Description

Benchmark is performed incorrectly while transport is enabled and the count of publisher is big (such as 200).

Expected Behavior

Benchmark is performed correctly while transport is enabled and the count of publisher is big (such as 200).

Actual Behavior

Benchmark is performed incorrectly

Get below error:

[benchmark_publishers-2] 1616403871.076306 [] benchmark_: create_thread: benchmark_publi: no free slot

And execution is terminated.

To Reproduce

1. benchmark config file --- 'test.yaml'

   rosbag2_performance_benchmarking:
   benchmark_node:
   ros__parameters:
     benchmark:
       summary_result_file:  "results.csv"
       db_root_folder:       "rosbag2_performance_test_results"
       repeat_each:          1     # How many times to run each configurations (to average results)
       no_transport:         False  # Whether to run storage-only or end-to-end (including transport) benchmark
       preserve_bags:        False # Whether to leave bag files after experiment (and between runs). Some configurations can take lots of space!
       parameters:                 # Each combination of parameters in this section will be benchmarked
         max_cache_size:      [100000000]
         max_bag_size:         [0]
         compression:            [""]
         compression_queue_size: [1]
         compression_threads:    [0]
         storage_config_file:    [""] 

2. producers config file --- '10k_300inst_100hz.yaml'

   rosbag2_performance_benchmarking_node:
   ros__parameters:
   publishers: # publisher_groups parameter needs to include all the subsequent groups
     publisher_groups: [ "10k_300inst" ] 
     wait_for_subscriptions: True
     10k_300inst:
       publishers_count:   300
       topic_root:         "benchmarking_10k_300inst"
       msg_size_bytes:     10000
       msg_count_each:     2000
       rate_hz:            100

3. Perform benchmark

   $ ros2 launch rosbag2_performance_benchmarking benchmark_launch.py benchmark:=/PATH/TO/test.yaml producers:=/PATH/TO/10k_300inst_100hz.ymal
    ...
    [ros2-1] [INFO] [1616403871.061948147] [rosbag2_transport]: Subscribed to topic '/rosbag2_performance_benchmarking_node/benchmarking_10k_300inst_165'
    [ros2-1] [INFO] [1616403871.067212137] [rosbag2_transport]: Subscribed to topic '/rosbag2_performance_benchmarking_node/benchmarking_10k_300inst_133'
    [ros2-1] [INFO] [1616403871.072642593] [rosbag2_transport]: Subscribed to topic '/rosbag2_performance_benchmarking_node/benchmarking_10k_300inst_198'
    [benchmark_publishers-2] 1616403871.076306 [] benchmark_: create_thread: benchmark_publi: no free slot
    [ros2-1] [INFO] [1616403871.078466443] [rosbag2_transport]: Subscribed to topic '/rosbag2_performance_benchmarking_node/benchmarking_10k_300inst_272'
    [ros2-1] [INFO] [1616403871.083757241] [rosbag2_transport]: Subscribed to topic '/rosbag2_performance_benchmarking_node/benchmarking_10k_300inst_145'
    [ros2-1] [INFO] [1616403871.089160870] [rosbag2_transport]: Subscribed to topic '/rosbag2_performance_benchmarking_node/benchmarking_10k_300inst_134'
    ...
    [ERROR] [benchmark_publishers-2]: process has died [pid 191720, exit code -6, cmd '/home/barry-xu/Work/ROS2/ros2_latest_ws/install/rosbag2_performance_benchmarking/lib/rosbag2_performance_benchmarking/benchmark_publishers --ros-args -r __node:=rosbag2_performance_benchmarking_node --params-file /home/barry-xu/Work/ROS2/ros2_latest_ws/src/ros2/rosbag2/rosbag2_performance/rosbag2_performance_benchmarking/config/producers/10k_100inst_100hz.ymal --params-file /tmp/launch_params_gfhe2ca9 --params-file /tmp/launch_params_22ve8q52 --params-file /tmp/launch_params_5rfwiuzu --params-file /tmp/launch_params_fwupe38p --params-file /tmp/launch_params_rnmr8tel --params-file /tmp/launch_params_o2tvsutj'].
    [INFO] [launch.user]: Writer error. Shutting down benchmark.
    ...

System (please complete the following information)

• OS: Ubuntu Bionic
• ROS 2 Distro: Rolling
• Version: rosbag2 b64cf74

Additional context

In my environment, If publishers_count is set to less than 119 (such as 118), the benchmark can work well.
From 119, the above error will occur.