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Bond is a tool which connects two units of code together with a heartbeat such that if one side goes down the other also goes down. See bond on the wiki for more information.
Nodelets use bond to connect the nodelet spawner to the dynamically loaded instance in the manager. By doing this if the manager dies, all the spawner instances come down, and if desired can be relaunched. And if a spawner process is killed (even with a -9, or a segfault) the nodelet will be unloaded when the bond is broken.
The nodelet spawner processes are separate processes which is why the connections are TCPROS.
| | 2 | replying to followup |
Bond is a tool which connects two units of code together with a heartbeat such that if one side goes down the other also goes down. See bond on the wiki for more information.
Nodelets use bond to connect the nodelet spawner to the dynamically loaded instance in the manager. By doing this if the manager dies, all the spawner instances come down, and if desired can be relaunched. And if a spawner process is killed (even with a -9, or a segfault) the nodelet will be unloaded when the bond is broken.
The nodelet spawner processes are separate processes which is why the connections are TCPROS.
Re: Followup on the overhead of bond.
The purpose of nodelets was to allow zero copy transports of high volume data (either fast or big or both). Passing images or PointClouds through the network interface with 1-2 memcopies is prohibitively expensive even on fast hardware. Bond only uses heartbeat at the default rate of 1Hz. Keeping a couple sockets open with a 1 Hz update is a low enough overhead that I doubt that the difference is measurable. The first implementation of nodelets did not have bond and it was added to provide more control, the ability to introspect, and to allow error recovery in the case of failures.
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