libtracer is a library that makes it easy to include trace-level debug logs in production systems by storing a configurable number of recent entries in an on-disk ring buffer. The ring buffer size can be limited by entry count.

This means that you can trace freely without worrying about cluttering your main logs or using valuable disk space. If an unexpected crash happens, you instantly have all the printf debugging you probably would have done readily available. If things run smoothly and nothing crashes, then you've only sacrificed an easily configurable amount of disk space.

If you only want to include tracing in certain configurations, you can simply skip the call to tracer_start and all invocations of the tracer macro will become no-ops, minus the cost of invoking a function.

Tracer is thread-safe as well. The act of committing an entry to disk is entirely atomic and completed in-thread so that entries are safely in the operating system's write buffers before returning. Since large parts of tracer invocations are serialized, however, excessive use of it in highly concurrent code can cause lock contention that slows your code down significantly.

void tracer_config_default(tracer_config_t*);
void tracer_config_set_path(tracer_config_t*, const char *path);
void tracer_config_set_max_entries(tracer_config_t*, long max_entries);

void tracer_start(tracer_t*, tracer_config_t*);

#define tracer(T, FORMAT...)

#include <tracer.h>

tracer_config_t my_tracer_config;
tracer_t my_tracer;

...

int main(int argc, char *argv[]) {
        tracer_config_default(&my_tracer_config);
        tracer_config_set_path(&my_tracer_config, "tracer.log");
        tracer_config_set_max_entries(&my_tracer_config, 1000);

        tracer_start(&my_tracer, &my_tracer_config);

        tracer(&my_tracer, "opened tracer with %d entries", 1000);

        ...

        tracer(&my_tracer, "iterating over %d values", count);
        for (i=0; i<count; i++) {
                tracer(&my_tracer, "iteration=%d", i);
                tracer(&my_tracer, "  value=%p", values[i]);
                tracer(&my_tracer, "    name=%s", values[i]->name);

                ...

                tracer(&my_tracer, "done, next iteration");
        }
        tracer(&my_tracer, "processing finished");
}

tracer is the command line tool for interacting with libtracer output files. Its usage is perhaps best captured in the help output:

usage: tracer dump FILE