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/*

 *  nWide.c

 *  Samples project

 *

 *  Created by Mensch on 5/1/09.

 *  Copyright 2009 Apple, Inc. All rights reserved.

 *

 */

#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>

#import <libkern/OSAtomic.h>

#include <string.h>

/*

 *  Demonstrate using dispatch_semaphore to create a concurrent queue that

 *  allows only a fixed number of blocks to be in flight at any given time

 */

int main (int argc, const char * argv[]) {

    dispatch_group_t    mg = dispatch_group_create();

    dispatch_semaphore_t ds;

    __block int numRunning = 0;

    int qWidth = 5;     

    int numWorkBlocks = 100;

    if (argc >= 2) {

        qWidth = atoi(argv[1]); // use the command 1st line parameter as the queue width

        if (qWidth==0) qWidth=1; // protect against bad values

    }

    if (argc >=3) {

        numWorkBlocks = atoi(argv[2]);  // use the 2nd command line parameter as the queue width

        if (numWorkBlocks==0) numWorkBlocks=1; // protect against bad values

    }

    printf("Starting dispatch semaphore test to simulate a %d wide dispatch queue\n", qWidth );

    ds = dispatch_semaphore_create(qWidth);

    int i;

    for (i=0; i<numWorkBlocks; i++) {

        // synchronize the whole shebang every 25 work units...

        if (i % 25 == 24) {

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

                // wait for all pending work units to finish up... 

                for (int x=0; x<qWidth; x++) dispatch_semaphore_wait(ds, DISPATCH_TIME_FOREVER);

                // do the thing that is critical here

                printf("doing something critical...while %d work units are running \n",numRunning);

                // and let work continue unimpeeded

                for (int x=0; x<qWidth; x++) dispatch_semaphore_signal(ds);

            });

        } else {

            // schedule the next block waiting when there are qWidth blocks running

            dispatch_semaphore_wait(ds, DISPATCH_TIME_FOREVER);             

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

                OSAtomicIncrement32( &numRunning );

                usleep(random() % 10000);   // simulate some random amount of work

                printf("Value of i is %d  Number of blocks in flight %d\n",i, numRunning);

                // tell the loop it's time to schedule the next block if there is one

                OSAtomicDecrement32( &numRunning );

                dispatch_semaphore_signal(ds);

            });

        }

    }

    dispatch_group_notify(mg, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        printf("And we are done!\n");

        dispatch_release(mg);

        dispatch_release(ds);

        exit(0);

    });

    dispatch_main();

    return 0;

}