使用 WKScriptMessageHandler 时内存泄漏

Question

不确定我是否遇到了 WebKit 中的错误，或者我做错了什么，但我不知道如何使用 WKScriptMessageHandler 而不导致 [=14] 中包含的任何值=] 泄漏。

我能够组建一个最小的 Mac 项目来隔离问题，但无济于事。

在主视图控制器中：

class ViewController: NSViewController {
  var webView: WKWebView?

  override func viewDidLoad() {
    super.viewDidLoad()
    let userContentController = WKUserContentController()
    userContentController.addScriptMessageHandler(self, name: "handler")
    let configuration = WKWebViewConfiguration()
    configuration.userContentController = userContentController
    webView = WKWebView(frame: CGRectZero, configuration: configuration)
    view.addSubview(webView!)

    let path = NSBundle.mainBundle().pathForResource("index", ofType: "html")
    let url = NSURL(fileURLWithPath: path!)!
    webView?.loadRequest(NSURLRequest(URL: url))
  }
}

extension ViewController: WKScriptMessageHandler {
  func userContentController(userContentController: WKUserContentController, didReceiveScriptMessage message: WKScriptMessage) {
     print(message.body)
   }
}

然后在 index.html 文件中：

<html>
  <head></head>
  <body>
    <script type="text/javascript">
      webkit.messageHandlers.handler.postMessage("Here's a random number for you: " + Math.random() * 10)
    </script>
  </body>
</html>

当我运行项目然后在 Instruments 中打开内存调试器时，我看到以下泄漏：

如果我添加一个重新加载请求的按钮，并且这样做几十次，应用程序的内存占用量会不断增加，并在达到特定阈值后崩溃。在这个最小的示例中，崩溃可能需要一段时间，但在我每秒收到多条消息的应用程序中，崩溃只需不到 10 秒。

整个项目可以downloaded here.

知道发生了什么事吗？

Answer 1

您看到的是一个 WebKit 错误：https://bugs.webkit.org/show_bug.cgi?id=136140. It was fixed in WebKit trunk a while ago，但似乎没有合并到任何 WebKit 更新中。

您可以通过将 -dealloc 添加到 WKScriptMessage 来解决这个问题，以补偿过度保留。它可能看起来像这样：

//
//  WKScriptMessage+WKScriptMessageLeakFix.m
//  TestWebkitMessages
//
//  Created by Mark Rowe on 6/27/15.
//  Copyright © Mark Rowe.
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
//  associated documentation files (the "Software"), to deal in the Software without restriction,
//  including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
//  and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so,
//  subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in all copies or substantial
//  portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
//  LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
//  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
//  WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
//  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

#import <mach-o/dyld.h>
#import <objc/runtime.h>
#import <WebKit/WebKit.h>

// Work around <https://webkit.org/b/136140> WKScriptMessage leaks its body

@interface WKScriptMessage (WKScriptMessageLeakFix)
@end

@implementation WKScriptMessage (WKScriptMessageLeakFix)

+ (void)load
{
    // <https://webkit.org/b/136140> was fixed in WebKit trunk prior to the first v601 build being released.
    // Enable the workaround in WebKit versions < 601. In the unlikely event that the fix is backported, this
    // version check will need to be updated.
    int32_t version = NSVersionOfRunTimeLibrary("WebKit");
    int32_t majorVersion = version >> 16;
    if (majorVersion > 600)
        return;

    // Add our -dealloc to WKScriptMessage. If -[WKScriptMessage dealloc] already existed
    // we'd need to swap implementations instead.
    Method fixedDealloc = class_getInstanceMethod(self, @selector(fixedDealloc));
    IMP fixedDeallocIMP = method_getImplementation(fixedDealloc);
    class_addMethod(self, @selector(dealloc), fixedDeallocIMP, method_getTypeEncoding(fixedDealloc));
}

- (void)fixedDealloc
{
    // Compensate for the over-retain in -[WKScriptMessage _initWithBody:webView:frameInfo:name:].
    [self.body release];

    // Call our WKScriptMessage's superclass -dealloc implementation.
    [super dealloc];
}

@end

将其放入项目的 Objective-C 文件中，将此文件的编译器标志设置为包含 -fno-objc-arc，它应该会为您解决泄漏问题。

Answer 2

我在 iOS 9 SDK 上遇到了同样的问题。

我注意到 userContentController.addScriptMessageHandler(self, name: "handler") 将保留处理程序的引用。为防止泄漏，只需在不再需要时删除消息处理程序即可。例如当您关闭所述控制器时，调用将调用 removeScriptMessageHandlerForName() 的清理方法。

您可以考虑将 addScriptMessageHandler() 移动到 viewWillAppear 并在 viewWillDisappear.

中添加相应的 removeScriptMessageHandlerForName() 调用

Answer 3

这里有一个保留周期。在您的代码中，ViewController 保留 WKWebView，WKWebView 保留 WKWebViewConfiguration，WKWebViewConfiguration 保留 WKUserContentController，您的 WKUserContentController 保留您的 ViewController。就像上面的评论一样，您必须在关闭视图控制器之前通过调用 removeScriptMessageHandlerForName 来删除 scriptHandler。

Answer 4

要修复保留周期，您可以对任何协议使用基于 NSProxy 的下一个通用解决方案：

@interface WeakProxy: NSProxy

@property (nonatomic, weak) id object;

@end

@implementation WeakProxy

+ (instancetype)weakProxy:(id)object {
    return [[WeakProxy alloc] initWithObject:object];
}

- (instancetype)initWithObject:(id)object {
    self.object = object;
    return self;
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)selector {
    return [self.object methodSignatureForSelector:selector];
}

- (void)forwardInvocation:(NSInvocation *)invocation {
    [invocation invokeWithTarget:self.object];
}

@end

您可以在代码中的某处编写：

let proxy = (id<WKScriptMessageHandler>)[WeakProxy weakProxy:self];
[configuration.userContentController addScriptMessageHandler:proxy name:KLoginResponseHandler];

使用 WKScriptMessageHandler 时内存泄漏

Memory leak when using WKScriptMessageHandler

macos

memory-leaks

webkit

ios

javascriptcore