ClientDiscardableManager Implementation

gpu/command_buffer/client/client_discardable_manager.cc

+// Copyright (c) 2017 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 "gpu/command_buffer/client/client_discardable_manager.h"
+
+#include "base/memory/ptr_util.h"
+#include "base/sys_info.h"
+
+namespace gpu {
+namespace {
+
+// Stores a set of offsets, initially 0 to |element_count_|. Allows callers to
+// take and return offsets from the set. Internally stores the offsets as a set
+// of ranges. This means that in the worst case (every other offset taken), the
+// set will use |element_count_| uints, but should typically use fewer.
+class FreeOffsetSet {
+ public:
+  // Creates a new set, containing 0 to |element_count|.
+  FreeOffsetSet(uint32_t element_count);
+
+  // Returns true if the set contains at least one element.
+  bool HasFreeOffset() const;
+
+  // Returns true if any element from the set has been taken.
+  bool HasUsedOffset() const;
+
+  // Takes a free offset from the set. Should only be called if HasFreeOffset().
+  uint32_t TakeFreeOffset();
+
+  // Returns an offset to the set.
+  void ReturnFreeOffset(uint32_t offset);
+
+ private:
+  struct FreeRange {
+    uint32_t start;
+    uint32_t end;
+  };
+  struct CompareFreeRanges {
+    bool operator()(const FreeRange& a, const FreeRange& b) const {
+      return a.start < b.start;
+    }
+  };
+
+  const uint32_t element_count_;
+  std::set<FreeRange, CompareFreeRanges> free_ranges_;
+
+  DISALLOW_COPY_AND_ASSIGN(FreeOffsetSet);
+};
+
+FreeOffsetSet::FreeOffsetSet(uint32_t element_count)
+    : element_count_(element_count) {
+  free_ranges_.insert({0, element_count_});
+}
+
+bool FreeOffsetSet::HasFreeOffset() const {
+  return !free_ranges_.empty();
+}
+
+bool FreeOffsetSet::HasUsedOffset() const {
+  if (free_ranges_.size() != 1 || free_ranges_.begin()->start != 0 ||
+      free_ranges_.begin()->end != element_count_)
+    return true;
+
+  return false;
+}
+
+uint32_t FreeOffsetSet::TakeFreeOffset() {
+  DCHECK(HasFreeOffset());
+
+  auto it = free_ranges_.begin();
+  uint32_t offset_to_return = it->start;
+
+  FreeRange new_range{it->start + 1, it->end};
+  free_ranges_.erase(it);
+  if (new_range.start != new_range.end)
+    free_ranges_.insert(new_range);
+
+  return offset_to_return;
+}
+
+void FreeOffsetSet::ReturnFreeOffset(uint32_t offset) {
+  FreeRange new_range{offset, offset + 1};
+
+  // Find the FreeRange directly before/after our new range.
+  auto next_range = free_ranges_.lower_bound(new_range);
+  auto prev_range = free_ranges_.end();
+  if (next_range != free_ranges_.begin()) {
+    prev_range = std::prev(next_range);
+  }
+
+  // Collapse ranges if possible.
+  if (next_range != free_ranges_.end() && next_range->start == new_range.end) {
+    new_range.end = next_range->end;
+    free_ranges_.erase(next_range);
+  }
+
+  if (prev_range != free_ranges_.end() && prev_range->end == new_range.start) {
+    new_range.start = prev_range->start;
+    free_ranges_.erase(prev_range);
+  }
+
+  free_ranges_.insert(new_range);
+}
+
+// Returns the size of the allocation which ClientDiscardableManager will
+// sub-allocate from. This should be at least as big as the minimum shared
+// memory allocation size.
+size_t AllocationSize() {
+  size_t allocation_size = base::SysInfo::VMAllocationGranularity();
+  // If the allocation is small (less than 2K), round it up to at least 4K.
+  allocation_size = std::max(static_cast<size_t>(2048), allocation_size);
+  return allocation_size;
+}
+
+}  // namespace
+
+struct ClientDiscardableManager::Allocation {
+  Allocation(uint32_t element_count) : free_offsets(element_count) {}
+
+  scoped_refptr<Buffer> buffer;
+  int32_t shm_id = 0;
+  FreeOffsetSet free_offsets;
+};
+
+ClientDiscardableManager::ClientDiscardableManager()
+    : allocation_size_(AllocationSize()) {}
+ClientDiscardableManager::~ClientDiscardableManager() = default;
+
+ClientDiscardableHandle ClientDiscardableManager::GetForTexture(
+    CommandBuffer* command_buffer,
+    uint32_t texture_id) {
+  auto found = texture_handles_.find(texture_id);
+  if (found != texture_handles_.end())
+    return found->second;
+
+  scoped_refptr<Buffer> buffer;
+  uint32_t offset = 0;
+  int32_t shm_id = 0;
+  FindAllocation(command_buffer, &buffer, &shm_id, &offset);
+  uint32_t byte_offset = offset * element_size_;
+  ClientDiscardableHandle handle(std::move(buffer), byte_offset, shm_id);
+  texture_handles_.emplace(texture_id, handle);
+  return handle;
+}
+
+void ClientDiscardableManager::FreeForTexture(uint32_t texture_id) {
+  auto found = texture_handles_.find(texture_id);
+  DCHECK(found != texture_handles_.end());
+  pending_handles_.push(found->second);
+  texture_handles_.erase(found);
+}
+
+void ClientDiscardableManager::FindAllocation(CommandBuffer* command_buffer,
+                                              scoped_refptr<Buffer>* buffer,
+                                              int32_t* shm_id,
+                                              uint32_t* offset) {
+  CheckPending(command_buffer);
+
+  for (auto& allocation : allocations_) {
+    if (!allocation->free_offsets.HasFreeOffset())
+      continue;
+
+    *offset = allocation->free_offsets.TakeFreeOffset();
+    *shm_id = allocation->shm_id;
+    *buffer = allocation->buffer;
+    return;
+  }
+
+  // We couldn't find an existing free entry. Allocate more space.
+  auto allocation = base::MakeUnique<Allocation>(elements_per_allocation_);
+  allocation->buffer = command_buffer->CreateTransferBuffer(
+      allocation_size_, &allocation->shm_id);
+
+  *offset = allocation->free_offsets.TakeFreeOffset();
+  *shm_id = allocation->shm_id;
+  *buffer = allocation->buffer;
+  allocations_.push_back(std::move(allocation));
+}
+
+void ClientDiscardableManager::ReturnAllocation(
+    CommandBuffer* command_buffer,
+    const ClientDiscardableHandle& handle) {
+  for (auto it = allocations_.begin(); it != allocations_.end(); ++it) {
+    Allocation* allocation = it->get();
+    if (allocation->shm_id != handle.shm_id())
+      continue;
+
+    allocation->free_offsets.ReturnFreeOffset(handle.byte_offset() /
+                                              element_size_);
+
+    if (!allocation->free_offsets.HasUsedOffset()) {
+      command_buffer->DestroyTransferBuffer(allocation->shm_id);
+      allocations_.erase(it);
+      return;
+    }
+  }
+}
+
+void ClientDiscardableManager::CheckPending(CommandBuffer* command_buffer) {
+  while (pending_handles_.size() > 0 &&
+         pending_handles_.front().CanBeReUsed()) {
+    ReturnAllocation(command_buffer, pending_handles_.front());
+    pending_handles_.pop();
+  }
+}
+
+}  // namespace gpu