feat(imageloader): dedicated thread pool for blocking IO

include/tev/Common.h

@@ -318,6 +318,10 @@ template <typename... Callable> struct visitor : Callable... {
 
 template <typename T> concept trivially_copyable = std::is_trivially_copyable_v<T>;
 
+template <typename T> std::span<T> toSpan(const std::istringstream& stream) {
+    return std::span<T>{reinterpret_cast<const T*>(stream.view().data()), stream.view().size()};
+}
+
 // Stricter version of from_chars that only returns true if the entire input was consumed and no error occurred.
 template <typename T> bool fromChars(const char* begin, const char* end, T& value) {
     const auto result = std::from_chars(begin, end, value);

include/tev/Image.h

@@ -32,11 +32,11 @@
 #include <array>
 #include <atomic>
 #include <expected>
-#include <istream>
 #include <map>
 #include <memory>
 #include <optional>
 #include <span>
+#include <sstream>
 #include <string>
 #include <vector>
 
@@ -344,10 +344,10 @@ Task<nanogui::Vector2i> orientToTopLeft(PixelBuffer& data, nanogui::Vector2i siz
 using ImageLoadResult = std::expected<std::vector<std::shared_ptr<Image>>, ImageLoadError>;
 
 Task<ImageLoadResult> tryLoadImage(
-    int imageId, fs::path path, std::istream& iStream, std::string_view channelSelector, const ImageLoaderSettings& settings, bool groupChannels
+    int imageId, fs::path path, std::istringstream& iStream, std::string_view channelSelector, const ImageLoaderSettings& settings, bool groupChannels
 );
 Task<ImageLoadResult> tryLoadImage(
-    fs::path path, std::istream& iStream, std::string_view channelSelector, const ImageLoaderSettings& settings, bool groupChannels
+    fs::path path, std::istringstream& iStream, std::string_view channelSelector, const ImageLoaderSettings& settings, bool groupChannels
 );
 Task<ImageLoadResult>
     tryLoadImage(int imageId, fs::path path, std::string_view channelSelector, const ImageLoaderSettings& settings, bool groupChannels);

include/tev/ThreadPool.h

@@ -45,6 +45,11 @@ class ThreadPool {
         return pool;
     }
 
+    static ThreadPool& blockingIo() {
+        static ThreadPool pool;
+        return pool;
+    }
+
     template <std::invocable F> auto enqueueTask(F&& f, int priority, bool stopToken = false) {
         using return_type = std::invoke_result_t<F>;
 

include/tev/imageio/BmpImageLoader.h

@@ -21,15 +21,15 @@
 #include <tev/Image.h>
 #include <tev/imageio/ImageLoader.h>
 
-#include <istream>
+#include <sstream>
 #include <optional>
 
 namespace tev {
 
 class BmpImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> loadWithoutFileHeader(
-        std::istream& iStream,
+        std::istringstream& iStream,
         const fs::path& path,
         std::string_view channelSelector,
         const ImageLoaderSettings& settings,
@@ -46,7 +46,7 @@ class BmpImageLoader final : public ImageLoader {
     ) const;
 
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "BMP"; }

include/tev/imageio/ClipboardImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class ClipboardImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "clipboard"; }

include/tev/imageio/DdsImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class DdsImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "DDS"; }

include/tev/imageio/DicomImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class DicomImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "DICOM"; }

include/tev/imageio/EmptyImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class EmptyImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "IPC"; }

include/tev/imageio/ExrImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class ExrImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "OpenEXR"; }

include/tev/imageio/FitsImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class FitsImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "FITS"; }

include/tev/imageio/HeifImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class HeifImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "HEIF"; }

include/tev/imageio/IcoImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class IcoImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "ICO"; }

include/tev/imageio/ImageLoader.h

@@ -217,7 +217,7 @@ class ImageLoader {
     virtual ~ImageLoader() {}
 
     virtual Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const = 0;
 
     virtual std::string name() const = 0;

include/tev/imageio/Jpeg2000ImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class Jpeg2000ImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     Task<std::vector<ImageData>> load(

include/tev/imageio/JpegTurboImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class JpegTurboImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "JPEG Turbo"; }

include/tev/imageio/JxlImageLoader.h

@@ -30,7 +30,7 @@ namespace tev {
 class JxlImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     Task<std::vector<ImageData>> load(

include/tev/imageio/JxrImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class JxrImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "JXR"; }

include/tev/imageio/PfmImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class PfmImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "PFM/PAM"; }

include/tev/imageio/PngImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class PngImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "PNG"; }

include/tev/imageio/QoiImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class QoiImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "QOI"; }

include/tev/imageio/RawImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class RawImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "RAW"; }

include/tev/imageio/StbiImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class StbiImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "STBI"; }

include/tev/imageio/TiffImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class TiffImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "TIFF"; }

include/tev/imageio/WebpImageLoader.h

@@ -28,7 +28,7 @@ namespace tev {
 class WebpImageLoader final : public ImageLoader {
 public:
     Task<std::vector<ImageData>> load(
-        std::istream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
+        std::istringstream& iStream, const fs::path& path, std::string_view channelSelector, const ImageLoaderSettings& settings, int priority
     ) const override;
 
     std::string name() const override { return "WEBP"; }

src/BackgroundImagesLoader.cpp

@@ -73,8 +73,9 @@ void BackgroundImagesLoader::enqueue(const fs::path& path, string_view channelSe
     invokeTaskDetached([loadId, path, cs = string{channelSelector}, shallSelect, toReplace, this]() -> Task<void> {
         const int taskPriority = -Image::drawId();
 
