BufferManager
时间: 2024-06-09 18:01:26 浏览: 95
Buffer Manager是数据库管理系统中的一个重要组件,主要负责管理内存和存储之间的数据传输,对数据库的性能指标有着直接的影响。当进程需要读取数据页或索引页时,会先将带着buffer tag的请求发送到Buffer Manager,如果Buffer Pool中已经存在此page,Buffer Manager直接返回Buffer Pool数组的下标Buffer ID,如果不存在,则从存储中读取数据页放在Buffer Pool中,并返回下标Buffer ID。进程读取Buffer ID对应的页。同时,Buffer Manager还可以修改Buffer Pool中的数据页,数据页在没有被flush到存储上时被认为是dirty page。为了保证并发访问的正确性,Buffer Manager还需要实现相应的锁机制。在数据库设计中,Buffer Manager是最重要的话题之一,无论是MySQL还是PostgreSQL,都有其良好的Buffer Manager设计。
相关问题
实验5 wcf消息通信练习代码
以下是一个简单的WCF消息通信的示例代码,供参考:
服务契约:
```csharp
[ServiceContract]
public interface IMyService
{
[OperationContract]
MyResponseMessage DoSomething(MyRequestMessage request);
}
[MessageContract]
public class MyRequestMessage
{
[MessageBodyMember]
public string Text { get; set; }
}
[MessageContract]
public class MyResponseMessage
{
[MessageBodyMember]
public int Result { get; set; }
}
```
服务实现:
```csharp
public class MyService : IMyService
{
public MyResponseMessage DoSomething(MyRequestMessage request)
{
int result = 0;
// 处理请求消息
// ...
// 返回响应消息
return new MyResponseMessage { Result = result };
}
}
```
客户端代理:
```csharp
public class MyClient : ClientBase<IMyService>, IMyService
{
public MyResponseMessage DoSomething(MyRequestMessage request)
{
// 将消息序列化为XML格式
XmlSerializer serializer = new XmlSerializer(typeof(MyRequestMessage));
StringWriter writer = new StringWriter();
serializer.Serialize(writer, request);
string xml = writer.ToString();
// 调用服务操作
string resultXml = base.Channel.DoSomething(xml);
// 将响应消息反序列化为对象
XmlSerializer resultSerializer = new XmlSerializer(typeof(MyResponseMessage));
StringReader resultReader = new StringReader(resultXml);
MyResponseMessage result = (MyResponseMessage)resultSerializer.Deserialize(resultReader);
return result;
}
}
```
自定义编解码器:
```csharp
public class MyMessageEncoder : MessageEncoder
{
private const string XmlMediaType = "text/xml";
private readonly XmlWriterSettings _writerSettings;
public MyMessageEncoder()
{
_writerSettings = new XmlWriterSettings
{
Encoding = Encoding.UTF8,
OmitXmlDeclaration = true
};
}
public override string ContentType => XmlMediaType;
public override string MediaType => XmlMediaType;
public override MessageVersion MessageVersion => MessageVersion.Soap11;
public override bool IsContentTypeSupported(string contentType)
{
return contentType == XmlMediaType || base.IsContentTypeSupported(contentType);
}
public override Message ReadMessage(ArraySegment<byte> buffer, BufferManager bufferManager, string contentType)
{
byte[] messageBytes = buffer.Array;
int messageOffset = buffer.Offset;
int messageLength = buffer.Count;
MemoryStream stream = new MemoryStream(messageBytes, messageOffset, messageLength);
XmlReader reader = XmlReader.Create(stream);
return Message.CreateMessage(reader, int.MaxValue, MessageVersion);
}
public override ArraySegment<byte> WriteMessage(Message message, int maxMessageSize, BufferManager bufferManager, int messageOffset)
