PolySat Process Library (libproc)

libproc is a lightweight event loop and inter-process communication library built by PolySat. It powers every one of our satellite core processes!

Building

libproc is a POSIX C library. It has been tested on Linux and MacOS, but it will probably run on any unix system.

It can be built with make and installed with make install.

Event loop functionality

The event loop allows programs to react to specific events that happen in the operating system.

Some of the event types supported by libproc are:

• File actions: file reading, writing, and errors
• Scheduled events: schedule events to run at specific times
• Incoming commands: React to incoming commands via UDP packets
• Signals: Handle operating system signals, such as SIGINT
• Pending power-off

Inter-process communication

libproc makes it easy to communicate with other processes. On start-up, libproc reads the process command file definition (proc_name.cmd.cfg) and binds to an UDP port.

Using this command definition, other processes can message this process.

In addition to inter-process communication, libproc also supports multicasting, where multiple processes can subscribe to message streams.

Open-Source Programs Using libproc

• ADCS Sensor Reader: Used to read attitude determination sensors on PolySat missions without full ADCS.

Hello World using libproc

#include <stdio.h>
#include <polysat/polysat.h>

/*
 * The event callback function. Will be called once a second.
 */
int my_timed_event(void *arg)
{
   printf("Hello World\n");
   /* Returning EVENT_KEEP will reschedule the event to run again on the event loop */
   return EVENT_KEEP;
}

int main(void)
{
   /* Where libproc stores its state */
   struct ProcessData *proc;

   /* Initialize the process */
   proc = PROC_init("test1", WD_DISABLED);
   if (!proc) {
      printf("error: failed to initialize process\n");
      return -1;
   }

   /* Schedule my_timed_event to run once a second on the event loop */
   EVT_sched_add(PROC_evt(proc), EVT_ms2tv(1000), &my_timed_event, NULL);

   /* Start the event loop */
   printf("Starting the event loop...\n");
   EVT_start_loop(PROC_evt(proc));

   /* Clean up libproc */
   printf("Cleaning up process...\n");
   PROC_cleanup(proc);

   printf("Done.\n");
   return 0;
}

Additional Examples

Stopwatch using libproc