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ha_innodb.cc:

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A flawed fix of the thd->query race in SHOW INNODB STATUS; see the comments in code about how to fix this properly; we cannot use LOCK_thread_count to protect thd->query, because that will cause a deadlock of threads


sql/ha_innodb.cc:
  A flawed fix of the thd->query race in SHOW INNODB STATUS; see the comments in code about how to fix this properly; we cannot use LOCK_thread_count to protect thd->query, because that will cause a deadlock of threads
This commit is contained in:
unknown 2004-05-13 20:02:05 +03:00
parent 9e20f63aec
commit 6be0dc1273
1 changed files with 26 additions and 4 deletions
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sql/ha_innodb.cc
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@ -325,10 +325,18 @@ innobase_mysql_print_thd(
{
const THD* thd;
const char* s;
char buf[301];
thd = (const THD*) input_thd;
VOID(pthread_mutex_lock(&LOCK_thread_count));
/* We cannot use LOCK_thread_count to protect this operation because we own
the InnoDB kernel_mutex when we enter this function, but in freeing of a
THD object, MySQL first reserves LOCK_thread_count and AFTER THAT InnoDB
reserves kernel_mutex when freeing the trx object => a deadlock can occur.
The solution is for MySQL to use a separate mutex to protect thd->query and
thd->query_len. Someone should do that! This bug has been here for 3 years!
VOID(pthread_mutex_lock(&LOCK_thread_count)); */
fprintf(f, "MySQL thread id %lu, query id %lu",
thd->thread_id, thd->query_id);
@ -354,15 +362,29 @@ innobase_mysql_print_thd(
if ((s = thd->query)) {
/* determine the length of the query string */
uint32 i, len = thd->query_length;
uint32 i, len;
len = thd->query_length;
if (len > 300) {
len = 300; /* A TEMPORARY SOLUTION: print at most
300 chars to reduce the probability of
a seg fault in a race */
}
for (i = 0; i < len && s[i]; i++);
memcpy(buf, s, i); /* use memcpy to reduce the timeframe
for a race, compared to fwrite() */
buf[300] = '\0';
putc('\n', f);
fwrite(s, 1, i, f);
fwrite(buf, 1, i, f);
}
putc('\n', f);
VOID(pthread_mutex_unlock(&LOCK_thread_count));
/* VOID(pthread_mutex_unlock(&LOCK_thread_count)); */
}
/*************************************************************************