Add a wrapper codec source that does readahead

src/audio/CMakeLists.txt

@@ -5,7 +5,7 @@
 idf_component_register(
   SRCS "audio_decoder.cpp" "fatfs_audio_input.cpp" "i2s_audio_output.cpp"
   "track_queue.cpp" "audio_fsm.cpp" "audio_converter.cpp" "resample.cpp"
-  "fatfs_source.cpp" "bt_audio_output.cpp"
+  "fatfs_source.cpp" "bt_audio_output.cpp" "readahead_source.cpp"
   INCLUDE_DIRS "include"
   REQUIRES "codecs" "drivers" "cbor" "result" "tasks" "span" "memory" "tinyfsm"
   "database" "system_fsm" "playlist" "speexdsp")

src/audio/audio_fsm.cpp

@@ -105,7 +105,8 @@ void Uninitialised::react(const system_fsm::BootComplete& ev) {
   StreamBufferHandle_t stream = xStreamBufferCreateWithCaps(
       kDrainBufferSize, sizeof(sample::Sample) * 2, MALLOC_CAP_DMA);
 
-  sFileSource.reset(new FatfsAudioInput(sServices->tag_parser()));
+  sFileSource.reset(
+      new FatfsAudioInput(sServices->tag_parser(), sServices->bg_worker()));
   sI2SOutput.reset(new I2SAudioOutput(stream, sServices->gpios()));
   sBtOutput.reset(new BluetoothAudioOutput(stream, sServices->bluetooth()));
 

src/audio/fatfs_audio_input.cpp

@@ -23,6 +23,7 @@
 #include "freertos/portmacro.h"
 #include "freertos/projdefs.h"
 #include "idf_additions.h"
+#include "readahead_source.hpp"
 #include "span.hpp"
 
 #include "audio_events.hpp"
@@ -42,9 +43,11 @@
 
 namespace audio {
 
-FatfsAudioInput::FatfsAudioInput(database::ITagParser& tag_parser)
+FatfsAudioInput::FatfsAudioInput(database::ITagParser& tag_parser,
+                                 tasks::Worker& bg_worker)
     : IAudioSource(),
       tag_parser_(tag_parser),
+      bg_worker_(bg_worker),
       new_stream_mutex_(),
       new_stream_(),
       has_new_stream_(false),
@@ -142,7 +145,9 @@ auto FatfsAudioInput::OpenFile(const std::pmr::string& path) -> bool {
     return false;
   }
 
-  new_stream_.reset(new FatfsSource(stream_type.value(), std::move(file)));
+  auto source =
+      std::make_unique<FatfsSource>(stream_type.value(), std::move(file));
+  new_stream_.reset(new ReadaheadSource(bg_worker_, std::move(source)));
   return true;
 }
 

src/audio/include/fatfs_audio_input.hpp

@@ -19,6 +19,7 @@
 #include "codec.hpp"
 #include "future_fetcher.hpp"
 #include "tag_parser.hpp"
+#include "tasks.hpp"
 #include "types.hpp"
 
 namespace audio {
@@ -30,7 +31,7 @@ namespace audio {
  */
 class FatfsAudioInput : public IAudioSource {
  public:
-  explicit FatfsAudioInput(database::ITagParser& tag_parser);
+  explicit FatfsAudioInput(database::ITagParser&, tasks::Worker&);
   ~FatfsAudioInput();
 
