bug#33018: 26.1.50; thread starvation with async processes and accept-process-output

["Basil L. Contovounesios" <contovob@tcd.ie>]

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#0  0x00007ffff766a2a4 in __GI___libc_write (fd=1, buf=0x5555559c1b30, nbytes=4096)
    at ../sysdeps/unix/sysv/linux/write.c:27
#1  0x00007ffff75fb56d in _IO_new_file_write (f=0x7ffff7739760 <_IO_2_1_stdout_>, 
    data=0x5555559c1b30, n=4096) at fileops.c:1203
#2  0x00007ffff75fa88f in new_do_write (fp=0x7ffff7739760 <_IO_2_1_stdout_>, 
    data=0x5555559c1b30 "pan></span></h2>\n<p>Emacs is primarily a <a href=\"/wiki/Text_editor\" title=\"Text editor\">text editor</a> and is designed for manipulating pieces of text, although it is capable of formatting and print"..., to_do=to_do@entry=4096) at fileops.c:457
#3  0x00007ffff75fc6f9 in _IO_new_do_write (fp=<optimized out>, data=<optimized out>, 
    to_do=4096) at fileops.c:433
#4  0x00007ffff75fa6d8 in _IO_new_file_sync (fp=0x7ffff7739760 <_IO_2_1_stdout_>)
    at fileops.c:813
#5  0x00007ffff75ef6ed in __GI__IO_fflush (fp=0x7ffff7739760 <_IO_2_1_stdout_>) at iofflush.c:40
#6  0x00005555555918bb in write_data (out=0x7ffff7739760 <_IO_2_1_stdout_>, out2=0x0, 
    buf=0x5555559a9590 "pan></span></h2>\n<p>Emacs is primarily a <a href=\"/wiki/Text_editor\" title=\"Text editor\">text editor</a> and is designed for manipulating pieces of text, although it is capable of formatting and print"..., bufsize=4096, skip=0x7fffffffd0e8, 
    written=0x7fffffffd0e0) at retr.c:207
#7  0x000055555559204f in fd_read_body (downloaded_filename=0x5555555e18a0 "-", fd=4, 
    out=0x7ffff7739760 <_IO_2_1_stdout_>, toread=198224, startpos=0, qtyread=0x7fffffffda20, 
    qtywritten=0x7fffffffd9d0, elapsed=0x7fffffffda28, flags=1, out2=0x0) at retr.c:498
#8  0x000055555557d09d in read_response_body (hs=0x7fffffffd9d0, sock=4, 
    fp=0x7ffff7739760 <_IO_2_1_stdout_>, contlen=198224, contrange=0, 
    chunked_transfer_encoding=false, url=0x5555555ff920 "https://en.wikipedia.org/wiki/Emacs", 
    warc_timestamp_str=0x7fffffffd470 "\f\335\377\377\377\177", 
    warc_request_uuid=0x7fffffffd440 ",", warc_ip=0x0, type=0x5555559c8fc0 "text/html", 
    statcode=200, 
    head=0x5555559b35d0 "HTTP/1.1 200 OK\r\nDate: Wed, 17 Oct 2018 17:29:35 GMT\r\nContent-Type: text/html; charset=UTF-8\r\nContent-Length: 198224\r\nConnection: keep-alive\r\nServer: mw1325.eqiad.wmnet\r\nVary: Accept-Encoding,Cookie,A"...) at http.c:1717
#9  0x0000555555581b06 in gethttp (u=0x5555555ff8b0, original_url=0x5555555ff8b0, 
    hs=0x7fffffffd9d0, dt=0x7fffffffdd0c, proxy=0x0, iri=0x5555555ff880, count=1) at http.c:4129
#10 0x0000555555582239 in http_loop (u=0x5555555ff8b0, original_url=0x5555555ff8b0, 
    newloc=0x7fffffffdb68, local_file=0x7fffffffdb58, referer=0x0, dt=0x7fffffffdd0c, 
    proxy=0x0, iri=0x5555555ff880) at http.c:4363
#11 0x0000555555592ca4 in retrieve_url (orig_parsed=0x5555555ff8b0, 
    origurl=0x5555555ff490 "https://en.wikipedia.org/wiki/Emacs", file=0x7fffffffdd18, 
    newloc=0x7fffffffdd10, refurl=0x0, dt=0x7fffffffdd0c, recursive=false, iri=0x5555555ff880, 
    register_status=true) at retr.c:957
#12 0x000055555558b33e in main (argc=3, argv=0x7fffffffdef8) at main.c:2158

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Eli Zaretskii <eliz@gnu.org> writes:

> Can you attach a debugger to the wget process that's stuck, and see
> where it is stuck?  You will probably need to rebuild wget with debug
> info, or install one from your package repository (if they offer
> such).  This could give us hints for where to look further.

I did the following:

0. Build wget 1.19.5 from Debian's repositories:
   apt-get build-dep wget
   apt-get source wget
   configure CC='ccache gcc' CFLAGS='-O0 -g3 -ggdb -gdwarf-4 -pipe'
             --config-cache --enable-assert --with-gnu-ld
   make
1. Substitute resulting wget file name in original test.el program
2. emacs26 -Q -l test.el -f test-threads
3. gdb -p <pid of stuck wget>
4. set logging on
5. bt

I attach the resulting gdb.txt log file.

Thanks,

-- 
Basil