player: update cache state only if requested

Add a mechanism to the client API code, which allows the player core to
query whether a client API event is needed at all. Use it for the cache
update.

In this case, this is probably a pure microoptimization; but the
mechanism will be useful for other things too.

player/client.c

@@ -59,6 +59,7 @@ struct mp_client_api {
     // -- protected by lock
     struct mpv_handle **clients;
     int num_clients;
+    uint64_t event_masks;   // combined events of all clients, or 0 if unknown
 };
 
 struct observe_property {
@@ -150,6 +151,13 @@ int mp_clients_num(struct MPContext *mpctx)
     return num_clients;
 }
 
+static void invalidate_global_event_mask(struct mpv_handle *ctx)
+{
+    pthread_mutex_lock(&ctx->clients->lock);
+    ctx->clients->event_masks = 0;
+    pthread_mutex_unlock(&ctx->clients->lock);
+}
+
 static struct mpv_handle *find_client(struct mp_client_api *clients,
                                       const char *name)
 {
@@ -199,12 +207,14 @@ struct mpv_handle *mp_new_client(struct mp_client_api *clients, const char *name
     pthread_mutex_init(&client->wakeup_lock, NULL);
     pthread_cond_init(&client->wakeup, NULL);
 
-    mpv_request_event(client, MPV_EVENT_TICK, 0);
 
     MP_TARRAY_APPEND(clients, clients->clients, clients->num_clients, client);
 
+    clients->event_masks = 0;
     pthread_mutex_unlock(&clients->lock);
 
+    mpv_request_event(client, MPV_EVENT_TICK, 0);
+
     return client;
 }
 
@@ -502,6 +512,29 @@ static void dup_event_data(struct mpv_event *ev)
     }
 }
 
+// Return whether there's any client listening to this event.
+// If false is returned, the core doesn't need to send it.
+bool mp_client_event_is_registered(struct MPContext *mpctx, int event)
+{
+    struct mp_client_api *clients = mpctx->clients;
+
+    pthread_mutex_lock(&clients->lock);
+
+    if (!clients->event_masks) { // lazy update
+        for (int n = 0; n < clients->num_clients; n++) {
+            struct mpv_handle *ctx = clients->clients[n];
+            pthread_mutex_lock(&ctx->lock);
+            clients->event_masks |= ctx->event_mask | ctx->property_event_masks;
+            pthread_mutex_unlock(&ctx->lock);
+        }
+    }
+    bool r = clients->event_masks & (1ULL << event);
+
+    pthread_mutex_unlock(&clients->lock);
+
+    return r;
+}
+
 void mp_client_broadcast_event(struct MPContext *mpctx, int event, void *data)
 {
     struct mp_client_api *clients = mpctx->clients;
@@ -555,6 +588,7 @@ int mpv_request_event(mpv_handle *ctx, mpv_event_id event, int enable)
     uint64_t bit = 1ULL << event;
     ctx->event_mask = enable ? ctx->event_mask | bit : ctx->event_mask & ~bit;
     pthread_mutex_unlock(&ctx->lock);
+    invalidate_global_event_mask(ctx);
     return 0;
 }
 
@@ -1140,6 +1174,7 @@ int mpv_observe_property(mpv_handle *ctx, uint64_t userdata,
     ctx->property_event_masks |= prop->event_mask;
     ctx->lowest_changed = 0;
     pthread_mutex_unlock(&ctx->lock);
+    invalidate_global_event_mask(ctx);
     return 0;
 }
 
@@ -1168,6 +1203,7 @@ int mpv_unobserve_property(mpv_handle *ctx, uint64_t userdata)
     }
     ctx->lowest_changed = 0;
     pthread_mutex_unlock(&ctx->lock);
+    invalidate_global_event_mask(ctx);
     return count;
 }
 

player/client.h

@@ -17,6 +17,7 @@ int mp_clients_num(struct MPContext *mpctx);
 void mp_client_broadcast_event(struct MPContext *mpctx, int event, void *data);
 int mp_client_send_event(struct MPContext *mpctx, const char *client_name,
                          int event, void *data);
+bool mp_client_event_is_registered(struct MPContext *mpctx, int event);
 void mp_client_property_change(struct MPContext *mpctx, const char *name);
 
 struct mpv_handle *mp_new_client(struct mp_client_api *clients, const char *name);

player/playloop.c

@@ -49,6 +49,7 @@
 #include "video/out/vo.h"
 
 #include "core.h"
+#include "client.h"
 #include "command.h"
 
 void pause_player(struct MPContext *mpctx)
@@ -556,7 +557,11 @@ static void handle_pause_on_low_cache(struct MPContext *mpctx)
     }
 
     // Also update cache properties.
-    bool busy = idle == 0 || !s.idle;
+    bool busy = idle == 0;
+    if (!s.idle) {
+        busy |= idle != -1;
+        busy |= mp_client_event_is_registered(mpctx, MP_EVENT_CACHE_UPDATE);
+    }
     if (busy || mpctx->next_cache_update > 0) {
         double now = mp_time_sec();
         if (mpctx->next_cache_update <= now) {