branches/zip: Some non-functional changes related to Issue #155.

buf_page_struct: Note that space and offset are also protected by
buf_pool_mutex.  They are only assigned to by
buf_block_set_file_page().  Thus, it suffices for buf_flush_batch() to
hold just buf_pool_mutex when checking these fields.

buf_flush_try_page(): Rename "locked" to "is_s_latched", per Heikki's request.

buf_flush_batch(): Move the common statement mutex_exit(block_mutex)
from all if-else if-else branches before the if block.  Remove the
redundant test (buf_pool->init_flush[flush_type] == FALSE) that was
apparently copied from buf_flush_write_complete().

buf_flush_write_block_low(): Note why it is safe not to hold buf_pool_mutex
or block_mutex.  Enumerate the assumptions in debug assertions.

ChangeLog

@@ -7,7 +7,9 @@
 
 2009-01-09	The InnoDB Team
 
-	* buf/buf0flu.c: Simplify the function buf_flush_try_page().
+	* buf/buf0flu.c: Simplify the functions buf_flush_try_page() and
+	buf_flush_batch().  Add debug assertions and an explanation to
+	buf_flush_write_block_low().
 
 2009-01-07	The InnoDB Team
 

buf/buf0flu.c

@@ -653,6 +653,16 @@ buf_flush_write_block_low(
 
 	ut_ad(buf_page_in_file(bpage));
 
+	/* We are not holding buf_pool_mutex or block_mutex here.
+	Nevertheless, it is safe to access bpage, because it is
+	io_fixed and oldest_modification != 0.  Thus, it cannot be
+	relocated in the buffer pool or removed from flush_list or
+	LRU_list. */
+	ut_ad(!buf_pool_mutex_own());
+	ut_ad(!mutex_own(buf_page_get_mutex(bpage)));
+	ut_ad(buf_page_get_io_fix(bpage) == BUF_IO_WRITE);
+	ut_ad(bpage->oldest_modification != 0);
+
 #ifdef UNIV_IBUF_COUNT_DEBUG
 	ut_a(ibuf_count_get(bpage->space, bpage->offset) == 0);
 #endif
@@ -731,7 +741,6 @@ buf_flush_try_page(
 {
 	buf_page_t*	bpage;
 	mutex_t*	block_mutex;
-	ibool		locked;
 	ibool		is_uncompressed;
 
 	ut_ad(flush_type == BUF_FLUSH_LRU || flush_type == BUF_FLUSH_LIST
@@ -768,16 +777,18 @@ buf_flush_try_page(
 
 	buf_pool->n_flush[flush_type]++;
 
-	is_uncompressed = buf_page_get_state(bpage) == BUF_BLOCK_FILE_PAGE;
+	is_uncompressed = (buf_page_get_state(bpage) == BUF_BLOCK_FILE_PAGE);
+	ut_ad(is_uncompressed == (block_mutex != &buf_pool_zip_mutex));
 
 	switch (flush_type) {
+		ibool	is_s_latched;
 	case BUF_FLUSH_LIST:
 		/* If the simulated aio thread is not running, we must
 		not wait for any latch, as we may end up in a deadlock:
 		if buf_fix_count == 0, then we know we need not wait */
 
-		locked = bpage->buf_fix_count == 0;
-		if (locked && is_uncompressed) {
+		is_s_latched = (bpage->buf_fix_count == 0);
+		if (is_s_latched && is_uncompressed) {
 			rw_lock_s_lock_gen(&((buf_block_t*) bpage)->lock,
 					   BUF_IO_WRITE);
 		}
@@ -785,7 +796,7 @@ buf_flush_try_page(
 		mutex_exit(block_mutex);
 		buf_pool_mutex_exit();
 
-		if (!locked) {
+		if (!is_s_latched) {
 			buf_flush_buffered_writes();
 
 			if (is_uncompressed) {
@@ -1031,19 +1042,20 @@ flush_next:
 		function a pointer to a block in the list! */
 
 		do {
-			mutex_t* block_mutex = buf_page_get_mutex(bpage);
+			mutex_t*block_mutex = buf_page_get_mutex(bpage);
+			ibool	ready;
 
 			ut_a(buf_page_in_file(bpage));
 
 			mutex_enter(block_mutex);
+			ready = buf_flush_ready_for_flush(bpage, flush_type);
+			mutex_exit(block_mutex);
 
-			if (buf_flush_ready_for_flush(bpage, flush_type)) {
-
+			if (ready) {
 				space = buf_page_get_space(bpage);
 				offset = buf_page_get_page_no(bpage);
 
 				buf_pool_mutex_exit();
-				mutex_exit(block_mutex);
 
 				old_page_count = page_count;
 
@@ -1059,15 +1071,10 @@ flush_next:
 				goto flush_next;
 
 			} else if (flush_type == BUF_FLUSH_LRU) {
-
-				mutex_exit(block_mutex);
-
 				bpage = UT_LIST_GET_PREV(LRU, bpage);
 			} else {
 				ut_ad(flush_type == BUF_FLUSH_LIST);
 
-				mutex_exit(block_mutex);
-
 				bpage = UT_LIST_GET_PREV(list, bpage);
 				ut_ad(!bpage || bpage->in_flush_list);
 			}
@@ -1080,8 +1087,7 @@ flush_next:
 
 	buf_pool->init_flush[flush_type] = FALSE;
 
-	if ((buf_pool->n_flush[flush_type] == 0)
-	    && (buf_pool->init_flush[flush_type] == FALSE)) {
+	if (buf_pool->n_flush[flush_type] == 0) {
 
 		/* The running flush batch has ended */
 

include/buf0buf.h

@@ -981,8 +981,10 @@ struct buf_page_struct{
 	since they can be stored in the same machine word.  Some of them are
 	additionally protected by buf_pool_mutex. */
 
-	unsigned	space:32;	/* tablespace id */
-	unsigned	offset:32;	/* page number */
+	unsigned	space:32;	/* tablespace id; also protected
+					by buf_pool_mutex. */
+	unsigned	offset:32;	/* page number; also protected
+					by buf_pool_mutex. */
 
 	unsigned	state:3;	/* state of the control block
 					(@see enum buf_page_state); also