Move memory mapping setup to a function

So we don't need to repeat this twice.

src/common/audio-shm.cpp

@@ -21,14 +21,7 @@ AudioShmBuffer::AudioShmBuffer(const Config& config)
       shm(boost::interprocess::open_or_create,
           config.name.c_str(),
           boost::interprocess::read_write) {
-    // Apparently you get a `Resource temporarily unavailable` when calling
-    // `ftruncate()` with a size of 0 on shared memory
-    if (config.size > 0) {
-        shm.truncate(config.size);
-        buffer = boost::interprocess::mapped_region(
-            shm, boost::interprocess::read_write, 0, config.size, nullptr,
-            MAP_LOCKED);
-    }
+    setup_mapping();
 }
 
 AudioShmBuffer::~AudioShmBuffer() noexcept {
@@ -40,22 +33,6 @@ 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;
-    if (config.size > 0) {
-        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)),
@@ -71,3 +48,25 @@ AudioShmBuffer& AudioShmBuffer::operator=(AudioShmBuffer&& o) noexcept {
 
     return *this;
 }
+
+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;
+    setup_mapping();
+}
+
+void AudioShmBuffer::setup_mapping() {
+    // Apparently you get a `Resource temporarily unavailable` when calling
+    // `ftruncate()` with a size of 0 on shared memory
+    if (config.size > 0) {
+        shm.truncate(config.size);
+        buffer = boost::interprocess::mapped_region(
+            shm, boost::interprocess::read_write, 0, config.size, nullptr,
+            MAP_LOCKED);
+    }
+}

src/common/audio-shm.h

@@ -181,6 +181,11 @@ class AudioShmBuffer {
     Config config;
 
    private:
+    /**
+     * Resize the shared memory object, and set up the memory mapping.
+     */
+    void setup_mapping();
+
     boost::interprocess::shared_memory_object shm;
     boost::interprocess::mapped_region buffer;