Bug #45058 init_available_charsets uses double checked locking

      
As documented in the bug report, the double checked locking
pattern has inherent issues, and cannot guarantee correct
initialization.

This patch replaces the logic in init_available_charsets()
with the use of pthread_once(3). A wrapper function,
my_pthread_once(), is introduced and is used in lieu of direct
calls to init_available_charsets(). Related defines
MY_PTHREAD_ONCE_* are also introduced.

For the Windows platform, the implementation in lp:sysbench is
ported. For single-thread use, a simple define calls the
function and sets the pthread_once control variable.

Charset initialization is modified to use my_pthread_once().

include/my_no_pthread.h:
  Dummy my_pthread_once() for single thread use.
include/my_pthread.h:
  Declaration for new function my_pthread_once().
mysys/charset.c:
  Logic in init_available_charsets() is simplified. 
  Using my_pthread_once() for all calls to this func.
mysys/my_winthread.c:
  Windows implementation of my_pthread_once().

1 files changed, 0 insertions, 1 deletions

diff --git a/include/my_sys.h b/include/my_sys.h
index b4aac3a17bd..a4ff5c30de7 100644
--- a/include/my_sys.h
+++ b/include/my_sys.h
@@ -951,7 +951,6 @@ extern my_bool resolve_collation(const char *cl_name,
                                  CHARSET_INFO *default_cl,
                                  CHARSET_INFO **cl);
 
-extern void free_charsets(void);
 extern char *get_charsets_dir(char *buf);
 extern my_bool my_charset_same(CHARSET_INFO *cs1, CHARSET_INFO *cs2);
 extern my_bool init_compiled_charsets(myf flags);