[ros2] multi threaded executor with single node always makes the wall-timer hung. Some of the most common types of Executor are described below. Some ideas come to mind: Very quick and very dirty solution: Have the timer callback check the thread id and the time since it last complete update, return immediately if on wrong thread, otherwise do a regular update. You signed in with another tab or window. (, Version or commit hash: master or dashing. get() will block indefinitely waiting on the submitted task to complete. Clone with Git or checkout with SVN using the repositorys web address. . The return type of the call() method is used to type the Future returned by the ExecutorService. @liqinghua I'm closing this due to long time inactivity, we can reopen the issue if you provide an example of the problem. I created the backport PR in #869. We create a class that extends the java.lang.Thread class. The executor uses a single thread to execute all tasks. The main pieces are Executor interface, its sub-interface ExecutorService and the ThreadPoolExecutor class that implements both interfaces. ThreadPoolExecutor class. Think of it as fire and forget asynchronous task. I will also try from binaries, to double check. The talker will publish on the /chatter topic, and the . See the original article here. In the method above, we create a new Thread t1 and pass a Runnable to its constructor. As you can see the launch file we created (demo.launch.py) is a Python file. srv . Waiting indefinitely for a result is usually not ideal. privacy statement. 0' Execute the same task which we executed with CustomThreadPool and 2 worker threads. The latest version of mtexec_example is current. stack, registers, program code etc. mtexec_example has no issues reported. So it looks like we should probably put this in the patch release, EDIT: oops I see that you're already aware of this. Dealing with threads directly can be cumbersome, so Oracle simplified things by providing a layer of abstraction via its Executor API. Creates a single thread to execute all tasks. There are no pull requests. . To review, open the file in an editor that reveals hidden Unicode characters. Write your first ROS2 launch file. As well as allowing you to submit of a single Callable, the ExecutorService allows you to submit a Collection of Callable using the invokeAll method. mtexec_example has a low active ecosystem. Since thread 1 is executing the timer callback, the memory strategy does not add the timer handle to wait_set and thread 2 goes into rcl_wait with a wait_set that has no timer handle, and when thread 1 finishes executing the timer callback it is waiting for thread 2 to unlock; That was fixed and backported to Dashing #869 at about the same time that @liqinghua opened this issue. @liqinghua I'm closing this due to long time inactivity, we can reopen the issue if you provide an example of the problem. 1'. Note that submitting multiple Callable s will require the size of the thread pool to be tweaked if we want most or all of the submitted tasks can be executed in parallel. The snippet below creates a fixed thread pool ExecutorService with a pool size of 2. Program counter: a register which stores the address of the instruction currently being executed by thread. At the same time, the lock is released and the other thread waiting, thread 2, goes into 'wait_for_work'. However, if I call "ros2 param list" while the node is running, the call appears to hang forever. By clicking Sign up for GitHub, you agree to our terms of service and It had no major release in the last 12 months. # SOLUTION FOR THE ROS ONLINE INDUSTRIAL WORKSHOP, PROVIDED BY THECONSTRUCT, # issue, please contact with duckfrost@theconstructsim.com, This service has to move the robot using the odometry data from the origin, # We move first forward , checking the laser scan to not crash, # We move again checkng scan and distance, # We turn again to be ready to return to base, "Too CLOSE TO OBSTACLE, CANT MOVE front_laser==", # We have to check the abs, to be compatible with both turn right+, turn left negative, # We get the front Section, no only one value, # pause the program execution, waits for a request to kill the node (ctrl+c). A thread pool is a collection of pre-initialized threads. Opinions expressed by DZone contributors are their own. ros2 run examples_tf2_py async_waits_for . PS: There was a thread safety problem that made MultiThreadedExecutor hung when using timers. ros2 run examples_rclcpp_minimal_composition composition_composed scheduled_timers_ is solely used to keep track of the timers used. As always, feel free to post comments or questions below. Future has a few useful methods for checking the status of a task that's been submitted to the ExecutorService. async_waits_for_transforms.py. After all the tasks have completed, its important to shut down the ExecutorService gracefully so that resources used can be reclaimed. The code snippet above submits 8 Callable to the ExecutorService and retrieves a List containing 8 Future. I'll use this ExecutorService in the sections that follow. (, Fix TSA warnings when building with clang thread analysis. There will always be a delay of 10 seconds between the completion time of the first task and the start time of the second task. By voting up you can indicate which examples are most useful and appropriate. It also shares the best practices, algorithms & solutions and frequently asked interview questions. I'm testing rclcpp::executors::MultiThreadedExecutor. @ivanpauno if they were building release-latest from source then it should be identical to the current dashing release and there wouldn't be any PRs that are not already part of the binaries. Learn more about bidirectional Unicode characters. ROS-Industrial Conference 2020 Advanced Execution Management with ROS 2 Dr. Ralph Lange Bosch Corporate Research a program that is under execution. When thread 1 goes into wait_for_work and adds the timer handle to wait_set and is woken by the timer, it starts executing the timer. 