For the record, removing the update hook from the update hook works as expected
in both SQLite 3.19.3 and 3.21, with a connection which is opened with the
SQLITE_OPEN_NOMUTEX flag, and the guarantee that no two threads use the same
connection at the same time.
But I'm just not sure if this is a guaranteed behavior?
Gwendal
> Le 14 janv. 2018 à 18:05, Gwendal Roué <gwendal.r...@gmail.com> a écrit :
>
> Hello,
>
> Is it valid to change the update hook from the update hook itself?
>
> The reason for this question is the following: when a notified database
> change makes it useless to perform further observation, one may want to
> remove the update hook alltogether. Can it be done from the update hook
> itself?
>
> Here is a quick and dirty sample code, for the context: it installs an update
> hook that tracks any modification to the "players" table, and attempts to
> remove the update hook as soon as the "players" table is modified:
>
> typedef struct {
> sqlite3 *conn;
> int players_table_was_modified;
> } info;
>
> void update_hook(info *info, int change, char const *db, char const
> *table, sqlite3_int64 rowed) {
> if (strcmp(table, "players") == 0) {
> info->players_table_was_modified = 1;
>
> // Is it valid?
> sqlite3_update_hook(info->conn, NULL, NULL);
> }
> }
>
> sqlite3 *conn = ...;
> info info = { conn, 0 };
> sqlite3_update_hook(conn, update_hook, &info);
>
> Quoting https://sqlite.org/c3ref/update_hook.html:
> <https://sqlite.org/c3ref/update_hook.html:>
>
>> The update hook implementation must not do anything that will modify the
>> database connection that invoked the update hook. Any actions to modify the
>> database connection must be deferred until after the completion of the
>> sqlite3_step() call that triggered the update hook. Note that
>> sqlite3_prepare_v2() and sqlite3_step() both modify their database
>> connections for the meaning of "modify" in this paragraph.
>
> According to this documentation, I'm note sure if sqlite3_update_hook itself
> modifies the database connection for the meaning of "modify" in the quoted
> documentation paragraph, and is thus forbidden, or not.
>
> Can anyone lift this doubt?
>
> Thanks in advance,
> Gwendal Roué
>
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