diff --git a/src/audio/readahead_source.cpp b/src/audio/readahead_source.cpp index e7fc8c56..9ef6c43f 100644 --- a/src/audio/readahead_source.cpp +++ b/src/audio/readahead_source.cpp @@ -42,64 +42,64 @@ ReadaheadSource::~ReadaheadSource() { } auto ReadaheadSource::Read(cpp::span 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; + size_t bytes_written = 0; + // Fill the destination from our buffer, until either the buffer is drained + // or the destination is full. + while (!dest.empty() && (is_refilling_ || !xStreamBufferIsEmpty(buffer_))) { + size_t bytes_read = xStreamBufferReceive(buffer_, dest.data(), + dest.size_bytes(), portMAX_DELAY); + tell_ += bytes_read; + bytes_written += bytes_read; + dest = dest.subspan(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); + // After the loop, we've either written everything that was asked for, or + // we're out of data. + if (!dest.empty()) { + // Out of data in the buffer. Finish using the wrapped stream. + size_t extra_bytes = wrapped_->Read(dest); + tell_ += extra_bytes; + bytes_written += extra_bytes; + + // Check for EOF in the wrapped stream. + if (extra_bytes < dest.size_bytes()) { + return bytes_written; + } } - - // 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 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( - 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); + // After this point, we're done writing to `dest`. It's either empty, or the + // underlying source is EOF. + + // If we're here, then there is more data to be read from the wrapped stream. + // Ensure the readahead is running. + if (!is_refilling_ && + xStreamBufferBytesAvailable(buffer_) < kBufferSize / 4) { + is_refilling_ = true; + std::function refill = [this]() { + // Try to keep larger than most reasonable FAT sector sizes for more + // efficient disk reads. + constexpr size_t kMaxSingleRead = 1024 * 16; + std::byte working_buf[kMaxSingleRead]; + for (;;) { + size_t bytes_to_read = std::min( + 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; + } } - if (read < bytes_to_read) { - break; - } - } - is_refilling_ = false; - is_refilling_.notify_all(); - }; - worker_.Dispatch(refill); + is_refilling_ = false; + is_refilling_.notify_all(); + }; + worker_.Dispatch(refill); + } - return bytes_read; + return bytes_written; } auto ReadaheadSource::CanSeek() -> bool { @@ -109,6 +109,7 @@ auto ReadaheadSource::CanSeek() -> bool { 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. + ESP_LOGI(kTag, "dropping readahead due to seek"); is_refilling_.wait(true); // It's now safe to clear out the buffer. xStreamBufferReset(buffer_);