Cleanup

.gitignore

@@ -1,4 +1,5 @@
 build/
+test_package/CMakeUserPresets.json
 .clangd
 .clang-format
 pyrightconfig.json

CMakeLists.txt

@@ -11,6 +11,18 @@ set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 
 find_package(modulus CONFIG REQUIRED)
+find_package(miniaudio CONFIG REQUIRED)
+
+set(SONUS_MINIAUDIO_TARGET "")
+if(TARGET miniaudio::miniaudio)
+  set(SONUS_MINIAUDIO_TARGET miniaudio::miniaudio)
+elseif(TARGET miniaudio)
+  set(SONUS_MINIAUDIO_TARGET miniaudio)
+endif()
+
+if(NOT SONUS_MINIAUDIO_TARGET)
+  message(FATAL_ERROR "miniaudio package did not define a supported CMake target")
+endif()
 
 add_library(sonus
   src/detail/errors.cpp
@@ -22,7 +34,7 @@ target_include_directories(sonus PUBLIC
 )
 target_compile_features(sonus PUBLIC cxx_std_23)
 target_include_directories(sonus PRIVATE
-  $<BUILD_INTERFACE:$<TARGET_PROPERTY:modulus::miniaudio,INTERFACE_INCLUDE_DIRECTORIES>>
+  $<BUILD_INTERFACE:$<TARGET_PROPERTY:${SONUS_MINIAUDIO_TARGET},INTERFACE_INCLUDE_DIRECTORIES>>
 )
 target_link_libraries(sonus PUBLIC
   modulus::modulus

README.md

@@ -4,6 +4,18 @@ Sonus is a C++23 audio playback library built on miniaudio. It provides a small
 
 Sonus keeps miniaudio out of public headers and is intended for embedded Linux applications where startup cost, predictable ownership, and low callback overhead matter.
 
+## Devices And Threading
+
+`enumerate_playback_devices()` returns device descriptions or a Modulus error if the audio backend cannot initialize or enumerate. A successful empty list means no playback devices were reported. Copy a description's `id` to `audio_config::playback_device_id` before creating an engine. IDs are opaque tokens derived from enumeration order and metadata, intended for immediate reuse; re-enumerate after hardware or backend changes. They are not permanent hardware identifiers.
+
+Selection tries the ID first, then an exact `playback_device_name` fallback. Duplicate names select the first match, so use the ID to distinguish them. Empty selectors preserve the backend's default device. An unresolved explicit selector returns an error. `no_device` rejects device selectors and enables manual rendering instead.
+
+Period size may be requested in frames or milliseconds (not both), with an optional period count and performance profile. The backend may adjust these requests to hardware capabilities.
+
+Control calls on one engine are serialized and may run concurrently with playback. `update_metronome()` preserves the running/stopped state at publication. Render callbacks use immutable click buffers and lock-free snapshot reads; reclamation runs on control threads. Idle publications reclaim previous snapshots immediately. Snapshots retired during rendering are collected by subsequent metronome controls, `collect_finished()`, `active_sound_count()`, playback, or device stop. Manual renders are serialized. Do not move or destroy an engine while another thread is calling it.
+
+Call `collect_finished()` periodically to release sounds that reach EOF without further playback or status calls. Sonus compiles miniaudio internally; installed consumers link `sonus::sonus` and need only Modulus core and its Boost dependency. Miniaudio headers are needed only to build Sonus.
+
 ## Build
 
 Configure, build, and test the default target:

conanfile.py

@@ -37,6 +37,7 @@ class sonus_conan(conan.ConanFile):
     "include/sonus/detail/*.hpp",
     "src/*.cpp",
     "src/detail/*.cpp",
+    "src/detail/*.hpp",
     "tests/CMakeLists.txt",
     "tests/*.cpp",
     "tests/*.hpp",
@@ -56,6 +57,12 @@ class sonus_conan(conan.ConanFile):
       transitive_headers=True,
       transitive_libs=True,
     )
+    self.requires(
+      "miniaudio/0.11.22",
+      visible=False,
+      transitive_headers=False,
+      transitive_libs=False,
+    )
 
   def generate(self):
     dependencies = conan.tools.cmake.CMakeDeps(self)
@@ -80,7 +87,6 @@ class sonus_conan(conan.ConanFile):
       "openssl",
       "sqlite3",
       "raylib",
-      "miniaudio",
     ):
       if requirement in self.info.requires.pkg_names:
         self.info.requires.remove(requirement)

include/sonus/config.hpp

@@ -18,6 +18,7 @@ struct audio_config {
   std::uint32_t channels{2};
   std::float32_t master_volume{0.70F};
   std::bool_t no_device{false};
+  std::string playback_device_id{};
   std::string playback_device_name{};
   std::uint32_t period_size_frames{0};
   std::uint32_t period_size_milliseconds{0};
@@ -25,6 +26,12 @@ struct audio_config {
   sonus::performance_profile performance{sonus::performance_profile::LOW_LATENCY};
 };
 