   /*
@@ -54,6 +55,7 @@ class FatfsAudioInput : public IAudioSource {
       -> std::optional<codecs::StreamType>;
 
   database::ITagParser& tag_parser_;
+  tasks::Worker& bg_worker_;
 
   std::mutex new_stream_mutex_;
   std::shared_ptr<codecs::IStream> new_stream_;

src/audio/include/readahead_source.hpp

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2023 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+#include <memory>
+
+#include "freertos/FreeRTOS.h"
+
+#include "ff.h"
+#include "freertos/stream_buffer.h"
+
+#include "audio_source.hpp"
+#include "codec.hpp"
+#include "tasks.hpp"
+
+namespace audio {
+
+/*
+ * Wraps another stream, proactively buffering large chunks of it into memory
+ * at a time.
+ */
+class ReadaheadSource : public codecs::IStream {
+ public:
+  ReadaheadSource(tasks::Worker&, std::unique_ptr<codecs::IStream>);
+  ~ReadaheadSource();
+
+  auto Read(cpp::span<std::byte> dest) -> ssize_t override;
+
+  auto CanSeek() -> bool override;
+
+  auto SeekTo(int64_t destination, SeekFrom from) -> void override;
+
+  auto CurrentPosition() -> int64_t override;
+
+  ReadaheadSource(const ReadaheadSource&) = delete;
+  ReadaheadSource& operator=(const ReadaheadSource&) = delete;
+
+ private:
+  tasks::Worker& worker_;
+  std::unique_ptr<codecs::IStream> wrapped_;
+
+  std::atomic<bool> is_refilling_;
+  StreamBufferHandle_t buffer_;
+  int64_t tell_;
+};
+
+}  // namespace audio

src/audio/readahead_source.cpp

@@ -0,0 +1,124 @@
+/*
+ * Copyright 2023 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#include "readahead_source.hpp"
+
+#include <cstddef>
+#include <cstdint>
+#include <memory>
+
+#include "esp_heap_caps.h"
+#include "esp_log.h"
+#include "ff.h"
+
+#include "audio_source.hpp"
+#include "codec.hpp"
+#include "freertos/portmacro.h"
+#include "idf_additions.h"
+#include "spi.hpp"
+#include "tasks.hpp"
+#include "types.hpp"
+
+namespace audio {
+
+static constexpr char kTag[] = "readahead";
+static constexpr size_t kBufferSize = 1024 * 512;
+
+ReadaheadSource::ReadaheadSource(tasks::Worker& worker,
+                                 std::unique_ptr<codecs::IStream> wrapped)
+    : IStream(wrapped->type()),
+      worker_(worker),
+      wrapped_(std::move(wrapped)),
+      is_refilling_(false),
+      buffer_(xStreamBufferCreateWithCaps(kBufferSize, 1, MALLOC_CAP_SPIRAM)),
+      tell_(wrapped_->CurrentPosition()) {}
+
+ReadaheadSource::~ReadaheadSource() {
+  vStreamBufferDeleteWithCaps(buffer_);
+}
+
+auto ReadaheadSource::Read(cpp::span<std::byte> dest) -> ssize_t {
+  // Optismise for the most frequent case: the buffer already contains enough
+  // data for this call.
+  size_t bytes_read =
+      xStreamBufferReceive(buffer_, dest.data(), dest.size_bytes(), 0);
+
+  tell_ += bytes_read;
+  if (bytes_read == dest.size_bytes()) {
+    return bytes_read;
+  }
+
+  dest = dest.subspan(bytes_read);
+
+  // Are we currently fetching more bytes?
+  ssize_t extra_bytes = 0;
+  if (!is_refilling_) {
+    // No! Pass through directly to the wrapped source for the fastest
+    // response.
+    extra_bytes = wrapped_->Read(dest);
+  } else {
+    // Yes! Wait for the refill to catch up, then try again.
+    is_refilling_.wait(true);
+    extra_bytes =
+        xStreamBufferReceive(buffer_, dest.data(), dest.size_bytes(), 0);
+  }
+
+  // No need to check whether the dest buffer is actually filled, since at this
+  // point we've read as many bytes as were available.
+  tell_ += extra_bytes;
+  bytes_read += extra_bytes;
+
+  // Before returning, make sure the readahead task is kicked off again.
+  ESP_LOGI(kTag, "triggering readahead");
+  is_refilling_ = true;
+  std::function<void(void)> refill = [this]() {
+    // Try to keep larger than most reasonable FAT sector sizes for more
+    // efficient disk reads.
+    constexpr size_t kMaxSingleRead = 1024 * 64;
+    std::byte working_buf[kMaxSingleRead];
+    for (;;) {
+      size_t bytes_to_read = std::min<size_t>(
+          kMaxSingleRead, xStreamBufferSpacesAvailable(buffer_));
+      if (bytes_to_read == 0) {
+        break;
+      }
+      size_t read = wrapped_->Read({working_buf, bytes_to_read});
+      if (read > 0) {
+        xStreamBufferSend(buffer_, working_buf, read, 0);
+      }
+      if (read < bytes_to_read) {
+        break;
+      }
+    }
+    is_refilling_ = false;
+    is_refilling_.notify_all();
+  };
+  worker_.Dispatch(refill);
+
+  return bytes_read;
+}
+
+auto ReadaheadSource::CanSeek() -> bool {
+  return wrapped_->CanSeek();
+}
+
+auto ReadaheadSource::SeekTo(int64_t destination, SeekFrom from) -> void {
+  // Seeking blows away all of our prefetched data. To do this safely, we
+  // first need to wait for the refill task to finish.
+  is_refilling_.wait(true);
+  // It's now safe to clear out the buffer.
+  xStreamBufferReset(buffer_);
+
+  wrapped_->SeekTo(destination, from);
+
+  // Make sure our tell is up to date with the new location.
+  tell_ = wrapped_->CurrentPosition();
+}
+
+auto ReadaheadSource::CurrentPosition() -> int64_t {
+  return tell_;
+}
+}  // namespace audio

