@Override
    public void sendHeaders(Metadata metadata) {
        if (ctx.eventLoop().inEventLoop()) {
            doSendHeaders(metadata);
        } else {
            ctx.eventLoop().execute(() -> doSendHeaders(metadata));
        }
    }
Cancels a call when the call was closed by a client, not by server.
grpc/src/main/java/com/linecorp/armeria/internal/server/grpc/AbstractServerCall.java