From e8f21b1f0ac499f672703bb7d382e19f9111b3e3 Mon Sep 17 00:00:00 2001
From: wm4 <wm4@nowhere>
Date: Sun, 15 Dec 2013 21:33:31 +0100
Subject: input: avoid using wakeup pipe if it's not needed

If input is not waiting for select(), writing to the wakeup pipe is
wasteful, and, if there are many wakeups, might even block the wakeup
threads if the pipe gets full.

However, if it's waiting for select(), the wakup pipe must be used to
unblock the waiting thread. Actually there's a small race condition: we
might determine that the main thread is in select(), and write to the
wakeup pipe (whether we do this while unlocked or locked doesn't really
matter). Then, the main thread might leave select() before reading from
the wakup pipe. This should be harmless, because at worst more wakeups
than needed happen, but never fewer.
---
 mpvcore/input/input.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/mpvcore/input/input.c b/mpvcore/input/input.c
index 26ab1a62ad..df6c11b032 100644
--- a/mpvcore/input/input.c
+++ b/mpvcore/input/input.c
@@ -607,6 +607,7 @@ struct input_ctx {
 
     struct cmd_queue cmd_queue;
 
+    bool in_select;
     int wakeup_pipe[2];
 };
 
@@ -1798,6 +1799,7 @@ static void input_wait_read(struct input_ctx *ictx, int time)
     tv.tv_sec = time / 1000;
     tv.tv_usec = (time % 1000) * 1000;
     time_val = &tv;
+    ictx->in_select = true;
     input_unlock(ictx);
     if (select(max_fd + 1, &fds, NULL, NULL, time_val) < 0) {
         if (errno != EINTR)
@@ -1805,6 +1807,7 @@ static void input_wait_read(struct input_ctx *ictx, int time)
         FD_ZERO(&fds);
     }
     input_lock(ictx);
+    ictx->in_select = false;
     for (int i = 0; i < ictx->num_fds; i++) {
         if (ictx->fds[i].select && !FD_ISSET(ictx->fds[i].fd, &fds))
             continue;
@@ -1874,6 +1877,7 @@ int mp_input_queue_cmd(struct input_ctx *ictx, mp_cmd_t *cmd)
     if (cmd)
         queue_add_tail(&ictx->cmd_queue, cmd);
     input_unlock(ictx);
+    mp_input_wakeup(ictx);
     return 1;
 }
 
@@ -2511,8 +2515,12 @@ static int print_cmd_list(m_option_t *cfg, char *optname, char *optparam)
 
 void mp_input_wakeup(struct input_ctx *ictx)
 {
+    input_lock(ictx);
+    bool send_wakeup = ictx->in_select;
+    ictx->got_new_events = true;
+    input_unlock(ictx);
     // Safe without locking
-    if (ictx->wakeup_pipe[1] >= 0)
+    if (send_wakeup && ictx->wakeup_pipe[1] >= 0)
         write(ictx->wakeup_pipe[1], &(char){0}, 1);
 }
 
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