#At file:///net/atum21.norway/export/home/tmp/ss156133/z/45058-51/ based on revid:magnus.blaudd@stripped
3153 Staale Smedseng 2009-10-16
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 is a new patch with an alternative solution, intended to
avoid any possible API incompatibilities introduced in the
initial patch.
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().
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.
@ 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.
modified:
include/my_no_pthread.h
include/my_pthread.h
mysys/charset.c
mysys/my_winthread.c
netware/libmysqlmain.c
=== modified file 'include/my_no_pthread.h'
--- a/include/my_no_pthread.h 2006-12-23 19:20:40 +0000
+++ b/include/my_no_pthread.h 2009-10-16 14:54:10 +0000
@@ -47,4 +47,8 @@
#define rw_unlock(A)
#define rwlock_destroy(A)
+#define PTHREAD_ONCE_DONE 2
+#define my_pthread_once(C,F) \
+ do { if (*(C) != PTHREAD_ONCE_DONE) { F(); *(C)= PTHREAD_ONCE_DONE; } } while(0)
+
#endif
=== modified file 'include/my_pthread.h'
--- a/include/my_pthread.h 2008-10-15 22:28:26 +0000
+++ b/include/my_pthread.h 2009-10-16 14:54:10 +0000
@@ -69,6 +69,11 @@ typedef int pthread_mutexattr_t;
#define pthread_handler_t EXTERNC void * __cdecl
typedef void * (__cdecl *pthread_handler)(void *);
+typedef volatile LONG pthread_once_t;
+#define PTHREAD_ONCE_INIT 0
+#define PTHREAD_ONCE_INPROGRESS 1
+#define PTHREAD_ONCE_DONE 2
+
/*
Struct and macros to be used in combination with the
windows implementation of pthread_cond_timedwait
@@ -114,6 +119,7 @@ int pthread_attr_init(pthread_attr_t *co
int pthread_attr_setstacksize(pthread_attr_t *connect_att,DWORD stack);
int pthread_attr_setprio(pthread_attr_t *connect_att,int priority);
int pthread_attr_destroy(pthread_attr_t *connect_att);
+int my_pthread_once(pthread_once_t *once_control,void (*init_routine)(void));
struct tm *localtime_r(const time_t *timep,struct tm *tmp);
struct tm *gmtime_r(const time_t *timep,struct tm *tmp);
@@ -209,6 +215,7 @@ extern int my_pthread_getprio(pthread_t
#define pthread_detach_this_thread()
#define pthread_handler_t EXTERNC void *
typedef void *(* pthread_handler)(void *);
+#define my_pthread_once(C,F) pthread_once(C,F)
/* Test first for RTS or FSU threads */
=== modified file 'mysys/charset.c'
--- a/mysys/charset.c 2009-06-10 08:59:49 +0000
+++ b/mysys/charset.c 2009-10-16 14:54:10 +0000
@@ -399,51 +399,31 @@ 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 pthread_once_t charsets_initialized= 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;
+
+ strmov(get_charsets_dir(fname), MY_CHARSET_INDEX);
+ my_read_charset_file(fname, MYF(0));
}
@@ -455,7 +435,7 @@ void free_charsets(void)
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 +443,7 @@ uint get_collation_number(const char *na
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 +460,7 @@ uint get_charset_number(const char *char
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 +518,7 @@ CHARSET_INFO *get_charset(uint cs_number
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 +540,7 @@ CHARSET_INFO *get_charset_by_name(const
{
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 +565,7 @@ CHARSET_INFO *get_charset_by_csname(cons
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;
=== modified file 'mysys/my_winthread.c'
--- a/mysys/my_winthread.c 2007-10-03 19:38:32 +0000
+++ b/mysys/my_winthread.c 2009-10-16 14:54:10 +0000
@@ -137,4 +137,36 @@ int win_pthread_setspecific(void *a,void
return 0;
}
+
+/*
+ One time initialization. For simplicity, we assume initializer thread
+ does not exit within init_routine().
+*/
+int my_pthread_once(pthread_once_t *once_control,
+ void (*init_routine)(void))
+{
+ LONG state= InterlockedCompareExchange(once_control, PTHREAD_ONCE_INPROGRESS,
+ PTHREAD_ONCE_INIT);
+ switch(state)
+ {
+ case PTHREAD_ONCE_INIT:
+ /* This is initializer thread */
+ (*init_routine)();
+ *once_control= PTHREAD_ONCE_DONE;
+ break;
+
+ case PTHREAD_ONCE_INPROGRESS:
+ /* init_routine in progress. Wait for its completion */
+ while(*once_control == PTHREAD_ONCE_INPROGRESS)
+ {
+ Sleep(1);
+ }
+ break;
+ case PTHREAD_ONCE_DONE:
+ /* Nothing to do */
+ break;
+ }
+ return 0;
+}
+
#endif
=== modified file 'netware/libmysqlmain.c'
--- a/netware/libmysqlmain.c 2003-01-31 23:42:26 +0000
+++ b/netware/libmysqlmain.c 2009-10-16 14:54:10 +0000
@@ -18,7 +18,7 @@
#include "my_global.h"
-my_bool init_available_charsets(myf myflags);
+void init_available_charsets(void);
/* this function is required so that global memory is allocated against this
library nlm, and not against a paticular client */
@@ -31,7 +31,7 @@ int _NonAppStart(void *NLMHandle, void *
{
mysql_server_init(0, NULL, NULL);
- init_available_charsets(MYF(0));
+ init_available_charsets();
return 0;
}
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