[ios]NSLock锁

线程同步:

1，原子操作

2，内存屏蔽和volatile变量

只确保每次操作都是从内存中获取信息，而不用寄存器内保存的数据

OSMemoryBarrier函数，设置内存屏蔽

volatile变量

线程安全设计技巧:

 

＝＝＝代码一－－－有风险的代码

    NSLock* arrayLock = [self GetArrayLock];

    NSMutableArray* myArray = GetSharedArray();

    

    id anObject;

    [arrayLock lock];

    anObject = [myArray objectAtIndex:0];

    [arrayLock unlock];

    

     // 在处理doSomething的时候共享资源myArray可能被修改，下面的操作就是有风险的操作

    ［anObject doSomething];

＝＝＝代码二－－－低效率的代码

        NSLock * arrayLock = [ self   GetArrayLock ];

    NSMutableArray* myArray = GetSharedArray();

    

    id anObject;

    [arrayLock lock];

    anObject = [myArray objectAtIndex:0];

    // 在处理doSomething放到Lock里面，如果doSomething处理时间比较长，那么就形成了效率瓶颈，影响程序效率

    ［anObject doSomething];

    [arrayLock unlock];

＝＝＝代码三－－－高效率的代码

    NSLock* arrayLock = [self GetArrayLock];

    NSMutableArray* myArray = GetSharedArray();

    

    id anObject;

    [arrayLock lock];

    anObject = [myArray objectAtIndex:0];

    // 把对象retain and save，防止在unlock，myArray里面的内容被修改

    [anObject retain];

    [arrayLock unlock];

    

    ［anObject doSomething];

    [anObject release];

转载：http://www.cnblogs.com/jinjiantong/archive/2013/03/25/2980258.html

NSLock* arrayLock = GetArrayLock(); NSMutableArray* myArray = GetSharedArray(); id anObject; [arrayLock lock]; anObject = [myArray objectAtIndex:0]; [anObject retain]; [arrayLock unlock]; [anObject doSomething]; [anObject release];

And the question is: Is there any way to solve the problem while using ARC?

Answer:

ARC solves this problem for you automatically; by default every pointer is a strong pointer, which means that the object is guaranteed to be retained until you are done using that pointer.

This means that whenever you get an object out of an array, ARC always retains that object. This guarantees its lifetime, even if the object is later removed from the array.

参考：http://stackoverflow.com/questions/16836843/thread-safe-design-with-arc