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, 25 insertions, 52 deletions

diff --git a/mysys/charset.c b/mysys/charset.c
index b23ab084e90..d59be4ab6c7 100644
--- a/mysys/charset.c
+++ b/mysys/charset.c
@@ -321,7 +321,6 @@ static int add_collation(CHARSET_INFO *cs)
 #define MY_CHARSET_INDEX "Index.xml"
 
 const char *charsets_dir= NULL;
-static int charset_initialized=0;
 
 
 static my_bool my_read_charset_file(const char *filename, myf myflags)
@@ -399,63 +398,37 @@ static void *cs_alloc(size_t size)
 }
 
 
-#ifdef __NETWARE__
-my_bool STDCALL init_available_charsets(myf myflags)
-#else
-static my_bool init_available_charsets(myf myflags)
-#endif
+static my_pthread_once_t charsets_initialized= MY_PTHREAD_ONCE_INIT;
+
+static void init_available_charsets(void)
 {
   char fname[FN_REFLEN + sizeof(MY_CHARSET_INDEX)];
-  my_bool error=FALSE;
-  /*
-    We have to use charset_initialized to not lock on THR_LOCK_charset
-    inside get_internal_charset...
-  */
-  if (!charset_initialized)
+  CHARSET_INFO **cs;
+
+  bzero(&all_charsets,sizeof(all_charsets));
+  init_compiled_charsets(MYF(0));
+      
+  /* Copy compiled charsets */
+  for (cs=all_charsets;
+       cs < all_charsets+array_elements(all_charsets)-1 ;
+       cs++)
   {
-    CHARSET_INFO **cs;
-    /*
-      To make things thread safe we are not allowing other threads to interfere
-      while we may changing the cs_info_table
-    */
-    pthread_mutex_lock(&THR_LOCK_charset);
-    if (!charset_initialized)
+    if (*cs)
     {
-      bzero(&all_charsets,sizeof(all_charsets));
-      init_compiled_charsets(myflags);
-      
-      /* Copy compiled charsets */
-      for (cs=all_charsets;
-           cs < all_charsets+array_elements(all_charsets)-1 ;
-           cs++)
-      {
-        if (*cs)
-        {
-          if (cs[0]->ctype)
-            if (init_state_maps(*cs))
-              *cs= NULL;
-        }
-      }
-      
-      strmov(get_charsets_dir(fname), MY_CHARSET_INDEX);
-      error= my_read_charset_file(fname,myflags);
-      charset_initialized=1;
+      if (cs[0]->ctype)
+        if (init_state_maps(*cs))
+          *cs= NULL;
     }
-    pthread_mutex_unlock(&THR_LOCK_charset);
   }
-  return error;
-}
-
-
-void free_charsets(void)
-{
-  charset_initialized=0;
+      
+  strmov(get_charsets_dir(fname), MY_CHARSET_INDEX);
+  my_read_charset_file(fname, MYF(0));
 }
 
 
 uint get_collation_number(const char *name)
 {
-  init_available_charsets(MYF(0));
+  my_pthread_once(&charsets_initialized, init_available_charsets);
   return get_collation_number_internal(name);
 }
 
@@ -463,7 +436,7 @@ uint get_collation_number(const char *name)
 uint get_charset_number(const char *charset_name, uint cs_flags)
 {
   CHARSET_INFO **cs;
-  init_available_charsets(MYF(0));
+  my_pthread_once(&charsets_initialized, init_available_charsets);
   
   for (cs= all_charsets;
        cs < all_charsets+array_elements(all_charsets)-1 ;
@@ -480,7 +453,7 @@ uint get_charset_number(const char *charset_name, uint cs_flags)
 const char *get_charset_name(uint charset_number)
 {
   CHARSET_INFO *cs;
-  init_available_charsets(MYF(0));
+  my_pthread_once(&charsets_initialized, init_available_charsets);
 
   cs=all_charsets[charset_number];
   if (cs && (cs->number == charset_number) && cs->name )
@@ -538,7 +511,7 @@ CHARSET_INFO *get_charset(uint cs_number, myf flags)
   if (cs_number == default_charset_info->number)
     return default_charset_info;
 
-  (void) init_available_charsets(MYF(0));	/* If it isn't initialized */
+  my_pthread_once(&charsets_initialized, init_available_charsets);
   
   if (!cs_number || cs_number >= array_elements(all_charsets)-1)
     return NULL;
@@ -560,7 +533,7 @@ CHARSET_INFO *get_charset_by_name(const char *cs_name, myf flags)
 {
   uint cs_number;
   CHARSET_INFO *cs;
-  (void) init_available_charsets(MYF(0));	/* If it isn't initialized */
+  my_pthread_once(&charsets_initialized, init_available_charsets);
 
   cs_number=get_collation_number(cs_name);
   cs= cs_number ? get_internal_charset(cs_number,flags) : NULL;
@@ -585,7 +558,7 @@ CHARSET_INFO *get_charset_by_csname(const char *cs_name,
   DBUG_ENTER("get_charset_by_csname");
   DBUG_PRINT("enter",("name: '%s'", cs_name));
 
-  (void) init_available_charsets(MYF(0));	/* If it isn't initialized */
+  my_pthread_once(&charsets_initialized, init_available_charsets);
 
   cs_number= get_charset_number(cs_name, cs_flags);
   cs= cs_number ? get_internal_charset(cs_number, flags) : NULL;