ring buffer: fewer mallocs during init

src/os.cpp

@@ -132,14 +132,6 @@ pthread_mutex_t init_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 static int page_size;
 
-struct SoundIoOsMirroredMemoryPrivate {
-    SoundIoOsMirroredMemory pub;
-#if defined(SOUNDIO_OS_WINDOWS)
-    HANDLE handle;
-#endif
-};
-
-
 double soundio_os_get_time(void) {
 #if defined(SOUNDIO_OS_WINDOWS)
     unsigned __int64 time;
@@ -613,19 +605,14 @@ int soundio_os_page_size(void) {
     return page_size;
 }
 
-struct SoundIoOsMirroredMemory *soundio_os_create_mirrored_memory(size_t requested_capacity) {
-    SoundIoOsMirroredMemoryPrivate *m = create<SoundIoOsMirroredMemoryPrivate>();
-    if (!m)
-        return nullptr;
-    SoundIoOsMirroredMemory *mem = &m->pub;
-
+int soundio_os_init_mirrored_memory(struct SoundIoOsMirroredMemory *mem, size_t requested_capacity) {
     size_t actual_capacity = ceil(requested_capacity / (double)page_size) * page_size;
 
 #if defined(SOUNDIO_OS_WINDOWS)
     BOOL ok;
     HANDLE hMapFile = CreateFileMapping(INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE, 0, actual_capacity * 2, NULL);
     if (!hMapFile)
-        return nullptr;
+        return SoundIoErrorNoMem;
 
     for (;;) {
         // find a free address space with the correct size
@@ -633,7 +620,7 @@ struct SoundIoOsMirroredMemory *soundio_os_create_mirrored_memory(size_t request
         if (!address) {
             ok = CloseHandle(hMapFile);
             assert(ok);
-            return nullptr;
+            return SoundIoErrorNoMem;
         }
 
         // found a big enough address space. hopefully it will remain free
@@ -649,7 +636,7 @@ struct SoundIoOsMirroredMemory *soundio_os_create_mirrored_memory(size_t request
             } else {
                 ok = CloseHandle(hMapFile);
                 assert(ok);
-                return nullptr;
+                return SoundIoErrorNoMem;
             }
         }
 
@@ -665,30 +652,31 @@ struct SoundIoOsMirroredMemory *soundio_os_create_mirrored_memory(size_t request
             } else {
                 ok = CloseHandle(hMapFile);
                 assert(ok);
-                return nullptr;
+                return SoundIoErrorNoMem;
             }
         }
 
+        mem->priv = hMapFile;
         mem->address = address;
         break;
     }
 #else
     char *address = (char*)mmap(NULL, actual_capacity * 2, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
     if (address == MAP_FAILED)
-        return nullptr;
+        return SoundIoErrorNoMem;
 
     char *other_address = (char*)mmap(address, actual_capacity, PROT_READ|PROT_WRITE,
             MAP_ANONYMOUS|MAP_FIXED|MAP_SHARED, -1, 0);
     if (other_address != address) {
         munmap(address, 2 * actual_capacity);
-        return nullptr;
+        return SoundIoErrorNoMem;
     }
 
     other_address = (char*)mmap(address + actual_capacity, actual_capacity,
             PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_FIXED|MAP_SHARED, -1, 0);
     if (other_address != address + actual_capacity) {
         munmap(address, 2 * actual_capacity);
-        return nullptr;
+        return SoundIoErrorNoMem;
     }
 
     mem->address = address;
@@ -696,24 +684,20 @@ struct SoundIoOsMirroredMemory *soundio_os_create_mirrored_memory(size_t request
 #endif
 
