Improve performance of getting/setting download mode

audio/src/fetch/mod.rs

@@ -5,7 +5,7 @@ use std::{
     fs,
     io::{self, Read, Seek, SeekFrom},
     sync::{
-        atomic::{AtomicUsize, Ordering},
+        atomic::{AtomicBool, AtomicUsize, Ordering},
         Arc,
     },
     time::{Duration, Instant},
@@ -138,9 +138,9 @@ pub struct StreamingRequest {
 #[derive(Debug)]
 pub enum StreamLoaderCommand {
     Fetch(Range),     // signal the stream loader to fetch a range of the file
-    RandomAccessMode(), // optimise download strategy for random access
-    StreamMode(),       // optimise download strategy for streaming
-    Close(),            // terminate and don't load any more data
+    RandomAccessMode, // optimise download strategy for random access
+    StreamMode,       // optimise download strategy for streaming
+    Close,            // terminate and don't load any more data
 }
 
 #[derive(Clone)]
@@ -299,17 +299,17 @@ impl StreamLoaderController {
 
     pub fn set_random_access_mode(&self) {
         // optimise download strategy for random access
-        self.send_stream_loader_command(StreamLoaderCommand::RandomAccessMode());
+        self.send_stream_loader_command(StreamLoaderCommand::RandomAccessMode);
     }
 
     pub fn set_stream_mode(&self) {
         // optimise download strategy for streaming
-        self.send_stream_loader_command(StreamLoaderCommand::StreamMode());
+        self.send_stream_loader_command(StreamLoaderCommand::StreamMode);
     }
 
     pub fn close(&self) {
         // terminate stream loading and don't load any more data for this file.
-        self.send_stream_loader_command(StreamLoaderCommand::Close());
+        self.send_stream_loader_command(StreamLoaderCommand::Close);
     }
 }
 
@@ -325,25 +325,13 @@ struct AudioFileDownloadStatus {
     downloaded: RangeSet,
 }
 
-#[derive(Debug, Copy, Clone, PartialEq, Eq)]
-enum DownloadStrategy {
-    RandomAccess(),
-    Streaming(),
-}
-
-impl Default for DownloadStrategy {
-    fn default() -> Self {
-        Self::Streaming()
-    }
-}
-
 struct AudioFileShared {
     cdn_url: CdnUrl,
     file_size: usize,
     bytes_per_second: usize,
     cond: Condvar,
     download_status: Mutex<AudioFileDownloadStatus>,
-    download_strategy: Mutex<DownloadStrategy>,
+    download_streaming: AtomicBool,
     number_of_open_requests: AtomicUsize,
     ping_time_ms: AtomicUsize,
     read_position: AtomicUsize,
@@ -462,7 +450,7 @@ impl AudioFileStreaming {
                 requested: RangeSet::new(),
                 downloaded: RangeSet::new(),
             }),
-            download_strategy: Mutex::new(DownloadStrategy::default()),
+            download_streaming: AtomicBool::new(true),
             number_of_open_requests: AtomicUsize::new(0),
             ping_time_ms: AtomicUsize::new(INITIAL_PING_TIME_ESTIMATE.as_millis() as usize),
             read_position: AtomicUsize::new(0),
@@ -507,9 +495,7 @@ impl Read for AudioFileStreaming {
             return Ok(0);
         }
 
-        let length_to_request = match *(self.shared.download_strategy.lock()) {
-            DownloadStrategy::RandomAccess() => length,
-            DownloadStrategy::Streaming() => {
+        let length_to_request = if self.shared.download_streaming.load(Ordering::Acquire) {
             // Due to the read-ahead stuff, we potentially request more than the actual request demanded.
             let ping_time_seconds =
                 Duration::from_millis(self.shared.ping_time_ms.load(Ordering::Relaxed) as u64)
@@ -517,14 +503,15 @@ impl Read for AudioFileStreaming {
 
             let length_to_request = length
                 + max(
-                        (READ_AHEAD_DURING_PLAYBACK.as_secs_f32()
-                            * self.shared.bytes_per_second as f32) as usize,
+                    (READ_AHEAD_DURING_PLAYBACK.as_secs_f32() * self.shared.bytes_per_second as f32)
+                        as usize,
                     (READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS
                         * ping_time_seconds
                         * self.shared.bytes_per_second as f32) as usize,
                 );
             min(length_to_request, self.shared.file_size - offset)
-            }
+        } else {
+            length
         };
 
         let mut ranges_to_request = RangeSet::new();
@@ -575,7 +562,7 @@ impl Read for AudioFileStreaming {
 
 impl Seek for AudioFileStreaming {
     fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
-        // If we are already at this position, we don't need to switch download strategy.
+        // If we are already at this position, we don't need to switch download mode.
         // These checks and locks are less expensive than interrupting streaming.
         let current_position = self.position as i64;
         let requested_pos = match pos {
@@ -595,13 +582,17 @@ impl Seek for AudioFileStreaming {
             .downloaded
             .contains(requested_pos as usize);
 
