Multi reader/writer cache/buffer

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 "media/blink/multibuffer.h"
+
+#include "base/bind.h"
+
+namespace media {
+
+// Returns the block ID closest to (but less or equal than) |pos| from |index|.
+template<class T>
+static MultiBuffer::BlockId ClosestPreviousEntry(
+    const std::map<MultiBuffer::BlockId, T>& index,
+    MultiBuffer::BlockId pos) {
+  auto i = index.upper_bound(pos);
+  DCHECK(i == index.end() || i->first > pos);
+  if (i == index.begin()) {
+    return std::numeric_limits<MultiBufferBlockId>::min();
+  }
+  --i;
+  DCHECK_LE(i->first, pos);
+  return i->first;
+}
+
+// Returns the block ID closest to (but greter than or equal to) |pos|
+// from |index|.
+template<class T>
+static MultiBuffer::BlockId ClosestNextEntry(
+    const std::map<MultiBuffer::BlockId, T>& index,
+    MultiBuffer::BlockId pos) {
+  auto i = index.lower_bound(pos);
+  if (i == index.end()) {
+    return std::numeric_limits<MultiBufferBlockId>::max();
+  }
+  DCHECK_GE(i->first, pos);
+  return i->first;
+}
+
+//
+// MultiBuffer::GlobalLRU
+//
+MultiBuffer::GlobalLRU::GlobalLRU() : max_size_(0), data_size_(0) {}
+
+MultiBuffer::GlobalLRU::~GlobalLRU() {
+  // By the time we're freed, all blocks should have been removed,
+  // and our sums should be zero.
+  DCHECK(lru_.Empty());
+  DCHECK_EQ(max_size_, 0);
+  DCHECK_EQ(data_size_, 0);
+}
+
+void MultiBuffer::GlobalLRU::Use(MultiBuffer* multibuffer,
+                                 MultiBufferBlockId block_id) {
+  GlobalBlockId id(multibuffer, block_id);
+  lru_.Use(id);
+}
+
+void MultiBuffer::GlobalLRU::Insert(MultiBuffer* multibuffer,
+                                    MultiBufferBlockId block_id) {
+  GlobalBlockId id(multibuffer, block_id);
+  lru_.Insert(id);
+}
+
+void MultiBuffer::GlobalLRU::Remove(MultiBuffer* multibuffer,
+                                    MultiBufferBlockId block_id) {
+  GlobalBlockId id(multibuffer, block_id);
+  lru_.Remove(id);
+}
+
+bool MultiBuffer::GlobalLRU::Contains(MultiBuffer* multibuffer,
+                                      MultiBufferBlockId block_id) {
+  GlobalBlockId id(multibuffer, block_id);
+  return lru_.Contains(id);
+}
+
+void MultiBuffer::GlobalLRU::IncrementDataSize(int64_t blocks) {
+  data_size_ += blocks;
+  DCHECK_GE(data_size_, 0);
+}
+
+void MultiBuffer::GlobalLRU::IncrementMaxSize(int64_t blocks) {
+  max_size_ += blocks;
+  DCHECK_GE(max_size_, 0);
+}
+
+void MultiBuffer::GlobalLRU::Prune(size_t max_to_free) {
+  // Group the blocks by multibuffer, then free them.
+  std::map<MultiBuffer*, std::vector<MultiBufferBlockId> > to_free;
+  size_t freed = 0;
+  while (data_size_ - freed > max_size_ &&
+         !lru_.Empty() &&
+         freed < max_to_free) {
+    GlobalBlockId block_id = lru_.Pop();
+    to_free[block_id.first].push_back(block_id.second);
+    freed--;

[DaleCurtis, 2015/10/28 23:06:13]

How does this work? freed is zero and doesn't seem to be set then you subtract
from it? Seems like this overflows "-1" unsigned.

[hubbe, 2015/10/29 17:52:44]

OOps, should be ++.
Added test as well.

+  }
+  for (const auto &to_free_pair : to_free) {

[DaleCurtis, 2015/10/28 23:06:13]

auto&

[hubbe, 2015/10/29 17:52:44]

Done.

+    to_free_pair.first->ReleaseBlocks(to_free_pair.second);
+  }
+}
+
+//
+// MultiBuffer
+//
+MultiBuffer::MultiBuffer(int32_t block_size_shift,
+                         scoped_refptr<GlobalLRU> global_lru) :

[DaleCurtis, 2015/10/28 23:06:13]

const&

[hubbe, 2015/10/29 17:52:44]

Done.

