LeapPollConnection Blocks When No Device Is Connected

[bjornbytes]

Hello, this LeapC sample causes the process to hang after a few events when no device is connected:

#include <LeapC.h>
#include <stdio.h>

LEAP_CONNECTION connection;
LEAP_CONNECTION_MESSAGE message;

int main(int argc, char** argv) {
  if (LeapCreateConnection(NULL, &connection) != eLeapRS_Success)
    return printf("Could not create connection\n"), 1;

  if (LeapOpenConnection(connection) != eLeapRS_Success)
    return printf("Could not open connection\n"), 1;

  while (1) {
    printf("Polling for events...\n");
    LeapPollConnection(connection, 0, &message);
    printf("Poll complete\n");
  }

  return 0;
}

This is problematic for me because I would like to create an application that works whether or not the user has Leap Motion hardware connected, but I can't find any way to determine whether Leap Motion hardware is available without polling for the LEAP_CONNECTION_EVENT message, which causes the deadlock.

I'm using the 4.0.0+52173 version of the SDK. Any help would be appreciated!

[ohaaaaaaaaaaaaan]

Hello,

To avoid the deadlock caused by blocking at LeapPollConnection, you should run another thread and call LeapPollConnection on it. Now you can check if some device is connected or not on the main thread without blocked:slight_smile:

It'd be worth mentioning that when you call LeapCloseConnection on the main thread, LeapPollConnection will return soon with CloseConnection event, thus you can gracefully terminate the thread for the Leap Motion message loop.
Having a look at ExampleConnection.h/c would be quite helpful to catch some details.