eclipse - windows environment variable not visible in eclipse ant target

Question

I have an ant task that set environment variables by calling the setenv.bat file:

<target name="setEnvWindows" if="isWindows" >
    <exec dir="C:\Oracle\Middleware\Oracle_OSB1\tools\configjar" executable="cmd">
        <arg value="/c"/>
        <arg value="setenv.bat"/>
    </exec>
    <echo message="SetEnvWindows"/>
</target>

Next I have another task that uses these variables:

<property environment="env"/>
<echo message="${env.OSB_HOME}"/>

However the variable set in the first target : OSB_HOME is not visible for the remaining targets. It becomes visible only after restarting eclipse.

How can I define the environment variable such that they are visible for subsequent targets without restarting eclipse?