Many to many service communication

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Hi all,

as far as I understood a service can be used by different clients as long as in the source code the ServiceServer and the ServiceClient are declared with the same service name (see code below, each line belongs to a different node).

ros::ServiceServer service = n.advertiseService("add_two_ints", add);
ros::ServiceClient client1 = n.serviceClient<beginner_tutorials::AddTwoInts>("add_two_ints");
ros::ServiceClient client2 = n.serviceClient<beginner_tutorials::AddTwoInts>("add_two_ints");

How are multiple concurrent requests managed? As far as I understood they are processed in a synchronous way according to a FIFO policy, right?

I'm also wondering if it is possible to have a many-to-many connection (multiple servers)

ros::ServiceServer service = n.advertiseService("add_two_ints", add);
ros::ServiceServer service2 = n.advertiseService("add_two_ints", add);
    ros::ServiceClient client1 = n.serviceClient<beginner_tutorials::AddTwoInts>("add_two_ints");
    ros::ServiceClient client2 = n.serviceClient<beginner_tutorials::AddTwoInts>("add_two_ints");

How are requests managed in this case?

Finally, are these concepts valid also for actions?