内存泄露一直是一个头疼的问题，需要工程化的阶段来解决。之前在每个VC的deinit打印一些日志，因为日志太多，看到泄露信息并不容易。跑Instruments成本也比较高，很多时候并不想去跑。所以对比了一下Memory Debug Graph和FBMemoryProfiler。
Memory Debug Graph
Memory Debug Graph是Xcode8新增的feature，跟Xcode无缝融合，用起来比较方便，模拟器开发测试一段时间之后，不妨看一下Xcode Runtime issue，是否有警告。
如果想要看到右侧的内存申请时的堆栈，需要在Scheme里面勾选上Malloc Stack。
打开Malloc Stack选项之后，会在沙箱的/tmp/目录下会产生巨大的日志文件，平时最好把它关掉。
-rw-r--r-- 1 henshao staff 30M 12 26 10:31 stack-logs.3214.102414000.CloudConsoleApp.SrkAcU.indexMemory Debug Graph的缺点是只有图形化界面，没有SDK，这样的话只能连着Xcode操作。如果有SDK的话，可以在代码里面检测内存警告，发现有内存泄露上传日志，弹个框什么的。
FBMemoryProfiler
FBMemoryProfiler是Facebook开源的一个工具，有SDK可以用，接入是非常之方便的。但是目前来看，对Swift并不支持，所以用Swift的同学就不要使用这个工具了。
测试代码
代码中构造了两种内存泄露，一种是简单的循环引用，另外一种是block capture。
import UIKit
import FBMemoryProfiler
class RetainCycleLoggerPlugin : NSObject, FBMemoryProfilerPluggable {
func memoryProfilerDidFindRetainCycles(_ retainCycles: Set<AnyHashable>) {
print("==FBMemoryProfiler: \(retainCycles)")
}
}
class Foo {
var vc : MemoryLeakViewController?
}
typealias BarBlock = ()->Void
class MemoryLeakViewController : UIViewController {
var foo : Foo?
var barBlock : BarBlock?
override func viewDidLoad() {
super.viewDidLoad()
self.title = "Memory Leak VC"
self.view.backgroundColor = UIColor.blue
// self.foo = Foo()
// self.foo?.vc = self
self.barBlock = {
self.view.backgroundColor = UIColor.white
}
self.barBlock?()
}
}
class ViewController: UIViewController {
let memoryProfiler = FBMemoryProfiler(plugins: [RetainCycleLoggerPlugin()], retainCycleDetectorConfiguration: nil)
override func viewDidLoad() {
super.viewDidLoad()
self.title = "Root VC"
self.view.backgroundColor = UIColor.white
memoryProfiler.enable()
}
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
let memoryLeakVC = MemoryLeakViewController()
self.navigationController?.pushViewController(memoryLeakVC, animated: true)
}
}对比结果
Memory Debug Graph探测是非常精准的，两种内存泄露都发现了。
FBMemoryProfiler什么都没有发现。
==FBMemoryProfiler: []
==FBMemoryProfiler: []
==FBMemoryProfiler: []
==FBMemoryProfiler: [AnyHashable(<__NSArrayM 0x600000244410>(
-> target -> FBMemoryProfilerViewController ,
-> _timer -> __NSCFTimer
)
)]
==FBMemoryProfiler: [AnyHashable(<__NSArrayM 0x600000246360>(
-> (null) ,
-> (null)
)
)]
==FBMemoryProfiler: []
==FBMemoryProfiler: []
==FBMemoryProfiler: []
==FBMemoryProfiler: []
==FBMemoryProfiler: [AnyHashable(<__NSArrayM 0x60000024c960>(
-> target -> FBMemoryProfilerViewController ,
-> _timer -> __NSCFTimer
)
)]
==FBMemoryProfiler: [AnyHashable(<__NSArrayM 0x600000254700>(
-> target -> FBMemoryProfilerViewController ,
-> _timer -> __NSCFTimer
)
)]
==FBMemoryProfiler: []
==FBMemoryProfiler: []
==FBMemoryProfiler: []实战情况
我们使用Debug Memory Graph还真发现了一个二方模块的循环引用。这也说明了添加特定前缀的重要性。比如我们的前缀是ALY，我在模拟器里面使用一阵子之后，跑去Debug Memory Graph的runtime issue搜索ALY，就可以知道我们自己代码的内存泄露啦。
泄露的代码如下所示。presenter的completion block capture了VC，而VC的eventHandler又拿住了presenter，导致循环引用。只要在presenter的completion block对VC做一个weak即可解决问题。
ALYPatternLockPresenter *presenter = [[ALYPatternLockPresenter alloc] init];
ALYPatternLockViewController *vc = [[ALYPatternLockViewController alloc] initWithNibName:@"ALYPatternLockViewController" bundle:[NSBundle mainBundle]];
if ([self patternLockWasSet]) {
[vc setActionPrompt:title];
// 如果强制验证，无法取消，隐藏取消按钮
[vc setCancelButtonHidden:force];
presenter.userInterface = vc;
presenter.mode = ALYPatternLockValidateMode;
WEAK_SELF
presenter.completion = ^(BOOL result, NSError *error) {
STRONG_SELF
if (result) {
[self dismissViewControllerAboveAWindow:vc animated:animated completion:^{
completion(YES, nil);
}];
} else {
[self dismissViewControllerAboveAWindow:vc animated:animated completion:^{
completion(NO, error);
if (error.code == ALYPatternLockErrorTooManyAttempts
|| error.code == ALYPatternLockErrorForget) {
if (self.callback != nil) {
self.callback();
}
}
}];
}
};
vc.eventHandler = presenter;
vc.touchIDEnabled = [[ALYPatternLockService sharedInstance] touchIDEnabled];
[vc setActionPrompt:title];
[self presentViewControllerAboveAWindow:vc animated:animated];