+    max_size_(0),
+    block_size_shift_(block_size_shift),
+    lru_(global_lru) {
+}
+
+MultiBuffer::~MultiBuffer() {
+  // Delete all writers.
+  for (const auto& i : writer_index_) {
+    delete i.second;
+  }
+  // Remove all blocks from the LRU.
+  for (const auto& i : data_) {
+    lru_->Remove(this, i.first);
+  }
+  lru_->IncrementDataSize(-static_cast<int64_t>(data_.size()));
+  lru_->IncrementMaxSize(-max_size_);
+}
+
+void MultiBuffer::AddReader(const BlockId& pos, Reader* reader) {
+  std::set<Reader*> &set_of_readers = readers_[pos];
+  bool already_waited_for = !set_of_readers.empty();
+  set_of_readers.insert(reader);
+
+  if (already_waited_for || Contains(pos)) {
+    return;
+  }
+
+  // We may need to create a new data provider to service this request.
+  // Look for an existing data provider first.
+  DataProvider* provider = NULL;
+  BlockId closest_writer = ClosestPreviousEntry(writer_index_, pos);
+
+  if (closest_writer > pos - kMaxWaitForWriterOffset) {
+    auto i = present_.find(pos);
+    BlockId closest_block;
+    if (i.value()) {
+      closest_block = pos;
+    } else if (i == present_.begin()) {
+      closest_block = -1;
+    } else {
+      closest_block = i.range_begin() - 1;
+    }
+
+    if (closest_writer > closest_block) {
+      provider = writer_index_[closest_writer];
+      DCHECK(provider);
+    }
+  }
+  if (!provider) {
+    DCHECK(writer_index_.find(pos) == writer_index_.end());
+    provider = writer_index_[pos] = CreateWriter(pos);
+    provider->SetAvailableCallback(
+        base::Bind(&MultiBuffer::DataProviderEvent,
+                   base::Unretained(this),
+                   base::Unretained(provider)));
+  }
+  provider->SetDeferred(false);
+}
+
+void MultiBuffer::RemoveReader(const BlockId& pos, Reader* reader) {
+  auto i = readers_.find(pos);
+  if (i == readers_.end())
+    return;
+  i->second.erase(reader);
+  if (i->second.empty()) {
+    readers_.erase(i);
+  }
+}
+
+void MultiBuffer::CleanupWriters(const BlockId& pos) {
+  BlockId closest_writer = ClosestPreviousEntry(writer_index_, pos);
+  if (closest_writer < 0)
+    return;
+  if (pos - closest_writer > kMaxWaitForWriterOffset)
+    return;
+  DCHECK(writer_index_[closest_writer]);
+  DataProviderEvent(writer_index_[closest_writer]);
+}
+
+bool MultiBuffer::Contains(const BlockId& pos) const {
+  DCHECK(present_[pos] == 0 || present_[pos] == 1)
+      << " pos = " << pos
+      << " present_[pos] " << present_[pos];
+  DCHECK_EQ(present_[pos], data_.find(pos) != data_.end() ? 1 : 0);
+  return !!present_[pos];
+}
+
+MultiBufferBlockId MultiBuffer::FindNextUnavailable(const BlockId& pos) const {
+  auto i = present_.find(pos);
+  if (i.value())
+    return i.range_end();
+  return pos;
+}
+
+void MultiBuffer::NotifyAvailableRange(
+    const Range<MultiBufferBlockId>& observer_range,
+    const Range<MultiBufferBlockId>& new_range) {
+  std::set<Reader*> tmp;
+  for (auto i = readers_.lower_bound(observer_range.begin);
+       i != readers_.end() && i->first < observer_range.end;
+       ++i) {
+    tmp.insert(i->second.begin(), i->second.end());
+  }
+  for (Reader* reader: tmp) {
+    reader->NotifyAvailableRange(new_range);
+  }
+}
+
+void MultiBuffer::ReleaseBlocks(const std::vector<MultiBufferBlockId> blocks) {
+  RangeMap<BlockId, int32_t> freed;
+  for (MultiBufferBlockId to_free : blocks) {

[DaleCurtis, 2015/10/28 23:06:13]

const auto&?

[hubbe, 2015/10/29 17:52:44]

It's an integer type though, using "const auto&" seems to imply that it's
something big and complicated that I don't want to copy.

