/*

 * Copyright (c) 2008 Apple Inc.  All rights reserved.

 *

 * @APPLE_DTS_LICENSE_HEADER_START@

 * 

 * IMPORTANT:  This Apple software is supplied to you by Apple Computer, Inc.

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 * please do not use, install, modify or redistribute this Apple software.

 * 

 * In consideration of your agreement to abide by the following terms, and

 * subject to these terms, Apple grants you a personal, non-exclusive license,

 * under Apple's copyrights in this original Apple software (the "Apple Software"),

 * to use, reproduce, modify and redistribute the Apple Software, with or without

 * modifications, in source and/or binary forms; provided that if you redistribute

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 * The Apple Software is provided by Apple on an "AS IS" basis.  APPLE MAKES NO

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 * PURPOSE, REGARDING THE APPLE SOFTWARE OR ITS USE AND OPERATION ALONE OR IN

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 * @APPLE_DTS_LICENSE_HEADER_END@

 */

#include <stdio.h>

#include <unistd.h>

#include <stdlib.h>

#include <sys/errno.h>

#include <assert.h>

#include <dispatch/dispatch.h>

#include <mach/mach_time.h>

#define kIT 10

uint64_t        elapsed_time;

void    timer_start() {

        elapsed_time = mach_absolute_time();

}

double  timer_milePost() {

    static dispatch_once_t      justOnce;

    static double       scale;

    dispatch_once(&justOnce, ^{

        mach_timebase_info_data_t   tbi;

        mach_timebase_info(&tbi);

        scale = tbi.numer;

        scale = scale/tbi.denom;

        printf("Scale is %10.4f  Just computed once courtesy of dispatch_once()\n", scale);

    });

    uint64_t    now = mach_absolute_time()-elapsed_time;

    double  fTotalT = now;

    fTotalT = fTotalT * scale;          // convert this to nanoseconds...

    fTotalT = fTotalT / 1000000000.0;

    return fTotalT;

}

int

main(void)

{

    dispatch_queue_t myQueue = dispatch_queue_create("myQueue", NULL);

    dispatch_group_t myGroup = dispatch_group_create();

// dispatch_apply on a serial queue finishes each block in order so the following code will take a little more than a second

    timer_start();

    dispatch_apply(kIT, myQueue, ^(size_t current){

        printf("Block #%ld of %d is being run\n",

               current+1, // adjusting the zero based current iteration we get passed in

               kIT);    

        usleep(USEC_PER_SEC/10);

    }); 

    printf("and dispatch_apply( serial queue ) returned after %10.4lf seconds\n",timer_milePost());

// dispatch_apply on a concurrent queue returns after all blocks are finished, however it can execute them concurrently with each other

// so this will take quite a bit less time

    timer_start();  

    dispatch_apply(kIT, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(size_t current){

        printf("Block #%ld of %d is being run\n",current+1, kIT);

        usleep(USEC_PER_SEC/10);

    });

    printf("and dispatch_apply( concurrent queue) returned after %10.4lf seconds\n",timer_milePost());

// To execute all blocks in a dispatch_apply asynchonously, you will need to perform the dispatch_apply

// asynchonously, like this (NOTE the nested dispatch_apply inside of the async block.)

// Also note the use of the dispatch_group so that we can ultimatly know when the work is

// all completed

    timer_start();  

    dispatch_group_async(myGroup, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ 

        dispatch_apply(kIT, myQueue, ^(size_t current){

            printf("Block #%ld of %d is being run\n",current+1, kIT);

            usleep(USEC_PER_SEC/10);

        });

    });

    printf("and dispatch_group_async( dispatch_apply( )) returned after %10.4lf seconds\n",timer_milePost());

    printf("Now to wait for the dispatch group to finish...\n");

    dispatch_group_wait(myGroup, UINT64_MAX);

    printf("and we are done with dispatch_group_async( dispatch_apply( )) after %10.4lf seconds\n",timer_milePost()); 

    return 0;

}