Support flattening multiple CommandAllocators

This introduces CommandAllocator::AcquireCommandBlocks, which accepts a
vector of CommandAllocators and flattens them into a single iterable
sequence of commands. To support this, CommandAllocator is made movable.

Bug: dawn:809
Change-Id: I3984c243e4bd74568eccba1a8a58ec26324c8ffa
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/63822
Commit-Queue: Ken Rockot <rockot@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>

src/dawn_native/CommandAllocator.cpp

@@ -20,6 +20,7 @@
 #include <algorithm>
 #include <climits>
 #include <cstdlib>
+#include <utility>
 
 namespace dawn_native {
 
@@ -43,22 +44,32 @@ namespace dawn_native {
 
     CommandIterator& CommandIterator::operator=(CommandIterator&& other) {
         ASSERT(IsEmpty());
-        mBlocks = std::move(other.mBlocks);
-        other.Reset();
+        if (!other.IsEmpty()) {
+            mBlocks = std::move(other.mBlocks);
+            other.Reset();
+        }
         Reset();
         return *this;
     }
 
-    CommandIterator::CommandIterator(CommandAllocator&& allocator)
+    CommandIterator::CommandIterator(CommandAllocator allocator)
         : mBlocks(allocator.AcquireBlocks()) {
         Reset();
     }
 
-    CommandIterator& CommandIterator::operator=(CommandAllocator&& allocator) {
+    void CommandIterator::AcquireCommandBlocks(std::vector<CommandAllocator> allocators) {
         ASSERT(IsEmpty());
-        mBlocks = allocator.AcquireBlocks();
+        mBlocks.clear();
+        for (CommandAllocator& allocator : allocators) {
+            CommandBlocks blocks = allocator.AcquireBlocks();
+            if (!blocks.empty()) {
+                mBlocks.reserve(mBlocks.size() + blocks.size());
+                for (BlockDef& block : blocks) {
+                    mBlocks.push_back(std::move(block));
+                }
+            }
+        }
         Reset();
-        return *this;
     }
 
     bool CommandIterator::NextCommandIdInNewBlock(uint32_t* commandId) {
@@ -92,7 +103,7 @@ namespace dawn_native {
             return;
         }
 
-        for (auto& block : mBlocks) {
+        for (BlockDef& block : mBlocks) {
             free(block.block);
         }
         mBlocks.clear();
@@ -114,13 +125,49 @@ namespace dawn_native {
     //  - Better block allocation, maybe have Dawn API to say command buffer is going to have size
     //    close to another
 
-    CommandAllocator::CommandAllocator()
-        : mCurrentPtr(reinterpret_cast<uint8_t*>(&mDummyEnum[0])),
-          mEndPtr(reinterpret_cast<uint8_t*>(&mDummyEnum[1])) {
+    CommandAllocator::CommandAllocator() {
+        ResetPointers();
     }
 
     CommandAllocator::~CommandAllocator() {
-        ASSERT(mBlocks.empty());
+        Reset();
+    }
+
+    CommandAllocator::CommandAllocator(CommandAllocator&& other)
+        : mBlocks(std::move(other.mBlocks)), mLastAllocationSize(other.mLastAllocationSize) {
+        other.mBlocks.clear();
+        if (!other.IsEmpty()) {
+            mCurrentPtr = other.mCurrentPtr;
+            mEndPtr = other.mEndPtr;
+        } else {
+            ResetPointers();
+        }
+        other.Reset();
+    }
+
+    CommandAllocator& CommandAllocator::operator=(CommandAllocator&& other) {
+        Reset();
+        if (!other.IsEmpty()) {
+            std::swap(mBlocks, other.mBlocks);
+            mLastAllocationSize = other.mLastAllocationSize;
+            mCurrentPtr = other.mCurrentPtr;
+            mEndPtr = other.mEndPtr;
+        }
+        other.Reset();
+        return *this;
+    }
+
+    void CommandAllocator::Reset() {
+        for (BlockDef& block : mBlocks) {
+            free(block.block);
+        }
+        mBlocks.clear();
+        mLastAllocationSize = kDefaultBaseAllocationSize;
+        ResetPointers();
+    }
+
+    bool CommandAllocator::IsEmpty() const {
+        return mCurrentPtr == reinterpret_cast<const uint8_t*>(&mDummyEnum[0]);
     }
 
