branches/zip: Map current_thd to NULL in the Windows plugin, and use

ha_thd() whenever possible.

EQ_CURRENT_THD(thd): New predicate, for use in assertions.

innobase_drop_database(): Tolerate current_thd == NULL, so that the
Windows plugin will work.  In the Windows plugin, it will be
impossible to skip foreign key checks in this function.  However,
DROP DATABASE will drop each table (that MySQL knows about) individually
before calling this function.  Thus, the foreign key checks can be disabled
also in the Windows plugin, unless some .frm files are missing.

handler/ha_innodb.cc

@@ -94,6 +94,16 @@ static bool innodb_inited = 0;
 
 #define INSIDE_HA_INNOBASE_CC
 
+/* In the Windows plugin, the return value of current_thd is
+undefined.  Map it to NULL. */
+#if defined MYSQL_DYNAMIC_PLUGIN && defined __WIN__
+# undef current_thd
+# define current_thd NULL
+# define EQ_CURRENT_THD(thd) TRUE
+#else /* MYSQL_DYNAMIC_PLUGIN && __WIN__ */
+# define EQ_CURRENT_THD(thd) ((thd) == current_thd)
+#endif /* MYSQL_DYNAMIC_PLUGIN && __WIN__ */
+
 #ifdef MYSQL_DYNAMIC_PLUGIN
 /* These must be weak global variables in the dynamic plugin. */
 struct handlerton* innodb_hton_ptr;
@@ -1088,7 +1098,7 @@ check_trx_exists(
 {
 	trx_t*&	trx = thd_to_trx(thd);
 
-	ut_ad(thd == current_thd);
+	ut_ad(EQ_CURRENT_THD(thd));
 
 	if (trx == NULL) {
 		DBUG_ASSERT(thd != NULL);
@@ -1181,7 +1191,7 @@ ha_innobase::update_thd()
 /*=====================*/
 {
 	THD*	thd = ha_thd();
-	ut_ad(thd == current_thd);
+	ut_ad(EQ_CURRENT_THD(thd));
 	update_thd(thd);
 }
 
@@ -2562,7 +2572,7 @@ ha_innobase::table_flags() const
 {
        /* Need to use tx_isolation here since table flags is (also)
           called before prebuilt is inited. */
-        ulong const tx_isolation = thd_tx_isolation(current_thd);
+        ulong const tx_isolation = thd_tx_isolation(ha_thd());
         if (tx_isolation <= ISO_READ_COMMITTED)
                 return int_table_flags;
         return int_table_flags | HA_BINLOG_STMT_CAPABLE;
@@ -2917,7 +2927,7 @@ ha_innobase::close(void)
 
 	DBUG_ENTER("ha_innobase::close");
 
-	thd = current_thd;  // avoid calling current_thd twice, it may be slow
+	thd = ha_thd();
 	if (thd != NULL) {
 		innobase_release_temporary_latches(ht, thd);
 	}
@@ -6167,7 +6177,6 @@ innobase_drop_database(
 			the database name is 'test' */
 {
 	ulint	len		= 0;
-	trx_t*	parent_trx;
 	trx_t*	trx;
 	char*	ptr;
 	int	error;
@@ -6179,12 +6188,16 @@ innobase_drop_database(
 
 	DBUG_ASSERT(hton == innodb_hton_ptr);
 
-	parent_trx = check_trx_exists(thd);
+	/* In the Windows plugin, thd = current_thd is always NULL */
+	if (thd) {
+		trx_t*	parent_trx = check_trx_exists(thd);
 
-	/* In case MySQL calls this in the middle of a SELECT query, release
-	possible adaptive hash latch to avoid deadlocks of threads */
+		/* In case MySQL calls this in the middle of a SELECT
+		query, release possible adaptive hash latch to avoid
+		deadlocks of threads */
 
-	trx_search_latch_release_if_reserved(parent_trx);
+		trx_search_latch_release_if_reserved(parent_trx);
+	}
 
 	ptr = strend(path) - 2;
 
@@ -6204,10 +6217,15 @@ innobase_drop_database(
 #endif
 	trx = trx_allocate_for_mysql();
 	trx->mysql_thd = thd;
-	trx->mysql_query_str = thd_query(thd);
+	if (thd) {
+		trx->mysql_query_str = thd_query(thd);
 
-	if (thd_test_options(thd, OPTION_NO_FOREIGN_KEY_CHECKS)) {
-		trx->check_foreigns = FALSE;
+		if (thd_test_options(thd, OPTION_NO_FOREIGN_KEY_CHECKS)) {
+			trx->check_foreigns = FALSE;
+		}
+	} else {
+		/* In the Windows plugin, thd = current_thd is always NULL */
+		trx->mysql_query_str = NULL;
 	}
 
 	error = row_drop_database_for_mysql(namebuf, trx);
@@ -7421,7 +7439,7 @@ ha_innobase::external_lock(
 	if (lock_type == F_WRLCK)
 	{
 		ulong const binlog_format= thd_binlog_format(thd);
-		ulong const tx_isolation = thd_tx_isolation(current_thd);
+		ulong const tx_isolation = thd_tx_isolation(ha_thd());
 		if (tx_isolation <= ISO_READ_COMMITTED &&
 		    binlog_format == BINLOG_FORMAT_STMT)
 		{
@@ -7990,7 +8008,7 @@ ha_innobase::store_lock(
 		}
 	}
 
-	DBUG_ASSERT(thd == current_thd);
+	DBUG_ASSERT(EQ_CURRENT_THD(thd));
 	const bool in_lock_tables = thd_in_lock_tables(thd);
 	const uint sql_command = thd_sql_command(thd);