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https://issues.apache.org/jira/browse/FELIX-4195?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13742000#comment-13742000
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Matt Wiselka commented on FELIX-4195:
-------------------------------------
At least in my case it makes a huge difference. Consider the probability that a
power loss happens inbetween these calls and compare it to the probability of a
power loss in the 30-60 seconds it might take the OS to actually write the
changes to the flash memory.
Also, in our case if we would just silently ignore the empty preferences file
that would basically mean a reset. No more settings are available and the
bundle has to be reconfigured. In my case that would lead to an inconsistent
state that would make using the application impossible.
> Sync on a Preference doesn't do a OS side sync
> ----------------------------------------------
>
> Key: FELIX-4195
> URL: https://issues.apache.org/jira/browse/FELIX-4195
> Project: Felix
> Issue Type: Bug
> Components: Preferences Service
> Affects Versions: prefs-1.0.6
> Environment: Angstroem Embedded Linux
> UBIFS on a flash drive
> Reporter: Matt Wiselka
>
> I ran in to the following problem using the Preferences Service on an
> embedded device with a flash memory:
> When a preference is changed the sync method is called to persist it. A
> sudden power loss occurs. On restart the preference file in the bundle cache
> is empty and causes a BackingStoreException: Could not load preference.
> It seems to me as that the OS is caching the write to the flash drive and the
> change is not actually persisted. I was able to fix this issue by performing
> a sync on the FileDescriptor of the OutputStream in the store method of the
> DataFileBackingStoreImpl
> try {
> final FileOutputStream os = (FileOutputStream)
> this.getOutputStream(root.getDescription());
> this.write(root, os);
> os.getFD().sync();
> os.close();
> }
> catch (IOException ioe) {
> throw new BackingStoreException("Unable to store preferences.", ioe);
> }
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