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Thread safety and rospy Timer

asked 2015-11-11 15:54:23 -0600

etappan
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I'm a little confused by how rospy.Timer works with regards to thread-safety. My understanding of callbacks in rospy in general is they're essentially handled sequentially during calls to Sleep and Spin, meaning they're implicitly threadsafe and I can modify the same data from multiple callbacks within a node without locks or other safeguards.

Timers represent a totally separate thread of execution, albeit one that still runs off of a Rate.sleep() loop. Is it safe to work with data that a Timer interacts with, or do I need to start adding locks in any nodes that have both Subscriptions and Timers?

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answered 2017-08-10 17:44:05 -0600

Ed Venator

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My understanding of callbacks in rospy in general is they're essentially handled sequentially during calls to Sleep and Spin, meaning they're implicitly threadsafe and I can modify the same data from multiple callbacks within a node without locks or other safeguards.

Unfortunately, no. Unlike roscpp, rospy creates a new thread for every Subscriber and Timer. In fact, rospy.spin() is just an infinite loop of half-second waits. As such, callbacks in rospy are not threadsafe. You should use locks in any rospy node where multiple callbacks of any kind might interact.

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Asked: 2015-11-11 15:54:23 -0600

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Last updated: Aug 10 '17

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