How to determine the Set function execution time

How can I tell how to set the function execution time?
function A () {
//...
return true;
}
Function B () {
//...
return false;
}
Now start calling a ();

Imagine if a (), after 1.2 seconds did not return the result, immediately call B ();
What's the nice way to deal with it?

------Solution--------------------

Don't be too yourself, and don't make PHP any harder.

My solution
1, Ajax time-out interpretation disadvantage: Time is not accurate advantage: This feature can be temporarily implemented
2, PHP's C language extension disadvantage: The difficulty is big cost-effective not high advantage: time accurate efficiency high
3. Wait for Daniel ....
------Solution--------------------
Libevent can implement the function of the timer, but your a function should be to perform network tasks, if so, there must be a timeout setting
------Solution--------------------
PHP itself provides this type of functionality
Whether it is beautiful, you judge by yourself
Not all operations are calculated in PHP run time, you can verify it yourself

Register_shutdown_function ("Time_out_callback");
Set_time_limit (2);//Assuming 2 seconds to timeout
Analog timeout
@c ();
Error_reporting ($es);//Restore settings

function Time_out_callback () {
  if (connection_status () = = 2) {
    b ();    
  }
}
Function C () {
  Your possible time-out code
  echo __function__, ';
  while (true) {
    echo '. ';
            Echo Connection_status (). "
";//echo 0
    Usleep (100000);//give the CPU a breath
  }
}
Function B () {
  Echo '
' . __function__, ";
  Echo ' C Timeout connection status: '. Connection_status ();//echo 2,c Timeout
}

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