Hangs when closing db drivers

[rblazek]

Module hangs if db drivers are not closed in revers order to the order in which were opened. For example open driver A, open driver B, close driver A hangs forever on waitpid() in G_wait() because driver process does not exit when its stdin is closed in db_shutdown_driver() by fclose(driver->send). fclose() returns 0 (ok). The driver is probably hanging on db__recv_procnum() even if stdin was closed.

It is fixed by enabling procedure DB_PROC_SHUTDOWN_DRIVER like it is used on Window. Patch attached.

[rblazek]

Annother fix suggested by Glynn and resolving the real problem also works ​https://lists.osgeo.org/pipermail/grass-dev/2015-October/076925.html

        void close_on_exec(int fd)
        {
        #ifndef __MINGW32__
            int flags = fcntl(fd, F_GETFD);
            fcntl(fd, F_SETFD, flags | FD_CLOEXEC);
        #endif
        }

        close_on_exec(p1[READ]);
        close_on_exec(p1[WRITE]);
        close_on_exec(p2[READ]);
        close_on_exec(p2[WRITE]);

Patch attached.

[rblazek]

Suggested by Glynn, FD_CLOEXEC

[neteler]

To apply the second patch? Also backport it?

[rblazek]

More from Glynn about the possibility to close all descriptors ​https://lists.osgeo.org/pipermail/grass-dev/2015-October/077010.html which does not seem to be optimal.

I think that both patches should be applied. The second is resolving the real problem. The first, explicitly sending close procedure to driver cannot harm and it should also cover all cases when a descriptor is opened (even not db related) without setting FD_CLOEXEC.

Backport would be useful.

[neteler]

Likely relevant for the winGRASS (64bit), promoting to blocker since patches are provided.

[martinl]

I took liberty to apply both patches in trunk (r67290). Testing highly welcomed before we do backport to relbr70 (must be done before 7.0.3RC1)

[mlennert]

Replying to martinl:

I took liberty to apply both patches in trunk (r67290). Testing highly welcomed before we do backport to relbr70 (must be done before 7.0.3RC1)

Any ideas of how to test this specifically ?

[martinl]

Replying to mlennert:

Replying to martinl:

I took liberty to apply both patches in trunk (r67290). Testing highly welcomed before we do backport to relbr70 (must be done before 7.0.3RC1)

Any ideas of how to test this specifically ?

svn cat https://svn.osgeo.org/grass/sandbox/martinl/test-2775.c > test-2775.c
gcc test-2775.c -I/path/to/grassheaders -lgrass_dbmiclient -L/path/to/grasslibs
./a.out

will hang when closing db1

closing db1

[martinl]

After testing I took liberty to backport changes also to relbr70 - r67369. Now the sample program finishes successfully also here.

closing db1
closing db2

[martinl]

Closing the ticket, feel free to re-open if needed.