/guava/android/guava/src/com/google/common/util/concurrent/AbstractFuture.java
if ( old != update) {   future.waiters = update; }
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} } @Override Listener gasListeners(AbstractFuture<?> future, Listener update) { synchronized (future) { Listener old = future.listeners; <extra_id_0> future.listeners = update; } return old; } } @Override