Re: [PATCH v2 06/16] sequencer: refactor sequencer_add_exec_commands() to work on a todo_list

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On 27/10/2018 22:29, Alban Gruin wrote:
This refactors sequencer_add_exec_commands() to work on a todo_list to
avoid redundant reads and writes to the disk.

An obvious way to do this would be to insert the `exec' command between
the other commands, and reparse it once this is done.  This is not what
is done here.  Instead, the command is appended to the buffer once, and
a new list of items is created.  Items from the old list are copied to
it, and new `exec' items are appended when necessary.  This eliminates
the need to reparse the todo list, but this also means its buffer cannot
be directly written to the disk, hence todo_list_write_to_disk().

I'd reword this slightly, maybe

Instead of just inserting the `exec' command between the other commands, and re-parsing the buffer at the end the exec command is appended to the buffer once, and a new list of items is created. Items from the old list are copied across and new `exec' items are appended when necessary. This eliminates the need to reparse the buffer, but this also means we have to use todo_list_write_to_disk() to write the file.

sequencer_add_exec_commands() still reads the todo list from the disk,
as it is needed by rebase -p.  todo_list_add_exec_commands() works on a
todo_list structure, and reparses it at the end.

I think the saying 'reparses' is confusing as that is what we're trying to avoid.

complete_action() still uses sequencer_add_exec_commands() for now.
This will be changed in a future commit.

Signed-off-by: Alban Gruin <alban.gruin@xxxxxxxxx>
---
  sequencer.c | 69 +++++++++++++++++++++++++++++++++++++----------------
  1 file changed, 49 insertions(+), 20 deletions(-)

diff --git a/sequencer.c b/sequencer.c
index e12860c047..12a3efeca8 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -4216,6 +4216,50 @@ int sequencer_make_script(FILE *out, int argc, const char **argv,
  	return 0;
  }
+static void todo_list_add_exec_commands(struct todo_list *todo_list,
+					const char *commands)
+{
+	struct strbuf *buf = &todo_list->buf;
+	const char *old_buf = buf->buf;
+	size_t commands_len = strlen(commands + strlen("exec ")) - 1;
+	int i, first = 1, nr = 0, alloc = 0;

Minor nit pick, I think it is clearer if first is initialized just before the loop as it is in the deleted code below.

+	struct todo_item *items = NULL,
+		base_item = {TODO_EXEC, NULL, 0, 0, commands_len, 0};
+
+	strbuf_addstr(buf, commands);
+	base_item.offset_in_buf = buf->len - commands_len - 1;
+	base_item.arg = buf->buf + base_item.offset_in_buf;

I think if the user gives --exec more than once on the command line then commands will contain more than one exec command so this needs to parse commands and create one todo_item for each command.

+
+	/*
+	 * Insert <commands> after every pick. Here, fixup/squash chains
+	 * are considered part of the pick, so we insert the commands *after*
+	 * those chains if there are any.
+	 */
+	for (i = 0; i < todo_list->nr; i++) {
+		enum todo_command command = todo_list->items[i].command;
+		if (todo_list->items[i].arg)
+			todo_list->items[i].arg = todo_list->items[i].arg - old_buf + buf->buf;
+
+		if (command == TODO_PICK && !first) {
+			ALLOC_GROW(items, nr + 1, alloc);
+			memcpy(items + nr++, &base_item, sizeof(struct todo_item));

I think it would be clearer to say
	items[nr++] = base_item;
rather than using memcpy. This applies below and to some of the other patches as well. Also this needs to loop over all the base_items if the user gave --exec more than once on the command line.

Best Wishes

Phillip

+		}
+
+		ALLOC_GROW(items, nr + 1, alloc);
+		memcpy(items + nr++, todo_list->items + i, sizeof(struct todo_item));
+		first = 0;
+	}
+
+	/* insert or append final <commands> */
+	ALLOC_GROW(items, nr + 1, alloc);
+	memcpy(items + nr++, &base_item, sizeof(struct todo_item));
+
+	FREE_AND_NULL(todo_list->items);
+	todo_list->items = items;
+	todo_list->nr = nr;
+	todo_list->alloc = alloc;
+}
+
  /*
   * Add commands after pick and (series of) squash/fixup commands
   * in the todo list.
@@ -4224,10 +4268,7 @@ int sequencer_add_exec_commands(const char *commands)
  {
  	const char *todo_file = rebase_path_todo();
  	struct todo_list todo_list = TODO_LIST_INIT;
-	struct todo_item *item;
-	struct strbuf *buf = &todo_list.buf;
-	size_t offset = 0, commands_len = strlen(commands);
-	int i, first;
+	int res;
if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
  		return error(_("could not read '%s'."), todo_file);
@@ -4237,23 +4278,11 @@ int sequencer_add_exec_commands(const char *commands)
  		return error(_("unusable todo list: '%s'"), todo_file);
  	}
- first = 1;
-	/* insert <commands> before every pick except the first one */
-	for (item = todo_list.items, i = 0; i < todo_list.nr; i++, item++) {
-		if (item->command == TODO_PICK && !first) {
-			strbuf_insert(buf, item->offset_in_buf + offset,
-				      commands, commands_len);
-			offset += commands_len;
-		}
-		first = 0;
-	}
-
-	/* append final <commands> */
-	strbuf_add(buf, commands, commands_len);
-
-	i = write_message(buf->buf, buf->len, todo_file, 0);
+	todo_list_add_exec_commands(&todo_list, commands);
+	res = todo_list_write_to_file(&todo_list, todo_file, NULL, NULL, 0, 0, -1, 0);
  	todo_list_release(&todo_list);
-	return i;
+
+	return res;
  }
static void todo_list_to_strbuf(struct todo_list *todo_list, struct strbuf *buf,





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