From 521bb3cb6c2df817b9b626bccec79f86c91820c9 Mon Sep 17 00:00:00 2001
From: Omooo <869759698@qq.com>
Date: Mon, 30 Mar 2020 16:08:28 +0800
Subject: [PATCH] =?UTF-8?q?Create=20IdleHandler=20=E5=8E=9F=E7=90=86.md?=
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 .../线程通信相关/IdleHandler 原理.md  | 87 +++++++++++++++++++
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 create mode 100644 blogs/Android/Framework/Interview/线程通信相关/IdleHandler 原理.md

diff --git a/blogs/Android/Framework/Interview/线程通信相关/IdleHandler 原理.md b/blogs/Android/Framework/Interview/线程通信相关/IdleHandler 原理.md
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@@ -0,0 +1,87 @@
+---
+IdleHandler 原理
+---
+
+1. 了解 IdleHandler 的作用以及调用方式
+2. 了解 IdleHandler 有哪些使用场景
+3. 熟悉 IdleHandler 的实现原理
+
+```java
+public static interface IdleHandler{
+	boolean queueIdle();
+}
+```
+
+```java
+Looper.myQueue().addIdleHandler(new MessageQueue.IdleHandler()){
+	@Override
+    public boolean queueIdle(){
+        return true;
+    }
+}
+
+public void addIdleHandler(IdleHandler handler){
+    synchronized(this){
+        mIdleHandler.add(handler);
+    }
+}
+Message next(){
+    for(;;){
+        nativePollOnce(ptr, nextPollTimeoutMillis);
+        // 看消息列表是否有消息可以分发的，如果有，就返回该消息
+        // 走到这说明没有消息可以分发，下一个 for 循环就要进入休眠了
+        if(pendingIdleHandlerCount<0){
+            pendingIdleHandlercount = mIdleHandlers.size();
+        }
+        if(pendingIdleHandlerCount<0){
+            continue;
+        }
+        mPendingIdleHandlers = mIdleHandlers.toArray(mPendingIdleHandlers);
+        for(int i=0;i<pendingIdleHandlerCount;i++){
+            final IdleHandler idler = mPendingIdleHandlers[i];
+            if(!(idler.queueIdle())){
+                mIdleHandlers.remove(idler);
+            }
+        }
+    }
+}
+```
+
+Framework 哪些地方用到了 IdleHandler 呢？
+
+```java
+// ActivityThread#scheduleGcIdler
+void scheduleGcIdler(){
+	if(!mGcIdlerScheduled){
+        mGcIdlerScheduled = true;
+        Looper.myQueue().addIdleHandler(mGcIdler);
+    }
+    mH.removeMessages(H.GC_WHEN_IDLE);
+}
+final class GcIdler implements MessageQueue.IdleHandler{
+    @Override
+    public final boolean queueIdle(){
+        // BinderInternal.forceGc("bg");
+        doGcIfNeeded();
+        return false;
+    }
+}
+// ActivityThread#waitForIdle
+public void waitForIdle(Runnable recipient){
+    mMessageQueue.addIdleHandler(new Idler(recipient));
+    mThread.getHandler().post(new EmptyRunnable());
+}
+private static final class Idler implements MessageQueue.IdleHandler{
+    public final boolean queueIdle(){
+        if(mCallback!=null){
+            mCallback.run();
+        }
+        return false;
+    }
+}
+```
+
+#### 适用场景
+
+1. 延时处理
+2. 批量任务
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