-        let mut old_strategy = DownloadStrategy::default();
+        let mut was_streaming = false;
         if !available {
             // Ensure random access mode if we need to download this part.
-            old_strategy = std::mem::replace(
-                &mut *(self.shared.download_strategy.lock()),
-                DownloadStrategy::RandomAccess(),
-            );
+            // Checking whether we are streaming now is a micro-optimization
+            // to save an atomic load.
+            was_streaming = self.shared.download_streaming.load(Ordering::Acquire);
+            if was_streaming {
+                self.shared
+                    .download_streaming
+                    .store(false, Ordering::Release);
+            }
         }
 
         self.position = self.read_file.seek(pos)?;
@@ -609,8 +600,10 @@ impl Seek for AudioFileStreaming {
             .read_position
             .store(self.position as usize, Ordering::Release);
 
-        if !available && old_strategy != DownloadStrategy::RandomAccess() {
-            *(self.shared.download_strategy.lock()) = old_strategy;
+        if !available && was_streaming {
+            self.shared
+                .download_streaming
+                .store(true, Ordering::Release);
         }
 
         Ok(self.position)

audio/src/fetch/receive.rs

@@ -16,9 +16,9 @@ use librespot_core::{session::Session, Error};
 use crate::range_set::{Range, RangeSet};
 
 use super::{
-    AudioFileError, AudioFileResult, AudioFileShared, DownloadStrategy, StreamLoaderCommand,
-    StreamingRequest, FAST_PREFETCH_THRESHOLD_FACTOR, MAXIMUM_ASSUMED_PING_TIME,
-    MAX_PREFETCH_REQUESTS, MINIMUM_DOWNLOAD_SIZE, PREFETCH_THRESHOLD_FACTOR,
+    AudioFileError, AudioFileResult, AudioFileShared, StreamLoaderCommand, StreamingRequest,
+    FAST_PREFETCH_THRESHOLD_FACTOR, MAXIMUM_ASSUMED_PING_TIME, MAX_PREFETCH_REQUESTS,
+    MINIMUM_DOWNLOAD_SIZE, PREFETCH_THRESHOLD_FACTOR,
 };
 
 struct PartialFileData {
@@ -157,8 +157,8 @@ enum ControlFlow {
 }
 
 impl AudioFileFetch {
-    fn get_download_strategy(&mut self) -> DownloadStrategy {
-        *(self.shared.download_strategy.lock())
+    fn is_download_streaming(&mut self) -> bool {
+        self.shared.download_streaming.load(Ordering::Acquire)
     }
 
     fn download_range(&mut self, offset: usize, mut length: usize) -> AudioFileResult {
@@ -337,15 +337,17 @@ impl AudioFileFetch {
     ) -> Result<ControlFlow, Error> {
         match cmd {
             StreamLoaderCommand::Fetch(request) => {
-                self.download_range(request.start, request.length)?;
+                self.download_range(request.start, request.length)?
             }
-            StreamLoaderCommand::RandomAccessMode() => {
-                *(self.shared.download_strategy.lock()) = DownloadStrategy::RandomAccess();
-            }
-            StreamLoaderCommand::StreamMode() => {
-                *(self.shared.download_strategy.lock()) = DownloadStrategy::Streaming();
-            }
-            StreamLoaderCommand::Close() => return Ok(ControlFlow::Break),
+            StreamLoaderCommand::RandomAccessMode => self
+                .shared
+                .download_streaming
+                .store(false, Ordering::Release),
+            StreamLoaderCommand::StreamMode => self
+                .shared
+                .download_streaming
+                .store(true, Ordering::Release),
+            StreamLoaderCommand::Close => return Ok(ControlFlow::Break),
         }
 
         Ok(ControlFlow::Continue)
@@ -430,7 +432,7 @@ pub(super) async fn audio_file_fetch(
             else => (),
         }
 
-        if fetch.get_download_strategy() == DownloadStrategy::Streaming() {
+        if fetch.is_download_streaming() {
             let number_of_open_requests =
                 fetch.shared.number_of_open_requests.load(Ordering::SeqCst);
             if number_of_open_requests < MAX_PREFETCH_REQUESTS {