共享preferences和线程安全 [英] SharedPreferences and Thread Safety

问题描述

纵观<一href="http://developer.android.com/reference/android/content/Shared$p$pferences.html">Shared$p$pferences文档它说：

注：目前这一类不   跨多个进程的支持使用。   这将在以后添加。

"Note: currently this class does not support use across multiple processes. This will be added later."

所以本身它不会出现是线程安全的。但是，什么样的担保都是由在问候commit（）和应用（）？

So in and of itself it doesn't appear to be Thread Safe. However, what kind of guarantees are made in regards to commit() and apply()?

例如：

synchronized(uniqueIdLock){
   uniqueId = sharedPreferences.getInt("UNIQUE_INCREMENTING_ID", 0);
   uniqueId++;
   sharedPreferences.edit().putInt("UNIQUE_INCREMENTING_ID", uniqueId).commit();
}

难道是保证了UNIQUEID总是在这种情况下，唯一的？

Would it be guaranteed that the uniqueId was always unique in this case?

如果不是，是否有更好的方法来跟踪一个独特的ID为持续申请？

If not, is there a better way to keep track of a unique id for an application that persists?

推荐答案

进程和线程不同。在Android上的共享preferences实现是线程安全的，但不是过程安全。通常，您的应用程序将在同一个进程中运行的所有，但它可能为你把它配置在AndroidManifest.xml所以，比如说，该服务运行在比，也就是说，活动一个单独的进程。

Processes and Threads are different. The SharedPreferences implementation in Android is thread-safe but not process-safe. Normally your app will run all in the same process, but it's possible for you to configure it in the AndroidManifest.xml so, say, the service runs in a separate process than, say, the activity.

要验证的纤维性安全，请参阅ContextImpl.java的共享preferenceImpl从AOSP。注意：有一个同步的，无论你期望那里是一个。

To verify the thready safety, see the ContextImpl.java's SharedPreferenceImpl from AOSP. Note there's a synchronized wherever you'd expect there to be one.

private static final class SharedPreferencesImpl implements SharedPreferences {
...
    public String getString(String key, String defValue) {
        synchronized (this) {
            String v = (String)mMap.get(key);
            return v != null ? v : defValue;
        }
   }
...
    public final class EditorImpl implements Editor {
        public Editor putString(String key, String value) {
            synchronized (this) {
                mModified.put(key, value);
                return this;
            }
        }
    ...
    }
}

不过，对于你的情况的唯一ID看来你还是要同步，你不希望它get和看跌之间切换。

However for your case of the unique id it seems you'd still want a synchronized as you don't want it to change between the get and the put.

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