1' As you might expect, instead of returning a single Future, a Collection of Futures is returned. I couldn't reproduce the problem in master. This interrupt in Executor::execute_any_executable: exist to avoid a thread, in the case the executor is multithreaded and the threads are not mutually exclusive, waiting indefinitely in rcl_wait in wait.c in rcl. Process. Creates a thread pool that maintains enough threads to support the given parallelism level. The text was updated successfully, but these errors were encountered: Context: [ros2] multi threaded executor with single node always makes the wall-timer hung. Each part of such program is called a thread. Now I tried with newer release of ROS2 Dashing with 'apt upgrade' command and same problem occurs. Synchronizing Threads. The source code that accompanies this post is available on GitHub so why not pull the code and have a play around. Thread's register set: registers assigned . ExecutorService executorService = Executors.newFixedThreadPool(2); In the following sections, we'll look at how ExecutorService can be used to create and manage asynchronous tasks. Did you use the binaries of the first release, or Dashing release patch 1 binaries? Creating a thread in Java is an expensive operation. The basic code is structured as follows: The code compiles and appears to set up the correct publishers and subscribers (which are all abstracted into the "Health" object). 1. It must be run with a MultiThreadedExecutor so the TransformListener can execute callbacks for it's subscriptions. Have a question about this project? It is. Generally, the collection size is fixed, but it is not mandatory. Over 2 million developers have joined DZone. On Master, will block until next_exec_timeout_. ScheduledThreadPoolExecutor provides 4 methods that offer different capabilities to execute the tasks repeatedly. @peterpena I don't see the connection between your comment and @liqinghua bug report. https://github.com/ros2/examples/blob/master/rclcpp/minimal_composition/src/composed.cpp. Fixed thread pools or cached thread pools are good when executing one unique task only once. @Mygao or @ivanpauno have either of you tried reproducing this issue with the Dashing binary archive? Execute Tasks with Thread Pool Executor, Java ThreadPoolExecutor with BlockingQueue, Java Inter-thread Communication PipedReader and PipedWriter, Difference between Runnable vs Thread in Java. Well occasionally send you account related emails. A process can have multiple threads, all. Program output. When a Callable is submitted to the ExecutorService, we receive a Future with the return type of the call() method. It has a neutral sentiment in the developer community. Yet if you would like to create it for your learning, the given below is such thread pool implementation in Java. to your account, This can be reproduced by modifying ros2 composition examples source code: SingleThreadedExecutor->MultiThreadedExecutor (https://github.com/ros2/examples/blob/master/rclcpp/minimal_composition/src/composed.cpp), Message output goes on and on with count increasing without hanging, Message output hangs. 4.2. So, threads are light-weight processes within a process. shutDownNow() returns a list of tasks that were queued for execution when the shutdown was initiated. I tested the multithreaded executor with one timer to verify. An Executor allows you to process tasks asynchronously without having to deal with threads directly. Creates a thread pool that can schedule commands to run after a given delay or to execute periodically. Let's look at a simple example below. Both examples create a Callable and pass it to the execute method. It is responsible for executing, instantiating, and running the tasks with necessary threads. Have a question about this project? If I change my executor to a SingleThreadedExecutor or use rclcpp::spin . more than the program code as it includes the program counter, process. here is the code. This package has examples for using the tf2_ros API from python. effectively, having thread 1 and 2 waiting indefinitely. Here are the examples of the python api rclpy.executors.MultiThreadedExecutor taken from open source projects. Trying with release-latest from source to confirm @Mygao's findings seems prudent as well to avoid chasing shadows. A Future is an object that represents the pending response from an asynchronous task. Here we'll simply start the talker/listener example from the official ROS2 demos. The acquire (blocking) method of the new lock object is used to force threads to run synchronously. Also, note that incorrect pooling or queue handling can result in deadlocks or resource thrashing. Think of it as a handle that can be used to check the status of the task or retrieve its result when the task completes. That was fixed and backported to Dashing #869 at about the same time that @liqinghua opened this issue. I will try to figure out what PR solved the problem, and add it to the patch release 2 list (if it's not already there). I thought those two callback funcs would be executed at the same time, but in fact, one of them would not be executed until 10 seconds after the other started. 