mutex lock example for objective-C

mutex

- (void)sampleMethod
{
    NSOperationQueue *operationQueue = [NSOperationQueue new];
    MockService *service = [MockService sharedService];
    [operationQueue addOperationWithBlock:^{
        NSString *key = @"url_1";
        [service runServiceByKey:key];
    }];

    [operationQueue addOperationWithBlock:^{
        NSString *key = @"url_2";
        [service runServiceByKey:key];
    }];

    [operationQueue addOperationWithBlock:^{
        NSString *key = @"url_1";
        [service runServiceByKey:key];
    }];

    [operationQueue addOperationWithBlock:^{
        NSString *key = @"url_3";
        [service runServiceByKey:key];
    }];
}

///////////////////////////////////////////////////////////////////

#import <Foundation/Foundation.h>

@interface MockService : NSObject

+ (MockService *)sharedService;

- (void)runServiceByKey:(NSString *)key;

@end

///////////////////////////////////////////////////////////////////

#import "MockService.h"
#import <pthread.h>

pthread_mutex_t mutex;

@interface MockService ()

@property (nonatomic) NSMutableSet *keys;

@end

@implementation MockService

+ (MockService *)sharedService
{
    static dispatch_once_t onceToken;
    static MockService *instance;
    dispatch_once(&onceToken, ^{
        instance = [[MockService alloc] init];
        instance.keys = [NSMutableSet set];
        pthread_mutex_init(&mutex, NULL);
    });
    return instance;
}

- (void)runServiceByKey:(NSString *)key
{
    NSLog(@"%@: %@ <-- try get lock", [NSThread currentThread], key);
    if (![self isRepeatedKey:key]) {
        NSLog(@"%@: %@ <-- not repeat, run!", [NSThread currentThread], key);
        sleep(1);
        NSLog(@"%@: %@ -->", [NSThread currentThread], key);
        pthread_mutex_lock(&mutex);
        [self.keys removeObject:key];
        pthread_mutex_unlock(&mutex);
    }
    else {
        NSLog(@"%@: %@ --> repeated, skip", [NSThread currentThread], key);
    }
    return;
}

- (BOOL)isRepeatedKey:(NSString *)key
{
    BOOL isRepeated;
    int lock_res = pthread_mutex_lock(&mutex);
    if (!lock_res) {
        NSLog(@"%@: %@ <-- get lock success", [NSThread currentThread], key);
    }
    else {
        NSLog(@"%@: %@ <-- get lock failure", [NSThread currentThread], key);
    }
    isRepeated = [self.keys containsObject:key];
    if (!isRepeated) {
        [self.keys addObject:key];
    }
    pthread_mutex_unlock(&mutex);
    return isRepeated;
}

@end

///////////////////////////////////////////////////////////////////

<NSThread: 0x604000265d40>{number = 4, name = (null)}: url_1 <-- try get lock
<NSThread: 0x60c0002638c0>{number = 3, name = (null)}: url_1 <-- try get lock
<NSThread: 0x600000275140>{number = 6, name = (null)}: url_2 <-- try get lock
<NSThread: 0x600000078b40>{number = 5, name = (null)}: url_3 <-- try get lock
<NSThread: 0x60c0002638c0>{number = 3, name = (null)}: url_1 <-- get lock success
<NSThread: 0x60c0002638c0>{number = 3, name = (null)}: url_1 <-- not repeat, run!
<NSThread: 0x604000265d40>{number = 4, name = (null)}: url_1 <-- get lock success
<NSThread: 0x600000275140>{number = 6, name = (null)}: url_2 <-- get lock success
<NSThread: 0x604000265d40>{number = 4, name = (null)}: url_1 --> repeated, skip
<NSThread: 0x600000275140>{number = 6, name = (null)}: url_2 <-- not repeat, run!
<NSThread: 0x600000078b40>{number = 5, name = (null)}: url_3 <-- get lock success
<NSThread: 0x600000078b40>{number = 5, name = (null)}: url_3 <-- not repeat, run!
<NSThread: 0x60c0002638c0>{number = 3, name = (null)}: url_1 -->
<NSThread: 0x600000275140>{number = 6, name = (null)}: url_2 -->
<NSThread: 0x600000078b40>{number = 5, name = (null)}: url_3 -->