bug#19860: Acknowledgement (25.0.50; One url-retrieve-synchronously call running concurrently with another can freeze it)

[Dmitry Gutov]

And here's me attaching to that process:

0x00007fae43df32d9 in __pselect (nfds=nfds@entry=14, 
readfds=readfds@entry=0x7fffa07d4370, writefds=0x7fffa07d43f0, 
exceptfds=exceptfds@entry=0x0, timeout=<optimized out>, 
timeout@entry=0x7fffa07d4920,
    sigmask=sigmask@entry=0x0) at ../sysdeps/unix/sysv/linux/pselect.c:77
77      ../sysdeps/unix/sysv/linux/pselect.c: No such file or directory.
(gdb) finish
Run till exit from #0  0x00007fae43df32d9 in __pselect 
(nfds=nfds@entry=14, readfds=readfds@entry=0x7fffa07d4370, 
writefds=0x7fffa07d43f0, exceptfds=exceptfds@entry=0x0, 
timeout=<optimized out>,
    timeout@entry=0x7fffa07d4920, sigmask=sigmask@entry=0x0) at 
../sysdeps/unix/sysv/linux/pselect.c:77
0x00000000005b464a in xg_select (fds_lim=14, 
rfds=rfds@entry=0x7fffa07d4940, wfds=0x7fffa07d49c0, 
efds=efds@entry=0x0, timeout=timeout@entry=0x7fffa07d4920, 
sigmask=sigmask@entry=0x0) at xgselect.c:114
114       nfds = pselect (fds_lim, &all_rfds, have_wfds ? &all_wfds : NULL,
Value returned is $1 = 1
(gdb) finish
Run till exit from #0  0x00000000005b464a in xg_select (fds_lim=14, 
rfds=rfds@entry=0x7fffa07d4940, wfds=0x7fffa07d49c0, 
efds=efds@entry=0x0, timeout=timeout@entry=0x7fffa07d4920,
    sigmask=sigmask@entry=0x0) at xgselect.c:114
0x00000000005836e1 in wait_reading_process_output (time_limit=<optimized 
out>, nsecs=0, read_kbd=read_kbd@entry=0, 
do_display=do_display@entry=false, wait_for_cell=wait_for_cell@entry=0,
    wait_proc=0x351a938, just_wait_proc=0) at process.c:4597
4597              nfds = xg_select
Value returned is $2 = -1
(gdb) finish
Run till exit from #0  0x00000000005836e1 in wait_reading_process_output 
(time_limit=<optimized out>, nsecs=0, read_kbd=read_kbd@entry=0, 
do_display=do_display@entry=false,
    wait_for_cell=wait_for_cell@entry=0, wait_proc=0x351a938, 
just_wait_proc=0) at process.c:4597