Here is what I found in an open source project, and it works for me:
<extension
point="org.eclipse.ui.menus">
<menuContribution
locationURI="menu:org.eclipse.ui.main.menu?after=additions">
<menu
id="menu1"
label="Menu 1">
<visibleWhen checkEnabled="false">
<with variable="activeWorkbenchWindow.activePerspective">
<equals value="myperspective"/>
</with>
</visibleWhen>
<dynamic class="MenuPopulationClass"
id="MenuPopulation"/>
</menu>
</menuContribution>
</extension>
source
share