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Swift Memory

Automatic Reference Counting (ARC), Swift使用ARC管理对象.

Strong Reference Cycles for Closures

Resolving Strong Reference Cycles for Closures

• weak reference
• unowned reference

都不会ARC计算 区别: * weak 修改可选类型, 当对象被释放会设置nil * unowned 一直需要有值, 当对象被释放后再访问, 会有异常

Strong Reference Cycles for Closures

闭包中的强引用循环, 当对象得到一个闭包, 闭包中引用这个对象. 打破闭包中的强引用循环, 使用Capture List, 捕获列表是一系列weak和unowned

	lazy var someClosure = {
			[unowned self, weak delegate = self.delegate]
			(index: Int, stringToProcess: String) -> String in
			// closure body goes here
	}

Memory Safety

默认Swift会阻止不安全的内在访问:

1. 初始化前不能使用
2. 销毁后不能使用
3. 数组下标检查
4. Swift会自动管理内存, 大多数时间不用想内存多重访问冲突问题

Characteristics of Memory Access

符合下面两条就会产成内存冲突:

• At least one is a write access or a nonatomic access.
• They access the same location in memory.
• Their durations overlap.

instantaneous accesses 瞬时访问, 访问中不会有任何代码. 本质上, 两个瞬时访问不会 同时发生. 大多数内存访问是瞬时的.

long-term accesses 长期访问, 访问有可能会与其他的long-term accesses或者instantaneout accesses 重叠overlap. 长期访问, 主要出现在fund输入输出参数, 或者mutating fund中.

atomic operations

An operation is atomic if it uses only C atomic operations; otherwise it’s nonatomic. For a list of those functions, see the stdatomic(3) man page.

Reference

Automatic Reference Counting
Memory Safety
Transitioning to ARC Release Notes
What Is the Difference Between Weak and Unowned References in Swift

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