Function js::jsapi::JS_CallOnce

pub unsafe extern "C" fn JS_CallOnce(
    once: *mut JSCallOnceType, 
    func: JSInitCallback
) -> bool

The first call to JS_CallOnce by any thread in a process will call 'func'. Later calls to JS_CallOnce with the same JSCallOnceType object will be suppressed.

Equivalently: each distinct JSCallOnceType object will allow one JS_CallOnce to invoke its JSInitCallback.