src/dawn/utils/TerribleCommandBuffer.cpp

// Copyright 2017 The Dawn & Tint Authors
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#include "src/dawn/utils/TerribleCommandBuffer.h"

#include "src/utils/assert.h"
#include "src/utils/compiler.h"

namespace dawn::utils {

TerribleCommandBuffer::TerribleCommandBuffer() : mBuffer(mBackingBuffer) {}

TerribleCommandBuffer::TerribleCommandBuffer(dawn::wire::CommandHandler* handler)
    : mHandler(handler), mBuffer(mBackingBuffer) {}

void TerribleCommandBuffer::SetHandler(dawn::wire::CommandHandler* handler) {
    mHandler = handler;
}

size_t TerribleCommandBuffer::GetMaximumAllocationSize() const {
    return mBackingBuffer.size();
}

void* TerribleCommandBuffer::GetCmdSpace(size_t size) {
    // Note: This returns non-null even if size is zero.
    if (size > mBackingBuffer.size()) {
        return nullptr;
    }

    if (mBuffer.size() - size < mOffset) {
        if (!Flush()) {
            return nullptr;
        }
        return GetCmdSpace(size);
    }

    void* result = mBuffer.subspan(mOffset, size).data();
    mOffset += size;
    return result;
}

bool TerribleCommandBuffer::Flush() {
    Span<std::byte> flushRange = mBuffer.subspan(mLastFlushedOffset, mOffset - mLastFlushedOffset);
    mLastFlushedOffset = mOffset;

    // TODO(crbug.com/528027992): Remove the cast and use Span once we update the interface.
    bool success =
        mHandler->HandleCommands(reinterpret_cast<const volatile char*>(flushRange.data()),
                                 flushRange.size()) != nullptr;

    // After a flush, we can only reset |mOffset| to 0 if both offsets are equal. Otherwise, there
    // are unflushed commands, likely queued as a part of the last flush, so defer resetting
    // |mOffset| until those have been processed as well.
    if (mLastFlushedOffset == mOffset) {
        mOffset = 0;
        mLastFlushedOffset = 0;
    }
    return success;
}

bool TerribleCommandBuffer::Empty() {
    return mOffset == 0;
}

size_t TerribleCommandBuffer::GetOffsetForTesting() const {
    return mOffset;
}

void TerribleCommandBuffer::SetOffsetForTesting(size_t offset) {
    mOffset = offset;
}

Span<const std::byte> TerribleCommandBuffer::GetContentSubrange(size_t startOffset,
                                                                size_t endOffset) {
    DAWN_ASSERT(endOffset >= startOffset);
    return mBuffer.subspan(startOffset, endOffset - startOffset);
}

}  // namespace dawn::utils