MDB_CP_COMPACT comments

libraries/liblmdb/mdb.c

@@ -9765,7 +9765,10 @@ typedef struct mdb_copy {
 	HANDLE mc_fd;
 	int mc_toggle;			/**< Buffer number in provider */
 	int mc_new;				/**< (0-2 buffers to write) | (#MDB_EOF at end) */
-	volatile int mc_error;	/**< Error code, never cleared if set */
+	/** Error code.  Never cleared if set.  Both threads can set nonzero
+	 *	to fail the copy.  Not mutex-protected, LMDB expects atomic int.
+	 */
+	volatile int mc_error;
 } mdb_copy;
 
 	/** Dedicated writer thread for compacting copy. */
@@ -9850,7 +9853,11 @@ mdb_env_cthr_toggle(mdb_copy *my, int adjust)
 	return my->mc_error;
 }
 
-	/** Depth-first tree traversal for compacting copy. */
+	/** Depth-first tree traversal for compacting copy.
+	 * @param[in] my control structure.
+	 * @param[in,out] pg database root.
+	 * @param[in] flags includes #F_DUPDATA if it is a sorted-duplicate sub-DB.
+	 */
 static int ESECT
 mdb_env_cwalk(mdb_copy *my, pgno_t *pg, int flags)
 {