add atomic refcnt and locks.

It might be unnecessary, if open/close can be done without lock.

src/file.h

@@ -1,23 +1,59 @@
 #ifndef _FILE_H_
 #define _FILE_H_
 
+#include <pthread.h>
 #include <libssh/libssh.h>
 #include <libssh/sftp.h>
 #include <list.h>
+#include <atomic.h>
 
 struct file {
         struct list_head        list;   /* sscp->file_list */
 
-        char            *path;
-        bool            remote;
-        size_t          size;   /* size of this file */
+        char    *path;          /* copy source path */
+        char    *dst_path;      /* copy destination path */
+        bool    remote;
+        size_t  size;   /* size of this file */
+
+        int     state;  /* destination file state */
+        lock    lock;   /* mutex to protect state */
+        refcnt  refcnt; /* chunks referencing this file */
+
+        size_t  done;   /* copied bytes. a control thread totaling up done of chunks */
 };
+#define FILE_STATE_INIT         0
+#define FILE_STATE_OPENED       1
+#define FILE_STATE_DONE         2
+
+/* Allocating chunk increments refcnt of the associating file.
+ * Multiple threads copying files follows:
+ *
+ * acquire a chunk (inside a global lock)
+ *
+ * if the file state of the chunk is INIT:
+ *     acquire the file lock
+ * *         if file state is INIT:
+ *             create destination file
+ *             set file state OPENED.
+ *             // only the first thread in the lock open the destination file
+ *     release the file lock
+ * endif
+ *
+ * copy the chunk to the destination.
+ * decrement the refcnt of the file.
+ *
+ * if refcnt == 0:
+ *     all chunks are copied.
+ *     set the file state DONE, print something useful output.
+ * endif
+ */
 
 struct chunk {
         struct list_head        list;   /* sscp->chunk_list */
         struct file *f;
         size_t  off;    /* offset of this chunk on the file f */
         size_t  len;    /* length of this chunk */
+        size_t  done;   /* copied bytes for this chunk by a thread */
 };
 
 char *file_find_hostname(char *path);
@@ -26,12 +62,14 @@ int file_is_directory(char *path, sftp_session sftp);
 
 int file_fill(sftp_session sftp, struct list_head *head, char **src_array, int count);
 
-int chunk_fill(struct list_head *file_head, struct list_head *chunk_head,
+int chunk_fill(struct list_head *file_list, struct list_head *chunk_list,
                int nr_conn, int min_chunk_sz, int max_chunk_sz);
 
+struct chunk *chunk_acquire(struct list_head *chunk_list);
+
 #ifdef DEBUG
-void file_dump(struct list_head *file_head);
-void chunk_dump(struct list_head *chunk_head);
+void file_dump(struct list_head *file_list);
+void chunk_dump(struct list_head *chunk_list);
 #endif