Test thread safety of random number generators.

RandomThreadSafetyTest.m

//  Testing thread safety of rand() and random(); for more see:
//    http://adampreble.net/blog/2012/09/mtrandom-an-objective-c-random-number-generator/
//  Created by Adam Preble on 9/3/12
//  Copyright (c) 2012 Adam Preble. All rights reserved.
//

#import <Foundation/Foundation.h>

#if 1
#define test_srandom srandom
#define test_random random
#else
#define test_srandom srand
#define test_random rand
#endif

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

    @autoreleasepool {
        
        NSMutableArray *allResults = [[NSMutableArray alloc] init];
        
        dispatch_group_t group = dispatch_group_create();
        dispatch_queue_t workQueue = dispatch_queue_create("net.adampreble.randomtest.work", DISPATCH_QUEUE_CONCURRENT);
        dispatch_queue_t resultQueue = dispatch_queue_create("net.adampreble.randomtest.results", DISPATCH_QUEUE_SERIAL);
        
        int numThreads = 4;
        for (int i = 0; i < numThreads; i++)
        {
            dispatch_group_async(group, workQueue, ^{
                
                NSMutableArray *numbers = [[NSMutableArray alloc] init];
                
                test_srandom(5);
                
                for (int i = 0; i < 5; i++)
                {
                    [numbers addObject:@(test_random())];
                    usleep(1);
                }
                
                dispatch_group_async(group, resultQueue, ^{
                    [allResults addObject:numbers];
                    NSLog(@"%@", [numbers componentsJoinedByString:@", "]);
                });
            });
        }
        
        dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
        
        for (NSUInteger i = 1; i < allResults.count; i++)
        {
            if ([allResults[0] isEqual:allResults[i]] == NO)
            {
                NSLog(@"Not thread safe!");
                return 1;
            }
        }
        NSLog(@"Thread safe -- this time!");
    }
    return 0;
}

/* Sample output:
RandomTest[58269:1703] 590011675, 2131925610, 940455586, 976522863, 62604080
RandomTest[58269:1703] 678669015, 1653846685, 1854676444, 1374022803, 1236797572
RandomTest[58269:1703] 590011675, 99788765, 1323721571, 2068056359, 99788765
RandomTest[58269:1703] 590011675, 2131925610, 171864072, 317159276, 171035632
RandomTest[58269:303] Not thread safe!
 */