Many to many service communication

asked 2013-06-03 00:21:46 -0600

maverik
3 ●1 ●2 ●4

updated 2013-06-03 05:08:41 -0600

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?

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Thanks! What you said makes sense from a theoretical point of view! However I tried to create two nodes that advertise the same service and when I lunched them I didn't see any error. However the services were always provided by the same node, probably the second I lunched.

maverik ( 2013-06-03 23:45:48 -0600 )edit

For topics, the publisher advertises. The many-to-one typically means many subscribers.

joq ( 2013-06-04 16:42:56 -0600 )edit

"I'm not certain, but I believe service requests are handled serially by design." - this is true on the client side, but the service provider executes requests concurrently on separate threads... at least in rospy.

FrankAllen ( 2015-07-11 06:24:41 -0600 )edit

roscpp handles service requests serially, unless you explicitly create a multithreaded async spinner to handle service callbacks.

ahendrix ( 2015-07-11 18:26:10 -0600 )edit

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