EventSource.WriteEventCore(Int32, Int32, EventSource+EventData*) Method

Definition

Namespace:

System.Diagnostics.Tracing

Assembly:

System.Diagnostics.Tracing.dll

Source:

EventSource.cs

Important

This API is not CLS-compliant.

Creates a new WriteEvent overload by using the provided event identifier and event data.

protected:
 void WriteEventCore(int eventId, int eventDataCount, System::Diagnostics::Tracing::EventSource::EventData* data);

[System.CLSCompliant(false)]
protected void WriteEventCore (int eventId, int eventDataCount, System.Diagnostics.Tracing.EventSource.EventData* data);

[<System.CLSCompliant(false)>]
member this.WriteEventCore : int * int * nativeptr<System.Diagnostics.Tracing.EventSource.EventData> -> unit

Parameters

eventId

Int32

The event identifier.

eventDataCount

Int32

The number of event data items.

data

EventSource.EventData

The structure that contains the event data.

Attributes

CLSCompliantAttribute

Remarks

eventid should be greater than 0 or less than 65535 or errors can occur in the operation. If errors do occur, you can get more information about the source of the error by checking the output stream of the debugger, if you have a debugger attached to the process firing events. You can also look for errors reported in the ETW event stream, if you have an ETW listener on the event source where the error occurs.

This protected method enables users to define new WriteEvent overloads that are faster than the provided overloads. Creating a new overload involves unsafe code. The basic procedure is to stack-allocate an array of event data descriptors that matches the number of payload items. For each payload item, set the correct size and value in the event data array.Call WriteEventCore with the initialized array.

The following example shows how to add a WriteEvent overload that accepts four arguments. An example would be if you have a logging event that logs a string and 3 integers.

[Event(1)]
public void LogTime(string tag, int hour, int minute, int second)
{
    WriteEvent(1, tag, hour, minute, second);
}

You could do this without calling WriteEventCore, but it would be slower than it needs to be. That is because it uses arrays and reflection to figure out what to do. If you log these at a high rate (> 1000 / sec), it can be worth making a fast helper, as shown in the following example. The method shadows the existing WriteEvent. Thus the original caller code (LogTime) does not actually change, but the C# compiler will use the more specialized version which will be faster.

To compile unsafe code, you must specify the /unsafe (C# Compiler Options) compiler option.

class AnotherEventSource : EventSource {

    [NonEvent]
    public unsafe void WriteEvent(int eventId, string arg1, int arg2, int arg3, int arg4)
    {

        fixed (char* arg1Ptr = arg1)
        {
            EventData* dataDesc = stackalloc EventData[4];

            dataDesc[0].DataPointer = (IntPtr)arg1Ptr;
            dataDesc[0].Size = (arg1.Length + 1) * 2; // Size in bytes, including a null terminator.
            dataDesc[1].DataPointer = (IntPtr)(&arg2);
            dataDesc[1].Size = 4;
            dataDesc[2].DataPointer = (IntPtr)(&arg3);
            dataDesc[2].Size = 4;
            dataDesc[3].DataPointer = (IntPtr)(&arg4);
            dataDesc[3].Size = 4;

            WriteEventCore(eventId, 4, dataDesc);
        }
    }
}

These are the expected sizes and data encodings for standard serializable types:

// bool arg
int temp = arg ? 1 : 0;
desc.DataPointer = (IntPtr)(&temp);
desc.Size = 4;

// byte arg
desc.DataPointer = (IntPtr)(&arg);
desc.Size = 1;

// sbyte arg
desc.DataPointer = (IntPtr)(&arg);
desc.Size = 1;

// char arg
desc.DataPointer = (IntPtr)(&arg);
desc.Size = 2;

// short arg
desc.DataPointer = (IntPtr)(&arg);
desc.Size = 2;

// ushort arg
desc.DataPointer = (IntPtr)(&arg);
desc.Size = 2;

// int arg
desc.DataPointer = (IntPtr)(&arg);
desc.Size = 4;

// uint arg
desc.DataPointer = (IntPtr)(&arg);
desc.Size = 4;

// long arg
desc.DataPointer = (IntPtr)(&arg);
desc.Size = 8;

// ulong arg
desc.DataPointer = (IntPtr)(&arg);
desc.Size = 8;

// float arg
desc.DataPointer = (IntPtr)(&arg);
desc.Size = 4;

// double arg
desc.DataPointer = (IntPtr)(&arg);
desc.Size = 8;

// decimal arg
desc.DataPointer = (IntPtr)(&arg);
desc.Size = 16;

// Guid arg
desc.DataPointer = (IntPtr)(&arg);
desc.Size = 16;

// IntPtr arg
desc.DataPointer = (IntPtr)(&arg);
desc.Size = IntPtr.Size;

// UIntPtr arg
desc.DataPointer = (IntPtr)(&arg);
desc.Size = UIntPtr.Size;

// DateTime arg
long fileTime = arg.ToUniversalTime() > new DateTime(1601, 1, 1) ? arg.ToFileTimeUtc() : 0;
desc.DataPointer = (IntPtr)(&fileTime);
desc.Size = 8;

// string arg
fixed(char* ptr = arg)
{
    desc.DataPointer = (IntPtr)ptr;
    // strings use 2 byte per char UTF16 encoding and a null terminator at the end
    // only strings without embedded null characters are supported
    desc.Size = (arg.Length + 1) * 2;
}

// byte[] arg
// This one is encoded using two adjacent EventData elements.
fixed(byte* ptr = arg)
{
    int length = arg.Length;
    desc[i].DataPointer = (IntPtr)(&length);
    desc[i].Size = 4;
    desc[i + 1].DataPointer = (IntPtr)ptr;
    desc[i + 1].Size = arg.Length;
}

// enums should be converted to their underlying type and then serialized
// as byte, short, or int.