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Cygwin: FIFO: allow any reader to take ownership

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Add a take_ownership method, used by raw_read and select.cc:peek_fifo.
It wakes up all fifo_reader_threads and allows the caller to become
owner.  The work is done by the fifo_reader_threads.

For synchronization we introduce several new fhandler_fifo data
members and methods:

- update_needed_evt signals the current owner to stop listening for
  writer connections and update its fc_handler list.

- shared_fc_handler() gets and sets the status of the fc_handler
  update process.

- get_pending_owner() and set_pending_owner() get and set the reader
  that is requesting ownership.

Finally, a new 'reading_lock' prevents two readers from trying to take
ownership simultaneously.
This commit is contained in:
Ken Brown
2020-04-25 09:54:18 -04:00
parent f35dfff3de
commit bf66a56cca
3 changed files with 122 additions and 16 deletions
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28
winsup/cygwin/fhandler.h
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@ -1323,12 +1323,13 @@ struct fifo_reader_id_t
class fifo_shmem_t
{
LONG _nreaders;
fifo_reader_id_t _owner, _prev_owner;
af_unix_spinlock_t _owner_lock;
fifo_reader_id_t _owner, _prev_owner, _pending_owner;
af_unix_spinlock_t _owner_lock, _reading_lock;
/* Info about shared memory block used for temporary storage of the
owner's fc_handler list. */
LONG _sh_nhandlers, _sh_shandlers, _sh_fc_handler_committed;
LONG _sh_nhandlers, _sh_shandlers, _sh_fc_handler_committed,
_sh_fc_handler_updated;
public:
int inc_nreaders () { return (int) InterlockedIncrement (&_nreaders); }
@ -1338,9 +1339,13 @@ public:
void set_owner (fifo_reader_id_t fr_id) { _owner = fr_id; }
fifo_reader_id_t get_prev_owner () const { return _prev_owner; }
void set_prev_owner (fifo_reader_id_t fr_id) { _prev_owner = fr_id; }
fifo_reader_id_t get_pending_owner () const { return _pending_owner; }
void set_pending_owner (fifo_reader_id_t fr_id) { _pending_owner = fr_id; }
void owner_lock () { _owner_lock.lock (); }
void owner_unlock () { _owner_lock.unlock (); }
void reading_lock () { _reading_lock.lock (); }
void reading_unlock () { _reading_lock.unlock (); }
int get_shared_nhandlers () const { return (int) _sh_nhandlers; }
void set_shared_nhandlers (int n) { InterlockedExchange (&_sh_nhandlers, n); }
@ -1350,6 +1355,9 @@ public:
{ return (size_t) _sh_fc_handler_committed; }
void set_shared_fc_handler_committed (size_t n)
{ InterlockedExchange (&_sh_fc_handler_committed, (LONG) n); }
bool shared_fc_handler_updated () const { return _sh_fc_handler_updated; }
void shared_fc_handler_updated (bool val)
{ InterlockedExchange (&_sh_fc_handler_updated, val); }
};
class fhandler_fifo: public fhandler_base
@ -1362,6 +1370,7 @@ class fhandler_fifo: public fhandler_base
/* 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. */
HANDLE update_needed_evt; /* shared_fc_handler needs updating. */
/* Handles to non-shared events needed for fifo_reader_threads. */
HANDLE cancel_evt; /* Signal thread to terminate. */
@ -1409,6 +1418,11 @@ 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); }
fifo_reader_id_t get_pending_owner () const
{ return shmem->get_pending_owner (); }
void set_pending_owner (fifo_reader_id_t fr_id)
{ shmem->set_pending_owner (fr_id); }
void owner_needed ()
{
ResetEvent (owner_found_evt);
@ -1430,6 +1444,10 @@ class fhandler_fifo: public fhandler_base
{ shmem->set_shared_fc_handler_committed (n); }
int update_my_handlers (bool from_exec = false);
int update_shared_handlers ();
bool shared_fc_handler_updated () const
{ return shmem->shared_fc_handler_updated (); }
void shared_fc_handler_updated (bool val)
{ shmem->shared_fc_handler_updated (val); }
public:
fhandler_fifo ();
@ -1449,6 +1467,10 @@ public:
void owner_lock () { shmem->owner_lock (); }
void owner_unlock () { shmem->owner_unlock (); }
void take_ownership ();
void reading_lock () { shmem->reading_lock (); }
void reading_unlock () { shmem->reading_unlock (); }
int open (int, mode_t);
off_t lseek (off_t offset, int whence);
int close ();