rcl_init called multiple times about rcl HOT 9 CLOSED

I'm quite certain that Gazebo does not load its plugins in parallel. I don't think that multithreaded access will be an issue there.

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From @BrannonKing on August 31, 2017 20:16

I suppose catching the exception in Gazebo is fine. I just wanted the logging removed (since it already throws an exception). BTW, this should move to rcl; it's logged in the wrong spot.

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@BrannonKing Can you please provide more information about how the API is being used and if possible how to reproduce the problem.

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I start up multiple Gazebo plugins. Each one has to call rclcpp::init because you don't know which plugin will start first. They all run in the same process, but init prints a message and throws an error about having been called already for every subsequent plugin. I can eat the exception but can't hide the message.

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You could just ignore the ones that fail to init for this particular reason (assuming that some other code managed to init first). However we should make sure rclcpp::init is thread-safe. rcl_init is not:

https://github.com/ros2/rcl/blob/master/rcl/include/rcl/rcl.h#L108

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I think that is what he is trying to do but the calls which throw also print an error message which he currently can't avoid. I will come up with a PR to fix this...

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The rcl error just needs to be cleared here: https://github.com/ros2/rclcpp/blob/master/rclcpp/src/rclcpp/utilities.cpp#L168

@dirk-thomas I'll let you do that since you already said you were working on it.

But we should also make sure it is thread-safe, because right now it is not I think.

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The rcl error just needs to be cleared here: https://github.com/ros2/rclcpp/blob/master/rclcpp/src/rclcpp/utilities.cpp#L168

Indeed: ros2/rclcpp#366

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I'll just reiterate that rclcpp::init() is not thread-safe. So we either could use a pr to make it so, or @BrannonKing you should take care to protect it in your code.

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