b/src/video_output/control.c
@@ -43,10 +43,8 @@ void vout_control_cmd_Clean(vout_control_cmd_t *cmd)
 /* */
 void vout_control_Init(vout_control_t *ctrl)
 {
-    vlc_mutex_init(&ctrl->lock);
-    vlc_cond_init(&ctrl->wait_available);
+    vlc_sem_init(&ctrl->lock, 1);
 
-    ctrl->is_held = false;
     atomic_init(&ctrl->is_dead, false);
     ARRAY_INIT(ctrl->cmd);
 }
@@ -68,13 +66,14 @@ void vout_control_Dead(vout_control_t *ctrl)
 
 static void vout_control_Push(vout_control_t *ctrl, vout_control_cmd_t *cmd)
 {
-    vlc_mutex_lock(&ctrl->lock);
+    bool locked = vlc_sem_trywait(&ctrl->lock) == 0;
     if (!atomic_load(&ctrl->is_dead)) {
         ARRAY_APPEND(ctrl->cmd, *cmd);
     } else {
         vout_control_cmd_Clean(cmd);
     }
-    vlc_mutex_unlock(&ctrl->lock);
+    if (locked)
+        vlc_sem_post(&ctrl->lock);
 }
 
 void vout_control_PushVoid(vout_control_t *ctrl, int type)
@@ -110,28 +109,17 @@ void vout_control_PushMouse(vout_control_t *ctrl, int type, const vlc_mouse_t *m
 
 void vout_control_Hold(vout_control_t *ctrl)
 {
-    vlc_mutex_lock(&ctrl->lock);
-    while (ctrl->is_held)
-        vlc_cond_wait(&ctrl->wait_available, &ctrl->lock);
-    ctrl->is_held = true;
-    vlc_mutex_unlock(&ctrl->lock);
+    vlc_sem_wait(&ctrl->lock);
 }
 
 void vout_control_Release(vout_control_t *ctrl)
 {
-    vlc_mutex_lock(&ctrl->lock);
-    assert(ctrl->is_held);
-    ctrl->is_held = false;
-    vlc_cond_signal(&ctrl->wait_available);
-    vlc_mutex_unlock(&ctrl->lock);
+    vlc_sem_post(&ctrl->lock);
 }
 
 int vout_control_Pop(vout_control_t *ctrl, vout_control_cmd_t *cmd)
 {
-    vlc_mutex_lock(&ctrl->lock);
-
-    while (ctrl->is_held)
-        vlc_cond_wait(&ctrl->wait_available, &ctrl->lock);
+    vlc_sem_wait(&ctrl->lock);
 
     int ret;
     if (ctrl->cmd.i_size > 0) {
@@ -141,7 +129,7 @@ int vout_control_Pop(vout_control_t *ctrl, vout_control_cmd_t *cmd)
     } else {
         ret = VLC_EGENERIC;
     }
-    vlc_mutex_unlock(&ctrl->lock);
+    vlc_sem_post(&ctrl->lock);
 
     return ret;
 }
diff --git a/src/video_output/control.h b/src/video_output/control.h
index 882b887b959..91afdd92f64 100644
--- a/src/video_output/control.h
+++ b/src/video_output/control.h
@@ -47,12 +47,10 @@ typedef struct {
 void vout_control_cmd_Clean(vout_control_cmd_t *);
 
 typedef struct {
-    vlc_mutex_t lock;
-    vlc_cond_t  wait_available;
+    vlc_sem_t   lock;
 
     /* */
     atomic_bool is_dead;
-    bool is_held;
     DECL_ARRAY(vout_control_cmd_t) cmd;
 } vout_control_t;
 
-- 
2.26.2