Experimental Physics and
Industrial Control System

Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov> · Thu, 3 Mar 2022 08:47:59 -0800

On 3/3/22 08:16, Dudley, David via Tech-talk wrote:

If I do define ‘USE_TMPFILE’ (which was my original idea), it creates the temporary file, writes a proper record to it (I have checked this), and then calls ‘dbReadDatabaseFP’.

In this case, the IOC shows that it loaded the database, closed the file, and then I get a ‘free(): double free detected in tcache 2’ error and the IOC aborts.

It looks like dbReadDatabaseFP() will close the provided 'FILE*' on success,
and sometimes on failure[1].

So your code should not call fclose() after dbReadDatabaseFP().

eg.

https://github.com/mdavidsaver/pyDevSup/blob/ea5f0d62412085dfc941e8fe758695abdfdab548/devsupApp/src/dbapi.c#L219-L221

It may be worth noting that pyDevSup is the only usage of dbReadDatabaseFP()
I could find, and I doubt this aspect has had much testing.

fyi.  If you only need Linux support, you might look into fmemopen()

https://man7.org/linux/man-pages/man3/fmemopen.3.html

@Andrew

[1] Should the first error check should be changed to set 'status' and
    'goto cleanup' instead of returning immediately?

https://github.com/epics-base/epics-base/blob/d8c537945354f13433c685b5a6c6a30bc6dc6848/modules/database/src/ioc/dbStatic/dbLexRoutines.c#L226-L227

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System