Add tests and fix (create) mapping zero-sized buffers

When creating a zero-sized buffer mapped, StagingBuffer creation
is skipped. This required adding a new MappedAtCreation state
since mStagingBuffer couldn't be used as a tag value for that.

Made the OpenGL backend always create non-zero-sized buffers.

Finally added tests for MapRead/WriteAsync and CreateBufferMapped
of zero-sized buffers.

Bug: dawn:446
Change-Id: I04f6fe98fd646f1867c21065cd1cd33a1595e19f
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/21481
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

src/dawn_native/Buffer.cpp

@@ -163,14 +163,22 @@ namespace dawn_native {
         ASSERT(!IsError());
         ASSERT(mappedPointer != nullptr);
 
-        mState = BufferState::Mapped;
+        // Mappable buffers don't use a staging buffer and are just as if mapped through MapAsync.
-
         if (IsMapWritable()) {
             DAWN_TRY(MapAtCreationImpl(mappedPointer));
+            mState = BufferState::Mapped;
             ASSERT(*mappedPointer != nullptr);
             return {};
         }
 
+        mState = BufferState::MappedAtCreation;
+
+        // 0-sized buffers are not supposed to be written to, Return back any non-null pointer.
+        if (mSize == 0) {
+            *mappedPointer = reinterpret_cast<uint8_t*>(intptr_t(0xCAFED00D));
+            return {};
+        }
+
         // If any of these fail, the buffer will be deleted and replaced with an
         // error buffer.
         // TODO(enga): Suballocate and reuse memory from a larger staging buffer so we don't create
@@ -190,6 +198,7 @@ namespace dawn_native {
             case BufferState::Destroyed:
                 return DAWN_VALIDATION_ERROR("Destroyed buffer used in a submit");
             case BufferState::Mapped:
+            case BufferState::MappedAtCreation:
                 return DAWN_VALIDATION_ERROR("Buffer used in a submit while mapped");
             case BufferState::Unmapped:
                 return {};
@@ -309,11 +318,15 @@ namespace dawn_native {
         ASSERT(!IsError());
 
         if (mState == BufferState::Mapped) {
-            if (mStagingBuffer == nullptr) {
+            Unmap();
-                Unmap();
+        } else if (mState == BufferState::MappedAtCreation) {
+            if (mStagingBuffer != nullptr) {
+                mStagingBuffer.reset();
+            } else {
+                ASSERT(mSize == 0);
             }
-            mStagingBuffer.reset();
         }
+
         DestroyInternal();
     }
 
@@ -342,9 +355,7 @@ namespace dawn_native {
         }
         ASSERT(!IsError());
 
-        if (mStagingBuffer != nullptr) {
+        if (mState == BufferState::Mapped) {
-            GetDevice()->ConsumedError(CopyFromStagingBuffer());
-        } else {
             // A map request can only be called once, so this will fire only if the request wasn't
             // completed before the Unmap.
             // Callbacks are not fired if there is no callback registered, so this is correct for
@@ -352,11 +363,20 @@ namespace dawn_native {
             CallMapReadCallback(mMapSerial, WGPUBufferMapAsyncStatus_Unknown, nullptr, 0u);
             CallMapWriteCallback(mMapSerial, WGPUBufferMapAsyncStatus_Unknown, nullptr, 0u);
             UnmapImpl();
+
+            mMapReadCallback = nullptr;
+            mMapWriteCallback = nullptr;
+            mMapUserdata = 0;
+
+        } else if (mState == BufferState::MappedAtCreation) {
+            if (mStagingBuffer != nullptr) {
+                GetDevice()->ConsumedError(CopyFromStagingBuffer());
+            } else {
+                ASSERT(mSize == 0);
+            }
         }
+
         mState = BufferState::Unmapped;
-        mMapReadCallback = nullptr;
-        mMapWriteCallback = nullptr;
-        mMapUserdata = 0;
     }
 
