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是否适合使用AtomicReference.compareAndSet来设置对数据库调用结果的引用？(Is it appropriate to use AtomicReference.compareAndSet to set a reference to the results of a database call?)
是否适合使用AtomicReference.compareAndSet来设置对数据库调用结果的引用？(Is it appropriate to use AtomicReference.compareAndSet to set a reference to the results of a database call?)
我正在实现一个简单的缓存，缓存存储为AtomicReference。
private AtomicReference<Map<String, String>> cacheData;应该从数据库表中填充（延迟）缓存对象。
我提供了一种方法来将缓存数据返回给调用者，但如果数据为空（即未加载），则代码需要从数据库加载数据。 为避免同步我想到使用compareAndSet（）方法：
public Object getCacheData() { cacheData.compareAndSet(null, getDataFromDatabase()); // atomic reload only if data not set! return Collections.unmodifiableMap(cacheData.get()); }以这种方式使用compareAndSet是否可以。 将数据库调用作为原子操作的一部分？ 是否比同步方法更好/更差？
非常感谢任何建议..
I am implementing a simple cache with the cache stored as an AtomicReference.
private AtomicReference<Map<String, String>> cacheData;The cache object should be populated (lazily) from a database table.
I provide a method to return the cache data to a caller, but if the data is null (ie. not loaded), then the code needs to load the data from the database. To avoid synchronized I thought of using the compareAndSet() method:
public Object getCacheData() { cacheData.compareAndSet(null, getDataFromDatabase()); // atomic reload only if data not set! return Collections.unmodifiableMap(cacheData.get()); }Is it ok to use compareAndSet in this way ie. to involve a database call as part of the atomic action? Is it any better/worse than just synchronizing the method?
Many thanks for any advice..
原文：https://stackoverflow.com/questions/12992478
更新时间：2023-11-10 09:11
最满意答案
布局：
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/activity_main" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:paddingBottom="@dimen/activity_vertical_margin" android:paddingTop="@dimen/activity_vertical_margin" tools:context="android.sample.MainActivity"> <TextView android:id="@+id/txtFont_size_hint" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Sizes"/> <LinearLayout android:id="@+id/ll" android:layout_width="match_parent" android:layout_height="wrap_content" android:padding="10dp" android:weightSum="5"> <LinearLayout android:id="@+id/ll" android:layout_width="match_parent" android:layout_height="wrap_content" android:weightSum="5"> <TextView android:id="@+id/txtSize1" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:gravity="center" android:text="@string/setting_font_text" android:textSize="15sp"/> <TextView android:id="@+id/txtSize_18" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:gravity="center" android:text="@string/setting_font_text" android:textSize="20sp"/> <TextView android:id="@+id/txtSize_24" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:focusable="false" android:gravity="center" android:text="@string/setting_font_text" android:textSize="25sp"/> <TextView android:id="@+id/textSize_30" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:focusable="false" android:gravity="center" android:text="@string/setting_font_text" android:textSize="30sp"/> <TextView android:id="@+id/txtSize_36" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:focusable="false" android:gravity="center" android:text="@string/setting_font_text" android:textSize="35sp"/> </LinearLayout> <SeekBar android:id="@+id/seekBarSetting_font_size" android:layout_width="match_parent" android:layout_height="wrap_content" android:max="4"/>现在我所做的是将Seekbar的宽度对齐到最后一个
TextView的中心，在这种情况下是txtSize_36并将ems设置为android:max="4"所以有五个可能的值（你可以将其更改为你想要的很多）活动代码是：
public class MainActivity extends AppCompatActivity { SeekBar seekBar; private LinearLayout bar, ll; TextView txtSize_14, txtSize_36; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); seekBar = (SeekBar) findViewById(R.id.seekBarSetting_font_size); txtSize_14 = (TextView) findViewById(R.id.txtSize1); txtSize_36 = (TextView) findViewById(R.id.txtSize_36); ll = (LinearLayout) findViewById(R.id.ll); } float density; @Override protected void onResume() { super.onResume(); ViewTreeObserver vto = ll.getViewTreeObserver(); //****old code (may not work on all orientations)**** /*vto.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() { @Override public void onGlobalLayout() { if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN) { ll.getViewTreeObserver().removeGlobalOnLayoutListener(this); } else { ll.getViewTreeObserver().removeOnGlobalLayoutListener(this); } int width = ll.getMeasuredWidth(); int height = ll.getMeasuredHeight(); ViewGroup.LayoutParams params = seekBar.getLayoutParams(); density = getResources().getDisplayMetrics().density; int newwidth = (int) (txtSize_14.getLeft() / density); newwidth = newwidth+ (txtSize_36.getLeft() + txtSize_36.getRight()) / 2; params.width = newwidth; seekBar.setLayoutParams(params); } });*/ //****new code (should work on all orientations)**** vto.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() { @Override public void onGlobalLayout() { if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN) { ll.getViewTreeObserver().removeGlobalOnLayoutListener(this); } else { ll.getViewTreeObserver().removeOnGlobalLayoutListener(this); } seekBar.setPadding(15, 0, 15, 0); seekBar.setX(((txtSize_14.getLeft() + txtSize_14.getRight()) / 2) - 15); ViewGroup.LayoutParams params = seekBar.getLayoutParams(); int centerwidth = ((txtSize_36.getLeft() + txtSize_36.getRight()) / 2) - ((txtSize_14.getLeft() + txtSize_14.getRight()) / 2) + 15; params.width = centerwidth; seekBar.setLayoutParams(params); } }); } }这是截图供参考（我已经为搜索栏的所有位置添加了棒球）：
