fix mirrored memory not working on linux

add mirrored memory unit test

src/os.cpp

@@ -668,26 +668,56 @@ int soundio_os_init_mirrored_memory(struct SoundIoOsMirroredMemory *mem, size_t
         break;
     }
 #else
+    char shm_path[] = "/dev/shm/soundio-XXXXXX";
+    char tmp_path[] = "/tmp/soundio-XXXXXX";
+    char *chosen_path;
+
+    int fd = mkstemp(shm_path);
+    if (fd < 0) {
+        fd = mkstemp(tmp_path);
+        if (fd < 0) {
+            return SoundIoErrorSystemResources;
+        } else {
+            chosen_path = tmp_path;
+        }
+    } else {
+        chosen_path = shm_path;
+    }
+
+    if (unlink(chosen_path)) {
+        close(fd);
+        return SoundIoErrorSystemResources;
+    }
+
+    if (ftruncate(fd, actual_capacity)) {
+        close(fd);
+        return SoundIoErrorSystemResources;
+    }
+
     char *address = (char*)mmap(NULL, actual_capacity * 2, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
     if (address == MAP_FAILED)
         return SoundIoErrorNoMem;
 
     char *other_address = (char*)mmap(address, actual_capacity, PROT_READ|PROT_WRITE,
-            MAP_ANONYMOUS|MAP_FIXED|MAP_SHARED, -1, 0);
+            MAP_FIXED|MAP_SHARED, fd, 0);
     if (other_address != address) {
         munmap(address, 2 * actual_capacity);
+        close(fd);
         return SoundIoErrorNoMem;
     }
 
     other_address = (char*)mmap(address + actual_capacity, actual_capacity,
-            PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_FIXED|MAP_SHARED, -1, 0);
+            PROT_READ|PROT_WRITE, MAP_FIXED|MAP_SHARED, fd, 0);
     if (other_address != address + actual_capacity) {
         munmap(address, 2 * actual_capacity);
+        close(fd);
         return SoundIoErrorNoMem;
     }
 
     mem->address = address;
 
+    if (close(fd))
+        return SoundIoErrorSystemResources;
 #endif
 
     mem->capacity = actual_capacity;

test/unit_tests.cpp

@@ -15,7 +15,7 @@ static inline void ok_or_panic(int err) {
 }
 
 static void test_os_get_time(void) {
-    soundio_os_init();
+    ok_or_panic(soundio_os_init());
     double prev_time = soundio_os_get_time();
     for (int i = 0; i < 1000; i += 1) {
         double time = soundio_os_get_time();
@@ -165,6 +165,24 @@ static void test_ring_buffer_threaded(void) {
     soundio_destroy(soundio);
 }
 
+static void test_mirrored_memory(void) {
+    struct SoundIoOsMirroredMemory mem;
+    ok_or_panic(soundio_os_init());
+
+    static const int requested_bytes = 1024;
+    ok_or_panic(soundio_os_init_mirrored_memory(&mem, requested_bytes));
+    const int size_bytes = mem.capacity;
+
+    for (int i = 0; i < size_bytes; i += 1) {
+        mem.address[i] = rand() % CHAR_MAX;
+    }
+    for (int i = 0; i < size_bytes; i += 1) {
+        assert(mem.address[i] == mem.address[size_bytes+i]);
+    }
+
+    soundio_os_deinit_mirrored_memory(&mem);
+}
+
 struct Test {
     const char *name;
     void (*fn)(void);
@@ -175,6 +193,7 @@ static struct Test tests[] = {
     {"create output stream", test_create_outstream},
     {"ring buffer basic", test_ring_buffer_basic},
     {"ring buffer threaded", test_ring_buffer_threaded},
+    {"mirrored memory", test_mirrored_memory},
     {NULL, NULL},
 };