From c59ca06a0fff432ac4cae012bb0299a8db9a00d3 Mon Sep 17 00:00:00 2001
From: wm4 <wm4@nowhere>
Date: Fri, 14 Feb 2020 16:07:13 +0100
Subject: stream_file: cache file size

Some cache logic in demux.c queries the raw byte stream size on every
packet read. This is because it reports the value to the user. (It has
to be polled like this because there is no change notification in most
underlying I/O APIs, and also the user can't just block on the demuxer
thread to update it explicitly.)

This causes a very high number of get_size calls with low packet sizes,
so cache the size, and update it on every read. Reads only happen
approximately all 64KB read with default settings, which is way less
frequent than every packet in such extreme cases.

In theory, this could in theory cause problems in some cases. Actually
this is whole commit complete non-sense, because why micro-optimize for
broken cases like patent troll codecs. I don't need to justify it
anyway.

As a minor detail, off_t is actually specified as signed, so the off_t
cast is never needed.
---
 stream/stream_file.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/stream/stream_file.c b/stream/stream_file.c
index a79ef0e913..6e69f33c94 100644
--- a/stream/stream_file.c
+++ b/stream/stream_file.c
@@ -64,6 +64,7 @@ struct priv {
     bool use_poll;
     bool regular_file;
     bool appending;
+    int64_t cached_size; // -2: invalid, -1: unknown
     int64_t orig_size;
     struct mp_cancel *cancel;
 };
@@ -75,15 +76,20 @@ struct priv {
 static int64_t get_size(stream_t *s)
 {
     struct priv *p = s->priv;
-    off_t size = lseek(p->fd, 0, SEEK_END);
-    lseek(p->fd, s->pos, SEEK_SET);
-    return size == (off_t)-1 ? -1 : size;
+    if (p->cached_size == -2) {
+        off_t size = lseek(p->fd, 0, SEEK_END);
+        lseek(p->fd, s->pos, SEEK_SET);
+        p->cached_size = size < 0 ? -1 : size;
+    }
+    return p->cached_size;
 }
 
 static int fill_buffer(stream_t *s, void *buffer, int max_len)
 {
     struct priv *p = s->priv;
 
+    p->cached_size = -2; // always invalidate cached size
+
 #ifndef __MINGW32__
     if (p->use_poll) {
         int c = mp_cancel_get_fd(p->cancel);
@@ -245,7 +251,8 @@ static int open_f(stream_t *stream)
 {
     struct priv *p = talloc_ptrtype(stream, p);
     *p = (struct priv) {
-        .fd = -1
+        .fd = -1,
+        .cached_size = -2,
     };
     stream->priv = p;
     stream->is_local_file = true;
-- 
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