layout for this :
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/activity_main" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:paddingBottom="@dimen/activity_vertical_margin" android:paddingTop="@dimen/activity_vertical_margin" tools:context="android.sample.MainActivity"> <TextView android:id="@+id/txtFont_size_hint" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Sizes"/> <LinearLayout android:id="@+id/ll" android:layout_width="match_parent" android:layout_height="wrap_content" android:padding="10dp" android:weightSum="5"> <LinearLayout android:id="@+id/ll" android:layout_width="match_parent" android:layout_height="wrap_content" android:weightSum="5"> <TextView android:id="@+id/txtSize1" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:gravity="center" android:text="@string/setting_font_text" android:textSize="15sp"/> <TextView android:id="@+id/txtSize_18" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:gravity="center" android:text="@string/setting_font_text" android:textSize="20sp"/> <TextView android:id="@+id/txtSize_24" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:focusable="false" android:gravity="center" android:text="@string/setting_font_text" android:textSize="25sp"/> <TextView android:id="@+id/textSize_30" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:focusable="false" android:gravity="center" android:text="@string/setting_font_text" android:textSize="30sp"/> <TextView android:id="@+id/txtSize_36" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:focusable="false" android:gravity="center" android:text="@string/setting_font_text" android:textSize="35sp"/> </LinearLayout> <SeekBar android:id="@+id/seekBarSetting_font_size" android:layout_width="match_parent" android:layout_height="wrap_content" android:max="4"/>Now what i have done is aligned the width of Seekbar till the center of the last
TextViewwhich in this case istxtSize_36and have set the ems asandroid:max="4"so there are five possible values(you can change this to as much as you want)Code for Activity is :
public class MainActivity extends AppCompatActivity { SeekBar seekBar; private LinearLayout bar, ll; TextView txtSize_14, txtSize_36; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); seekBar = (SeekBar) findViewById(R.id.seekBarSetting_font_size); txtSize_14 = (TextView) findViewById(R.id.txtSize1); txtSize_36 = (TextView) findViewById(R.id.txtSize_36); ll = (LinearLayout) findViewById(R.id.ll); } float density; @Override protected void onResume() { super.onResume(); ViewTreeObserver vto = ll.getViewTreeObserver(); //****old code (may not work on all orientations)**** /*vto.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() { @Override public void onGlobalLayout() { if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN) { ll.getViewTreeObserver().removeGlobalOnLayoutListener(this); } else { ll.getViewTreeObserver().removeOnGlobalLayoutListener(this); } int width = ll.getMeasuredWidth(); int height = ll.getMeasuredHeight(); ViewGroup.LayoutParams params = seekBar.getLayoutParams(); density = getResources().getDisplayMetrics().density; int newwidth = (int) (txtSize_14.getLeft() / density); newwidth = newwidth+ (txtSize_36.getLeft() + txtSize_36.getRight()) / 2; params.width = newwidth; seekBar.setLayoutParams(params); } });*/ //****new code (should work on all orientations)**** vto.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() { @Override public void onGlobalLayout() { if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN) { ll.getViewTreeObserver().removeGlobalOnLayoutListener(this); } else { ll.getViewTreeObserver().removeOnGlobalLayoutListener(this); } seekBar.setPadding(15, 0, 15, 0); seekBar.setX(((txtSize_14.getLeft() + txtSize_14.getRight()) / 2) - 15); ViewGroup.LayoutParams params = seekBar.getLayoutParams(); int centerwidth = ((txtSize_36.getLeft() + txtSize_36.getRight()) / 2) - ((txtSize_14.getLeft() + txtSize_14.getRight()) / 2) + 15; params.width = centerwidth; seekBar.setLayoutParams(params); } }); } }Here is screenshot for reference (I have clubbed for all positions of seekbar):
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