[gpsd-users] Shared memory interface with gpsd restart results in no data for client

[Michael Lum]

Hi,

 

I'm using the source from gpsd 3.17 on CentOS 7, Ublox NEO 7 GPS receiver, shared memory interface.

 

If I send a SIGSEGV to the gpsd or just do a quick stop/start my client program does not "see" any data

for a long time.

 

The shared memory segment is the old one because the client is still attached.

 

Code executing in gpsd:

 

shmexport.c

 

'tick' that goes into the bookends is a static (initialized to zero, correct?).

Incremented immediately and used in the bookends.

So everytime gpsd starts the tick value in the bookend will start at '1'.

 

Code executing in client:

 

libgps_shm.c

 

gps_shm_open() uses malloc() to allocate memory for privdata_t.

This contains the pointer to the shared memory segment and a

 

int tick

 

member. 

(Shouldn't 'tick' have been zeroed?)

 

gps_shm_waiting() checks that the bookend1 value is greater than the 'tick' in the privdata.

　

But the privdata->tick could be very large depending on how long the original gpsd instance was running.

 

 

In addition I believe there will be a wrap around problem when the bookend1 value wraps to a negative.

 

 

Best regards,

 

Michael Lum

 

Michael Lum (address@hidden) | STAR SOLUTIONS | Principal Software Engineer

4600 Jacombs Road, Richmond BC, Canada V6V 3B1 | +1.604.303.2315