[PATCH 12/12] Cygwin: FIFO: update commentary
Thu Jul 16 16:19:15 GMT 2020
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
@@ -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
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