semaphore access speed Post: 302242365

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Top Forums Programming semaphore access speed Post 302242365 by migurus on Wednesday 1st of October 2008 07:17:39 PM

10-01-2008

Registered User

help me understand the code

This is a little off-topic, but I am afraid I do not fully understand the code.

My understanding of the purpose of the initial loop

Quote:

Originally Posted by otheus

Code:

    for (i = 0; i < 1000; ++i) {
        usleep(10);
        last=time(NULL);
        if (last > start) break;
    }

is to start the whole measurement at the point of change of the second. Right?

Next,
we have two loops: first run 8750000 times, given the maxloop value of 1000000,

Then we run loop up to 1250000 times where every 100th iteration we check for time and if second changed, we break out

Quote:

Originally Posted by otheus

Code:

    stop=time(NULL);
    for (i = maxloop - maxloop/8; i < maxloop; ++i) {
      if ( !(i % estimate) ) {
        last=time(NULL);
        if (last > stop) break;
        stop=last;
      }
 
      /* repeat semaphore opts */
      if ((sid = semget(key, NSEMS, IPC_CREAT | 0777)) == -1) {
          perror("Can Not Get Semaphore ID");
      }
      if (semctl(sid, NSEMS, GETALL, vals) == -1) {
          perror("Can Not Get Semaphore Values");
      }
    }
    stop=last;

What is this technique of checking every Nth iteration for? why not check time every iteration? is it because this would add to many extra time calls and muddy the measurements?

Your clarification would be appreciated.

migurus

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LEARN ABOUT SUNOS

break

break(1)							   User Commands							  break(1)

NAME

       break, continue - shell built-in functions to escape from or advance within a controlling while, for, foreach, or until	loop

SYNOPSIS

   sh
       break [n]

       continue [n]

   csh
       break

       continue

   ksh
       *break [n]

       *continue [n]

DESCRIPTION

   sh
       The break utility exits from the enclosing for or while loop, if any. If n is specified, break n levels.

       The continue utility resumes the next iteration of the enclosing for or while loop. If n is specified, resume at the n-th enclosing loop.

   csh
       The  break  utility  resumes  execution after the end of the nearest enclosing foreach or while loop. The remaining commands on the current
       line are executed. This allows multilevel breaks to be written as a list of break commands, all on one line.

       The continue utility continues execution of the next iteration of the nearest enclosing while or foreach loop.

   ksh
       The break utility exits from the enclosed for, while, until, or select loop, if any. If n is specified,	then  break  n	levels.  If  n	is
       greater than the number of enclosing loops, the outermost enclosing loop shall be exited.

       The  continue utility resumes the next iteration of the enclosed for, while, until, or select loop. If n is specified then resume at the n-
       th enclosed loop. If n is greater than the number of enclosing loops, the outermost enclosing loop shall be used.

       On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:

       1.  Variable assignment lists preceding the command remain in effect when the command completes.

       2.  I/O redirections are processed after variable assignments.

       3.  Errors cause a script that contains them to abort.

       4.  Words that follow a command preceded by ** that are in the format of a variable assignment are expanded with the same rules as a  vari-
	   able  assignment.  This means that tilde substitution is performed after the = sign, and also that word splitting and file name genera-
	   tion are not performed.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       csh(1), exit(1), ksh(1), sh( 1), attributes(5)

SunOS 5.10							    17 Jul 2002 							  break(1)

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break