From 0370c64f9909af53167b2c8c3ec088399f442992 Mon Sep 17 00:00:00 2001
From: Robbert van der Helm <mail@robbertvanderhelm.nl>
Date: Thu, 10 Jun 2021 14:13:18 +0200
Subject: [PATCH] Allow resizing shared memory buffers

---
 src/common/audio-shm.cpp | 23 +++++++++++++++++++++++
 src/common/audio-shm.h   | 19 +++++++++++++++----
 2 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/src/common/audio-shm.cpp b/src/common/audio-shm.cpp
index a2d7d3bc..99dafd43 100644
--- a/src/common/audio-shm.cpp
+++ b/src/common/audio-shm.cpp
@@ -36,9 +36,32 @@ AudioShmBuffer::~AudioShmBuffer() noexcept {
     }
 }
 
+void AudioShmBuffer::resize(const Config& new_config) {
+    if (new_config.name != config.name) {
+        throw std::invalid_argument("Expected buffer configuration for \"" +
+                                    config.name + "\", got \"" +
+                                    new_config.name + "\"");
+    }
+
+    config = new_config;
+    shm.truncate(config.size);
+    buffer =
+        boost::interprocess::mapped_region(shm, boost::interprocess::read_write,
+                                           0, config.size, nullptr, MAP_LOCKED);
+}
+
 AudioShmBuffer::AudioShmBuffer(AudioShmBuffer&& o) noexcept
     : config(std::move(o.config)),
       shm(std::move(o.shm)),
       buffer(std::move(o.buffer)) {
     o.is_moved = true;
 }
+
+AudioShmBuffer& AudioShmBuffer::operator=(AudioShmBuffer&& o) noexcept {
+    config = std::move(o.config);
+    shm = std::move(o.shm);
+    buffer = std::move(o.buffer);
+    o.is_moved = true;
+
+    return *this;
+}
diff --git a/src/common/audio-shm.h b/src/common/audio-shm.h
index 74f2bc1d..cc8a3ee0 100644
--- a/src/common/audio-shm.h
+++ b/src/common/audio-shm.h
@@ -121,11 +121,21 @@ class AudioShmBuffer {
     AudioShmBuffer& operator=(const AudioShmBuffer&) = delete;
 
     AudioShmBuffer(AudioShmBuffer&&) noexcept;
-    AudioShmBuffer& operator=(AudioShmBuffer&&) = delete;
+    AudioShmBuffer& operator=(AudioShmBuffer&&) noexcept;
+
+    /**
+     * Adapt to a new buffer size or channel layout. The name of the buffer
+     * needs to remain the same.
+     *
+     * @throw `std::invalid_argument` If the config is for a buffer with a
+     *   different name.
+     */
+    void resize(const Config& new_config);
 
     /**
      * Get a pointer to the part of the buffer where this input audio channel is
-     * stored in. Both the bus and the channel indices start at zero.
+     * stored in. Both the bus and the channel indices start at zero. These
+     * addresses might change after a call to `resize()`.
      */
     template <typename T>
     T* input_channel_ptr(const uint32_t bus, const uint32_t channel) {
@@ -135,7 +145,8 @@ class AudioShmBuffer {
 
     /**
      * Get a pointer to the part of the buffer where this output audio channel
-     * is stored in. Both the bus and the channel indices start at zero.
+     * is stored in. Both the bus and the channel indices start at zero. These
+     * addresses might change after a call to `resize()`.
      */
     template <typename T>
     T* output_channel_ptr(const uint32_t bus, const uint32_t channel) {
@@ -143,7 +154,7 @@ class AudioShmBuffer {
                config.output_offsets[bus][channel];
     }
 
-    const Config config;
+    Config config;
 
    private:
     boost::interprocess::shared_memory_object shm;