+struct device_info {
+  std::string id{};
+  std::string name{};
+  std::bool_t is_default{false};
+};
+
 struct metronome_config {
   std::uint32_t bpm{120};
   std::uint32_t beats_per_bar{4};

include/sonus/engine.hpp

@@ -4,6 +4,7 @@
 #include <expected>
 #include <filesystem>
 #include <memory>
+#include <vector>
 
 #include <modulus.hpp>
 #include <sonus/config.hpp>
@@ -13,6 +14,7 @@ namespace sonus {
 auto validate(sonus::audio_config const& config) -> std::expected<void, modulus::error>;
 auto validate(sonus::metronome_config const& config) -> std::expected<void, modulus::error>;
 auto validate(sonus::playback_options const& options) -> std::expected<void, modulus::error>;
+auto enumerate_playback_devices() -> std::expected<std::vector<sonus::device_info>, modulus::error>;
 
 class engine {
 public:

src/detail/playback_devices.hpp

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <cstddef>
+#include <optional>
+#include <span>
+#include <string_view>
+
+#include <sonus/config.hpp>
+
+namespace sonus::detail {
+
+inline auto find_playback_device(std::span<device_info const> devices, std::string_view id, std::string_view name) -> std::optional<std::size_t> {
+  if (!id.empty()) {
+    for (auto index = std::size_t{}; index < devices.size(); ++index) {
+      if (devices[index].id == id) {
+        return index;
+      }
+    }
+  }
+  if (!name.empty()) {
+    for (auto index = std::size_t{}; index < devices.size(); ++index) {
+      if (devices[index].name == name) {
+        return index;
+      }
+    }
+  }
+  return std::nullopt;
+}
+
+}

src/detail/render_snapshot.hpp

@@ -0,0 +1,63 @@
+#pragma once
+
+#include <atomic>
+#include <cstdint>
+#include <memory>
+#include <utility>
+#include <vector>
+
+namespace sonus::detail {
+
+// Publishers/collectors must be serialized; readers never lock or destroy snapshots.
+template<typename T>
+class render_snapshot {
+  static_assert(std::atomic<std::uint32_t>::is_always_lock_free);
+  static_assert(std::atomic<T const*>::is_always_lock_free);
+
+public:
+  class read_guard {
+  public:
+    explicit read_guard(render_snapshot& owner) : owner_(owner) {
+      owner_.active_render_count_.fetch_add(1, std::memory_order_seq_cst);
+      value_ = owner_.active_.load(std::memory_order_seq_cst);
+    }
+    read_guard(read_guard const&) = delete;
+    auto operator=(read_guard const&) -> read_guard& = delete;
+    ~read_guard() {
+      owner_.active_render_count_.fetch_sub(1, std::memory_order_seq_cst);
+    }
+    auto get() const -> T const* { return value_; }
+
+  private:
+    render_snapshot& owner_;
+    T const* value_{};
+  };
+
+  auto read() -> read_guard { return read_guard{*this}; }
+  auto current() const -> T const* { return current_.get(); }
+
+  auto publish(std::unique_ptr<T> next) -> void {
+    if (current_) {
+      retired_.push_back(std::move(current_));
+    }
+    current_ = std::move(next);
+    active_.store(current_.get(), std::memory_order_seq_cst);
+    collect();
+  }
+
+  auto collect() -> void {
+    // SC orders publication/count observation against reader entry/pointer load:
+    // a reader either contributes to the count or sees the new snapshot.
+    if (active_render_count_.load(std::memory_order_seq_cst) == 0U) {
+      retired_.clear();
+    }
+  }
+
+private:
+  std::unique_ptr<T> current_{};
+  std::vector<std::unique_ptr<T>> retired_{};
+  std::atomic<T const*> active_{nullptr};
+  std::atomic<std::uint32_t> active_render_count_{0};
+};
+
+}

src/engine.cpp

@@ -23,6 +23,8 @@
 #include <modulus.hpp>
 
 #include <sonus/detail/errors.hpp>
+#include "detail/render_snapshot.hpp"
+#include "detail/playback_devices.hpp"
 
 namespace {
 
@@ -58,6 +60,28 @@ auto contains_null(std::string_view value) -> std::bool_t {
   return value.find('\0') != std::string_view::npos;
 }
 
+auto make_playback_device_id(ma_uint32 index, ma_device_info const& info) -> std::string {
+  auto result = std::to_string(index);
+  result += ':';
+  result += (info.isDefault == MA_TRUE ? '1' : '0');
+  result += ':';
+  result += info.name;
+  return result;
+}
+
+auto describe_playback_devices(ma_device_info const* devices, ma_uint32 count) -> std::vector<sonus::device_info> {
+  auto result = std::vector<sonus::device_info>{};
+  result.reserve(count);
+  for (auto index = ma_uint32{}; index < count; ++index) {
+    result.push_back(sonus::device_info{
+      .id = make_playback_device_id(index, devices[index]),
+      .name = devices[index].name,
+      .is_default = devices[index].isDefault == MA_TRUE,
+    });
+  }
+  return result;
+}
+
 auto to_miniaudio_profile(sonus::performance_profile profile) -> ma_performance_profile {
   switch (profile) {
     case sonus::performance_profile::LOW_LATENCY:
@@ -107,6 +131,21 @@ struct active_sound {
   }
 };
 