     MaybeError BufferBase::ValidateMap(wgpu::BufferUsage requiredUsage,
@@ -369,6 +389,7 @@ namespace dawn_native {
 
         switch (mState) {
             case BufferState::Mapped:
+            case BufferState::MappedAtCreation:
                 return DAWN_VALIDATION_ERROR("Buffer already mapped");
             case BufferState::Destroyed:
                 return DAWN_VALIDATION_ERROR("Buffer is destroyed");
@@ -390,6 +411,7 @@ namespace dawn_native {
 
         switch (mState) {
             case BufferState::Mapped:
+            case BufferState::MappedAtCreation:
                 // A buffer may be in the Mapped state if it was created with CreateBufferMapped
                 // even if it did not have a mappable usage.
                 return {};

src/dawn_native/Buffer.h

@@ -35,6 +35,7 @@ namespace dawn_native {
         enum class BufferState {
             Unmapped,
             Mapped,
+            MappedAtCreation,
             Destroyed,
         };
 

src/dawn_native/opengl/BufferGL.cpp

@@ -22,9 +22,13 @@ namespace dawn_native { namespace opengl {
 
     Buffer::Buffer(Device* device, const BufferDescriptor* descriptor)
         : BufferBase(device, descriptor) {
+        // TODO(cwallez@chromium.org): Have a global "zero" buffer instead of creating a new 4-byte
+        // buffer?
+        uint64_t size = std::max(GetSize(), uint64_t(4u));
+
         device->gl.GenBuffers(1, &mBuffer);
         device->gl.BindBuffer(GL_ARRAY_BUFFER, mBuffer);
-        device->gl.BufferData(GL_ARRAY_BUFFER, GetSize(), nullptr, GL_STATIC_DRAW);
+        device->gl.BufferData(GL_ARRAY_BUFFER, size, nullptr, GL_STATIC_DRAW);
     }
 
     Buffer::~Buffer() {

src/dawn_wire/server/ServerBuffer.cpp

@@ -202,6 +202,7 @@ namespace dawn_wire { namespace server {
             // to Unmap and attempt to update mapped data of an error buffer.
             return false;
         }
+
         // Deserialize the flush info and flush updated data from the handle into the target
         // of the handle. The target is set via WriteHandle::SetTarget.
         return buffer->writeHandle->DeserializeFlush(writeFlushInfo,

src/tests/end2end/BufferTests.cpp

@@ -108,6 +108,17 @@ TEST_P(BufferMapReadTests, LargeRead) {
     UnmapBuffer(buffer);
 }
 
+// Test mapping a zero-sized buffer.
+TEST_P(BufferMapReadTests, ZeroSized) {
+    wgpu::BufferDescriptor descriptor;
+    descriptor.size = 0;
+    descriptor.usage = wgpu::BufferUsage::MapRead | wgpu::BufferUsage::CopyDst;
+    wgpu::Buffer buffer = device.CreateBuffer(&descriptor);
+
+    MapReadAsyncAndWait(buffer);
+    UnmapBuffer(buffer);
+}
+
 DAWN_INSTANTIATE_TEST(BufferMapReadTests, D3D12Backend(), MetalBackend(), OpenGLBackend(), VulkanBackend());
 
 class BufferMapWriteTests : public DawnTest {
@@ -202,6 +213,17 @@ TEST_P(BufferMapWriteTests, LargeWrite) {
     EXPECT_BUFFER_U32_RANGE_EQ(myData.data(), buffer, 0, kDataSize);
 }
 
+// Test mapping a zero-sized buffer.
+TEST_P(BufferMapWriteTests, ZeroSized) {
+    wgpu::BufferDescriptor descriptor;
+    descriptor.size = 0;
+    descriptor.usage = wgpu::BufferUsage::MapWrite | wgpu::BufferUsage::CopySrc;
+    wgpu::Buffer buffer = device.CreateBuffer(&descriptor);
+
+    MapWriteAsyncAndWait(buffer);
+    UnmapBuffer(buffer);
+}
+
 // Stress test mapping many buffers.
 TEST_P(BufferMapWriteTests, ManyWrites) {
     constexpr uint32_t kDataSize = 1000;
@@ -370,6 +392,21 @@ TEST_P(CreateBufferMappedTests, NonMappableUsageLarge) {
     EXPECT_BUFFER_U32_RANGE_EQ(myData.data(), result.buffer, 0, kDataSize);
 }
 