{
MemoryStream stream = new MemoryStream();
XmlWriter writer = XmlWriter.Create(stream, _writerSettings);
message.WriteMessage(writer);
writer.Flush();
byte[] messageBytes = stream.ToArray();
int totalLength = messageBytes.Length + messageOffset;
byte[] totalBytes = bufferManager.TakeBuffer(totalLength);
Array.Copy(messageBytes, 0, totalBytes, messageOffset, messageBytes.Length);
ArraySegment<byte> byteArray = new ArraySegment<byte>(totalBytes, messageOffset, messageBytes.Length);
return byteArray;
}
}
```
客户端代理使用自定义编解码器:
```csharp
public class MyClient : ClientBase<IMyService>, IMyService
{
public MyResponseMessage DoSomething(MyRequestMessage request)
{
// 将消息序列化为XML格式
XmlSerializer serializer = new XmlSerializer(typeof(MyRequestMessage));
StringWriter writer = new StringWriter();
serializer.Serialize(writer, request);
string xml = writer.ToString();
// 使用自定义编解码器发送消息
MyMessageEncoder encoder = new MyMessageEncoder();
Message requestMessage = Message.CreateMessage(MessageVersion.Soap11, "", xml);
requestMessage.Headers.To = new Uri(base.Endpoint.Address.Uri, "DoSomething");
Message responseMessage = base.Channel.Request(requestMessage, encoder);
// 将响应消息反序列化为对象
XmlSerializer resultSerializer = new XmlSerializer(typeof(MyResponseMessage));
StringReader resultReader = new StringReader(responseMessage.GetBody<string>());
MyResponseMessage result = (MyResponseMessage)resultSerializer.Deserialize(resultReader);
return result;
}
}
```
服务端使用自定义编解码器:
```csharp
public class MyService : IMyService
{
public MyResponseMessage DoSomething(MyRequestMessage request)
{
// 将消息反序列化为对象
XmlSerializer serializer = new XmlSerializer(typeof(MyRequestMessage));
StringReader reader = new StringReader(request);
MyRequestMessage message = (MyRequestMessage)serializer.Deserialize(reader);
int result = 0;
// 处理请求消息
// ...
// 返回响应消息
MyResponseMessage response = new MyResponseMessage { Result = result };
// 将响应消息序列化为XML格式
StringWriter writer = new StringWriter();
XmlSerializer resultSerializer = new XmlSerializer(typeof(MyResponseMessage));
resultSerializer.Serialize(writer, response);
string resultXml = writer.ToString();
// 使用自定义编解码器发送响应消息
MyMessageEncoder encoder = new MyMessageEncoder();
Message responseMessage = Message.CreateMessage(MessageVersion.Soap11, "", resultXml);
return responseMessage;
}
}
```
配置WCF服务和客户端:
```xml
<system.serviceModel>
<bindings>
<customBinding>
<binding name="MyBinding">
<textMessageEncoding messageVersion="Soap11" />
<httpTransport />
</binding>
</customBinding>
</bindings>
<services>
<service name="MyService">
<endpoint address="" binding="customBinding" bindingConfiguration="MyBinding" contract="IMyService" />
</service>
</services>
<client>
<endpoint address="http://localhost/MyService" binding="customBinding" bindingConfiguration="MyBinding" contract="IMyService" />
</client>
</system.serviceModel>
```
以上是一个简单的WCF消息通信的示例,可以根据实际需求进行修改和扩展。
如何在vendor/qcom/proprietary/chi-cdk/下获取yuv420图像