+    DCHECK(data_[to_free]);
+    DCHECK_EQ(pinned_[to_free], 0);
+    DCHECK_EQ(present_[to_free], 1);
+    data_.erase(to_free);
+    freed.IncrementRange(to_free, to_free + 1, 1);
+    present_.IncrementRange(to_free, to_free + 1, -1);
+  }
+  lru_->IncrementDataSize(-blocks.size());
+
+  for (const auto& freed_range : freed) {
+    if (freed_range.second) {
+      // Technically, there shouldn't be any observers in this range
+      // as all observers really should be pinning the range where it's
+      // actually observing.
+      NotifyAvailableRange(
+          freed_range.first,
+          // Empty range.
+          Range<BlockId>(freed_range.first.begin,
+                         freed_range.first.begin));
+
+      auto i = present_.find(freed_range.first.begin);
+      DCHECK_EQ(i.value(), 0);
+      DCHECK_LE(i.range_begin(), freed_range.first.begin);
+      DCHECK_LE(freed_range.first.end, i.range_end());
+
+      if (i.range_begin() == freed_range.first.begin) {
+        // Notify the previous range that it contains fewer blocks.
+        auto j = i;
+        --j;
+        DCHECK_EQ(j.value(), 1);
+        NotifyAvailableRange(j.range(), j.range());
+      }
+      if (i.range_end() == freed_range.first.end) {
+        // Notify the following range that it contains fewer blocks.
+        auto j = i;
+        ++j;
+        DCHECK_EQ(j.value(), 1);
+        NotifyAvailableRange(j.range(), j.range());
+      }
+    }
+  }
+}
+
+void MultiBuffer::AddProvider(scoped_ptr<DataProvider> provider) {
+  // If there is already a provider in the same location, we delete it.
+  DCHECK(!provider->Available());
+  BlockId pos = provider->Tell();
+  DataProvider** place = &writer_index_[pos];
+  DCHECK_NE(*place, provider.get());
+  if (*place) delete *place;
+  *place = provider.release();
+}
+
+scoped_ptr<MultiBuffer::DataProvider> MultiBuffer::RemoveProvider(
+    DataProvider *provider) {
+  BlockId pos = provider->Tell();
+  DCHECK_EQ(writer_index_[pos], provider);
+  writer_index_.erase(pos);
+  return scoped_ptr<DataProvider>(provider);
+}
+
+MultiBuffer::ProviderState MultiBuffer::SuggestProviderState(
+    const BlockId& pos) const {
+  MultiBufferBlockId next_reader_pos = ClosestNextEntry(readers_, pos);
+  if (next_reader_pos != std::numeric_limits<MultiBufferBlockId>::max() &&
+      (next_reader_pos - pos <= kMaxWaitForWriterOffset || !RangeSupported())) {
+    // Check if there is another writer between us and the next reader.
+    MultiBufferBlockId next_writer_pos = ClosestNextEntry(
+        writer_index_, pos + 1);
+    if (next_writer_pos > next_reader_pos) {
+      return ProviderStateLoad;
+    }
+  }
+
+  MultiBufferBlockId previous_reader_pos = ClosestPreviousEntry(
+      readers_, pos - 1);
+  if (previous_reader_pos != std::numeric_limits<MultiBufferBlockId>::min() &&
+      (pos - previous_reader_pos <= kMaxWaitForReaderOffset ||
+       !RangeSupported())) {
+    MultiBufferBlockId previous_writer_pos =
+        ClosestPreviousEntry(writer_index_, pos - 1);
+    if (previous_writer_pos < previous_reader_pos) {
+      return ProviderStateDefer;
+    }
+  }
+
+  return ProviderStateDead;
+}
+
+bool MultiBuffer::ProviderCollision(const BlockId& id) const {
+  // If there is a writer at the same location, it is always a collision.
+  if (writer_index_.find(id) != writer_index_.end())
+    return true;
+
+  // Data already exists at providers current position,
+  // if the URL supports ranges, we can kill the data provider.
+  if (RangeSupported() && Contains(id))
+    return true;
+
+  return false;
+}
+
+void MultiBuffer::Prune(size_t max_to_free) {
+  lru_->Prune(max_to_free);
+}
+
+void MultiBuffer::DataProviderEvent(DataProvider *provider_tmp) {
+  scoped_ptr<DataProvider> provider(RemoveProvider(provider_tmp));
+  BlockId start_pos = provider->Tell();
+  BlockId pos = start_pos;
+  bool eof = false;
+  int64_t blocks_added = -data_.size();

[DaleCurtis, 2015/10/28 23:06:13]

-size_t might be problematic?

[hubbe, 2015/10/29 17:52:44]

Assuming unary minus behaves anything like binary minus, it should always return
a signed type. (int or bigger)
However, making it more explicit will probably help the reader.

[hubbe, 2015/10/29 21:45:05]

Turns out you're right, - on size_t is problematic.
I should learn never to underestimate how quirky C++ is some day....

