chromium/third_party/dawn/src/dawn/native/RingBufferAllocator.cpp

// Copyright 2018 The Dawn & Tint Authors
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#include "dawn/native/RingBufferAllocator.h"

#include <utility>

#include "dawn/common/Math.h"

// Note: Current RingBufferAllocator implementation uses two indices (start and end) to implement a
// circular queue. However, this approach defines a full queue when one element is still unused.
//
// For example, [E,E,E,E] would be equivelent to [U,U,U,U].
//                 ^                                ^
//                S=E=1                            S=E=1
//
// The latter case is eliminated by counting used bytes >= capacity. This definition prevents
// (the last) byte and requires an extra variable to count used bytes. Alternatively, we could use
// only two indices that keep increasing (unbounded) but can be still indexed using bit masks.
// However, this 1) requires the size to always be a power-of-two and 2) remove tests that check
// used bytes.
namespace dawn::native {

RingBufferAllocator::RingBufferAllocator() = default;

RingBufferAllocator::RingBufferAllocator(uint64_t maxSize) : … { … }

RingBufferAllocator::RingBufferAllocator(const RingBufferAllocator&) = default;

RingBufferAllocator::~RingBufferAllocator() = default;

RingBufferAllocator& RingBufferAllocator::operator=(const RingBufferAllocator&) = default;

void RingBufferAllocator::Deallocate(ExecutionSerial lastCompletedSerial) { … }

uint64_t RingBufferAllocator::GetSize() const { … }

uint64_t RingBufferAllocator::GetUsedSize() const { … }

bool RingBufferAllocator::Empty() const { … }

// Sub-allocate the ring-buffer by requesting a chunk of the specified size.
// This is a serial-based resource scheme, the life-span of resources (and the allocations) get
// tracked by GPU progress via serials. Memory can be reused by determining if the GPU has
// completed up to a given serial. Each sub-allocation request is tracked in the serial offset
// queue, which identifies an existing (or new) frames-worth of resources. Internally, the
// ring-buffer maintains offsets of 3 "memory" states: Free, Reclaimed, and Used. This is done
// in FIFO order as older frames would free resources before newer ones.
uint64_t RingBufferAllocator::Allocate(uint64_t allocationSize,
                                       ExecutionSerial serial,
                                       uint64_t offsetAlignment) { … }
}  // namespace dawn::native