2. This class overrides the run () method available in . Sorry for bothering you XD. The Runnable will be executed as soon as a thread is available from the ExecutorService thread pool. And if you start creating a new thread instance everytime to accomplish a task, application performance will degrade. A watcher keeps watching the queue (usually BlockingQueue) for any new tasks. ThreadPoolExecutor separates the task creation and its execution. Creates a thread pool that creates new threads as needed, but will reuse previously constructed threads when they are available. It can bring down the system if the number of threads exceeds what the system can handle. Use it when you have only one task to execute. However, the cached thread pool has the disadvantage of constant lying threads for new tasks, so if you send too many tasks to this executor, you can overload the system. privacy statement. Note that if the code inside run() throws a checked Exception, it must be caught and handled inside the method. Well occasionally send you account related emails. We can create the following 5 types of thread pool executors with pre-built methods in java.util.concurrent.Executors interface. I have not clue about what PR solved the problem. This is likely a duplicate of that (already fixed) error. Join the DZone community and get the full member experience. No, I only tried with debians. You signed in with another tab or window. Instantly share code, notes, and snippets. You can certainly avoid these problems with the Executor framework which is well tested by the Java community. updated Sep 22 '20. Thread Identifier: Unique id (TID) is assigned to every new thread Stack pointer: Points to thread's stack in the process. Like execute(), the submit() method also takes a Runnable but differs from execute()because it returns a Future. Two code snippets below show how a Callable can be created via an anonymous inner class and a lambda expression. I used the first release binaries of ROS2 as environment. Already on GitHub? For example, There are two methods available, shutDown() and shutDownNow(). The return type of the call () method is used to type the Future returned by the ExecutorService. To indicate to the executor that you want to finish it, you can use the. Realize which control flow branches operate on a shared data and therefore need to be synchronized, and which can go in parallel. I tried with ROS2 built from source (latest-release) and the example above (running with MultiThreadedExecutor) worked fine. A new lock is created by calling the Lock () method, which returns the new lock. Since Java 5, the Java concurrency API provides a mechanism Executor framework. Sign in As soon as tasks come, threads start picking up tasks and executing them again. The answer is when we develop a simple, concurrent application in Java, we create some Runnable objects and then create the corresponding Thread objects to execute them. To scale your Boost.Asio application on multiple threads you should do the following: Create one io_context object. Python examples for tf2. The submitmethod is overloaded to take a Callable as well as a Runnable. Notice that it executes two tasks at a time. The first release was installed with debian package installation (https://index.ros.org/doc/ros2/Installation/Dashing/Linux-Install-Debians/). f Thread vs. We'll start by creating threads directly and then move on to explore the ExeutorService and how it can be used to simplify things. @Mygao could you check if this is still happening after the last patch release? I'm taking it off now but the fix was released. Like a Runnable, a Callable represents a task that is executed on another thread. I just checked with master (from source), and it was working. You can use XML instead if you want to, but with Python it will be easier to add logic. Sign in Thanks for the comment @eric1221bday, I didn't realize that #836 was a fix for this. You can run the code given to see this in effect: If the interrupt guard condition did not exist, your solution will still not work because the thread will be waiting in rcl_wait indefinitely, and even if the thread can erase the timer from the scheduled_timers_ set while the other thread is asleep, the thread in rcl_wait will not wake up. To ensure the ExecutorService is shut down in all cases and to avoid potential resource leaks, it's important that shutDown() or shutDownNow() is called inside afinallyblock. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Thanks for checking it! This is likely a . A process is an active program i.e. When you send a task to the executor, it tries to use a pooled thread to execute this task, to avoid the continuous spawning of threads. Please, share details of how you built it. When all tasks are completed, the threads remain active and wait for more tasks in the thread pool. And it would help if you were not creating your own custom thread pool without executor. This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. It has 6 star(s) with 1 fork(s). By voting up you can indicate which examples are most useful and appropriate. example_ros2_multithreading.py This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. on ROS Answers. Stack contains the local variables under thread's scope. Unlike the first Thread example, which used an anonymous inner class, the example above creates a Runnable using a lambda expression. I tested on 2 systems: Desktop and Laptop with both Ubuntu 18.04.2 LTS. This fix was released in Dashing Patch 4 but the issue wasn't removed from the board so it got bumped forward. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); document.getElementById( "ak_js_2" ).setAttribute( "value", ( new Date() ).getTime() ); HowToDoInJava provides tutorials and how-to guides on Java and related technologies. Server class: The steps involved on the server side are similar to the article Socket Programming in Java with a slight change to create the thread object after obtaining the streams and port number. 