+// Test destroying a non-mappable buffer mapped at creation.
+// This is a regression test for an issue where the D3D12 backend thought the buffer was actually
+// mapped and tried to unlock the heap residency (when actually the buffer was using a staging
+// buffer)
+TEST_P(CreateBufferMappedTests, DestroyNonMappableWhileMappedForCreation) {
+    wgpu::CreateBufferMappedResult result = CreateBufferMapped(wgpu::BufferUsage::CopySrc, 4);
+    result.buffer.Destroy();
+}
+
+// Test destroying a mappable buffer mapped at creation.
+TEST_P(CreateBufferMappedTests, DestroyMappableWhileMappedForCreation) {
+    wgpu::CreateBufferMappedResult result = CreateBufferMapped(wgpu::BufferUsage::MapRead, 4);
+    result.buffer.Destroy();
+}
+
 // Test that mapping a buffer is valid after CreateBufferMapped and Unmap
 TEST_P(CreateBufferMappedTests, CreateThenMapSuccess) {
     static uint32_t myData = 230502;
@@ -437,6 +474,48 @@ TEST_P(CreateBufferMappedTests, LargeBufferFails) {
     ASSERT_DEVICE_ERROR(device.CreateBuffer(&descriptor));
 }
 
+// Test that creating a zero-sized buffer mapped is allowed.
+TEST_P(CreateBufferMappedTests, ZeroSized) {
+    wgpu::BufferDescriptor descriptor;
+    descriptor.size = 0;
+    descriptor.usage = wgpu::BufferUsage::Vertex;
+    wgpu::CreateBufferMappedResult result = device.CreateBufferMapped(&descriptor);
+
+    ASSERT_EQ(0u, result.dataLength);
+    ASSERT_NE(nullptr, result.data);
+
+    // Check that unmapping the buffer works too.
+    UnmapBuffer(result.buffer);
+}
+
+// Test that creating a zero-sized mapppable buffer mapped. (it is a different code path)
+TEST_P(CreateBufferMappedTests, ZeroSizedMappableBuffer) {
+    wgpu::BufferDescriptor descriptor;
+    descriptor.size = 0;
+    descriptor.usage = wgpu::BufferUsage::MapWrite;
+    wgpu::CreateBufferMappedResult result = device.CreateBufferMapped(&descriptor);
+
+    ASSERT_EQ(0u, result.dataLength);
+    ASSERT_NE(nullptr, result.data);
+
+    // Check that unmapping the buffer works too.
+    UnmapBuffer(result.buffer);
+}
+
+// Test that creating a zero-sized error buffer mapped. (it is a different code path)
+TEST_P(CreateBufferMappedTests, ZeroSizedErrorBuffer) {
+    DAWN_SKIP_TEST_IF(IsDawnValidationSkipped());
+
+    wgpu::BufferDescriptor descriptor;
+    descriptor.size = 0;
+    descriptor.usage = wgpu::BufferUsage::MapWrite | wgpu::BufferUsage::Storage;
+    wgpu::CreateBufferMappedResult result;
+    ASSERT_DEVICE_ERROR(result = device.CreateBufferMapped(&descriptor));
+
+    ASSERT_EQ(0u, result.dataLength);
+    ASSERT_NE(nullptr, result.data);
+}
+
 DAWN_INSTANTIATE_TEST(CreateBufferMappedTests,
                       D3D12Backend(),
                       D3D12Backend({}, {"use_d3d12_resource_heap_tier2"}),
@@ -446,6 +525,7 @@ DAWN_INSTANTIATE_TEST(CreateBufferMappedTests,
 
 class BufferTests : public DawnTest {};
 
+// Test that creating a zero-buffer is allowed.
 TEST_P(BufferTests, ZeroSizedBuffer) {
     wgpu::BufferDescriptor desc;
     desc.size = 0;
@@ -453,6 +533,17 @@ TEST_P(BufferTests, ZeroSizedBuffer) {
     device.CreateBuffer(&desc);
 }
 
+// Test that creating a very large buffers fails gracefully.
+TEST_P(BufferTests, LargeBufferFails) {
+    // TODO(http://crbug.com/dawn/27): Missing support.
+    DAWN_SKIP_TEST_IF(IsOpenGL());
+
+    wgpu::BufferDescriptor descriptor;
+    descriptor.size = std::numeric_limits<uint64_t>::max();
+    descriptor.usage = wgpu::BufferUsage::MapRead | wgpu::BufferUsage::CopyDst;
+    ASSERT_DEVICE_ERROR(device.CreateBuffer(&descriptor));
+}
+
 DAWN_INSTANTIATE_TEST(BufferTests,
                       D3D12Backend(),
                       MetalBackend(),