src/codecs/source_buffer.cpp

@@ -18,7 +18,7 @@
 namespace codecs {
 
 [[maybe_unused]] static constexpr char kTag[] = "dec_buf";
-static constexpr size_t kBufferSize = 1024 * 128;
+static constexpr size_t kBufferSize = 1024 * 16;
 static constexpr size_t kReadThreshold = 1024 * 8;
 
 SourceBuffer::SourceBuffer()

src/database/database.cpp

@@ -117,16 +117,15 @@ static auto CheckDatabase(leveldb::DB& db, locale::ICollator& col) -> bool {
 
 auto Database::Open(IFileGatherer& gatherer,
                     ITagParser& parser,
-                    locale::ICollator& collator)
+                    locale::ICollator& collator,
+                    tasks::Worker& bg_worker)
     -> cpp::result<Database*, DatabaseError> {
-  // TODO(jacqueline): Why isn't compare_and_exchange_* available?
   if (sIsDbOpen.exchange(true)) {
     return cpp::fail(DatabaseError::ALREADY_OPEN);
   }
 
   if (!leveldb::sBackgroundThread) {
-    leveldb::sBackgroundThread.reset(
-        tasks::Worker::Start<tasks::Type::kDatabaseBackground>());
+    leveldb::sBackgroundThread = &bg_worker;
   }
 
   std::shared_ptr<tasks::Worker> worker(

src/database/env_esp.cpp

@@ -41,7 +41,7 @@
 
 namespace leveldb {
 
-std::shared_ptr<tasks::Worker> sBackgroundThread;
+tasks::Worker *sBackgroundThread = nullptr;
 
 std::string ErrToStr(FRESULT err) {
   switch (err) {

src/database/include/database.hpp

@@ -95,7 +95,8 @@ class Database {
   };
   static auto Open(IFileGatherer& file_gatherer,
                    ITagParser& tag_parser,
-                   locale::ICollator& collator)
+                   locale::ICollator& collator,
+                   tasks::Worker& bg_worker)
       -> cpp::result<Database*, DatabaseError>;
 
   static auto Destroy() -> void;

src/database/include/env_esp.hpp

@@ -18,7 +18,7 @@
 
 namespace leveldb {
 
-extern std::shared_ptr<tasks::Worker> sBackgroundThread;
+extern tasks::Worker* sBackgroundThread;
 