+struct temporary_context {
+  ma_context context{};
+  std::bool_t initialized{false};
+
+  temporary_context() = default;
+  temporary_context(temporary_context const&) = delete;
+  auto operator=(temporary_context const&) -> temporary_context& = delete;
+
+  ~temporary_context() {
+    if (initialized) {
+      ma_context_uninit(&context);
+    }
+  }
+};
+
 struct metronome_render_config {
   std::bool_t enabled{false};
   std::uint32_t generation{0};
@@ -116,11 +155,6 @@ struct metronome_render_config {
   std::vector<std::float32_t> downbeat_click{};
 };
 
-struct retired_metronome_config {
-  std::unique_ptr<metronome_render_config> config{};
-  std::uint64_t retire_epoch{0};
-};
-
 }
 
 struct sonus::engine::impl {
@@ -138,11 +172,8 @@ struct sonus::engine::impl {
   std::unordered_map<sonus::sound_handle, std::unique_ptr<active_sound>> sounds{};
   sonus::sound_handle next_sound_handle{1};
 
-  std::unique_ptr<metronome_render_config> metronome_config{};
-  std::vector<retired_metronome_config> retired_metronome_configs{};
-  std::atomic<metronome_render_config const*> active_metronome_config{nullptr};
+  sonus::detail::render_snapshot<metronome_render_config> metronome_configs{};
   std::atomic_bool metronome_enabled{false};
-  std::atomic<std::uint64_t> render_epoch{0};
   std::uint32_t next_metronome_generation{1};
 
   std::uint32_t observed_metronome_generation{0};
@@ -242,6 +273,7 @@ struct sonus::engine::impl {
       static_cast<void>(ma_device_stop(&device));
     }
     started = false;
+    collect_retired_metronome_configs_locked();
   }
 
   auto shutdown() -> void {
@@ -264,14 +296,11 @@ struct sonus::engine::impl {
       context_initialized = false;
     }
     metronome_enabled.store(false, std::memory_order_release);
-    active_metronome_config.store(nullptr, std::memory_order_release);
-    metronome_config.reset();
-    retired_metronome_configs.clear();
     reset_metronome_render_state();
   }
 
   auto configure_playback_device(ma_device_config& device_config) -> std::expected<void, modulus::error> {
-    if (config.playback_device_name.empty()) {
+    if (config.playback_device_id.empty() && config.playback_device_name.empty()) {
       return {};
     }
 
@@ -289,23 +318,21 @@ struct sonus::engine::impl {
       return sonus::detail::fail_void(miniaudio_error(result, "failed to enumerate playback devices"));
     }
 
-    for (auto index = ma_uint32{}; index < playback_device_count; ++index) {
-      if (config.playback_device_name == playback_devices[index].name) {
-        playback_device_id = playback_devices[index].id;
-        device_config.playback.pDeviceID = &playback_device_id;
-        return {};
-      }
+    auto devices = describe_playback_devices(playback_devices, playback_device_count);
+    auto selected = sonus::detail::find_playback_device(devices, config.playback_device_id, config.playback_device_name);
+    if (selected) {
+      playback_device_id = playback_devices[*selected].id;
+      device_config.playback.pDeviceID = &playback_device_id;
+      return {};
     }
 
-    return sonus::detail::fail_void(sonus::detail::error_not_found, "playback device not found: " + config.playback_device_name);
+    auto selector = config.playback_device_id.empty() ? config.playback_device_name : config.playback_device_id;
+    return sonus::detail::fail_void(sonus::detail::error_not_found, "playback device not found: " + selector);
   }
 
   auto set_master_volume(std::float32_t volume) -> std::expected<void, modulus::error> {
-    auto next_config = config;
-    next_config.master_volume = volume;
-    auto valid = sonus::validate(next_config);
-    if (!valid) {
-      return valid;
+    if (!valid_unit_interval(volume)) {
+      return sonus::detail::fail_void(invalid("audio master_volume must be between 0 and 1"));
     }
 
     auto lock = std::scoped_lock{mutex};
@@ -422,19 +449,20 @@ struct sonus::engine::impl {
       return valid;
     }
 
