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Move Heikki's comment about thd->query comment to proper place

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(bad merge from 4.0)


sql/sql_class.h:
  Move a comment to proper place (bad merge from 4.0)
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2004-10-13 00:17:37 +04:00
parent 9b8586bfd1
commit 63af3d3a2e
1 changed files with 17 additions and 18 deletions
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35
sql/sql_class.h
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@ -544,6 +544,23 @@ public:
Points to the query associated with this statement. It's const, but
we need to declare it char * because all table handlers are written
in C and need to point to it.
Note that (A) if we set query = NULL, we must at the same time set
query_length = 0, and protect the whole operation with the
LOCK_thread_count mutex. And (B) we are ONLY allowed to set query to a
non-NULL value if its previous value is NULL. We do not need to protect
operation (B) with any mutex. To avoid crashes in races, if we do not
know that thd->query cannot change at the moment, one should print
thd->query like this:
(1) reserve the LOCK_thread_count mutex;
(2) check if thd->query is NULL;
(3) if not NULL, then print at most thd->query_length characters from
it. We will see the query_length field as either 0, or the right value
for it.
Assuming that the write and read of an n-bit memory field in an n-bit
computer is atomic, we can avoid races in the above way.
This printing is needed at least in SHOW PROCESSLIST and SHOW INNODB
STATUS.
*/
char *query;
uint32 query_length; // current query length
@ -684,24 +701,6 @@ public:
struct rand_struct rand; // used for authentication
struct system_variables variables; // Changeable local variables
pthread_mutex_t LOCK_delete; // Locked before thd is deleted
/*
Note that (A) if we set query = NULL, we must at the same time set
query_length = 0, and protect the whole operation with the
LOCK_thread_count mutex. And (B) we are ONLY allowed to set query to a
non-NULL value if its previous value is NULL. We do not need to protect
operation (B) with any mutex. To avoid crashes in races, if we do not
know that thd->query cannot change at the moment, one should print
thd->query like this:
(1) reserve the LOCK_thread_count mutex;
(2) check if thd->query is NULL;
(3) if not NULL, then print at most thd->query_length characters from
it. We will see the query_length field as either 0, or the right value
for it.
Assuming that the write and read of an n-bit memory field in an n-bit
computer is atomic, we can avoid races in the above way.
This printing is needed at least in SHOW PROCESSLIST and SHOW INNODB
STATUS.
*/
/* all prepared statements and cursors of this connection */
Statement_map stmt_map;
/*