Add a shared memory based audio buffer

We'll be using this to reduce the amount of copying we have to do during
audio processing.

src/common/audio-shm.cpp

@@ -0,0 +1,34 @@
+// yabridge: a Wine VST bridge
+// Copyright (C) 2020-2021 Robbert van der Helm
+//
+// 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 3 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, see <https://www.gnu.org/licenses/>.
+
+#include "audio-shm.h"
+
+AudioShmBuffer::AudioShmBuffer(const Config& config)
+    : config(config),
+      shm(boost::interprocess::open_or_create,
+          config.name.c_str(),
+          boost::interprocess::read_write) {
+    shm.truncate(config.size);
+    buffer = boost::interprocess::mapped_region(
+        shm, boost::interprocess::read_write, 0, config.size);
+}
+
+AudioShmBuffer::~AudioShmBuffer() noexcept {
+    // If either side drops this object then the buffer should always be
+    // removed, so we'll do it on both sides to reduce the chance that we leak
+    // shared memory
+    boost::interprocess::shared_memory_object::remove(config.name.c_str());
+}