-    auto next = make_metronome_config(value, enable);
-    if (!next) {
-      return sonus::detail::fail_void(next.error());
-    }
-
     auto lock = std::scoped_lock{mutex};
-    publish_metronome_locked(std::move(*next));
-    collect_retired_metronome_configs_locked();
-    return {};
+    return publish_metronome_config_locked(value, enable);
   }
 
   auto update_metronome(sonus::metronome_config value) -> std::expected<void, modulus::error> {
-    return store_metronome(value, metronome_enabled.load(std::memory_order_acquire));
+    auto valid = sonus::validate(value);
+    if (!valid) {
+      return valid;
+    }
+
+    auto lock = std::scoped_lock{mutex};
+    auto const* current = metronome_configs.current();
+    auto const enable = current != nullptr && current->enabled;
+    return publish_metronome_config_locked(value, enable);
   }
 
   auto stop_metronome() -> void {
@@ -443,6 +471,17 @@ struct sonus::engine::impl {
     collect_retired_metronome_configs_locked();
   }
 
+  auto publish_metronome_config_locked(sonus::metronome_config value, std::bool_t enable) -> std::expected<void, modulus::error> {
+    auto next = make_metronome_config(value, enable);
+    if (!next) {
+      return sonus::detail::fail_void(next.error());
+    }
+
+    publish_metronome_locked(std::move(*next));
+    collect_retired_metronome_configs_locked();
+    return {};
+  }
+
   auto make_metronome_config(sonus::metronome_config value, std::bool_t enable) -> std::expected<std::unique_ptr<metronome_render_config>, modulus::error> {
     auto click_frames = static_cast<std::uint64_t>(config.sample_rate) * static_cast<std::uint64_t>(value.click_duration.count()) / 1000U;
     click_frames = std::clamp<std::uint64_t>(click_frames, 1U, std::numeric_limits<std::uint32_t>::max());
@@ -471,25 +510,13 @@ struct sonus::engine::impl {
       next_metronome_generation = 1U;
     }
 
-    auto previous = std::move(metronome_config);
-    auto* next_pointer = next.get();
-    metronome_config = std::move(next);
-    active_metronome_config.store(next_pointer, std::memory_order_release);
-    metronome_enabled.store(next_pointer->enabled, std::memory_order_release);
-    if (previous) {
-      retired_metronome_configs.push_back(retired_metronome_config{
-        .config = std::move(previous),
-        .retire_epoch = render_epoch.load(std::memory_order_acquire),
-      });
-    }
+    auto const enabled = next->enabled;
+    metronome_configs.publish(std::move(next));
+    metronome_enabled.store(enabled, std::memory_order_release);
   }
 
   auto collect_retired_metronome_configs_locked() -> void {
-    auto const completed_epoch = render_epoch.load(std::memory_order_acquire);
-    auto first_removed = std::remove_if(retired_metronome_configs.begin(), retired_metronome_configs.end(), [completed_epoch](retired_metronome_config const& retired) {
-      return retired.retire_epoch < completed_epoch;
-    });
-    retired_metronome_configs.erase(first_removed, retired_metronome_configs.end());
+    metronome_configs.collect();
   }
 
   auto allocate_sound_handle_locked() -> std::expected<sonus::sound_handle, modulus::error> {
@@ -536,13 +563,7 @@ struct sonus::engine::impl {
       return MA_SUCCESS;
     }
 
-    struct epoch_guard {
-      std::atomic<std::uint64_t>& epoch;
-
-      ~epoch_guard() {
-        epoch.fetch_add(1, std::memory_order_acq_rel);
-      }
-    } guard{render_epoch};
+    auto guard = metronome_configs.read();
 
     auto const sample_count = frame_count * config.channels;
     std::fill(output, output + sample_count, 0.0F);
@@ -551,12 +572,11 @@ struct sonus::engine::impl {
       std::fill(output, output + sample_count, 0.0F);
       return result;
     }
-    mix_metronome(output, frame_count);
+    mix_metronome(output, frame_count, guard.get());
     return MA_SUCCESS;
   }
 
