Bug report

Required Info:

• Operating System:
  • Ubuntu 18.04 LTS
• Installation type:
  • Binaries
• Version or commit hash:
  • Eloquent
• DDS implementation:
  • CycloneDDS
• Client library (if applicable):
  • rclcpp

Steps to reproduce issue

I will work on creating a portable minimal environment that can reproduce this issue, since my application is somewhat complex.

I have three nodes;

• Node A contains an action server for a custom action type (for example, MyAction) advertised on /my_action. This node uses a multi-threaded executor. The action server is assigned to a MutuallyExclusive callback group.
• Node B contains a client for the same MyAction action on /my_action. This node uses the default single-threaded executor.
• Node C also contains a MyAction client also pointed at /my_action. This node uses a multi-threaded executor. The action client is assigned to a Reentrant callback group.

Node B and Node C send action goals using async_send_goal. The nodes do not send goals concurrently.

Expected behavior

Normal client/server action behavior where each client sends a goal and receives a result from the server.

Actual behavior

Node C throws an exception and crashes after either Node B or Node C call async_send_goal:

terminate called after throwing an instance of `std::runtime_error`
  what(): Executing action client but nothing is ready

Sometimes the error includes terminate called recursively.

Additional information

There is some discussion of this exception in #594, though a conclusive answer wasn't reached (since I expect that more info about the implementation of the nodes is needed).