     mem->capacity = actual_capacity;
-    return mem;
+    return 0;
 }
 
-void soundio_os_destroy_mirrored_memory(struct SoundIoOsMirroredMemory *mem) {
-    if (!mem)
-        return;
-    SoundIoOsMirroredMemoryPrivate *m = (SoundIoOsMirroredMemoryPrivate *)mem;
+void soundio_os_deinit_mirrored_memory(struct SoundIoOsMirroredMemory *mem) {
 #if defined(SOUNDIO_OS_WINDOWS)
     BOOL ok;
     ok = UnmapViewOfFile(mem->address);
     assert(ok);
     ok = UnmapViewOfFile(mem->address + mem->capacity);
     assert(ok);
-    ok = CloseHandle(m->handle);
+    ok = CloseHandle((HANDLE)mem->priv);
     assert(ok);
 #else
     int err = munmap(mem->address, 2 * mem->capacity);
     assert(!err);
 #endif
-    destroy(m);
 }

src/os.hpp

@@ -51,15 +51,16 @@ void soundio_os_cond_wait(struct SoundIoOsCond *cond,
 
 int soundio_os_page_size(void);
 
-// The size of this struct is not part of the API or ABI.
+// You may rely on the size of this struct as part of the API and ABI.
 struct SoundIoOsMirroredMemory {
     size_t capacity;
     char *address;
+    void *priv;
 };
 
 // returned capacity might be increased from capacity to be a multiple of the
 // system page size
-struct SoundIoOsMirroredMemory *soundio_os_create_mirrored_memory(size_t capacity);
-void soundio_os_destroy_mirrored_memory(struct SoundIoOsMirroredMemory *mem);
+int soundio_os_init_mirrored_memory(struct SoundIoOsMirroredMemory *mem, size_t capacity);
+void soundio_os_deinit_mirrored_memory(struct SoundIoOsMirroredMemory *mem);
 
 #endif

src/ring_buffer.cpp

@@ -42,7 +42,7 @@ int soundio_ring_buffer_capacity(struct SoundIoRingBuffer *rb) {
 }
 
 char *soundio_ring_buffer_write_ptr(struct SoundIoRingBuffer *rb) {
-    return rb->address + (rb->write_offset % rb->capacity);
+    return rb->mem.address + (rb->write_offset % rb->capacity);
 }
 
 void soundio_ring_buffer_advance_write_ptr(struct SoundIoRingBuffer *rb, int count) {
@@ -51,7 +51,7 @@ void soundio_ring_buffer_advance_write_ptr(struct SoundIoRingBuffer *rb, int cou
 }
 
 char *soundio_ring_buffer_read_ptr(struct SoundIoRingBuffer *rb) {
-    return rb->address + (rb->read_offset % rb->capacity);
+    return rb->mem.address + (rb->read_offset % rb->capacity);
 }
 
 void soundio_ring_buffer_advance_read_ptr(struct SoundIoRingBuffer *rb, int count) {
@@ -75,20 +75,16 @@ void soundio_ring_buffer_clear(struct SoundIoRingBuffer *rb) {
 }
 
 int soundio_ring_buffer_init(struct SoundIoRingBuffer *rb, int requested_capacity) {
-    rb->mem = soundio_os_create_mirrored_memory(requested_capacity);
-    if (!rb->mem) {
-        soundio_ring_buffer_deinit(rb);
-        return SoundIoErrorNoMem;
-    }
-    rb->address = rb->mem->address;
-    rb->capacity = rb->mem->capacity;
+    int err;
+    if ((err = soundio_os_init_mirrored_memory(&rb->mem, requested_capacity)))
+        return err;
     rb->write_offset = 0;
     rb->read_offset = 0;
+    rb->capacity = rb->mem.capacity;
 
     return 0;
 }
 
 void soundio_ring_buffer_deinit(struct SoundIoRingBuffer *rb) {
-    soundio_os_destroy_mirrored_memory(rb->mem);
-    rb->mem = nullptr;
+    soundio_os_deinit_mirrored_memory(&rb->mem);
 }

src/ring_buffer.hpp

@@ -12,11 +12,10 @@
 #include "os.hpp"
 
 struct SoundIoRingBuffer {
-    char *address;
-    int capacity;
+    SoundIoOsMirroredMemory mem;
     atomic_long write_offset;
     atomic_long read_offset;
-    SoundIoOsMirroredMemory *mem;
+    int capacity;
 };
 
 int soundio_ring_buffer_init(struct SoundIoRingBuffer *rb, int requested_capacity);