-  auto mix_metronome(std::float32_t* output, std::uint64_t frame_count) -> void {
-    auto const* metro = active_metronome_config.load(std::memory_order_acquire);
+  auto mix_metronome(std::float32_t* output, std::uint64_t frame_count, metronome_render_config const* metro) -> void {
     if (metro == nullptr || !metro->enabled) {
       if (metro != nullptr) {
         observed_metronome_generation = metro->generation;
@@ -594,7 +614,8 @@ struct sonus::engine::impl {
       if (sample != 0.0F) {
         auto* frame_out = output + frame * config.channels;
         for (auto channel = std::uint32_t{}; channel < config.channels; ++channel) {
-          frame_out[channel] = std::clamp(frame_out[channel] + sample, -1.0F, 1.0F);
+          auto const mixed = static_cast<std::float32_t>(frame_out[channel] + sample);
+          frame_out[channel] = std::clamp(mixed, static_cast<std::float32_t>(-1.0F), static_cast<std::float32_t>(1.0F));
         }
       }
       --frames_until_next_beat;
@@ -632,11 +653,14 @@ auto sonus::validate(sonus::audio_config const& config) -> std::expected<void, m
   if (!valid_unit_interval(config.master_volume)) {
     return sonus::detail::fail_void(invalid("audio master_volume must be between 0 and 1"));
   }
+  if (contains_null(config.playback_device_id)) {
+    return sonus::detail::fail_void(invalid("audio playback_device_id must not contain null bytes"));
+  }
   if (contains_null(config.playback_device_name)) {
     return sonus::detail::fail_void(invalid("audio playback_device_name must not contain null bytes"));
   }
-  if (config.no_device && !config.playback_device_name.empty()) {
-    return sonus::detail::fail_void(invalid("audio playback_device_name requires a playback device"));
+  if (config.no_device && (!config.playback_device_id.empty() || !config.playback_device_name.empty())) {
+    return sonus::detail::fail_void(invalid("audio playback device selectors require a playback device"));
   }
   if (config.period_size_frames != 0U && config.period_size_milliseconds != 0U) {
     return sonus::detail::fail_void(invalid("audio period_size_frames and period_size_milliseconds are mutually exclusive"));
@@ -653,6 +677,25 @@ auto sonus::validate(sonus::audio_config const& config) -> std::expected<void, m
   return {};
 }
 
+auto sonus::enumerate_playback_devices() -> std::expected<std::vector<sonus::device_info>, modulus::error> {
+  auto context = temporary_context{};
+  auto context_config = ma_context_config_init();
+  auto result = ma_context_init(nullptr, 0, &context_config, &context.context);
+  if (result != MA_SUCCESS) {
+    return sonus::detail::fail<std::vector<sonus::device_info>>(miniaudio_error(result, "failed to initialize miniaudio context"));
+  }
+  context.initialized = true;
+
+  ma_device_info* playback_devices = nullptr;
+  auto playback_device_count = ma_uint32{};
+  result = ma_context_get_devices(&context.context, &playback_devices, &playback_device_count, nullptr, nullptr);
+  if (result != MA_SUCCESS) {
+    return sonus::detail::fail<std::vector<sonus::device_info>>(miniaudio_error(result, "failed to enumerate playback devices"));
+  }
+
+  return describe_playback_devices(playback_devices, playback_device_count);
+}
+
 auto sonus::validate(sonus::metronome_config const& config) -> std::expected<void, modulus::error> {
   if (config.bpm == 0U || config.bpm > 400U) {
     return sonus::detail::fail_void(invalid("metronome bpm must be between 1 and 400"));

test_package/CMakeLists.txt

@@ -0,0 +1,35 @@
+cmake_minimum_required(VERSION 3.25)
+project(sonus-consumer LANGUAGES CXX)
+
+foreach(dependency miniaudio OpenSSL SQLite3 raylib)
+  set(CMAKE_DISABLE_FIND_PACKAGE_${dependency} TRUE)
+endforeach()
+find_package(sonus CONFIG REQUIRED)
+get_target_property(sonus_links sonus::sonus INTERFACE_LINK_LIBRARIES)
+if(sonus_links MATCHES "miniaudio|OpenSSL|SQLite|raylib")
+  message(FATAL_ERROR "Sonus exposes a private dependency: ${sonus_links}")
+endif()
+foreach(dependency modulus::miniaudio modulus::openssl modulus::sqlite modulus::raylib)
+  if(TARGET ${dependency})
+    message(FATAL_ERROR "Sonus discovered an unrelated bridge: ${dependency}")
+  endif()
+endforeach()
+
+option(SONUS_TEST_INSTALLED_CONFIG "Check installed Modulus component discovery" OFF)
+if(SONUS_TEST_INSTALLED_CONFIG)
+  find_package(modulus CONFIG REQUIRED OPTIONAL_COMPONENTS miniaudio unsupported)
+  if(modulus_miniaudio_FOUND OR modulus_unsupported_FOUND)
+    message(FATAL_ERROR "Unavailable optional components must not be found")
+  endif()
+  find_package(modulus CONFIG QUIET COMPONENTS unsupported)
+  if(modulus_FOUND)
+    message(FATAL_ERROR "An unknown required component must reject the package")
+  endif()
+  find_package(modulus CONFIG REQUIRED)
+endif()
+
+add_executable(sonus-consumer main.cpp)
+target_link_libraries(sonus-consumer PRIVATE sonus::sonus)
+target_compile_features(sonus-consumer PRIVATE cxx_std_23)
+enable_testing()
+add_test(NAME sonus-consumer COMMAND sonus-consumer)

