[ObjC] OSSpinLock.md

[ObjC] OSSpinLock

[TOC]

示例程序

代码

ViewController.m

#import "ViewController.h"
#import <libkern/OSAtomic.h>

@interface ViewController () {
    OSSpinLock _spinLock;
    NSUInteger _num;
}

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    _spinLock = OS_SPINLOCK_INIT;

    _num = 0;

    dispatch_queue_t concurrentDispatchQueue = dispatch_queue_create("queue", DISPATCH_QUEUE_CONCURRENT);

    for (NSUInteger i = 0; i < 10; ++i) {
        dispatch_async(concurrentDispatchQueue, ^{
            [self increaseNum];
        });
    }

}

- (void)increaseNum {
    OSSpinLockLock(&_spinLock);
    NSLog(@"_num = %tu", ++_num);
    OSSpinLockUnlock(&_spinLock);
}

@end

输出

_num = 1
_num = 2
_num = 3
_num = 4
_num = 5
_num = 6
_num = 7
_num = 8
_num = 9
_num = 10

说明

如果不使用 OSSpinLock 对临界区进行加锁，则可能的输出为

_num = 1
_num = 3
_num = 2
_num = 4
_num = 5
_num = 5
_num = 6
_num = 7
_num = 9
_num = 8

OSSpinLock 自 iOS 10.0 开始已经被显式地标记为弃用。

OSSpinLock 是一种自旋锁。