Bug #38969 Unused mutex LOCK_hostname

Description:
The following mutex:

sql/hostname.cc:static pthread_mutex_t LOCK_hostname;

is initialized and destroyed, but never locked / unlocked in the server code.

How to repeat:
Code review

Suggested fix:
Remove

On 6.0-bzr I've got:

openxs@suse:/home2/openxs/bzr/mysql-6.0> grep -r -n LOCK_hostname *
sql/hostname.cc:52:static pthread_mutex_t LOCK_hostname;
sql/hostname.cc:69:  (void) pthread_mutex_init(&LOCK_hostname,MY_MUTEX_INIT_SLOW);
sql/hostname.cc:78:    (void) pthread_mutex_destroy(&LOCK_hostname);
sql/udf_example.c:142:static pthread_mutex_t LOCK_hostname;
sql/udf_example.c:722:  (void) pthread_mutex_init(&LOCK_hostname,MY_MUTEX_INIT_SLOW);
sql/udf_example.c:730:  (void) pthread_mutex_destroy(&LOCK_hostname);
sql/udf_example.c:765:  pthread_mutex_lock(&LOCK_hostname);
sql/udf_example.c:768:    pthread_mutex_unlock(&LOCK_hostname);
sql/udf_example.c:772:  pthread_mutex_unlock(&LOCK_hostname);
sql/udf_example.c:802:  (void) pthread_mutex_init(&LOCK_hostname,MY_MUTEX_INIT_SLOW);
sql/udf_example.c:810:  (void) pthread_mutex_destroy(&LOCK_hostname);
sql/udf_example.c:869:  pthread_mutex_lock(&LOCK_hostname);
sql/udf_example.c:872:    pthread_mutex_unlock(&LOCK_hostname);
sql/udf_example.c:876:  pthread_mutex_unlock(&LOCK_hostname);

So, it is used.

On 5.1-bzr I've got:

openxs@suse:/home2/openxs/bzr/mysql-5.1> grep -r -n LOCK_hostname *
sql/hostname.cc:54:static pthread_mutex_t LOCK_hostname;
sql/hostname.cc:71:  (void) pthread_mutex_init(&LOCK_hostname,MY_MUTEX_INIT_SLOW);
sql/hostname.cc:79:    (void) pthread_mutex_destroy(&LOCK_hostname);
sql/hostname.cc:217:  VOID(pthread_mutex_lock(&LOCK_hostname));
sql/hostname.cc:220:    VOID(pthread_mutex_unlock(&LOCK_hostname));
sql/hostname.cc:230:    VOID(pthread_mutex_unlock(&LOCK_hostname));
sql/hostname.cc:236:    VOID(pthread_mutex_unlock(&LOCK_hostname));
sql/hostname.cc:240:  VOID(pthread_mutex_unlock(&LOCK_hostname));
sql/udf_example.c:142:static pthread_mutex_t LOCK_hostname;
sql/udf_example.c:722:  (void) pthread_mutex_init(&LOCK_hostname,MY_MUTEX_INIT_SLOW);
sql/udf_example.c:730:  (void) pthread_mutex_destroy(&LOCK_hostname);
sql/udf_example.c:765:  VOID(pthread_mutex_lock(&LOCK_hostname));
sql/udf_example.c:768:    VOID(pthread_mutex_unlock(&LOCK_hostname));
sql/udf_example.c:772:  VOID(pthread_mutex_unlock(&LOCK_hostname));
sql/udf_example.c:802:  (void) pthread_mutex_init(&LOCK_hostname,MY_MUTEX_INIT_SLOW);
sql/udf_example.c:810:  (void) pthread_mutex_destroy(&LOCK_hostname);
sql/udf_example.c:869:  VOID(pthread_mutex_lock(&LOCK_hostname));
sql/udf_example.c:872:    VOID(pthread_mutex_unlock(&LOCK_hostname));
sql/udf_example.c:876:  VOID(pthread_mutex_unlock(&LOCK_hostname));

So, it is also used, IMHO. Finally, with 5.0-bzr:

openxs@suse:/home2/openxs/bzr/mysql-5.0> grep -r -n LOCK_hostname *
sql/hostname.cc:49:static pthread_mutex_t LOCK_hostname;
sql/hostname.cc:66:  (void) pthread_mutex_init(&LOCK_hostname,MY_MUTEX_INIT_SLOW);
sql/hostname.cc:74:    (void) pthread_mutex_destroy(&LOCK_hostname);
sql/hostname.cc:212:  VOID(pthread_mutex_lock(&LOCK_hostname));
sql/hostname.cc:215:    VOID(pthread_mutex_unlock(&LOCK_hostname));
sql/hostname.cc:225:    VOID(pthread_mutex_unlock(&LOCK_hostname));
sql/hostname.cc:231:    VOID(pthread_mutex_unlock(&LOCK_hostname));
sql/hostname.cc:235:  VOID(pthread_mutex_unlock(&LOCK_hostname));
sql/udf_example.c:142:static pthread_mutex_t LOCK_hostname;
sql/udf_example.c:722:  (void) pthread_mutex_init(&LOCK_hostname,MY_MUTEX_INIT_SLOW);
sql/udf_example.c:730:  (void) pthread_mutex_destroy(&LOCK_hostname);
sql/udf_example.c:765:  VOID(pthread_mutex_lock(&LOCK_hostname));
sql/udf_example.c:768:    VOID(pthread_mutex_unlock(&LOCK_hostname));
sql/udf_example.c:772:  VOID(pthread_mutex_unlock(&LOCK_hostname));
sql/udf_example.c:802:  (void) pthread_mutex_init(&LOCK_hostname,MY_MUTEX_INIT_SLOW);
sql/udf_example.c:810:  (void) pthread_mutex_destroy(&LOCK_hostname);
sql/udf_example.c:869:  VOID(pthread_mutex_lock(&LOCK_hostname));
sql/udf_example.c:872:    VOID(pthread_mutex_unlock(&LOCK_hostname));
sql/udf_example.c:876:  VOID(pthread_mutex_unlock(&LOCK_hostname));

Isn't sql/hostname.cc a part of server's code?

There are 2 variables named "LOCK_hostname",
- one is in sql/hostname.cc, which is part of the server,
- one is in udf/udf_example.cc, which is not part of the server.
These two variables are independent (note the static keyword).

The grep in sql/hostname.cc just verified that this bug is present in 6.0-bzr only.

LOCK_hostname is used in 5.0 and 5.1, and should only be removed in 6.0

OK, so this is 6.0 bug.

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/52385

2684 Marc Alff	2008-08-23
      Bug#38969 (Unused mutex LOCK_hostname)
      
      Removed the unused mutex LOCK_hostname in sql/hostname.cc

Pushed into 6.0.7-alpha  (revid:marc.alff@sun.com-20080823233428-o2s8sbw33jndr8bq) (version source revid:marc.alff@sun.com-20080823233428-o2s8sbw33jndr8bq) (pib:5)

Cosmetic change. No changelog entry needed.