[vlc-commits] [Git][videolan/vlc][master] 3 commits: vout: rename "is_waiting" to "yielding"

[Romain Vimont (@rom1v)]

Romain Vimont pushed to branch master at VideoLAN / VLC


Commits:
936bceb9 by Romain Vimont at 2021-07-07T09:51:39+00:00
vout: rename "is_waiting" to "yielding"

This highlights that the flag is true when the vout thread is yielding
execution to another thread waiting on vout_control_Enter().

Avoiding the term "waiting" will allow to avoid confusion in next
commits when a new flag will be added.

- - - - -
036567a9 by Romain Vimont at 2021-07-07T09:51:39+00:00
vout: document a wait condition

The wait condition is not related to a single flag, but two. Document
the condition in a comment.

- - - - -
8fe76a5b by Romain Vimont at 2021-07-07T09:51:39+00:00
vout: always pass vout_control_Hold()

A thread calling vout_control_Hold() may only pass while
vout_control_Pop() is waiting.

Since f1bf7ce5b4480a3d38d54c7ae1d1564f0670d83f, in practice, it almost
never waits, so vout_control_Hold() may be blocked for a long time.

If there is at least one thread waiting on vout_control_Hold(), make
the vout thread wait from vout_control_Pop().

Fixes #25694

- - - - -


2 changed files:

- src/video_output/control.c
- src/video_output/control.h


Changes:

=====================================
src/video_output/control.c
=====================================
@@ -37,8 +37,9 @@ void vout_control_Init(vout_control_t *ctrl)
     vlc_cond_init(&ctrl->wait_available);
 
     ctrl->is_held = false;
-    ctrl->is_waiting = false;
+    ctrl->yielding = false;
     ctrl->forced_awake = false;
+    ctrl->pending_count = 0;
     ARRAY_INIT(ctrl->cmd);
 }
 
@@ -67,9 +68,14 @@ void vout_control_Wake(vout_control_t *ctrl)
 void vout_control_Hold(vout_control_t *ctrl)
 {
     vlc_mutex_lock(&ctrl->lock);
-    while (ctrl->is_held || !ctrl->is_waiting)
+    ++ctrl->pending_count;
+    vlc_cond_signal(&ctrl->wait_request);
+    while (ctrl->is_held || !ctrl->yielding)
         vlc_cond_wait(&ctrl->wait_available, &ctrl->lock);
     ctrl->is_held = true;
+    --ctrl->pending_count;
+    if (ctrl->pending_count == 0)
+        vlc_cond_signal(&ctrl->wait_request);
     vlc_mutex_unlock(&ctrl->lock);
 }
 
@@ -87,14 +93,32 @@ int vout_control_Pop(vout_control_t *ctrl, vlc_mouse_t *mouse, vlc_tick_t deadli
     bool has_cmd = false;
     vlc_mutex_lock(&ctrl->lock);
 
-    if (ctrl->cmd.i_size <= 0) {
-        /* Spurious wakeups are perfectly fine */
-        if (deadline != VLC_TICK_INVALID && !ctrl->forced_awake) {
-            ctrl->is_waiting = true;
+    bool timed_out = false;
+    for (;;)
+    {
+        if (ctrl->forced_awake)
+            break;
+
+        if (ctrl->pending_count != 0)
+        {
+            /* Let vout_control_Hold() callers pass */
+            ctrl->yielding = true;
+            vlc_cond_signal(&ctrl->wait_available);
+            vlc_cond_wait(&ctrl->wait_request, &ctrl->lock);
+            ctrl->yielding = false;
+        }
+        else if (timed_out)
+            break;
+        else if (ctrl->cmd.i_size <= 0 && deadline != VLC_TICK_INVALID)
+        {
+            ctrl->yielding = true;
             vlc_cond_signal(&ctrl->wait_available);
-            vlc_cond_timedwait(&ctrl->wait_request, &ctrl->lock, deadline);
-            ctrl->is_waiting = false;
+            timed_out =
+                vlc_cond_timedwait(&ctrl->wait_request, &ctrl->lock, deadline);
+            ctrl->yielding = false;
         }
+        else
+            break;
     }
 
     while (ctrl->is_held)


=====================================
src/video_output/control.h
=====================================
@@ -28,13 +28,14 @@
 /* */
 typedef struct {
     vlc_mutex_t lock;
-    vlc_cond_t  wait_request;
-    vlc_cond_t  wait_available;
+    vlc_cond_t wait_request;
+    vlc_cond_t wait_available; /* available: yielding && !is_held */
 
     /* */
     bool forced_awake;
-    bool is_waiting;
+    bool yielding;
     bool is_held;
+    unsigned pending_count;
     DECL_ARRAY(vlc_mouse_t) cmd;
 } vout_control_t;
 



View it on GitLab: https://code.videolan.org/videolan/vlc/-/compare/3af1b9dc30bcf6e378d81fc1229bd3f8ad3bf363...8fe76a5b9675809874d361f858b2b6b6362ffca4

-- 
View it on GitLab: https://code.videolan.org/videolan/vlc/-/compare/3af1b9dc30bcf6e378d81fc1229bd3f8ad3bf363...8fe76a5b9675809874d361f858b2b6b6362ffca4
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