[Asterisk-Dev] hang in ast_read/capi_read? Debug suggestions?

[Philip Warner]

I am using * from a CVS on the 16th, and I have a Fritz card used to 
receive incoming calls (with patches to make it work with the latest CVS). 
It works fine in normal circumstances. I added:

    exten => s,1,Wait,2

to the start of the initial context the ISDN call comes into, and it waited 
too short a time, so I changed it to:

    exten => s,1,Wait,12

Now, the Wait never returns.

Using 'capi debug' in the console produces no errors. I have attached to * 
using gdb, both before and after the timer would run out, and I see the 
following differences:

BEFORE expiry:

Thread 2 (Thread 1089379248 (LWP 3716)):
#0  0xffffe410 in ?? ()
#1  0x40ee33d8 in ?? ()
#2  0x00002ee0 in ?? ()
#3  0x00000002 in ?? ()
#4  0x401aa494 in poll () from /lib/tls/libc.so.6
#5  0x08061df7 in ast_waitfor_nandfds (c=0x40ee34f0, n=1, fds=0x0, nfds=0, 
exception=0x0, outfd=0x0, ms=0x40ee34f4)
     at channel.c:1113
#6  0x08062577 in ast_waitfor_n (c=0xfffffffc, n=-4, ms=0xfffffffc) at 
channel.c:1182
#7  0x080632e5 in ast_waitfor (c=0x40f00630, ms=12000) at channel.c:1189
#8  0x080635f2 in ast_safe_sleep (chan=0x40f00630, ms=12000) at channel.c:581
#9  0x08080dcd in pbx_exec (c=0x40f00630, app=0x80fd318, data=0x40ee7700, 
newstack=1) at pbx.c:528
#10 0x08081d01 in pbx_extension_helper (c=0x40f00630, con=Variable "con" is 
not available.
) at pbx.c:1640
#11 0x08083068 in ast_pbx_run (c=0x40f00630) at pbx.c:2289
#12 0x0808441f in pbx_thread (data=0xfffffffc) at pbx.c:2470
#13 0x400447f3 in start_thread () from /lib/tls/libpthread.so.0
#14 0x401b362a in clone () from /lib/tls/libc.so.6


AFTER expiry:

Thread 2 (Thread 1088674736 (LWP 3633)):
#0  0xffffe410 in ?? ()
#1  0x40e37498 in ?? ()
#2  0x00000030 in ?? ()
#3  0x08131060 in ?? ()
#4  0x40048f8b in __read_nocancel () from /lib/tls/libpthread.so.0
#5  0x404609f7 in capi_read (c=0xfffffe00) at chan_capi.c:949
#6  0x08061833 in ast_read (chan=0x40f00668) at channel.c:1415
#7  0x080635d5 in ast_safe_sleep (chan=0x40f00668, ms=2) at channel.c:585
#8  0x08080dcd in pbx_exec (c=0x40f00668, app=0x80fd318, data=0x40e3b700, 
newstack=1) at pbx.c:528
#9  0x08081d01 in pbx_extension_helper (c=0x40f00668, con=Variable "con" is 
not available.
) at pbx.c:1640
#10 0x08083068 in ast_pbx_run (c=0x40f00668) at pbx.c:2289
#11 0x0808441f in pbx_thread (data=0xfffffe00) at pbx.c:2470
#12 0x400447f3 in start_thread () from /lib/tls/libpthread.so.0
#13 0x401b362a in clone () from /lib/tls/libc.so.6

and it stays like this until the caller hangs up.

The relevant code is:

int ast_safe_sleep(struct ast_channel *chan, int ms)
{
         struct ast_frame *f;
         while(ms > 0) {
                 ms = ast_waitfor(chan, ms);
                 if (ms <0)
                         return -1;
                 if (ms > 0) {
???                     f = ast_read(chan);
                         if (!f)
                                 return -1;
                         ast_frfree(f);
                 }
         }
         return 0;
}

...in my case, ms is 2, so the '???' bit gets called.

I don't know enough about the internals of this to understand what is going 
on.

Naievely, I wondered if capi_read should return at all if the call has not 
yet been answered, so I added an 'Answer' before the 'Wait', and the 
problem went away. But this is not an option in the dialplan.

I would appreciate any insights or suggestions for further investigation.



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