     CommandBlocks&& CommandAllocator::AcquireBlocks() {
@@ -173,4 +220,9 @@ namespace dawn_native {
         return true;
     }
 
+    void CommandAllocator::ResetPointers() {
+        mCurrentPtr = reinterpret_cast<uint8_t*>(&mDummyEnum[0]);
+        mEndPtr = reinterpret_cast<uint8_t*>(&mDummyEnum[1]);
+    }
+
 }  // namespace dawn_native

src/dawn_native/CommandAllocator.h

@@ -75,8 +75,10 @@ namespace dawn_native {
         CommandIterator(CommandIterator&& other);
         CommandIterator& operator=(CommandIterator&& other);
 
-        CommandIterator(CommandAllocator&& allocator);
-        CommandIterator& operator=(CommandAllocator&& allocator);
+        // Shorthand constructor for acquiring CommandBlocks from a single CommandAllocator.
+        explicit CommandIterator(CommandAllocator allocator);
+
+        void AcquireCommandBlocks(std::vector<CommandAllocator> allocators);
 
         template <typename E>
         bool NextCommandId(E* commandId) {
@@ -149,6 +151,15 @@ namespace dawn_native {
         CommandAllocator();
         ~CommandAllocator();
 
+        // NOTE: A moved-from CommandAllocator is reset to its initial empty state.
+        CommandAllocator(CommandAllocator&&);
+        CommandAllocator& operator=(CommandAllocator&&);
+
+        // Frees all blocks held by the allocator and restores it to its initial empty state.
+        void Reset();
+
+        bool IsEmpty() const;
+
         template <typename T, typename E>
         T* Allocate(E commandId) {
             static_assert(sizeof(E) == sizeof(uint32_t), "");
@@ -186,6 +197,9 @@ namespace dawn_native {
         static constexpr size_t kWorstCaseAdditionalSize =
             sizeof(uint32_t) + kMaxSupportedAlignment + alignof(uint32_t) + sizeof(uint32_t);
 
+        // The default value of mLastAllocationSize.
+        static constexpr size_t kDefaultBaseAllocationSize = 2048;
+
         friend CommandIterator;
         CommandBlocks&& AcquireBlocks();
 
@@ -237,19 +251,21 @@ namespace dawn_native {
 
         bool GetNewBlock(size_t minimumSize);
 
+        void ResetPointers();
+
         CommandBlocks mBlocks;
-        size_t mLastAllocationSize = 2048;
+        size_t mLastAllocationSize = kDefaultBaseAllocationSize;
+
+        // Data used for the block range at initialization so that the first call to Allocate sees
+        // there is not enough space and calls GetNewBlock. This avoids having to special case the
+        // initialization in Allocate.
+        uint32_t mDummyEnum[1] = {0};
 
         // Pointers to the current range of allocation in the block. Guaranteed to allow for at
         // least one uint32_t if not nullptr, so that the special kEndOfBlock command id can always
         // be written. Nullptr iff the blocks were moved out.
         uint8_t* mCurrentPtr = nullptr;
         uint8_t* mEndPtr = nullptr;
-
-        // Data used for the block range at initialization so that the first call to Allocate sees
-        // there is not enough space and calls GetNewBlock. This avoids having to special case the
-        // initialization in Allocate.
-        uint32_t mDummyEnum[1] = {0};
     };
 