test_package/conanfile.py

@@ -0,0 +1,26 @@
+import os
+
+import conan
+import conan.tools.build
+import conan.tools.cmake
+
+
+class sonus_test_package(conan.ConanFile):
+  settings = "os", "arch", "compiler", "build_type"
+  generators = "CMakeDeps", "CMakeToolchain"
+  test_type = "explicit"
+
+  def requirements(self):
+    self.requires(self.tested_reference_str)
+
+  def layout(self):
+    conan.tools.cmake.cmake_layout(self)
+
+  def build(self):
+    cmake = conan.tools.cmake.CMake(self)
+    cmake.configure()
+    cmake.build()
+
+  def test(self):
+    if conan.tools.build.can_run(self):
+      self.run(os.path.join(self.cpp.build.bindirs[0], "sonus-consumer"), env="conanrun")

test_package/main.cpp

@@ -0,0 +1,22 @@
+#include <sonus.hpp>
+
+#include <algorithm>
+#include <vector>
+
+auto main() -> int {
+  auto config = sonus::audio_config{};
+  config.no_device = true;
+  auto engine = sonus::engine::create(config);
+  if (!engine || !engine->set_master_volume(0.5F) || !engine->start_metronome({})) {
+    return 1;
+  }
+  auto samples = std::vector<std::float32_t>(512U * engine->channels());
+  if (!engine->render(samples.data(), 512U)) {
+    return 2;
+  }
+  if (std::none_of(samples.begin(), samples.end(), [](auto value) { return value != 0.0F; })) {
+    return 3;
+  }
+  engine->stop_metronome();
+  return engine->metronome_active() ? 4 : 0;
+}

tests/CMakeLists.txt

@@ -1,14 +1,17 @@
 get_target_property(sonus_interface_libraries sonus INTERFACE_LINK_LIBRARIES)
-if(sonus_interface_libraries AND sonus_interface_libraries MATCHES "miniaudio")
-  message(FATAL_ERROR "sonus::sonus must not expose miniaudio in its public link interface")
+if(sonus_interface_libraries AND sonus_interface_libraries MATCHES "miniaudio|OpenSSL|SQLite|raylib")
+  message(FATAL_ERROR "sonus::sonus must not expose private audio or unrelated third-party libraries in its public link interface")
 endif()
 
 add_executable(sonus-test
   test.cpp
+  render_snapshot.cpp
+  control.cpp
 )
 find_package(Threads REQUIRED)
 target_include_directories(sonus-test PRIVATE
   ${CMAKE_CURRENT_SOURCE_DIR}
+  ${PROJECT_SOURCE_DIR}/src
 )
 target_link_libraries(sonus-test PRIVATE
   sonus::sonus

tests/control.cpp

@@ -0,0 +1,71 @@
+#include <boost/test/unit_test.hpp>
+
+#include <atomic>
+#include <barrier>
+#include <thread>
+#include <vector>
+
+#include <sonus.hpp>
+#include "detail/playback_devices.hpp"
+
+BOOST_AUTO_TEST_CASE(sonus_updates_cannot_undo_concurrent_start_or_stop) {
+  auto config = sonus::audio_config{};
+  config.no_device = true;
+  auto created = sonus::engine::create(config);
+  BOOST_REQUIRE(created);
+  auto rendezvous = std::barrier{2};
+  auto failed = std::atomic<bool>{false};
+  auto updater = std::thread{[&] {
+    for (auto index = 0; index < 1000; ++index) {
+      for (auto phase = 0; phase < 2; ++phase) {
+        rendezvous.arrive_and_wait();
+        if (!created->update_metronome({})) {
+          failed.store(true);
+        }
+        rendezvous.arrive_and_wait();
+      }
+    }
+  }};
+  for (auto index = 0; index < 1000; ++index) {
+    rendezvous.arrive_and_wait();
+    if (!created->start_metronome({})) {
+      failed.store(true);
+    }
+    rendezvous.arrive_and_wait();
+    if (!created->metronome_active()) {
+      failed.store(true);
+    }
+    rendezvous.arrive_and_wait();
+    created->stop_metronome();
+    rendezvous.arrive_and_wait();
+    if (created->metronome_active()) {
+      failed.store(true);
+    }
+  }
+  updater.join();
+  BOOST_TEST(!failed.load());
+}
+
+BOOST_AUTO_TEST_CASE(sonus_device_selection_handles_empty_and_duplicate_devices) {
+  auto devices = std::vector<sonus::device_info>{
+    {.id = "0:1:speaker", .name = "speaker", .is_default = true},
+    {.id = "1:0:speaker", .name = "speaker", .is_default = false},
+  };
+  auto select = [&](auto id, auto name) {
+    return sonus::detail::find_playback_device(devices, id, name);
+  };
+  auto selected = select(devices[1].id, "speaker");
+  BOOST_REQUIRE(selected);
+  BOOST_TEST(*selected == 1U);
+  selected = select("stale-id", "speaker");
+  BOOST_REQUIRE(selected);
+  BOOST_TEST(*selected == 0U);
+  selected = select("", "speaker");
+  BOOST_REQUIRE(selected);
+  BOOST_TEST(*selected == 0U);
+  BOOST_TEST(!select("stale-id", ""));
+  BOOST_TEST(!select("", ""));
+  BOOST_TEST(!select("", "missing"));
+  devices.clear();
+  BOOST_TEST(!select("0:1:speaker", "speaker"));
+}

