From: Ken Brown <kbrown@cornell.edu>
To: cygwin-patches@cygwin.com
Subject: [PATCH 12/12] Cygwin: FIFO: update commentary
Date: Thu, 16 Jul 2020 12:19:15 -0400 [thread overview]
Message-ID: <20200716161915.16994-13-kbrown@cornell.edu> (raw)
In-Reply-To: <20200716161915.16994-1-kbrown@cornell.edu>
---
winsup/cygwin/fhandler_fifo.cc | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/winsup/cygwin/fhandler_fifo.cc b/winsup/cygwin/fhandler_fifo.cc
index 30486304f..e9d0187d4 100644
--- a/winsup/cygwin/fhandler_fifo.cc
+++ b/winsup/cygwin/fhandler_fifo.cc
@@ -52,10 +52,23 @@
which is mostly idle. The thread wakes up if that reader might
need to take ownership.
- There is a block of shared memory, accessible to all readers,
- that contains information needed for the owner change process.
- It also contains some locks to prevent races and deadlocks
- between the various threads.
+ There is a block of named shared memory, accessible to all
+ fhandlers for a given FIFO. It keeps track of the number of open
+ readers and writers; it contains information needed for the owner
+ change process; and it contains some locks to prevent races and
+ deadlocks between the various threads.
+
+ The shared memory is created by the first reader to open the
+ FIFO. It is opened by subsequent readers and by all writers. It
+ is destroyed by Windows when the last handle to it is closed.
+
+ If a handle to it somehow remains open after all processes
+ holding file descriptors to the FIFO have closed, the shared
+ memory can persist and be reused with stale data by the next
+ process that opens the FIFO. So far I've seen this happen only
+ as a result of a bug in the code, but there are some debug_printf
+ statements in fhandler_fifo::open to help detect this if it
+ happens again.
At this writing, I know of only one application (Midnight
Commander when running under tcsh) that *explicitly* opens two
--
2.27.0
next prev parent reply other threads:[~2020-07-16 16:19 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-16 16:19 [PATCH 00/12] FIFO: fix multiple reader support Ken Brown
2020-07-16 16:19 ` [PATCH 01/12] Cygwin: FIFO: fix problems finding new owner Ken Brown
2020-07-16 16:19 ` [PATCH 02/12] Cygwin: FIFO: keep a writer count in shared memory Ken Brown
2020-07-16 16:19 ` [PATCH 03/12] Cygwin: fhandler_fifo::hit_eof: improve reliability Ken Brown
2020-07-16 16:19 ` [PATCH 04/12] Cygwin: FIFO: reduce I/O interleaving Ken Brown
2020-07-16 16:19 ` [PATCH 05/12] Cygwin: FIFO: improve taking ownership in fifo_reader_thread Ken Brown
2020-07-16 16:19 ` [PATCH 06/12] Cygwin: FIFO: fix indentation Ken Brown
2020-07-16 16:19 ` [PATCH 07/12] Cygwin: FIFO: make certain errors non-fatal Ken Brown
2020-07-16 16:19 ` [PATCH 08/12] Cygwin: FIFO: add missing lock Ken Brown
2020-07-16 16:19 ` [PATCH 09/12] Cygwin: fhandler_fifo::take_ownership: don't set event unnecessarily Ken Brown
2020-07-16 16:19 ` [PATCH 10/12] Cygwin: FIFO: allow take_ownership to be interrupted Ken Brown
2020-07-16 16:19 ` [PATCH 11/12] Cygwin: FIFO: clean up Ken Brown
2020-07-16 16:19 ` Ken Brown [this message]
2020-07-16 19:57 ` [PATCH 00/12] FIFO: fix multiple reader support Corinna Vinschen
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