漫畫安卓：LeakCanary源碼解析

時間 2019-11-08

標籤 leakcanary 源碼解析欄目 Android 简体版

原文原文鏈接

LeakCanary.install(this)源碼以下所示：

public static RefWatcher install(Application application) {
        return ((AndroidRefWatcherBuilder)refWatcher(application).listenerServiceClass(DisplayLeakService.class).excludedRefs(AndroidExcludedRefs.createAppDefaults().build())).buildAndInstall();
    }
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listenerServiceClass(DisplayLeakService.class)：用於分析內存泄漏結果信息，而後發送通知給用戶。 excludedRefs(AndroidExcludedRefs.createAppDefaults().build())：設置須要忽略的對象，好比某些系統漏洞不須要統計。 buildAndInstall()：真正檢測內存泄漏的方法，下面將展開分析該方法。bash

public RefWatcher buildAndInstall() {
        RefWatcher refWatcher = this.build();
        if(refWatcher != RefWatcher.DISABLED) {
            LeakCanary.enableDisplayLeakActivity(this.context);
            ActivityRefWatcher.installOnIcsPlus((Application)this.context, refWatcher);
        }

        return refWatcher;
    }
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能夠看到，上面方法主要作了三件事情： 1.實例化RefWatcher對象，該對象主要做用是檢測是否有對象未被回收致使內存泄漏； 2.設置APP圖標可見； 3.檢測內存 app

RefWatcher的使用後面講，這邊主要看第二件事情的處理過程，及enableDisplayLeakActivity方法的源碼

public static void enableDisplayLeakActivity(Context context) {
        LeakCanaryInternals.setEnabled(context, DisplayLeakActivity.class, true);
    }
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public static void setEnabled(Context context, final Class<?> componentClass, final boolean enabled) {
        final Context appContext = context.getApplicationContext();
        executeOnFileIoThread(new Runnable() {
            public void run() {
                LeakCanaryInternals.setEnabledBlocking(appContext, componentClass, enabled);
            }
        });
    }
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public static void setEnabledBlocking(Context appContext, Class<?> componentClass, boolean enabled) {
        ComponentName component = new ComponentName(appContext, componentClass);
        PackageManager packageManager = appContext.getPackageManager();
        int newState = enabled?1:2;
        packageManager.setComponentEnabledSetting(component, newState, 1);
    }
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可見，最後調用packageManager.setComponentEnabledSetting（）方法，實現應用圖標的隱藏和顯示。 dom

接下來，進入真正的內存檢查的方法installOnIcsPlus（）

public static void installOnIcsPlus(Application application, RefWatcher refWatcher) {
        if(VERSION.SDK_INT >= 14) {
            ActivityRefWatcher activityRefWatcher = new ActivityRefWatcher(application, refWatcher);
            activityRefWatcher.watchActivities();
        }
    }
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該方法實例化出ActivityRefWatcher 對象，該對象用來監聽activity的生命週期，具體實現以下所示：學習

public void watchActivities() {
        this.stopWatchingActivities();
        this.application.registerActivityLifecycleCallbacks(this.lifecycleCallbacks);
    }
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private final ActivityLifecycleCallbacks lifecycleCallbacks = new ActivityLifecycleCallbacks() {
        public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
        }

        public void onActivityStarted(Activity activity) {
        }

        public void onActivityResumed(Activity activity) {
        }

        public void onActivityPaused(Activity activity) {
        }

        public void onActivityStopped(Activity activity) {
        }

        public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
        }

        public void onActivityDestroyed(Activity activity) {
            ActivityRefWatcher.this.onActivityDestroyed(activity);
        }
    };
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調用了registerActivityLifecycleCallbacks方法後，當Activity執行onDestroy方法後，會觸發ActivityLifecycleCallbacks 的onActivityDestroyed方法，在當前方法中，調用refWatcher的watch方法，前面已經講過RefWatcher對象主要做用是檢測是否有對象未被回收致使內存泄漏。下面繼續看refWatcher的watch方法源碼：

public void watch(Object watchedReference) {
        this.watch(watchedReference, "");
    }

