multibuffer: Evict lower blocks first after inserting multiple blocks

media/blink/multibuffer.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <utility>
 
 #include "media/blink/multibuffer.h"
 
 #include "base/bind.h"
 #include "base/location.h"
@@ skipping 442 matching lines @@
                            const BlockId& to,
                            int32_t how_much) {
   DCHECK_NE(how_much, 0);
   DVLOG(3) << "PINRANGE [" << from << " - " << to << ") += " << how_much;
   pinned_.IncrementInterval(from, to, how_much);
   Interval<BlockId> modified_range(from, to);
 
   // Iterate over all the modified ranges and check if any of them have
   // transitioned in or out of the unlocked state. If so, we iterate over
   // all buffers in that range and add/remove them from the LRU as approperiate.
-  // We iterate *backwards* through the ranges, with the idea that data in a
-  // continous range should be freed from the end first.
 
   if (data_.empty())
     return;
 
   auto range = pinned_.find(to - 1);
   while (1) {
     DCHECK_GE(range.value(), 0);
     if (range.value() == 0 || range.value() == how_much) {
       bool pin = range.value() == how_much;
       Interval<BlockId> transition_range =
           modified_range.Intersect(range.interval());
       if (transition_range.Empty())
         break;
 
       // For each range that has transitioned to/from a pinned state,
       // we iterate over the corresponding ranges in |present_| to find
       // the blocks that are actually in the multibuffer.
-      for (auto present_block_range = present_.find(transition_range.end - 1);
-           present_block_range != present_.begin(); --present_block_range) {
+      for (auto present_block_range = present_.find(transition_range.begin);
+           present_block_range != present_.end(); ++present_block_range) {
         if (!present_block_range.value())
           continue;
         Interval<BlockId> present_transitioned_range =
             transition_range.Intersect(present_block_range.interval());
         if (present_transitioned_range.Empty())
           break;
-        for (BlockId block = present_transitioned_range.end - 1;
-             block >= present_transitioned_range.begin; --block) {
+        for (BlockId block = present_transitioned_range.begin;
+             block < present_transitioned_range.end; ++block) {
           DCHECK_GE(block, 0);
           DCHECK(data_.find(block) != data_.end());
           if (pin) {
             DCHECK(pinned_[block]);
             lru_->Remove(this, block);
           } else {
             DCHECK(!pinned_[block]);
             lru_->Insert(this, block);
           }
         }
@@ skipping 21 matching lines @@
 }
 
 int64_t MultiBuffer::UncommittedBytesAt(const MultiBuffer::BlockId& block) {
   auto i = writer_index_.find(block);
   if (writer_index_.end() == i)
     return 0;
   return i->second->AvailableBytes();
 }
 
 }  // namespace media