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Cygwin: FIFO: find a new owner when closing

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If the owning reader is closing, wait for another reader (if there is
one) to take ownership before closing the owner's pipe handles.

To synchronize the ownership transfer, add events owner_needed_evt and
owner_found_evt, and add methods owner_needed and owner_found to
set/reset them.

Modify the fifo_reader_thread function to wake up all non-owners when
a new owner is needed.

Make a cosmetic change in close so that fhandler_base::close is called
only if we have a write handle.  This prevents strace output from
being littered with statements that the null handle is being closed.
This commit is contained in:
Ken Brown
2020-04-24 09:05:12 -04:00
parent 39a9cd9465
commit f35dfff3de
2 changed files with 112 additions and 11 deletions
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14
winsup/cygwin/fhandler.h
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@@ -1359,6 +1359,10 @@ class fhandler_fifo: public fhandler_base
HANDLE write_ready; /* A writer is open; OK for a reader to open. */
HANDLE writer_opening; /* A writer is opening; no EOF. */
/* Handles to named events needed by all readers of a given FIFO. */
HANDLE owner_needed_evt; /* The owner is closing. */
HANDLE owner_found_evt; /* A new owner has taken over. */
/* Handles to non-shared events needed for fifo_reader_threads. */
HANDLE cancel_evt; /* Signal thread to terminate. */
HANDLE thr_sync_evt; /* The thread has terminated. */
@@ -1405,6 +1409,16 @@ class fhandler_fifo: public fhandler_base
fifo_reader_id_t get_prev_owner () const { return shmem->get_prev_owner (); }
void set_prev_owner (fifo_reader_id_t fr_id)
{ shmem->set_prev_owner (fr_id); }
void owner_needed ()
{
ResetEvent (owner_found_evt);
SetEvent (owner_needed_evt);
}
void owner_found ()
{
ResetEvent (owner_needed_evt);
SetEvent (owner_found_evt);
}
int get_shared_nhandlers () { return shmem->get_shared_nhandlers (); }
void set_shared_nhandlers (int n) { shmem->set_shared_nhandlers (n); }