Add support for building against libmysqlclient that lacks THR_KEY_mysys

In certain distributions (specifically Fedora 15 and later), maintainers
limit the number of visible symbols. If THR_KEY_mysys is hidden, then we
try to create the TLS keys in such an order that it results in the correct
behavior. And then hope for the best.

5 files changed, 53 insertions, 13 deletions

diff --git a/configure.ac b/configure.ac
index 01cf652..0902700 100644
--- a/configure.ac
+++ b/configure.ac
@@ -43,6 +43,10 @@ case $libmysqlclient_include in
     ;;
 esac
 
+if test x"$libmysqlclient_thr_key_visible" = xyes; then
+  AC_DEFINE([LIBODB_MYSQL_THR_KEY_VISIBLE], [1], ["THR_KEY_mysys is visible."])
+fi
+
 # Check for libodb.
 #
 LIBODB([],[AC_MSG_ERROR([libodb is not found; consider using --with-libodb=DIR])])
diff --git a/m4/libmysqlclient.m4 b/m4/libmysqlclient.m4
index e08a08e..84b4471 100644
--- a/m4/libmysqlclient.m4
+++ b/m4/libmysqlclient.m4
@@ -82,4 +82,26 @@ else
   AC_MSG_RESULT([no])
   $3
 fi
+
+# Check if the THR_KEY_mysys pthread key symbol is visible.
+#
+libmysqlclient_thr_key_visible=no
+
+if test x"$libmysqlclient_found" = xyes -a x"$1" = xposix; then
+
+CXX_LIBTOOL_LINK_IFELSE(
+AC_LANG_SOURCE([[
+#include <pthread.h>
+extern pthread_key_t THR_KEY_mysys;
+int
+main ()
+{
+  return pthread_getspecific (THR_KEY_mysys) != 0;
+}
+]]),
+[
+libmysqlclient_thr_key_visible=yes
+])
+fi
+
 ])dnl
diff --git a/odb/mysql/connection-factory.cxx b/odb/mysql/connection-factory.cxx
index ef3647e..cc23de5 100644
--- a/odb/mysql/connection-factory.cxx
+++ b/odb/mysql/connection-factory.cxx
@@ -2,21 +2,22 @@
 // copyright : Copyright (c) 2009-2012 Code Synthesis Tools CC
 // license   : GNU GPL v2; see accompanying LICENSE file
 
-#include <odb/details/config.hxx> // ODB_THREADS_*
+#include <odb/details/config.hxx>       // ODB_THREADS_*
+#include <odb/mysql/details/config.hxx> // LIBODB_MYSQL_THR_KEY_VISIBLE
 
-#ifdef ODB_THREADS_POSIX
+#if defined(ODB_THREADS_POSIX) && defined(LIBODB_MYSQL_THR_KEY_VISIBLE)
 #  include <pthread.h>
 #endif
 
 #include <cstdlib> // abort
 
+#include <odb/details/tls.hxx>
+#include <odb/details/lock.hxx>
+
 #include <odb/mysql/mysql.hxx>
 #include <odb/mysql/connection-factory.hxx>
 #include <odb/mysql/exceptions.hxx>
 
-#include <odb/details/tls.hxx>
-#include <odb/details/lock.hxx>
-
 // This key is in the mysql client library. We use it to resolve the
 // following problem: Some pthread implementations zero-out slots that
 // don't have destructors during thread termination. As a result, when
@@ -32,7 +33,7 @@
 // 1. MySQL doesn't use the destructor itself.
 // 2. Nobody else tried to call mysql_thread_end() before us.
 //
-#ifdef ODB_THREADS_POSIX
+#if defined(ODB_THREADS_POSIX) && defined(LIBODB_MYSQL_THR_KEY_VISIBLE)
 extern pthread_key_t THR_KEY_mysys;
 #endif
 
@@ -64,7 +65,7 @@ namespace odb
 
             init_ = true;
 
-#ifdef ODB_THREADS_POSIX
+#if defined(ODB_THREADS_POSIX) && defined(LIBODB_MYSQL_THR_KEY_VISIBLE)
             value_ = pthread_getspecific (THR_KEY_mysys);
 #endif
           }
@@ -74,7 +75,7 @@ namespace odb
         {
           if (init_)
           {
-#ifdef ODB_THREADS_POSIX
+#if defined(ODB_THREADS_POSIX) && defined(LIBODB_MYSQL_THR_KEY_VISIBLE)
             if (pthread_getspecific (THR_KEY_mysys) == 0)
               pthread_setspecific (THR_KEY_mysys, value_);
 #endif
@@ -84,7 +85,7 @@ namespace odb
 
       private:
         bool init_;
-#ifdef ODB_THREADS_POSIX
+#if defined(ODB_THREADS_POSIX) && defined(LIBODB_MYSQL_THR_KEY_VISIBLE)
         void* value_;
 #endif
 #endif // ODB_THREADS_NONE
@@ -96,21 +97,31 @@ namespace odb
       {
         mysql_process_init ()
         {
-          if (mysql_library_init (0 ,0, 0))
-            abort ();
-
+          // Force allocation of our thread-specific key before THR_KEY_mysys
+          // in MySQL. This will (hopefully) get us the desired order of TLS
+          // destructor calls (i.e., our destructor before zeroing-out the
+          // THR_KEY_mysys value). This is pretty much the only way (except
+          // maybe guessing the THR_KEY_mysys value) to get clean thread
+          // termination if THR_KEY_mysys symbol is hidden, as is the case
+          // in the Fedora build of libmysqlclient. See also the comment
+          // at the beginning of this file.
+          //
           main_thread_init_ = true;
           tls_get (mysql_thread_init_);
           main_thread_init_ = false;
+
+          if (mysql_library_init (0 ,0, 0))
+            abort ();
         }
 
         ~mysql_process_init ()
         {
+          mysql_library_end ();
+
           // Finalize the main thread now in case TLS destruction
           // doesn't happen for the main thread.
           //
           tls_free (mysql_thread_init_);
-          mysql_library_end ();
         }
       };
 
diff --git a/odb/mysql/details/config.h.in b/odb/mysql/details/config.h.in
index 8231ed8..6f70c3e 100644
--- a/odb/mysql/details/config.h.in
+++ b/odb/mysql/details/config.h.in
@@ -13,4 +13,6 @@
 #undef LIBODB_MYSQL_INCLUDE_SHORT
 #undef LIBODB_MYSQL_INCLUDE_LONG
 
+#undef LIBODB_MYSQL_THR_KEY_VISIBLE
+
 #endif /* ODB_MYSQL_DETAILS_CONFIG_H */
diff --git a/odb/mysql/makefile b/odb/mysql/makefile
index 1b14f60..4ae255f 100644
--- a/odb/mysql/makefile
+++ b/odb/mysql/makefile
@@ -80,6 +80,7 @@ $(out_base)/details/config.h: | $(out_base)/details/.
 	@echo '#define ODB_MYSQL_DETAILS_CONFIG_H'                      >>$@
 	@echo ''                                                        >>$@
 	@echo '#define LIBODB_MYSQL_INCLUDE_LONG 1'                     >>$@
+	@echo '#define LIBODB_MYSQL_THR_KEY_VISIBLE 1'			>>$@
 	@echo ''                                                        >>$@
 	@echo '#endif /* ODB_MYSQL_DETAILS_CONFIG_H */'                 >>$@