在 `vendor/qcom/proprietary/chi-cdk/` 目录下,如果你已经获取到源码并编译完成,可以使用以下步骤获取yuv420图像:
1. 找到要获取yuv420图像的摄像头的camera ID。你可以在 `vendor/qcom/proprietary/chi-cdk/Android.mk` 文件中找到这些摄像头的 ID。
2. 配置 `CameraDevice`。在 `vendor/qcom/proprietary/chi-cdk/frameworks/camx/src/core/camxdeviceapi/camxhwcontext.cpp` 文件中,你可以找到 `SetCameraDevice()` 函数,可以在该函数中配置 `CameraDevice`。例如,以下代码可以配置一个摄像头为前置摄像头(ID为0):
```
CAMX_LOG_INFO(CamxLogGroupHAL, "Open camera device for ID %d", cameraId);
m_hCameraDevice = CameraDevice::Create(cameraId, "qcom.camera.front", this);
```
3. 打开 `CameraDevice`。在 `vendor/qcom/proprietary/chi-cdk/frameworks/camx/src/core/camxdeviceapi/camxhwcontext.cpp` 文件中,你可以找到 `Initialize()` 函数,在该函数中可以打开 `CameraDevice`。例如:
```
m_hCameraDevice->Open();
```
4. 创建 `CameraBufferManager`。在 `vendor/qcom/proprietary/chi-cdk/frameworks/camx/src/core/camxhwcontext.cpp` 文件中,你可以找到 `Initialize()` 函数,在该函数中创建 `CameraBufferManager`。例如:
```
m_pBufferManager = BufferManager::Create("qcom.camera.front", m_hCameraDevice);
```
5. 获取 `CameraBufferManager`。在 `vendor/qcom/proprietary/chi-cdk/frameworks/camx/src/core/camxhwcontext.cpp` 文件中,你可以找到 `GetBufferManager()` 函数,可以通过该函数获取到 `CameraBufferManager` 的指针。例如:
```
CameraBufferManager* pBufferManager = GetBufferManager("qcom.camera.front");
```
6. 获取 `Stream`。在 `vendor/qcom/proprietary/chi-cdk/frameworks/camx/src/core/camxhwcontext.cpp` 文件中,你可以找到 `GetStream()` 函数,可以通过该函数获取到 `Stream` 的指针。例如:
```
Stream* pStream = GetStream("qcom.camera.front", streamId);
```
7. 获取 `Buffer`。在 `vendor/qcom/proprietary/chi-cdk/frameworks/camx/src/core/camxhwcontext.cpp` 文件中,你可以找到 `GetBuffer()` 函数,可以通过该函数获取到 `Buffer` 的指针。例如:
```
Buffer* pBuffer = pBufferManager->GetBuffer(pStream->GetFormat(), pStream->GetBufferProperties());
```
8. 获取 `ImageFormat`。在 `vendor/qcom/proprietary/chi-cdk/frameworks/camx/src/core/camxhwcontext.cpp` 文件中,你可以找到 `GetImageFormat()` 函数,可以通过该函数获取到 `ImageFormat` 的指针。例如:
```
const ImageFormat* pImageFormat = ImageFormatUtils::GetImageFormatFromPixelFormat(pStream->GetFormat());
```
9. 获取 `ImageBuffer`。在 `vendor/qcom/proprietary/chi-cdk/frameworks/camx/src/core/camxhwcontext.cpp` 文件中,你可以找到 `GetImageBuffer()` 函数,可以通过该函数获取到 `ImageBuffer` 的指针。例如:
```
ImageBuffer* pImageBuffer = ImageBufferUtils::GetImageBuffer(pBuffer->GetBuffer(), pImageFormat, pBuffer->GetPlaneStride(), pBuffer->GetPlaneOffset());
```
10. 获取 `Plane`。在 `vendor/qcom/proprietary/chi-cdk/frameworks/camx/src/core/camxhwcontext.cpp` 文件中,你可以找到 `GetPlane()` 函数,可以通过该函数获取到 `Plane` 的指针。例如:
```
Plane* pPlane = pImageBuffer->GetPlane(pImageFormat->componentOrder[0]);
```
11. 获取 `Plane` 的数据。在 `vendor/qcom/proprietary/chi-cdk/frameworks/camx/src/core/camxhwcontext.cpp` 文件中,你可以找到 `GetBuffer()` 函数,可以通过该函数获取到 `Plane` 的数据。例如:
```
UINT8* pPlaneData = static_cast<UINT8*>(pPlane->GetBuffer());
```
通过以上步骤,你就可以获取到 yuv420 图像数据了。注意,以上代码只是提供了获取 yuv420 图像数据的一个示例,实际上在使用时还需要根据具体的需求进行适当的修改和调整。
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