MDEV-19513: Remove rw_lock_t::magic_n

The magic_n only complicated object destruction and did not serve
any useful purpose.

storage/innobase/include/sync0rw.h

@@ -2,7 +2,7 @@
 
 Copyright (c) 1995, 2016, Oracle and/or its affiliates. All Rights Reserved.
 Copyright (c) 2008, Google Inc.
-Copyright (c) 2017, MariaDB Corporation. All Rights Reserved.
+Copyright (c) 2017, 2019, MariaDB Corporation.
 
 Portions of this file contain modifications contributed and copyrighted by
 Google, Inc. Those modifications are gratefully acknowledged and are described
@@ -625,35 +625,14 @@ struct rw_lock_t
 #endif /* UNIV_PFS_RWLOCK */
 
 #ifdef UNIV_DEBUG
-/** Value of rw_lock_t::magic_n */
-# define RW_LOCK_MAGIC_N	22643
-
-	/** Constructor */
-	rw_lock_t()
-	{
-		magic_n = RW_LOCK_MAGIC_N;
-	}
-
-	/** Destructor */
-	virtual ~rw_lock_t()
-	{
-		ut_ad(magic_n == RW_LOCK_MAGIC_N);
-		magic_n = 0;
-	}
-
 	virtual std::string to_string() const;
 
-	/** For checking memory corruption. */
-	ulint		magic_n;
-
 	/** In the debug version: pointer to the debug info list of the lock */
 	UT_LIST_BASE_NODE_T(rw_lock_debug_t) debug_list;
 
 	/** Level in the global latching order. */
 	latch_level_t	level;
-
 #endif /* UNIV_DEBUG */
-
 };
 #ifdef UNIV_DEBUG
 /** The structure for storing debug info of an rw-lock.  All access to this

storage/innobase/log/log0log.cc

@@ -2011,11 +2011,6 @@ void log_t::close()
   os_event_destroy(flush_event);
 
   rw_lock_free(&checkpoint_lock);
-  /* rw_lock_free() already called checkpoint_lock.~rw_lock_t();
-  tame the debug assertions when the destructor will be called once more. */
-  ut_ad(checkpoint_lock.magic_n == 0);
-  ut_d(checkpoint_lock.magic_n = RW_LOCK_MAGIC_N);
-
   mutex_free(&mutex);
   mutex_free(&write_mutex);
   mutex_free(&log_flush_order_mutex);

storage/innobase/sync/sync0rw.cc

@@ -238,12 +238,7 @@ rw_lock_create_func(
 	lock->is_block_lock = 0;
 
 	mutex_enter(&rw_lock_list_mutex);
-
-	ut_ad(UT_LIST_GET_FIRST(rw_lock_list) == NULL
-	      || UT_LIST_GET_FIRST(rw_lock_list)->magic_n == RW_LOCK_MAGIC_N);
-
 	UT_LIST_ADD_FIRST(rw_lock_list, lock);
-
 	mutex_exit(&rw_lock_list_mutex);
 }
 
@@ -268,12 +263,6 @@ rw_lock_free_func(
 	UT_LIST_REMOVE(rw_lock_list, lock);
 
 	mutex_exit(&rw_lock_list_mutex);
-
-	/* We did an in-place new in rw_lock_create_func() */
-	ut_d(lock->~rw_lock_t());
-	/* Sometimes (maybe when compiled with GCC -O3) the above call
-	to rw_lock_t::~rw_lock_t() will not actually assign magic_n=0. */
-	ut_d(lock->magic_n = 0);
 }
 
 /******************************************************************//**
@@ -858,7 +847,6 @@ rw_lock_validate(
 
 	lock_word = lock->lock_word.load(std::memory_order_relaxed);
 
-	ut_ad(lock->magic_n == RW_LOCK_MAGIC_N);
 	ut_ad(lock->waiters.load(std::memory_order_relaxed) < 2);
 	ut_ad(lock_word > -(2 * X_LOCK_DECR));
 	ut_ad(lock_word <= X_LOCK_DECR);

storage/innobase/trx/trx0purge.cc

@@ -192,10 +192,6 @@ void purge_sys_t::close()
   trx->state= TRX_STATE_NOT_STARTED;
   trx_free(trx);
   rw_lock_free(&latch);
-  /* rw_lock_free() already called latch.~rw_lock_t(); tame the
-  debug assertions when the destructor will be called once more. */
-  ut_ad(latch.magic_n == 0);
-  ut_d(latch.magic_n= RW_LOCK_MAGIC_N);
   mutex_free(&pq_mutex);
   os_event_destroy(event);
 }