Leaks
先看看 Leaks，从苹果的开发者文档里可以看到，一个 app 的内存分三类：
Leaked memory: Memory unreferenced by your application that cannot be used again or freed (also detectable by using the Leaks instrument).
Abandoned memory: Memory still referenced by your application that has no useful purpose.
Cached memory: Memory still referenced by your application that might be used again for better performance.
其中 Leaked memory 和 Abandoned memory 都属于应该释放而没释放的内存，都是内存泄露，而 Leaks 工具只负责检测 Leaked memory，而不管 Abandoned memory。在 MRC 时代 Leaked memory 很常见，因为很容易忘了调用 release，但在 ARC 时代更常见的内存泄露是循环引用导致的 Abandoned memory，Leaks 工具查不出这类内存泄露，应用有限。
1.通过Xcode-profile打开instrument
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2.选择真机运行
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3.选择 Allocations -- Generations 检测每次每次内存增长多少
4. 使用leaks查看的内存泄漏的具体代码