-        co_await ThreadPool::global().enqueueCoroutine(taskPriority);
+        co_await ThreadPool::blockingIo().enqueueCoroutine(taskPriority);
         const auto images = co_await tryLoadImage(taskPriority, path, cs, mImageLoaderSettings, mGroupChannels);
+        co_await ThreadPool::global().enqueueCoroutine(taskPriority);
 
         {
             const lock_guard lock{mPendingLoadedImagesMutex};

src/Image.cpp

@@ -1473,7 +1473,7 @@ Task<nanogui::Vector2i> orientToTopLeft(PixelBuffer& data, nanogui::Vector2i siz
 }
 
 Task<ImageLoadResult> tryLoadImage(
-    int taskPriority, fs::path path, istream& iStream, string_view channelSelector, const ImageLoaderSettings& settings, bool groupChannels
+    int taskPriority, fs::path path, istringstream& iStream, string_view channelSelector, const ImageLoaderSettings& settings, bool groupChannels
 ) {
     // No need to keep loading images if tev is already shutting down again.
     if (shuttingDown()) {
@@ -1550,7 +1550,11 @@ Task<ImageLoadResult> tryLoadImage(
 
         vector<shared_ptr<Image>> images = co_await awaitAll(imageTasks) | toVector;
         if (images.empty()) {
-            throw ImageLoadError{fmt::format("No parts/channels match channel selector :{}", channelSelector)};
+            if (channelSelector.empty()) {
+                throw ImageLoadError{fmt::format("No parts/channels found in image {}.", path)};
+            } else {
+                throw ImageLoadError{fmt::format("No parts/channels match channel selector :{}", channelSelector)};
+            }
         }
 
         const auto end = chrono::system_clock::now();
@@ -1568,7 +1572,7 @@ Task<ImageLoadResult> tryLoadImage(
 }
 
 Task<ImageLoadResult>
-    tryLoadImage(fs::path path, istream& iStream, string_view channelSelector, const ImageLoaderSettings& settings, bool groupChannels) {
+    tryLoadImage(fs::path path, istringstream& iStream, string_view channelSelector, const ImageLoaderSettings& settings, bool groupChannels) {
     co_return co_await tryLoadImage(-Image::drawId(), path, iStream, channelSelector, settings, groupChannels);
 }
 
@@ -1581,8 +1585,21 @@ Task<ImageLoadResult>
         // sure.
     }
 
-    ifstream fileStream{path, ios_base::binary};
-    co_return co_await tryLoadImage(taskPriority, path, fileStream, channelSelector, settings, groupChannels);
+    istringstream iStream;
+
+    {
+        co_await ThreadPool::blockingIo().enqueueCoroutine(taskPriority);
+
+        if (!shuttingDown()) {
+            ostringstream oStream;
+            ifstream fileStream{path, ios_base::binary};
+            oStream << fileStream.rdbuf();
+            iStream = istringstream{std::move(oStream).str()}; // C++20 rvalue .str() overload to avoid a copy of the string
+        }
+    }
+
+    co_await ThreadPool::global().enqueueCoroutine(taskPriority);
+    co_return co_await tryLoadImage(taskPriority, path, iStream, channelSelector, settings, groupChannels);
 }
 
 Task<ImageLoadResult> tryLoadImage(fs::path path, string_view channelSelector, const ImageLoaderSettings& settings, bool groupChannels) {

src/ImageViewer.cpp

@@ -2591,15 +2591,15 @@ void ImageViewer::copyImageNameToClipboard() const {
 }
 
 void ImageViewer::pasteImagesFromClipboard() {
-    stringstream imageStream;
+    istringstream imageStream;
     if (glfwGetPlatform() == GLFW_PLATFORM_WAYLAND) {
         const auto data = waylandGetClipboardPngImage();
         if (data.empty()) {
             throw runtime_error{"No image data found in clipboard."};
         }
 
         // TODO: use spanstream once it is available in C++23 to avoid the copy
-        imageStream = stringstream{string{data}, ios::in};
+        imageStream = istringstream{string{data}};
     } else if (glfwGetPlatform() == GLFW_PLATFORM_X11) {
         clip::lock l;
         if (!l.locked()) {
@@ -2615,16 +2615,18 @@ void ImageViewer::pasteImagesFromClipboard() {
         string data(len, '\0');
         l.get_data(f, data.data(), len);
 
-        imageStream = stringstream{std::move(data), ios::in};
+        imageStream = istringstream{std::move(data)};
     } else {
         clip::image clipImage;
         if (!clip::get_image(clipImage)) {
             throw runtime_error{"No image data found in clipboard."};
         }
 
-        imageStream << "clip";
-        imageStream.write(reinterpret_cast<const char*>(&clipImage.spec()), sizeof(clip::image_spec));
-        imageStream.write(clipImage.data(), clipImage.spec().bytes_per_row * clipImage.spec().height);
+        ostringstream oss;
+        oss << "clip";
+        oss.write(reinterpret_cast<const char*>(&clipImage.spec()), sizeof(clip::image_spec));
+        oss.write(clipImage.data(), clipImage.spec().bytes_per_row * clipImage.spec().height);
+        imageStream = istringstream{std::move(oss).str()};
     }
 
     tlog::info("Loading image from clipboard...");
@@ -2646,7 +2648,9 @@ void ImageViewer::showErrorDialog(string_view message, bool logToConsole) {
         tlog::error(message);
     }
 
-    new ErrorDialog(this, MessageDialog::Type::Warning, "Error", message, "OK", "Cancel", false, (int)(m_size.x() * 0.75f), (int)(m_size.y() * 0.75f));
+    new ErrorDialog(
+        this, MessageDialog::Type::Warning, "Error", message, "OK", "Cancel", false, (int)(m_size.x() * 0.75f), (int)(m_size.y() * 0.75f)
+    );
 }
 
 chroma_t ImageViewer::inspectionChroma() const {