MDEV-17441: Rename buf_pool_t::io_buf from buf_pool->tmp_arr

Make buf_pool_t::io_buf_t() a more proper class.

buf_pool_t::io_buf_t::io_buf_t(): Silence the GCC 8 -Wclass-memaccess
warning for initializing slots[], which no longer is a plain old datatype
(POD) due to the std::atomic member.

storage/innobase/buf/buf0buf.cc

@@ -121,6 +121,7 @@ struct set_numa_interleave_t
 #include "snappy-c.h"
 #endif
 
+#ifndef UNIV_INNOCHECKSUM
 inline void* aligned_malloc(size_t size, size_t align) {
     void *result;
 #ifdef _MSC_VER
@@ -144,6 +145,16 @@ inline void aligned_free(void *ptr) {
 #endif
 }
 
+buf_pool_t::io_buf_t::~io_buf_t()
+{
+	for (buf_tmp_buffer_t* s = slots, *e = slots + n_slots; s != e; s++) {
+		aligned_free(s->crypt_buf);
+		aligned_free(s->comp_buf);
+	}
+	ut_free(slots);
+}
+#endif /* !UNIV_INNOCHECKSUM */
+
 /*
 		IMPLEMENTATION OF THE BUFFER POOL
 		=================================
@@ -416,16 +427,9 @@ on the io_type */
 @return reserved buffer slot */
 static buf_tmp_buffer_t* buf_pool_reserve_tmp_slot(buf_pool_t* buf_pool)
 {
-	for (ulint i = 0; i < buf_pool->tmp_arr->n_slots; i++) {
-		buf_tmp_buffer_t* slot = &buf_pool->tmp_arr->slots[i];
-		if (slot->acquire()) {
-			return slot;
-		}
-	}
-
-	/* We assume that free slot is found */
-	ut_error;
-	return NULL;
+	buf_tmp_buffer_t* slot = buf_pool->io_buf.reserve();
+	ut_a(slot);
+	return slot;
 }
 
 /** Reserve a buffer for encryption, decryption or decompression.
@@ -1963,12 +1967,9 @@ buf_pool_init_instance(
 	new(&buf_pool->single_scan_itr) LRUItr(buf_pool, &buf_pool->mutex);
 
 	/* Initialize the temporal memory array and slots */
-	buf_pool->tmp_arr = (buf_tmp_array_t *)ut_malloc_nokey(sizeof(buf_tmp_array_t));
-	memset(buf_pool->tmp_arr, 0, sizeof(buf_tmp_array_t));
-	ulint n_slots = (srv_n_read_io_threads + srv_n_write_io_threads) * (8 * OS_AIO_N_PENDING_IOS_PER_THREAD);
-	buf_pool->tmp_arr->n_slots = n_slots;
-	buf_pool->tmp_arr->slots = (buf_tmp_buffer_t*)ut_malloc_nokey(sizeof(buf_tmp_buffer_t) * n_slots);
-	memset(buf_pool->tmp_arr->slots, 0, (sizeof(buf_tmp_buffer_t) * n_slots));
+	new(&buf_pool->io_buf) buf_pool_t::io_buf_t(
+		(srv_n_read_io_threads + srv_n_write_io_threads)
+		* (8 * OS_AIO_N_PENDING_IOS_PER_THREAD));
 
 	buf_pool_mutex_exit(buf_pool);
 
@@ -2046,26 +2047,7 @@ buf_pool_free_instance(
 	hash_table_free(buf_pool->page_hash);
 	hash_table_free(buf_pool->zip_hash);
 
-	/* Free all used temporary slots */
-	if (buf_pool->tmp_arr) {
-		for(ulint i = 0; i < buf_pool->tmp_arr->n_slots; i++) {
-			buf_tmp_buffer_t* slot = &(buf_pool->tmp_arr->slots[i]);
-			if (slot && slot->crypt_buf) {
-				aligned_free(slot->crypt_buf);
-				slot->crypt_buf = NULL;
-			}
-
-			if (slot && slot->comp_buf) {
-				aligned_free(slot->comp_buf);
-				slot->comp_buf = NULL;
-			}
-		}
-
-		ut_free(buf_pool->tmp_arr->slots);
-		ut_free(buf_pool->tmp_arr);
-		buf_pool->tmp_arr = NULL;
-	}
-
+	buf_pool->io_buf.~io_buf_t();
 	buf_pool->allocator.~ut_allocator();
 }
 

storage/innobase/include/buf0buf.h

@@ -2072,17 +2072,6 @@ struct buf_buddy_stat_t {
 	ib_uint64_t	relocated_usec;
 };
 
-/** @brief The temporary memory array structure.
-
-NOTE! The definition appears here only for other modules of this
-directory (buf) to see it. Do not use from outside! */
-
-typedef struct {
-	ulint		n_slots;	/*!< Total number of slots */
-	buf_tmp_buffer_t *slots;	/*!< Pointer to the slots in the
-					array */
-} buf_tmp_array_t;
-
 /** @brief The buffer pool structure.
 
 NOTE! The definition appears here only for other modules of this
@@ -2284,20 +2273,47 @@ struct buf_pool_t{
 #endif /* UNIV_DEBUG || UNIV_BUF_DEBUG */
 	UT_LIST_BASE_NODE_T(buf_buddy_free_t) zip_free[BUF_BUDDY_SIZES_MAX];
 					/*!< buddy free lists */
+#if BUF_BUDDY_LOW > UNIV_ZIP_SIZE_MIN
+# error "BUF_BUDDY_LOW > UNIV_ZIP_SIZE_MIN"
+#endif
+	/* @} */
 
 	buf_page_t*			watch;
 					/*!< Sentinel records for buffer
 					pool watches. Protected by
 					buf_pool->mutex. */
 
-	buf_tmp_array_t*		tmp_arr;
-					/*!< Array for temporal memory
-					used in compression and encryption */
+	/** Temporary memory for page_compressed and encrypted I/O */
+	struct io_buf_t {
+		/** number of elements in slots[] */
+		const ulint n_slots;
+		/** array of slots */
+		buf_tmp_buffer_t* const slots;
+
+		io_buf_t() = delete;
+
+		/** Constructor */
+		explicit io_buf_t(ulint n_slots) :
+			n_slots(n_slots),
+			slots(static_cast<buf_tmp_buffer_t*>(
+				      ut_malloc_nokey(n_slots
+						      * sizeof *slots)))
+		{
+			memset((void*) slots, 0, n_slots * sizeof *slots);
+		}
 
-#if BUF_BUDDY_LOW > UNIV_ZIP_SIZE_MIN
-# error "BUF_BUDDY_LOW > UNIV_ZIP_SIZE_MIN"
-#endif
-	/* @} */
+		~io_buf_t();
+
+		/** Reserve a buffer */
+		buf_tmp_buffer_t* reserve()
+		{
+			for (buf_tmp_buffer_t* s = slots, *e = slots + n_slots;
+			     s != e; s++) {
+				if (s->acquire()) return s;
+			}
+			return NULL;
+		}
+	} io_buf;
 };
 
 /** Print the given buf_pool_t object.