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.
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;
}
}
...
}
}
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.