input/buffered: proxy InputStream implementation which caches in a huge buffer

src/input/BufferedInputStream.cxx

@@ -0,0 +1,192 @@
+/*
+ * Copyright 2003-2018 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "BufferedInputStream.hxx"
+#include "thread/Cond.hxx"
+#include "thread/Name.hxx"
+
+#include <string.h>
+
+BufferedInputStream::BufferedInputStream(InputStreamPtr _input)
+	:InputStream(_input->GetURI(), _input->mutex),
+	 input(std::move(_input)),
+	 thread(BIND_THIS_METHOD(RunThread)),
+	 buffer(input->GetSize())
+{
+	assert(IsEligible(*input));
+
+	if (input->HasMimeType())
+		SetMimeType(input->GetMimeType());
+
+	size = input->GetSize();
+	seekable = input->IsSeekable();
+	offset = input->GetOffset();
+
+	SetReady();
+
+	thread.Start();
+}
+
+BufferedInputStream::~BufferedInputStream() noexcept
+{
+	{
+		const std::lock_guard<Mutex> lock(mutex);
+		stop = true;
+		wake_cond.signal();
+	}
+
+	thread.Join();
+}
+
+void
+BufferedInputStream::Check()
+{
+	if (input)
+		input->Check();
+}
+
+void
+BufferedInputStream::Seek(offset_type new_offset)
+{
+	auto r = buffer.Read(new_offset);
+	if (r.HasData())
+		/* nice, we already have some data at the desired
+		   offset and this method call is a no-op */
+		return;
+
+	seek_offset = new_offset;
+	seek = true;
+	wake_cond.signal();
+
+	while (seek)
+		client_cond.wait(mutex);
+
+	if (seek_error)
+		std::rethrow_exception(std::exchange(seek_error, {}));
+}
+
+bool
+BufferedInputStream::IsEOF() noexcept
+{
+	return offset == size;
+}
+
+bool
+BufferedInputStream::IsAvailable() noexcept
+{
+	return IsEOF() || buffer.Read(offset).HasData();
+}
+
+size_t
+BufferedInputStream::Read(void *ptr, size_t s)
+{
+	if (offset >= size)
+		return 0;
+
+	while (true) {
+		auto r = buffer.Read(offset);
+		if (r.HasData()) {
+			/* yay, we have some data */
+			size_t nbytes = std::min(s, r.defined_buffer.size);
+			memcpy(ptr, r.defined_buffer.data, nbytes);
+			offset += nbytes;
+			return nbytes;
+		}
+
+		if (read_error) {
+			wake_cond.broadcast();
+			std::rethrow_exception(std::exchange(read_error, {}));
+		}
+
+		if (idle) {
+			/* wake up the sleeping thread */
+			idle = false;
+			wake_cond.signal();
+		}
+
+		client_cond.wait(mutex);
+	}
+}
+
+void
+BufferedInputStream::RunThread() noexcept
+{
+	SetThreadName("input_buffered");
+
+	const std::lock_guard<Mutex> lock(mutex);
+
+	while (!stop) {
+		if (seek) {
+			try {
+				input->Seek(seek_offset);
+			} catch (...) {
+				seek_error = std::current_exception();
+			}
+
+			offset = input->GetOffset();
+
+			idle = false;
+			seek = false;
+			client_cond.signal();
+		} else if (!idle && !read_error &&
+			   input->IsAvailable() && !input->IsEOF()) {
+			const auto read_offset = input->GetOffset();
+			auto w = buffer.Write(read_offset);
+
+			if (w.empty()) {
+				auto r = buffer.Read(offset);
+				if (r.HasData()) {
+					/* we still have enough data
+					   for the next Read() - sleep
+					   until we need more data */
+					idle = true;
+				} else {
+					/* we need more data at our
+					   current position, because
+					   the next Read() will stall
+					   - seek our input to our
+					   offset to prepare filling
+					   the buffer from there */
+					try {
+						input->Seek(offset);
+					} catch (...) {
+						read_error = std::current_exception();
+						client_cond.signal();
+						InvokeOnAvailable();
+					}
+				}
+
+				continue;
+			}
+
+			try {
+				size_t nbytes = input->Read(w.data, w.size);
+				buffer.Commit(read_offset,
+					      read_offset + nbytes);
+			} catch (...) {
+				read_error = std::current_exception();
+			}
+
+			client_cond.signal();
+			InvokeOnAvailable();
+		} else
+			wake_cond.wait(mutex);
+	}
+}