Topic publishing always

[jpcloud1577]

System information

• **OS Platform and Distribution Linux Ubuntu 18.04
• **Apollo installed from source
• **Apollo version 5.0

I have a module that writes a message to a topic based on input from another topic. I however see that my topic is always broadcasted even when input topic is not received which I dont want. I have used these implementations for reader and writer

`control_cmd_reader_ = node_->CreateReader(
FLAGS_control_command_topic,
[this](const std::shared_ptr& cmd) {
ADEBUG << "Received control data: run control callback.";
std::lock_guardstd::mutex lock(mutex_);
control_cmd_.CopyFrom(*cmd);
});

mymodule_command_writer_ =
node_->CreateWriter(FLAGS_mymod_command_topic);`

I am later on populating an object of type InteliContcommand with values received from control_cmd_reader and writing it as such

mymodule_command_writer_->Write( std::make_shared<InteliContcommand>(inteli_cnt_cmd));

Please let me know how I can configure my reader/writer to write only when there is data coming in from the reader.

[daohu527]

There are two methods.

use trigger module

class YourComponent final : public cyber::Component<ControlCommand>

then send message in proc, when you receive ControlCommand then cyber will automatically call proc.

use reader callback

in your reader callback, you can add a function, and send message in the function.

control_cmd_reader_ = node_->CreateReader(
  FLAGS_control_command_topic,
  [this](const std::shared_ptr& cmd) {
    ADEBUG << "Received control data: run control callback.";
    std::lock_guardstd::mutex lock(mutex_);
    control_cmd_.CopyFrom(*cmd);
    callback(control_cmd_)  // which you can do something
  });

[jpcloud1577]

I am in fact using the trigger module like you suggested. proc has the writer publishing the message, but because of this, everytime cyber calls proc, I am publishing message, albeit with zero values.
I am not very clear on using reader callback. Can you please explain more on callback you have mentioned in the code? You man I should call proc? I guess not, but I am not clear.

[daohu527]

I am in fact using the trigger module like you suggested. proc has the writer publishing the message, but because of this, everytime cyber calls proc, I am publishing message, albeit with zero values.

1. Use trigger module is fine. It will call proc when receive ControlCommand. It will not when there's no message arrive. So, I don't know what you mean by zero values, if you send ControlCommand it will call proc, if you not it will not call.

2. It does not care whether the value in the message you send is empty, and sending an empty controlcommand itself is abnormal

3. You do need to check the module is

class YourComponent final : public cyber::Component<ControlCommand>

but not

class ControlComponent final : public apollo::cyber::TimerComponent

[daohu527]

Closed due to inactivity. If the problem persists, pls feel free to reopen it or create a new one and refer to it.