MSBuild: How to obtain number of warnings raised?

using System;
using Microsoft.Build.Framework;
using Microsoft.Build.Utilities;
using System.Threading;

namespace Intrahealth.Build.WarningLogger
{
    public sealed class WarningLoggerCheck : Task
    {
        public override bool Execute()
        {
            Log.LogMessage("WarningLoggerCheck:" + mutexName + "...");
            result = false;
            Mutex m = null;
            try
            {
                m = Mutex.OpenExisting(mutexName);
            }
            catch (WaitHandleCannotBeOpenedException)
            {
                result = true;
            }
            catch (Exception)
            {
            }

            if (result)
                Log.LogMessage("WarningLoggerCheck PASSED");
            else
                Log.LogError("Build log contains warnings. Build is FAILED");

            return result;
        }

        private bool result = true;
        [Output]
        public bool Result
        {
            get { return result; }
        }

        private string mutexName = "WarningLoggerMutex";
        public string MutexName
        {
            get { return mutexName; }
            set { mutexName = value ?? "WarningLoggerMutex"; }
        }
    }

    public class WarningLogger : Logger
    {
        internal static int warningsCount = 0;
        private string mutexName = String.Empty;
        private Mutex mutex = null;

        public override void Initialize(IEventSource eventSource)
        {
            eventSource.WarningRaised += new BuildWarningEventHandler(eventSource_WarningRaised);
        }

        private void SetMutex()
        {
            if (mutexName == String.Empty)
            {
                mutexName = "WarningLoggerMutex";
                if (this.Parameters != null && this.Parameters != String.Empty)
                {
                    mutexName = this.Parameters;
                }
            }

            mutex = new Mutex(false, mutexName);
        }

        void eventSource_WarningRaised(object sender, BuildWarningEventArgs e)
        {
            if (e.Message != null && e.Message.Contains("MSB3146"))
                return;
            if (e.Code != null && e.Code.Equals("MSB3146"))
                return;

            if (warningsCount == 0)
                SetMutex();
            warningsCount++;
        }
    }
}

namespace SampleLogger
{
    using System;
    using Microsoft.Build.Utilities;
    using Microsoft.Build.Framework;
    using DM.SharedMemory;

    public class MySimpleLogger : Logger
    {
        private Segment s;
        private int warningCount;

        public override void Initialize(IEventSource eventSource)
        {
            eventSource.WarningRaised += new BuildWarningEventHandler(eventSource_WarningRaised);

            this.s = new Segment("MSBuildMetadata", SharedMemoryCreationFlag.Create, 65535);
            this.s.SetData(this.warningCount.ToString());
        }

        void eventSource_WarningRaised(object sender, BuildWarningEventArgs e)
        {
            this.warningCount++;
            this.s.SetData(this.warningCount.ToString());
        }

        public override void Shutdown()
        {
            this.s.Dispose();
            base.Shutdown();
        }
    }
}

namespace SampleTasks
{
    using System;
    using Microsoft.Build.Utilities;
    using Microsoft.Build.Framework;
    using DM.SharedMemory;

    public class BuildMetadata : Task
    {
        public int warningCount;

        [Output]
        public int WarningCount
        {
            get
            {
                Segment s = new Segment("MSBuildMetadata", SharedMemoryCreationFlag.Attach, 0);
                int warningCount = Int32.Parse(s.GetData() as string);
                return warningCount;
            }
        }

        public override bool Execute()
        {
            return true;
        }
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003" DefaultTargets="Main">
    <UsingTask TaskName="BuildMetadata" AssemblyFile="F:tempSampleLoggerbindebugSampleTasks.dll" />

    <Target Name="Main">
    	<Warning Text="Sample warning #1" />
    	<Warning Text="Sample warning #2" />

    	<BuildMetadata>
    		<Output
    			TaskParameter="WarningCount"
    			PropertyName="WarningCount" />
    	</BuildMetadata>

    	<Error Text="A total of $(WarningCount) warning(s) were raised." Condition="$(WarningCount) > 0" />
    </Target>
</Project>

c:WINDOWSMicrosoft.NETFrameworkv2.0.50727MSBuild test.xml /logger:SampleLogger.dll

Microsoft (R) Build Engine Version 2.0.50727.3053
[Microsoft .NET Framework, Version 2.0.50727.3053]
Copyright (C) Microsoft Corporation 2005. All rights reserved.

Build started 30-09-2008 13:04:39.
__________________________________________________
Project "F:tempSampleLoggerbindebugtest.xml" (default targets):

Target Main:
    F:tempSampleLoggerbindebugtest.xml : warning : Sample warning #1
    F:tempSampleLoggerbindebugtest.xml : warning : Sample warning #2
    F:tempSampleLoggerbindebugtest.xml(15,3): error : A total of 2 warning(s) were raised.
Done building target "Main" in project "test.xml" -- FAILED.

Done building project "test.xml" -- FAILED.

Build FAILED.
F:tempSampleLoggerbindebugtest.xml : warning : Sample warning #1
F:tempSampleLoggerbindebugtest.xml : warning : Sample warning #2
F:tempSampleLoggerbindebugtest.xml(15,3): error : A total of 2 warning(s) were raised.
    2 Warning(s)
    1 Error(s)

Time Elapsed 00:00:00.01

msbuild.exe %~nx1 /t:Rebuild /p:Configuration=Release >> %MrB-BUILDLOG%
findstr /r /c:"[1-9][0-9]* Error(s)" >> %MrB-BUILDLOG%
if not errorlevel 1 (
   echo ERROR: sending notification email for build errors in '%~nx1'. >> %MrB-BUILDLOG%
) else (
   findstr /r /c:"[1-9][0-9]* Warning(s)" >> %MrB-BUILDLOG%
   if not errorlevel 1 (
       echo ERROR: sending notification email for build warnings in '%~nx1'. >>