Attention: Answers.ros.org is deprecated as of August the 11th, 2023. Please visit robotics.stackexchange.com to ask a new question. This site will remain online in read-only mode during the transition and into the foreseeable future. Selected questions and answers have been migrated, and redirects have been put in place to direct users to the corresponding questions on Robotics Stack Exchange. Additional details are available here.

Does a callback complete before being called again?

asked 2015-12-08 06:26:49 -0500

Jay4Ros
35 ●5 ●7 ●12

Hi!

Suppose I have a subscriber with a callback C. C manipulates a number of global variables and then calls a second method M, that builds a message from those global variables and publishes the message.

I am now wondering: Is is possible that C and M interfere, i.e., that M uses global variables that have been modified by a different call to C? Or, stated differently, is it possible to call C before the previous call to C has returned?

I was not able to figure out if ros::getGlobalCallbackQueue()->callAvailable blocks till completion. If interference in this situation can happen, how does one usually deal with it?

Thank you!

edit retag flag offensive close merge delete

add a comment

1 Answer

Sort by » oldest newest most voted

answered 2015-12-08 06:58:24 -0500

gvdhoorn
86574 ●283 ●1432 ●1054 http://cor.tudelft.nl/

Callback execution is single-threaded, unless you setup things differently, by using a Multithreaded or Asynchronous spinner fi. See also roscpp/Overview/Callbacks and Spinning.

Btw, this has been asked (and answered) many times before. A quick search immediately turned up ROS callbacks, threads and spinning fi.

edit flag offensive delete link

Comments

Hey! I saw the question you linked before, but I must have missed "Single thread spinner: the default one, takes the messages contained in a callback queue and process the callbacks one by one while blocking the execution of the thread that called it." Thanks!

Jay4Ros ( 2015-12-08 07:07:10 -0500 )edit

Oh, I guess if a program is single threaded a callback can only be called one by one.... My bad!

Jay4Ros ( 2015-12-08 07:07:54 -0500 )edit

add a comment

Question Tools

1 follower

Stats

Asked: 2015-12-08 06:26:49 -0500

Seen: 1,752 times

Last updated: Dec 08 '15

Does a callback complete before being called again? edit

1 Answer

Comments

Question Tools

Stats

Related questions

Does a callback complete before being called again?