Update binaryheap.h

src/include/lib/binaryheap.h

@@ -43,24 +43,24 @@ typedef int (*binaryheap_comparator)(Datum a, Datum b, void* arg);
  *		bh_nodes		variable-length array of "space" nodes
  */
 typedef struct binaryheap {
-    int bh_size;
-    int bh_space;
+    int bh_size;            /* number of nodes currently in heap */
+    int bh_space;           /* current size of bh_nodes array */
     bool bh_has_heap_property; /* debugging cross-check */
-    binaryheap_comparator bh_compare;
-    void* bh_arg;
-    Datum bh_nodes[FLEXIBLE_ARRAY_MEMBER];
+    binaryheap_comparator bh_compare;   /* comparison function */
+    void* bh_arg;               /* extra argument for comparison function */
+    Datum bh_nodes[FLEXIBLE_ARRAY_MEMBER];  /* VARIABLE LENGTH ARRAY */
 } binaryheap;
 
-extern binaryheap* binaryheap_allocate(int capacity, binaryheap_comparator compare, void* arg);
-extern void binaryheap_reset(binaryheap* heap);
-extern void binaryheap_free(binaryheap* heap);
-extern void binaryheap_add_unordered(binaryheap* heap, Datum d);
-extern void binaryheap_build(binaryheap* heap);
-extern void binaryheap_add(binaryheap* heap, Datum d);
-extern Datum binaryheap_first(binaryheap* heap);
-extern Datum binaryheap_remove_first(binaryheap* heap);
-extern void binaryheap_replace_first(binaryheap* heap, Datum d);
+extern binaryheap* binaryheap_allocate(int capacity, binaryheap_comparator compare, void* arg); /* allocates memory */
+extern void binaryheap_reset(binaryheap* heap); /* reset heap, but not free memory*/
+extern void binaryheap_free(binaryheap* heap);  /* frees memory */
+extern void binaryheap_add_unordered(binaryheap* heap, Datum d); /* add element to heap ,but may violate heap property */
+extern void binaryheap_build(binaryheap* heap); /* builds heap property */
+extern void binaryheap_add(binaryheap* heap, Datum d);  /*add element to heap*/
+extern Datum binaryheap_first(binaryheap* heap);        /* returns first element */
+extern Datum binaryheap_remove_first(binaryheap* heap);     /* removes first element */
+extern void binaryheap_replace_first(binaryheap* heap, Datum d);    /* replaces first element */
 
-#define binaryheap_empty(h) ((h)->bh_size == 0)
+#define binaryheap_empty(h) ((h)->bh_size == 0) /* judge whether heap is empty*/
 
 #endif /* BINARYHEAP_H */