You don't need to use controllers for this:

<style>
    .spinnerBg{
        width: 100%;
        height: 100%;
        position: absolute;
        background-color: #000;
        opacity: 0.2;
        z-index: 999999;
    }
    .spinner{
        width: 100%;
        height: 100%;
        position: absolute;
        background-image: url("/img/loading32.gif");
        background-size: 16px;
        background-repeat: no-repeat;
        background-attachment: fixed;
        background-position: center;
        z-index: 9999999;
        opacity: 1;
    }
</style>

<apex:actionStatus id="spinnerStatus">
    <apex:facet name="start">
        <div class="spinnerBg" />
        <div id="spinner" />
    </apex:facet>
</apex:actionStatus>

then you just reference the status id on your action as usual:

<apex:commandButton status="spinnerStatus"..

You don't need to use controllers for this:

<style>
    .spinnerBg{
        width: 100%;
        height: 100%;
        position: absolute;
        background-color: #000;
        opacity: 0.2;
        z-index: 999999;
    }
    .spinner{
        width: 100%;
        height: 100%;
        position: absolute;
        background-image: url("/img/loading32.gif");
        background-size: 16px;
        background-repeat: no-repeat;
        background-attachment: fixed;
        background-position: center;
        z-index: 9999999;
        opacity: 1;
    }
</style>

<apex:actionStatus id="spinnerStatus">
    <apex:facet name="start">
        <div class="spinnerBg" />
        <div class="spinner" />
    </apex:facet>
</apex:actionStatus>

then you just reference the status id on your action as usual:

<apex:commandButton status="spinnerStatus"..