tests/render_snapshot.cpp

@@ -0,0 +1,88 @@
+#include <boost/test/unit_test.hpp>
+
+#include <array>
+#include <atomic>
+#include <barrier>
+#include <memory>
+#include <thread>
+
+#include "detail/render_snapshot.hpp"
+
+namespace {
+
+struct snapshot {
+  std::atomic<int>& live;
+  std::array<int, 64> samples{};
+  explicit snapshot(std::atomic<int>& count, int value = 0) : live(count) {
+    ++live;
+    samples.fill(value);
+  }
+  ~snapshot() { --live; }
+};
+
+}
+
+BOOST_AUTO_TEST_CASE(sonus_snapshots_are_reclaimed_without_rendering) {
+  auto live = std::atomic<int>{0};
+  auto state = sonus::detail::render_snapshot<snapshot>{};
+  for (auto index = 0; index < 1000; ++index) {
+    state.publish(std::make_unique<snapshot>(live, index));
+    BOOST_TEST(live.load() == 1);
+  }
+  state.publish(nullptr);
+  BOOST_TEST(live.load() == 0);
+}
+
+BOOST_AUTO_TEST_CASE(sonus_snapshots_outlive_readers_and_are_collected_on_control_thread) {
+  auto live = std::atomic<int>{0};
+  auto state = sonus::detail::render_snapshot<snapshot>{};
+  state.publish(std::make_unique<snapshot>(live, 42));
+  {
+    auto first = state.read();
+    state.publish(std::make_unique<snapshot>(live, 43));
+    {
+      auto second = state.read();
+      state.publish(std::make_unique<snapshot>(live, 44));
+      state.collect();
+      BOOST_TEST(live.load() == 3);
+      BOOST_TEST(second.get()->samples.front() == 43);
+    }
+    state.collect();
+    BOOST_TEST(live.load() == 3);
+    BOOST_TEST(first.get()->samples.back() == 42);
+  }
+  BOOST_TEST(live.load() == 3);
+  state.collect();
+  BOOST_TEST(live.load() == 1);
+}
+
+BOOST_AUTO_TEST_CASE(sonus_snapshot_publication_overlaps_readers) {
+  auto live = std::atomic<int>{0};
+  auto state = sonus::detail::render_snapshot<snapshot>{};
+  state.publish(std::make_unique<snapshot>(live));
+  auto start = std::barrier{3};
+  auto failed = std::atomic<bool>{false};
+  auto reader = [&] {
+    start.arrive_and_wait();
+    for (auto index = 0; index < 20000; ++index) {
+      auto guard = state.read();
+      auto const* value = guard.get();
+      for (auto sample : value->samples) {
+        if (sample != value->samples.front()) {
+          failed.store(true);
+        }
+      }
+    }
+  };
+  auto first = std::thread{reader};
+  auto second = std::thread{reader};
+  start.arrive_and_wait();
+  for (auto index = 0; index < 20000; ++index) {
+    state.publish(std::make_unique<snapshot>(live, index));
+  }
+  first.join();
+  second.join();
+  state.collect();
+  BOOST_TEST(!failed.load());
+  BOOST_TEST(live.load() == 1);
+}

tests/test.cpp

@@ -30,7 +30,7 @@ auto test_file(std::string_view name) -> std::filesystem::path {
 }
 
 auto peak(std::vector<std::float32_t> const& samples, std::size_t begin_frame, std::size_t frame_count, std::size_t channels) -> std::float32_t {
-  auto result = 0.0F;
+  auto result = std::float32_t{};
   auto const begin = begin_frame * channels;
   auto const end = std::min(samples.size(), begin + frame_count * channels);
   for (auto index = begin; index < end; ++index) {
@@ -126,6 +126,14 @@ BOOST_AUTO_TEST_CASE(sonus_validates_configs) {
   audio.playback_device_name = "default";
   BOOST_TEST(!sonus::validate(audio));
   audio = {};
+  audio.no_device = true;
+  audio.playback_device_id = "0:1:default";
+  BOOST_TEST(!sonus::validate(audio));
+  BOOST_TEST(!sonus::engine::create(audio));
+  audio = {};
+  audio.playback_device_id.assign("a\0b", 3);
+  BOOST_TEST(!sonus::validate(audio));
+  audio = {};
   audio.playback_device_name.assign("a\0b", 3);
   BOOST_TEST(!sonus::validate(audio));
 
@@ -141,6 +149,26 @@ BOOST_AUTO_TEST_CASE(sonus_validates_configs) {
   BOOST_TEST(!sonus::validate(metronome));
 }
 
