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

[Eli Zaretskii <eliz@gnu.org>]

> From: "Basil L. Contovounesios" <contovob@tcd.ie>
> Cc: <michael.albinus@gmx.de>,  <33018@debbugs.gnu.org>
> Date: Wed, 17 Oct 2018 18:37:00 +0100
> 
> #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

Looks like the buffer of the pipe through which Emacs reads the stuff
is full, and wget waits for some space there?