+
+  while (!ProviderCollision(pos) && !eof) {
+    if (!provider->Available()) {
+      AddProvider(provider.Pass());
+      break;
+    }
+    DCHECK_GE(pos, 0);
+    data_[pos] = provider->Read();
+    eof = data_[pos]->end_of_stream();
+    if (!pinned_[pos])
+      lru_->Use(this, pos);
+    ++pos;
+  }
+  blocks_added += data_.size();
+
+  if (pos > start_pos) {
+    present_.SetRange(start_pos, pos, 1);
+    Range<BlockId> expanded_range = present_.find(start_pos).range();
+    NotifyAvailableRange(expanded_range, expanded_range);
+
+    lru_->IncrementDataSize(blocks_added);
+    Prune(blocks_added * kMaxFreesPerAdd + 1);
+  }
+
+  // Check that it's still there before we try to delete it.
+  auto i = writer_index_.find(pos);
+  if (i != writer_index_.end() && i->second == provider_tmp) {
+    switch (SuggestProviderState(pos)) {
+      case ProviderStateLoad:
+        // Not sure we actually need to do this
+        provider_tmp->SetDeferred(false);
+        break;
+      case ProviderStateDefer:
+        provider_tmp->SetDeferred(true);
+        break;
+      case ProviderStateDead:
+        RemoveProvider(provider_tmp);
+        break;
+    }
+  }
+}
+
+void MultiBuffer::MergeFrom(MultiBuffer* other) {
+  // Import data and update LRU.
+  for (auto data : other->data_) {

[DaleCurtis, 2015/10/28 23:06:13]

const auto& here and the three below.

[hubbe, 2015/10/29 17:52:44]

Done.

The range iterator used in the two cases below is slightly non-standard, and the
range that we get a const reference to would only exist in some temporary memory
somewhere, but it works...

+    if (data_.insert(std::make_pair(data.first, data.second)).second) {
+      if (!pinned_[data.first]) {
+        lru_->Insert(this, data.first);
+      }
+    }
+  }
+  // Update present_
+  for (auto r : other->present_) {
+    if (r.second) {
+      present_.SetRange(r.first.begin, r.first.end, 1);
+    }
+  }
+  // Notify existing readers.
+  auto last = present_.begin();
+  for (auto r : other->present_) {
+    if (r.second) {
+      auto i = present_.find(r.first.begin);
+      if (i != last) {
+        NotifyAvailableRange(i.range(), i.range());
+        last = i;
+      }
+    }
+  }
+}
+
+void MultiBuffer::PinRange(
+    const BlockId& from, const BlockId& to, int32_t how_much) {
+  DCHECK_NE(how_much, 0);
+  DVLOG(3) <<  "PINRANGE [" << from << " - " << to << ") += " << how_much;
+  pinned_.IncrementRange(from, to, how_much);
+  Range<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) {
+    if (range.value() == 0 || range.value() == how_much) {
+      bool pin = range.value() == how_much;
+      Range<BlockId> transition_range = modified_range.Intersect(range.range());
+      BlockId transition_begin = std::max(range.range_begin(), from);
+      BlockId transition_end = std::min(range.range_end(), to);
+      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_end - 1);

[DaleCurtis, 2015/10/28 23:06:13]

ditto.

[hubbe, 2015/10/29 17:52:44]

Ditto what? This is an iterator...

[DaleCurtis, 2015/10/29 17:59:05]

Ditto for const auto& unless you need the non-const iterator, it doesn't look
like it.

[hubbe, 2015/10/29 21:45:05]

A const iterator is an iterator to a const container, the iterator itself is not
const. (If it was, ++ wouldn't work.) If I make this const, then I get an error
on line 432 when it tries to decrement the iterator.

Perhaps I should just avoid using auto here, that might make it more clear?

+           present_block_range != present_.begin();
+           --present_block_range) {
+        if (!present_block_range.value())
+          continue;
+        Range<BlockId> present_transitioned_range =
+            transition_range.Intersect(present_block_range.range());
+        if (present_transitioned_range.Empty())
+          break;
+        for (BlockId block = present_transitioned_range.end - 1;
+             block >= present_transitioned_range.begin;
+             --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);
+          }
+        }
+      }
+    }
+    if (range == pinned_.begin()) break;
+    --range;
+  }
+}
+
+void MultiBuffer::PinRanges(const RangeMap<BlockId, int32_t>& ranges) {
+  for (const auto& r : ranges) {
+    if (r.second != 0) {
+      PinRange(r.first.begin, r.first.end, r.second);
+    }
+  }
+}
+
+void MultiBuffer::IncrementMaxSize(int32_t size) {
+  max_size_ += size;
+  lru_->IncrementMaxSize(size);
+  DCHECK_GE(max_size_, 0);
+  // Pruning only happens when blocks are added.
+}
+
+}  // namespace media