Slightly polish the buddy allocator and ensure mutual exclusion in it…

… (related to #118 and #220)

dart-impl/mpi/include/dash/dart/mpi/dart_mem.h

@@ -15,20 +15,47 @@
 #define DART_MAX_TEAM_NUMBER (256)
 #define DART_MAX_LENGTH (1024*1024*16)
 
-struct dart_buddy {
-	int level;
-	uint8_t tree[1];
-};
+struct dart_buddy;
+
 
 extern char* dart_mempool_localalloc;
 extern struct dart_buddy* dart_localpool;
 
+/**
+ * Create a new buddy allocator instance.
+ *
+ * The amount of memory allocatable through the allocator
+ * depends on the number of levels in the binary tree.
+ * The maximum number of bytes managed by the allocator is
+ * 2**(level). The internal memory requirements are
+ * O(2**(2*level)).
+ *
+ * \param level The number of levels of the internal binary tree.
+ */
 struct dart_buddy *
 dart_buddy_new(int level);
 
+/**
+ * Delete the given buddy allocator instance.
+ */
 void     dart_buddy_delete(struct dart_buddy *);
+
+/**
+ * Allocate memory from the external memory pool.
+ *
+ * \return The offset relative to the starting adddress of the external
+ *         memory block where the allocated memory begins.
+ */
 uint64_t dart_buddy_alloc(struct dart_buddy *, size_t size);
+
+/**
+ * Return the previously allocated memory chunk to the allocator for reuse.
+ */
 int      dart_buddy_free(struct dart_buddy *, uint64_t offset);
+
+/**
+ * ???
+ */
 int      buddy_size(struct dart_buddy *, uint64_t offset);
 void     buddy_dump(struct dart_buddy *);
 

dart-impl/mpi/src/dart_mem.c

@@ -1,6 +1,17 @@
-//https://github.com/cloudwu/buddy
+/*
+ * Buddy allocator to be used with externally allocated blocks.
+ *
+ * The main use for this allocator is \c dart_memalloc where a
+ * fixed-size pre-allocated shared window is used to facilitate
+ * shared-memory optimizations.
+ *
+ * The code was taken from https://github.com/cloudwu/buddy and
+ * the right to use it has been kindly granted by the author.
+ *
+ */
 
 #include <dash/dart/mpi/dart_mem.h>
+#include <dash/dart/base/mutex.h>
 
 /* For PRIu64, uint64_t in printf */
 #define __STDC_FORMAT_MACROS
@@ -11,6 +22,12 @@
 #define NODE_SPLIT 2
 #define NODE_FULL 3
 
+struct dart_buddy {
+  dart_mutex_t mutex;
+  int level;
+  uint8_t tree[1];
+};
+
 struct dart_buddy *
 	dart_buddy_new(int level)
 {
@@ -19,6 +36,7 @@ struct dart_buddy *
     malloc(sizeof(struct dart_buddy) + sizeof(uint8_t) * (size * 2 - 2));
 	self->level = level;
 	memset(self->tree, NODE_UNUSED, size * 2 - 1);
+	dart_mutex_init(&self->mutex);
 	return self;
 }
 
@@ -85,11 +103,14 @@ dart_buddy_alloc(struct dart_buddy * self, size_t s) {
 	int index = 0;
 	int level = 0;
 
+	dart_mutex_lock(&self->mutex);
+
 	while (index >= 0) {
 		if (size == length) {
 			if (self->tree[index] == NODE_UNUSED) {
 				self->tree[index] = NODE_USED;
 				_mark_parent(self, index);
+			  dart_mutex_unlock(&self->mutex);
 				return _index_offset(index, level, self->level);
 			}
 		}
@@ -104,6 +125,7 @@ dart_buddy_alloc(struct dart_buddy * self, size_t s) {
 				self->tree[index] = NODE_SPLIT;
 				self->tree[index * 2 + 1] = NODE_UNUSED;
 				self->tree[index * 2 + 2] = NODE_UNUSED;
+				// intentional fall-through (?)
 			default:
 				index = index * 2 + 1;
 				length /= 2;
@@ -120,6 +142,7 @@ dart_buddy_alloc(struct dart_buddy * self, size_t s) {
 			length *= 2;
 			index = (index + 1) / 2 - 1;
 			if (index < 0)
+			  dart_mutex_unlock(&self->mutex);
 				return -1;
 			if (index & 1) {
 				++index;
@@ -128,6 +151,7 @@ dart_buddy_alloc(struct dart_buddy * self, size_t s) {
 		}
 	}
 
+  dart_mutex_unlock(&self->mutex);
 	return -1;
 }
 
@@ -158,17 +182,21 @@ int dart_buddy_free(struct dart_buddy * self, uint64_t offset)
 		return -1;
 	}
 
+  dart_mutex_lock(&self->mutex);
 	for (;;) {
 		switch (self->tree[index]) {
 		case NODE_USED:
 			if (offset != left){
 				assert (offset == left);
+			  dart_mutex_unlock(&self->mutex);
 				return -1;
 			}
 			_combine(self, index);
+		  dart_mutex_unlock(&self->mutex);
 			return 0;
 		case NODE_UNUSED:
 			assert (0);
+		  dart_mutex_unlock(&self->mutex);
 			return -1;
 		default:
 			length /= 2;
@@ -182,6 +210,10 @@ int dart_buddy_free(struct dart_buddy * self, uint64_t offset)
 			break;
 		}
 	}
+
+  dart_mutex_unlock(&self->mutex);
+  // TODO: is this ever reached?
+	return -1;
 }
 
 int buddy_size(struct dart_buddy * self, uint64_t offset)
@@ -212,6 +244,9 @@ int buddy_size(struct dart_buddy * self, uint64_t offset)
 			break;
 		}
 	}
+
+  // TODO: is this ever reached?
+	return -1;
 }
 
 static void