SharedPreferences in Android not getting recently updated values across multiple running processes

Question

Description: I have two apps App1 and App2. I am using App1 to store some key value pair in SharedPreferences. I am accessing the same key value in App2.

I launch app1. Create a key with value abc. Now I keep app1 in background and launch App2 and I change the key value to def.

When I launch app1 from background to foreground and access the key value. Value retrieved is abc instead of updated value def. If I kill App2 from background and relaunch it then only updated value is getting reflected

Have you tried to call `getSharedPreferences()` with `MODE_WORLD_WRITEABLE`? Or `MODE_MULTI_PROCESS` (deprecated in API 23) ? — sininen, Oct 10 '17 at 16:40
Yes I tried this. It works if the mode is mode_multi_process. But my requirement is to use mode_private — Shivani srivastava, Oct 10 '17 at 16:44
With `MODE_PRIVATE` only applications with the same user ID can access the Shared Preferences. Take a look here: https://stackoverflow.com/questions/6354035/two-android-applications-with-the-same-user-id — sininen, Oct 10 '17 at 16:48
Are you trying to access the value of the SharedPreference in `onCreate`? If yes, try in `onResume`. — sininen, Oct 10 '17 at 17:02
https://developer.android.com/reference/android/content/Context.html#MODE_MULTI_PROCESS Here it says that `MODE_MULTI_PROCESS` was the standard behavior in Android 2.3. That's why it worked with API 8. If you don't want to change the mode maybe you should use a content provider: https://developer.android.com/guide/topics/providers/content-providers.html — sininen, Oct 10 '17 at 17:12
Thanks. Yes m researching on using content provider in place of SharedPreferences for my requirement — Shivani srivastava, Oct 10 '17 at 17:15

score 8 · Accepted Answer · answered Oct 10 '17 at 16:12

8

SharedPreferences has never supported multiple processes, let alone multiple apps. The documentation explicitly states:

Note: This class does not support use across multiple processes.

answered Oct 10 '17 at 16:12

CommonsWare

986,068
189
2,389
2,491

But this issue doesn't come if minsdk is set to 8 in app1. It only occurs when min sdk is greater than 8. How is this issue related to min sdk – Shivani srivastava Oct 10 '17 at 16:22
@Shivanisrivastava: `minSdkVersion` has no runtime impact. It merely controls where your app can be installed. – CommonsWare Oct 10 '17 at 16:53
https://stackoverflow.com/questions/8710076/cannot-share-sharedpreferences-between-activity-and-remote-service-android-bug – Shivani srivastava Oct 10 '17 at 17:00
The above link mention similar issue – Shivani srivastava Oct 10 '17 at 17:00
@Shivanisrivastava: `minSdkVersion` is not mentioned on that page, as you can tell by searching that page for `minSdkVersion`. – CommonsWare Oct 10 '17 at 17:01
But it It is happening in my case. – Shivani srivastava Oct 10 '17 at 17:02
@Shivanisrivastava: Since Google has indicated that `SharedPreferences` do not work across multiple processes, perhaps you should not use `SharedPreferences` across multiple processes. – CommonsWare Oct 10 '17 at 17:04
Yes will search for other possible solutions. But still if this issue could be resolved using SharedPreferences itself that would have been great – Shivani srivastava Oct 10 '17 at 17:12

score 0 · Answer 2 · answered Oct 10 '17 at 16:14

0

The value doesn't get updated as the SharedPreferences doesn't recognize data change across multiple processes.

answered Oct 10 '17 at 16:14

Kartik Shandilya

3,796
5
24
42

But this issue doesn't occur if the min sdk is set to 8 in manifest of app1. – Shivani srivastava Oct 10 '17 at 16:33
Are you sure with it? The Shared Preferences came in API Level 1 and this isn't mentioned in docs as well. – Kartik Shandilya Oct 10 '17 at 16:35
Yes there is no documentation related to this. But I am facing this issue. Not sure about the relation of SharedPreferences with min sdk. It works properly fine if I getsharedpreferences in multi_mode processes. But I want to use mode_private – Shivani srivastava Oct 10 '17 at 16:40

Nabin Bhandari · Answer 3 · 2017-10-10T16:21:01.577

0

The shared preferences of an app are stored in a separate file within the app's internal storage which no other apps can access. The shared preferences of two different apps are located in two different locations and are independent of each other.

So the shared preferences of an app cannot be accessed by any other apps and change in the shared preferences of an app is not reflected in any other apps.

edited Oct 10 '17 at 16:21

answered Oct 10 '17 at 16:14

Nabin Bhandari

15,949
6
45
59

It can be accessed if both of these apps have the same shared user id in manifest – Shivani srivastava Oct 10 '17 at 16:21

score 0 · Answer 4 · answered Oct 10 '17 at 16:35

When process reads the data from the SharedPreferences, it copies the values (data) and puts those data inside it's process inside the cache. It does this because reading/writing from disk is too slow. Generally, System creates cache process for Android Components. Now, your data from the SharedPreferences is stored in the component's cache process. Cache process has it's own memory space. Until the component is using the memory, it locks (critical section) in order to prevent other can't access that memory. The cache process should be killed so that other processes (or components) can now be able to access it. This is why when you relaunch you see the update.

Critical Section: https://en.wikipedia.org/wiki/Critical_section

Different Processes: https://developer.android.com/guide/components/activities/process-lifecycle.html

In thread-level, you use the keyword volatile, so that you see the one thread updated data from second thread. But SharedPreferences can't be volatile because it is persistent storage.

That's why they explicitly stated SharedPreferences doesn't support on multiple processes

I don't know yet. I don't think it is possible. Because when a process goes in critical section it locks its memory space. After it gets killed it flushes that data to SharedPreferences. Now, another process can get the updated value. I am also researching on it, will let you know if I know... — Uddhav P. Gautam, Oct 10 '17 at 17:01

score 0 · Answer 5 · answered Oct 10 '17 at 18:16

Sharedpreferences are not process safe as per their documentation. I ran into a similar problem. I was using a value from sharedpreferences within an activity and then in a service with another process. The same value was behaving like two different values.

Well i used this lib to solve this problem. Its basically the same approach and syntax and its process safe.

score 0 · Answer 6 · edited May 05 '20 at 14:47

0

SharedPreferences has never supported multiple processes, let alone multiple apps. The documentation explicitly states:

Note: This class does not support use across multiple processes.

SharedPreferences had to be replaced with content provider in my case.

edited May 05 '20 at 14:47

m02ph3u5

3,022
7
38
51

answered May 05 '20 at 13:36

Shivani srivastava

47
7

SharedPreferences in Android not getting recently updated values across multiple running processes

6 Answers6