0' I confirm that it isn't working when installing from debians. In this post, we looked at theExecutorService and how it can be used to simplify the creation and management of asynchronous tasks. Futures use generics to allow you to specify the return type of the task. In the example above, we'd need a thread pool with 8 threads to run all tasks in parallel. If additional tasks are submitted when all threads are active, they will wait in the queue until a thread is available. I will try to figure out what PR solved the problem, and add it to the patch release 2 list (if it's not already there). [INFO] [publisher_node]: Publisher: 'Hello, world! With the interrupt_guard_condition triggered, any thread waiting in rcl_wait will wake up and look for work to be executed. This is represented as Future in the example below. Only one timer + MultiThreadedExecutor will block executor. shutDown() triggers a shutdown of the ExecutorService, allowing currently processing tasks to finish but rejecting newly submitted tasks. I haven't tried with the binary archive. MultiThreadedExecutor with wall timer hung. The cached thread pool creates new threads if needed to execute the new tasks and reuses the existing ones if they have finished executing the task they were running, which are now available. Multithreading is a Java feature that allows concurrent execution of two or more parts of a program for maximum utilization of CPU. Run io_context::run member function of that object on multiple threads. I wrote two Subscription in a node, and at each callback function sleep for 10 seconds. It does what is expected. It shows how to broadcast and receive transforms between frames. The Callable interface has a single abstract method public T call() throws Exception and like Runable can be implemented with an anonymous inner class or lambda. You signed in with another tab or window. Comparing Lean, Agile, and Continuous Delivery, Architectural Patterns for Microservices With Kubernetes, Java Multi-Threading With the ExecutorService. I didn't try with release-latest. Two code snippets below show how a Callable can be created via an anonymous inner class and a . The Executors factory class is used to create an instance of an Executor, either an ExecutorService or anScheduledExecutorService. To review, open the file in an editor that reveals hidden Unicode characters. It goes beyond that and improves performance using a pool of threads. The list of Future returned is in the same order as the Callables were submitted. One way of retrieving the result from a Future is by calling its get() method. https://index.ros.org/doc/ros2/Installation/Dashing/Linux-Install-Debians/, https://github.com/ros2/ros2/releases/tag/release-dashing-20190614, Don't overwrite cur_ns pointer if reallocation fails (, Refactor parser.c for better testability (. When you need to execute a task, repeatedly N times, either N fixed number of times or infinitely after a fixed delay, you should use ScheduledThreadPoolExecutor. Before the Executor API came along, developers were responsible for instantiating and managing threads directly. Did you only download this repo (examples) and build it in a overlay workspace of the binary installation? Lets create a task that will take 2 seconds to complete, every time. A Future is returned representing the pending result of each submitted task. If there are more tasks than threads, then tasks need to wait in a queue like structure (FIFO First in first out). The execute method takes a Runnable and is useful when you want to run a task and are not concerned about checking its status or obtaining a result. PS: There was a thread safety problem that made MultiThreadedExecutor hung when using timers. We'd rather have more control over how we retrieve the result and take some action if a task doesn't complete within a certain amount of time. The text was updated successfully, but these errors were encountered: Could you provide an example of the problem? I tried from source using release-latest, and I couldn't reproduce the bug. But still, rather than perfecting the above code, focus on learning Java executor framework. Published at DZone with permission of Brian Hannaway, DZone MVB. With ThreadPoolExecutor, we only have to implement the Runnable objects and send them to the executor. Establishing the Connection: Server socket object is initialized and inside a while loop a socket . Thread state: can be running, ready, waiting, start or done. Thanks for checking it! When any thread completes its execution, it can pickup a new task from the queue and execute it. Same ROS2 Dashing setups. A Callable differs from a Runable because it returns a value and can throw a checked Exception. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. I cloned the examples repo and built it with colcon. @ivanpauno I actually just ran into this issue and I'm using the latest debian of dashing as far as I can tell, OK so I just found this #836 which is the PR that fixed this issue. to your account, On Dashing, will block executor, and cannot be recover Already on GitHub? The Callable is executed as soon as a thread is available. If the task doesn't complete or takes a long time to complete, the main application thread will remain blocked. I tried with ROS2 built from source (latest-release) and the example above(running with MultiThreadedExecutor) worked fine. [INFO] [publisher_node]: Publisher: 'Hello, world! 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