Debugging

Debugging is an essential part of software development. Dragon provides several tools and techniques to help you trace, identify and fix issues in your code. Below are some common debugging methods:

Using the Dragon Logger

Dragon includes a built-in logging system that allows you to log messages at various levels (e.g., DEBUG, INFO, WARNING, ERROR, CRITICAL). You can use the logger to track the flow of your application and identify where issues may be occurring. The Dragon logger is available both from Python and from C/C++. Depending on the -l LOGLEVEL passed to the dragon launcher, your application’s logs will be collected and written to stdout and to the dragon_*.log file.

Python Dragon Logger

To use the logger in Python, you can import it and log messages as follows:

import logging

from dragon.dlogging.util import setup_BE_logging

def main():
    _level, _fname = setup_BE_logging(service="My Application")
    log = logging.getLogger("user_app").getChild("multinode")

    log.warning("Hello from Python!")

if __name__ == "__main__":
    main()

To run the above example, save it to a file called py_logger.py and run it with the Dragon launcher:

dragon -l DEBUG py_logger.py

Depending upon the logging configuration and the log level of the message, the logged values will be printed to one or more of the following: stdout, dragon_*.log file, and/or LA_BE_*.log files in the current directory. The log message will be similar to the following:

2026-05-04 19:19:16,970 WARNING  user_app.multinode Logging Monitor (281471656268064) :: Hello from Python!

To help locate the relevant messages, you can search for the name passed to getLogger in the log files. In the above example, you would search for “user_app” to find the relevant log messages.

C/C++ Dragon Logger

In C/C++, to use the Dragon logger:

Include the “dragon/messages_api.h” and “err.h” header files
Attach to the dragon logger using dragon_logging_attach()
Log messages using dragon_log_message()
Detach from the logger using dragon_logging_detach()
Ensure that you link to the dragon library when compiling your application.

CC = gcc
INCLUDE = -I $(DRAGON_INCLUDE_DIR)
LIBS = -L $(DRAGON_BASE_DIR)/lib

%.c.o: %.c
    $(CC) $(INCLUDE) $(CFLAGS) -c $< -o $@

default: logging

logging: logging.c.o
    $(CC) $(INCLUDE) $(CFLAGS) -o logging $< $(LIBS) -ldragon -lrt

#include <stdio.h>
#include "err.h"
#include "dragon/messages_api.h"

int main(int argc, char *argv[]) {

    dragonError_t err;
    err = dragon_logging_attach();
    if (err != DRAGON_SUCCESS) {
        printf("Error attaching to logging FLI: %s\n", dragon_getlasterrstr(err));
        return -1;
    }

    err = dragon_log_message(
        "user_app",        /* name */
        "Hello from C!",   /* message */
        NULL,              /* time */
        NULL,              /* func */
        NULL,              /* hostname */
        NULL,              /* ipAddress */
        0,                 /* port */
        NULL,              /* service */
        LOG_LEVEL_INFO,    /* level */
        NULL               /* timeout */
    );
    if (err != DRAGON_SUCCESS) {
        printf("Error logging message: %s\n", dragon_getlasterrstr(err));
        return -1;
    }

    err = dragon_logging_detach();
    if (err != DRAGON_SUCCESS) {
        printf("Error detaching from logging FLI: %s\n", dragon_getlasterrstr(err));
        return -1;
    }

    return 0;
}

To run the above example, save it to a file called logger.c, compile it,and run it with the Dragon launcher:

dragon -l DEBUG ./logger

Depending upon the logging configuration and the log level of the message, the logged values will be printed to one or more of the following: stdout, dragon_*.log file, and/or LA_BE_*.log files in the current directory. The log message will be similar to the following:

2026-05-04 19:25:45,452 INFO     user_app Logging Monitor (281471899472160) :: Hello from C!

To help locate the relevant messages, you can search for the name value to dragon_log_message in the log files. In the above example, you would search for “user_app” to find the relevant log messages.

Note: Not all values passed to dragon_log_message are currently used. The only required values are the name, message, and level. The other values can be set to NULL or 0 if not needed.