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Limit number of prefetch requests.

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Konstantin Seiler 2019-11-18 10:54:44 +11:00
parent 05b281f085
commit db0e4a0422
1 changed files with 34 additions and 18 deletions
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52
audio/src/fetch.rs
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@ -49,13 +49,13 @@ pub const READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS: f64 = 2.0;
// Note: the calculations are done using the nominal bitrate of the file. The actual amount // Note: the calculations are done using the nominal bitrate of the file. The actual amount
// of audio data may be larger or smaller. // of audio data may be larger or smaller.
pub const READ_AHEAD_DURING_PLAYBACK_SECONDS: f64 = 1.0; pub const READ_AHEAD_DURING_PLAYBACK_SECONDS: f64 = 5.0;
// While playing back, this many seconds of data ahead of the current read position are // While playing back, this many seconds of data ahead of the current read position are
// requested. // requested.
// Note: the calculations are done using the nominal bitrate of the file. The actual amount // Note: the calculations are done using the nominal bitrate of the file. The actual amount
// of audio data may be larger or smaller. // of audio data may be larger or smaller.
pub const READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS: f64 = 2.0; pub const READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS: f64 = 10.0;
// Same as READ_AHEAD_DURING_PLAYBACK_SECONDS, but the time is taken as a factor of the ping // Same as READ_AHEAD_DURING_PLAYBACK_SECONDS, but the time is taken as a factor of the ping
// time to the Spotify server. // time to the Spotify server.
// Note: the calculations are done using the nominal bitrate of the file. The actual amount // Note: the calculations are done using the nominal bitrate of the file. The actual amount
@ -77,6 +77,13 @@ const FAST_PREFETCH_THRESHOLD_FACTOR: f64 = 1.5;
// performed while downloading. Values smaller than 1 cause the download rate to collapse and effectively // performed while downloading. Values smaller than 1 cause the download rate to collapse and effectively
// only PREFETCH_THRESHOLD_FACTOR is in effect. Thus, set to zero if bandwidth saturation is not wanted. // only PREFETCH_THRESHOLD_FACTOR is in effect. Thus, set to zero if bandwidth saturation is not wanted.
const MAX_PREFETCH_REQUESTS: usize = 4;
// Limit the number of requests that are pending simultaneously before pre-fetching data. Pending
// requests share bandwidth. Thus, havint too many requests can lead to the one that is needed next
// for playback to be delayed leading to a buffer underrun. This limit has the effect that a new
// pre-fetch request is only sent if less than MAX_PREFETCH_REQUESTS are pending.
pub enum AudioFile { pub enum AudioFile {
Cached(fs::File), Cached(fs::File),
Streaming(AudioFileStreaming), Streaming(AudioFileStreaming),
@ -726,10 +733,11 @@ impl AudioFileFetch {
} }
} }
fn pre_fetch_more_data(&mut self, bytes: usize) { fn pre_fetch_more_data(&mut self, bytes: usize, max_requests_to_send: usize) {
let mut bytes_to_go = bytes; let mut bytes_to_go = bytes;
let mut requests_to_go = max_requests_to_send;
while bytes_to_go > 0 { while bytes_to_go > 0 && requests_to_go > 0 {
// determine what is still missing // determine what is still missing
let mut missing_data = RangeSet::new(); let mut missing_data = RangeSet::new();
missing_data.add_range(&Range::new(0, self.shared.file_size)); missing_data.add_range(&Range::new(0, self.shared.file_size));
@ -750,6 +758,7 @@ impl AudioFileFetch {
let offset = range.start; let offset = range.start;
let length = min(range.length, bytes_to_go); let length = min(range.length, bytes_to_go);
self.download_range(offset, length); self.download_range(offset, length);
requests_to_go -=1;
bytes_to_go -= length; bytes_to_go -= length;
} else if !missing_data.is_empty() { } else if !missing_data.is_empty() {
// ok, the tail is downloaded, download something fom the beginning. // ok, the tail is downloaded, download something fom the beginning.
@ -757,6 +766,7 @@ impl AudioFileFetch {
let offset = range.start; let offset = range.start;
let length = min(range.length, bytes_to_go); let length = min(range.length, bytes_to_go);
self.download_range(offset, length); self.download_range(offset, length);
requests_to_go -=1;
bytes_to_go -= length; bytes_to_go -= length;
} else { } else {
return; return;
@ -899,23 +909,29 @@ impl Future for AudioFileFetch {
} }
if let DownloadStrategy::Streaming() = self.get_download_strategy() { if let DownloadStrategy::Streaming() = self.get_download_strategy() {
let bytes_pending: usize = {
let download_status = self.shared.download_status.lock().unwrap();
download_status.requested.minus(&download_status.downloaded).len()
};
let ping_time_seconds = let number_of_open_requests = self.shared.number_of_open_requests.load(atomic::Ordering::SeqCst);
0.001 * self.shared.ping_time_ms.load(atomic::Ordering::Relaxed) as f64; let max_requests_to_send = MAX_PREFETCH_REQUESTS - min(MAX_PREFETCH_REQUESTS, number_of_open_requests);
let download_rate = self.session.channel().get_download_rate_estimate();
let desired_pending_bytes = max( if (max_requests_to_send > 0) {
(PREFETCH_THRESHOLD_FACTOR * ping_time_seconds * self.shared.stream_data_rate as f64) let bytes_pending: usize = {
as usize, let download_status = self.shared.download_status.lock().unwrap();
(FAST_PREFETCH_THRESHOLD_FACTOR * ping_time_seconds * download_rate as f64) as usize, download_status.requested.minus(&download_status.downloaded).len()
); };
if bytes_pending < desired_pending_bytes { let ping_time_seconds =
self.pre_fetch_more_data(desired_pending_bytes - bytes_pending); 0.001 * self.shared.ping_time_ms.load(atomic::Ordering::Relaxed) as f64;
let download_rate = self.session.channel().get_download_rate_estimate();
let desired_pending_bytes = max(
(PREFETCH_THRESHOLD_FACTOR * ping_time_seconds * self.shared.stream_data_rate as f64)
as usize,
(FAST_PREFETCH_THRESHOLD_FACTOR * ping_time_seconds * download_rate as f64) as usize,
);
if bytes_pending < desired_pending_bytes {
self.pre_fetch_more_data(desired_pending_bytes - bytes_pending, max_requests_to_send);
}
} }
} }