 // Tracks the files locked by EspEnv::LockFile().
 //

src/system_fsm/booting.cpp

@@ -32,6 +32,7 @@
 #include "spi.hpp"
 #include "system_events.hpp"
 #include "tag_parser.hpp"
+#include "tasks.hpp"
 #include "touchwheel.hpp"
 #include "track_queue.hpp"
 #include "ui_fsm.hpp"
@@ -63,6 +64,10 @@ auto Booting::entry() -> void {
     return;
   }
 
+  ESP_LOGI(kTag, "starting bg worker");
+  sServices->bg_worker(std::unique_ptr<tasks::Worker>{
+      tasks::Worker::Start<tasks::Type::kDatabaseBackground>()});
+
   ESP_LOGI(kTag, "installing remaining drivers");
   sServices->samd(std::unique_ptr<drivers::Samd>(drivers::Samd::Create()));
   vTaskDelay(pdMS_TO_TICKS(1000));

src/system_fsm/include/service_locator.hpp

@@ -17,6 +17,7 @@
 #include "samd.hpp"
 #include "storage.hpp"
 #include "tag_parser.hpp"
+#include "tasks.hpp"
 #include "touchwheel.hpp"
 #include "track_queue.hpp"
 
@@ -111,6 +112,15 @@ class ServiceLocator {
     collator_ = std::move(i);
   }
 
+  auto bg_worker() -> tasks::Worker& {
+    assert(bg_worker_ != nullptr);
+    return *bg_worker_;
+  }
+
+  auto bg_worker(std::unique_ptr<tasks::Worker> w) -> void {
+    bg_worker_ = std::move(w);
+  }
+
   // Not copyable or movable.
   ServiceLocator(const ServiceLocator&) = delete;
   ServiceLocator& operator=(const ServiceLocator&) = delete;
@@ -129,6 +139,8 @@ class ServiceLocator {
   std::unique_ptr<database::ITagParser> tag_parser_;
   std::unique_ptr<locale::ICollator> collator_;
 
+  std::unique_ptr<tasks::Worker> bg_worker_;
+
   drivers::SdState sd_;
 };
 

src/system_fsm/running.cpp

@@ -55,8 +55,9 @@ void Running::entry() {
 
   ESP_LOGI(kTag, "opening database");
   sFileGatherer = new database::FileGathererImpl();
-  auto database_res = database::Database::Open(
-      *sFileGatherer, sServices->tag_parser(), sServices->collator());
+  auto database_res =
+      database::Database::Open(*sFileGatherer, sServices->tag_parser(),
+                               sServices->collator(), sServices->bg_worker());
   if (database_res.has_error()) {
     ESP_LOGW(kTag, "failed to open!");
     events::System().Dispatch(StorageError{});

src/tasks/tasks.cpp

@@ -195,8 +195,7 @@ Worker::~Worker() {
 }
 
 template <>
-auto Worker::Dispatch(const std::function<void(void)>& fn)
-    -> std::future<void> {
+auto Worker::Dispatch(const std::function<void(void)> fn) -> std::future<void> {
   std::shared_ptr<std::promise<void>> promise =
       std::make_shared<std::promise<void>>();
   WorkItem item{

src/tasks/tasks.hpp

@@ -106,7 +106,7 @@ class Worker {
    * asynchronously returns the result as a future.
    */
   template <typename T>
-  auto Dispatch(const std::function<T(void)>& fn) -> std::future<T> {
+  auto Dispatch(const std::function<T(void)> fn) -> std::future<T> {
     std::shared_ptr<std::promise<T>> promise =
         std::make_shared<std::promise<T>>();
     WorkItem item{
@@ -125,6 +125,6 @@ class Worker {
 
 /* Specialisation of Evaluate for functions that return nothing. */
 template <>
-auto Worker::Dispatch(const std::function<void(void)>& fn) -> std::future<void>;
+auto Worker::Dispatch(const std::function<void(void)> fn) -> std::future<void>;
 
 }  // namespace tasks