    public void watch(Object watchedReference, String referenceName) {
        if(this != DISABLED) {
            Preconditions.checkNotNull(watchedReference, "watchedReference");
            Preconditions.checkNotNull(referenceName, "referenceName");
            long watchStartNanoTime = System.nanoTime();
            String key = UUID.randomUUID().toString();
            this.retainedKeys.add(key);
            KeyedWeakReference reference = new KeyedWeakReference(watchedReference, key, referenceName, this.queue);
            this.ensureGoneAsync(watchStartNanoTime, reference);
        }
    }
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能夠看到，上面方法主要作了三件事情： 1.生成一個隨機數key存放在retainedKeys集合中，用來判斷對象是否被回收； 2.把當前Activity放到KeyedWeakReference（WeakReference的子類）中； 3.經過查找ReferenceQueue，看該Acitivity是否存在，存在則證實能夠被正常回收，不存在則證實可能存在內存泄漏。前兩件事很簡單，這邊主要看第三件事情的處理過程，及ensureGoneAsync方法的源碼：ui

private void ensureGoneAsync(final long watchStartNanoTime, final KeyedWeakReference reference) {
        this.watchExecutor.execute(new Retryable() {
            public Result run() {
                return RefWatcher.this.ensureGone(reference, watchStartNanoTime);
            }
        });
    }
    
  Result ensureGone(KeyedWeakReference reference, long watchStartNanoTime) {
        long gcStartNanoTime = System.nanoTime();
        long watchDurationMs = TimeUnit.NANOSECONDS.toMillis(gcStartNanoTime - watchStartNanoTime);
        this.removeWeaklyReachableReferences();
        if(this.debuggerControl.isDebuggerAttached()) {
            return Result.RETRY;
        } else if(this.gone(reference)) {
            return Result.DONE;
        } else {
            this.gcTrigger.runGc();
            this.removeWeaklyReachableReferences();
            if(!this.gone(reference)) {
                long startDumpHeap = System.nanoTime();
                long gcDurationMs = TimeUnit.NANOSECONDS.toMillis(startDumpHeap - gcStartNanoTime);
                File heapDumpFile = this.heapDumper.dumpHeap();
                if(heapDumpFile == HeapDumper.RETRY_LATER) {
                    return Result.RETRY;
                }

                long heapDumpDurationMs = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startDumpHeap);
                this.heapdumpListener.analyze(new HeapDump(heapDumpFile, reference.key, reference.name, this.excludedRefs, watchDurationMs, gcDurationMs, heapDumpDurationMs));
            }

            return Result.DONE;
        }
    }
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該方法中首先執行removeWeaklyReachableReferences()，從ReferenceQueue隊列中查詢是否存在該弱引用對象，若是不爲空，則說明已經被系統回收了，則將對應的隨機數key從retainedKeys集合中刪除。this

private void removeWeaklyReachableReferences() {
        KeyedWeakReference ref;
        while((ref = (KeyedWeakReference)this.queue.poll()) != null) {
            this.retainedKeys.remove(ref.key);
        }
    }
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而後經過判斷retainedKeys集合中是否存在對應的key判斷該對象是否被回收。spa

private boolean gone(KeyedWeakReference reference) {
        return !this.retainedKeys.contains(reference.key);
    }
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若是沒有被系統回收，則手動調用gcTrigger.runGc();後再調用removeWeaklyReachableReferences方法判斷該對象是否被回收。線程

GcTrigger DEFAULT = new GcTrigger() {
        public void runGc() {
            Runtime.getRuntime().gc();
            this.enqueueReferences();
            System.runFinalization();
        }

        private void enqueueReferences() {
            try {
                Thread.sleep(100L);
            } catch (InterruptedException var2) {
                throw new AssertionError();
            }
        }
    };
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第三行代碼爲手動觸發GC，緊接着線程睡100毫秒，給系統回收的時間，隨後經過System.runFinalization()手動調用已經失去引用對象的finalize方法。經過手動GC該對象還不能被回收的話，則存在內存泄漏，調用heapDumper.dumpHeap()生成.hprof文件目錄，並經過heapdumpListener回調到analyze()方法，後面關於dump文件的分析這邊就不介紹了，感興趣的能夠自行去看。 debug