Run-Time clock in the MPM

[Jean-Jacques Clar]

Having a time structure in the mpm keeping updated sec and uSEC

field could help performance for the web server.

It could replace most calls to apr_time_now() and apr_time_sec()

at run-time:

 

NetWare has its main thread resuming every 1000000 uSEC (1 sec)

to do the idle server maintenance.

The following code keep a local timeval structure, which could

return current time without having to call apr_time_now() every request.

 

Yes, only the tv_sec field is updated between call to gettimeofday().

 

Who cares about the uSEC precision anyway, apache is a web server,

 not a scientific clock application.

 

With the following function, calls to apr_time_now() in apache could

then be replaced with call to ap_time_now().

Or maybe just redefining apr_time_now() to ap_time_now() and

apr_time_sec() to ap_time_sec() will work for us.

 

I am thinking of using a set of functions like the following ones in the

NetWare mpm:

 

The synchonize_usec_clock() function is called every second by the main

thread when it resumes to do the idle maintenance.

It synchronizes the time fields every 5 seconds using the gettimeofday() function. 

 

Anyone sees problems with using a background thread to maintain

current time structure?

 

--- boc ---

static apr_int32_t mpm_clock_initialized;
static apr_time_t now;
struct timeval tv;

 

static void synchonize_usec_clock( void )
{
  static apr_int32_t counter;
 
  if (mpm_clock_initialized) {
    if(++counter > 4) {
      gettimeofday(&tv, NULL);
      now = tv.tv_sec * APR_USEC_PER_SEC + tv.tv_usec;
      counter = 0;
    }
    else {
      now += SCOREBOARD_MAINTENANCE_INTERVAL;

      tv.tv_sec++;

    }
  }
  else {
    gettimeofday(&tv, NULL);
    now = tv.tv_sec * APR_USEC_PER_SEC + tv.tv_usec;
    mpm_clock_initialized = 1;
  }
}

 

AP_DECLARE(apr_time_t) ap_time_now(void)
{
  if (mpm_clock_initialized) 
    return now;
  else
    return apr_time_now();
}

 

AP_DECLARE(apr_time_t) ap_time_sec(apr_time_t time)
{
  if (mpm_clock_initialized) 
    return tv.tv_sec;
  else
    return apr_time_sec(time);
}

--- eoc ---

 

Thank you,

 

Jean-Jacques