+BOOST_AUTO_TEST_CASE(sonus_playback_devices_can_be_enumerated) {
+  auto enumerated = sonus::enumerate_playback_devices();
+  if (!enumerated) {
+    BOOST_TEST(!enumerated.error().message().empty());
+    return;
+  }
+
+  for (auto const& device : *enumerated) {
+    BOOST_TEST(!device.id.empty());
+    BOOST_TEST(device.id.find('\0') == std::string::npos);
+    BOOST_TEST(device.name.find('\0') == std::string::npos);
+  }
+
+  if (!enumerated->empty()) {
+    auto config = sonus::audio_config{};
+    config.playback_device_id = enumerated->front().id;
+    BOOST_TEST(static_cast<bool>(sonus::validate(config)));
+  }
+}
+
 BOOST_AUTO_TEST_CASE(sonus_no_device_engine_renders_silence_when_idle) {
   auto created = sonus::engine::create(no_device_config());
   BOOST_REQUIRE(created);
@@ -154,6 +182,40 @@ BOOST_AUTO_TEST_CASE(sonus_no_device_engine_renders_silence_when_idle) {
   }));
 }
 
+BOOST_AUTO_TEST_CASE(sonus_master_volume_can_be_changed_concurrently) {
+  auto created = sonus::engine::create(no_device_config());
+  BOOST_REQUIRE(created);
+
+  auto failed = std::atomic_bool{false};
+  auto volume_worker = [&created, &failed](std::uint32_t offset) {
+    for (auto index = std::uint32_t{}; index < 250U; ++index) {
+      auto const volume = static_cast<std::float32_t>(((index + offset) % 101U)) / 100.0F;
+      if (!created->set_master_volume(volume)) {
+        failed.store(true, std::memory_order_release);
+      }
+    }
+  };
+  auto render_worker = [&created, &failed] {
+    auto samples = std::vector<std::float32_t>(256U * created->channels());
+    for (auto index = std::uint32_t{}; index < 250U; ++index) {
+      if (!created->render(samples.data(), 256U) || !created->update_metronome({})) {
+        failed.store(true, std::memory_order_release);
+      }
+    }
+  };
+
+  auto first = std::thread{volume_worker, 0U};
+  auto second = std::thread{volume_worker, 37U};
+  auto renderer = std::thread{render_worker};
+  first.join();
+  second.join();
+  renderer.join();
+
+  BOOST_TEST(!failed.load(std::memory_order_acquire));
+  BOOST_TEST(!created->set_master_volume(-0.01F));
+  BOOST_TEST(!created->set_master_volume(1.01F));
+}
+
 BOOST_AUTO_TEST_CASE(sonus_metronome_renders_accented_clicks) {
   auto config = no_device_config();
   config.sample_rate = 48000;
@@ -197,6 +259,36 @@ BOOST_AUTO_TEST_CASE(sonus_metronome_update_keeps_inactive_metronome_stopped) {
   BOOST_TEST(created->metronome_active());
 }
 
+BOOST_AUTO_TEST_CASE(sonus_stopped_metronome_updates_stay_silent_and_restart) {
+  auto config = no_device_config();
+  config.sample_rate = 48000;
+  config.channels = 2;
+  auto created = sonus::engine::create(config);
+  BOOST_REQUIRE(created);
+
+  for (auto index = std::uint32_t{}; index < 500U; ++index) {
+    auto metro = sonus::metronome_config{};
+    metro.bpm = 60U + (index % 180U);
+    metro.beats_per_bar = 1U + (index % 8U);
+    metro.click_duration = std::chrono::milliseconds{1 + static_cast<int>(index % 40U)};
+    BOOST_REQUIRE(created->update_metronome(metro));
+    BOOST_TEST(!created->metronome_active());
+  }
+
+  auto samples = std::vector<std::float32_t>(4096U * config.channels, 1.0F);
+  BOOST_REQUIRE(created->render(samples.data(), 4096U));
+  BOOST_TEST(std::all_of(samples.begin(), samples.end(), [](auto sample) {
+    return sample == 0.0F;
+  }));
+
+  auto metro = sonus::metronome_config{};
+  metro.bpm = 120;
+  BOOST_REQUIRE(created->start_metronome(metro));
+  BOOST_TEST(created->metronome_active());
+  BOOST_REQUIRE(created->render(samples.data(), 4096U));
+  BOOST_TEST(peak(samples, 0, 4096U, config.channels) > 0.1F);
+}
+
 BOOST_AUTO_TEST_CASE(sonus_metronome_can_be_updated_concurrently) {
   auto created = sonus::engine::create(no_device_config());
   BOOST_REQUIRE(created);
@@ -206,6 +298,7 @@ BOOST_AUTO_TEST_CASE(sonus_metronome_can_be_updated_concurrently) {
       auto metro = sonus::metronome_config{};
       metro.bpm = 80U + ((index + offset) % 80U);
       static_cast<void>(created->start_metronome(metro));
+      static_cast<void>(created->update_metronome(metro));
       if (index % 7U == 0U) {
         created->stop_metronome();
       }