 }  // namespace dawn_native

src/dawn_native/EncodingContext.cpp

@@ -48,7 +48,7 @@ namespace dawn_native {
 
     void EncodingContext::MoveToIterator() {
         if (!mWasMovedToIterator) {
-            mIterator = std::move(mAllocator);
+            mIterator = CommandIterator(std::move(mAllocator));
             mWasMovedToIterator = true;
         }
     }

src/tests/unittests/CommandAllocatorTests.cpp

@@ -428,7 +428,7 @@ TEST(CommandAllocator, AllocateDefaultInitializes) {
     iterator.MakeEmptyAsDataWasDestroyed();
 }
 
-// Test that the allcator correctly defaults initalizes data for AllocateData
+// Test that the allocator correctly default-initalizes data for AllocateData
 TEST(CommandAllocator, AllocateDataDefaultInitializes) {
     CommandAllocator allocator;
 
@@ -447,3 +447,57 @@ TEST(CommandAllocator, AllocateDataDefaultInitializes) {
     CommandIterator iterator(std::move(allocator));
     iterator.MakeEmptyAsDataWasDestroyed();
 }
+
+// Tests flattening of multiple CommandAllocators into a single CommandIterator using
+// AcquireCommandBlocks.
+TEST(CommandAllocator, AcquireCommandBlocks) {
+    constexpr size_t kNumAllocators = 2;
+    constexpr size_t kNumCommandsPerAllocator = 2;
+    const uint64_t pipelines[kNumAllocators][kNumCommandsPerAllocator] = {
+        {0xDEADBEEFBEEFDEAD, 0xC0FFEEF00DC0FFEE},
+        {0x1337C0DE1337C0DE, 0xCAFEFACEFACECAFE},
+    };
+    const uint32_t attachmentPoints[kNumAllocators][kNumCommandsPerAllocator] = {{1, 2}, {3, 4}};
+    const uint32_t firsts[kNumAllocators][kNumCommandsPerAllocator] = {{42, 43}, {5, 6}};
+    const uint32_t counts[kNumAllocators][kNumCommandsPerAllocator] = {{16, 32}, {4, 8}};
+
+    std::vector<CommandAllocator> allocators(kNumAllocators);
+    for (size_t j = 0; j < kNumAllocators; ++j) {
+        CommandAllocator& allocator = allocators[j];
+        for (size_t i = 0; i < kNumCommandsPerAllocator; ++i) {
+            CommandPipeline* pipeline = allocator.Allocate<CommandPipeline>(CommandType::Pipeline);
+            pipeline->pipeline = pipelines[j][i];
+            pipeline->attachmentPoint = attachmentPoints[j][i];
+
+            CommandDraw* draw = allocator.Allocate<CommandDraw>(CommandType::Draw);
+            draw->first = firsts[j][i];
+            draw->count = counts[j][i];
+        }
+    }
+
+    CommandIterator iterator;
+    iterator.AcquireCommandBlocks(std::move(allocators));
+    for (size_t j = 0; j < kNumAllocators; ++j) {
+        for (size_t i = 0; i < kNumCommandsPerAllocator; ++i) {
+            CommandType type;
+            bool hasNext = iterator.NextCommandId(&type);
+            ASSERT_TRUE(hasNext);
+            ASSERT_EQ(type, CommandType::Pipeline);
+
+            CommandPipeline* pipeline = iterator.NextCommand<CommandPipeline>();
+            ASSERT_EQ(pipeline->pipeline, pipelines[j][i]);
+            ASSERT_EQ(pipeline->attachmentPoint, attachmentPoints[j][i]);
+
+            hasNext = iterator.NextCommandId(&type);
+            ASSERT_TRUE(hasNext);
+            ASSERT_EQ(type, CommandType::Draw);
+
+            CommandDraw* draw = iterator.NextCommand<CommandDraw>();
+            ASSERT_EQ(draw->first, firsts[j][i]);
+            ASSERT_EQ(draw->count, counts[j][i]);
+        }
+    }
+    CommandType type;
+    ASSERT_FALSE(iterator.NextCommandId(&type));
+    iterator.MakeEmptyAsDataWasDestroyed();
+}