[PATCH 00/12] FIFO: fix multiple reader support

[Ken Brown]

There were several flaws in my previous attempt to add support for
explicitly opening a FIFO multiple times for reading.  (By
"explicitly" I mean by calling open rather than by calling
fork/exec/dup.)  See

  https://sourceware.org/pipermail/cygwin/2020-July/245456.html

for one indication of problems

The most important flaw was that I tried to use an indirect,
unreliable method for determining whether there are writers open.
This is fixed in the second patch of this series by adding a member
'_nwriters' to struct fifo_shmem_t, which counts the number of open
writers.

We now have to give writers access to the shared memory as well as
readers, so that they can increment _nwriters in open/fork/exec/dup
and decrement it in close.

The other patches contain miscellaneous fixes/improvements.

Ken Brown (12):
  Cygwin: FIFO: fix problems finding new owner
  Cygwin: FIFO: keep a writer count in shared memory
  Cygwin: fhandler_fifo::hit_eof: improve reliability
  Cygwin: FIFO: reduce I/O interleaving
  Cygwin: FIFO: improve taking ownership in fifo_reader_thread
  Cygwin: FIFO: fix indentation
  Cygwin: FIFO: make certain errors non-fatal
  Cygwin: FIFO: add missing lock
  Cygwin: fhandler_fifo::take_ownership: don't set event unnecessarily
  Cygwin: FIFO: allow take_ownership to be interrupted
  Cygwin: FIFO: clean up
  Cygwin: FIFO: update commentary

 winsup/cygwin/fhandler.h       |  55 +--
 winsup/cygwin/fhandler_fifo.cc | 725 ++++++++++++++++++---------------
 winsup/cygwin/select.cc        |  14 +-
 3 files changed, 433 insertions(+), 361 deletions(-)

-- 
2.27.0