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Cygwin: FIFO: keep track of the number of readers

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Add data and methods to the shared memory that keep track of the
number of open readers.

Increment this number in open, dup, fork, and exec.  Decrement it in
close.  Reset read_ready if there are no readers left.
This commit is contained in:
Ken Brown 2020-03-27 09:43:30 -04:00
parent 878eb22462
commit 365818a4a5
2 changed files with 22 additions and 8 deletions
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8
winsup/cygwin/fhandler.h
View File

@ -1303,6 +1303,11 @@ struct fifo_client_handler
/* Info needed by all readers of a FIFO, stored in named shared memory. */
class fifo_shmem_t
{
LONG _nreaders;
public:
int inc_nreaders () { return (int) InterlockedIncrement (&_nreaders); }
int dec_nreaders () { return (int) InterlockedDecrement (&_nreaders); }
};
class fhandler_fifo: public fhandler_base
@ -1342,6 +1347,9 @@ class fhandler_fifo: public fhandler_base
int create_shmem ();
int reopen_shmem ();
int inc_nreaders () { return shmem->inc_nreaders (); }
int dec_nreaders () { return shmem->dec_nreaders (); }
public:
fhandler_fifo ();
bool hit_eof ();

22
winsup/cygwin/fhandler_fifo.cc
View File

@ -570,8 +570,9 @@ fhandler_fifo::open (int flags, mode_t)
SetEvent (read_ready);
if (create_shmem () < 0)
goto err_close_writer_opening;
inc_nreaders ();
if (!(cancel_evt = create_event ()))
goto err_close_shmem;
goto err_dec_nreaders;
if (!(thr_sync_evt = create_event ()))
goto err_close_cancel_evt;
new cygthread (fifo_reader_thread, this, "fifo_reader", thr_sync_evt);
@ -680,7 +681,10 @@ err_close_reader:
return 0;
err_close_cancel_evt:
NtClose (cancel_evt);
err_close_shmem:
err_dec_nreaders:
if (dec_nreaders () == 0)
ResetEvent (read_ready);
/* err_close_shmem: */
NtUnmapViewOfSection (NtCurrentProcess (), shmem);
NtClose (shmem_handle);
err_close_writer_opening:
@ -1003,15 +1007,13 @@ fhandler_fifo::close ()
{
if (reader)
{
if (dec_nreaders () == 0)
ResetEvent (read_ready);
cancel_reader_thread ();
if (cancel_evt)
NtClose (cancel_evt);
if (thr_sync_evt)
NtClose (thr_sync_evt);
/* FIXME: There could be several readers open because of
dup/fork/exec; we should only reset read_ready when the last
one closes. */
ResetEvent (read_ready);
if (shmem)
NtUnmapViewOfSection (NtCurrentProcess (), shmem);
if (shmem_handle)
@ -1116,8 +1118,8 @@ fhandler_fifo::dup (fhandler_base *child, int flags)
goto err_close_handlers;
if (!(fhf->thr_sync_evt = create_event ()))
goto err_close_cancel_evt;
new cygthread (fifo_reader_thread, fhf, "fifo_reader",
fhf->thr_sync_evt);
inc_nreaders ();
new cygthread (fifo_reader_thread, fhf, "fifo_reader", fhf->thr_sync_evt);
}
return 0;
err_close_cancel_evt:
@ -1161,6 +1163,7 @@ fhandler_fifo::fixup_after_fork (HANDLE parent)
api_fatal ("Can't create reader thread cancel event during fork, %E");
if (!(thr_sync_evt = create_event ()))
api_fatal ("Can't create reader thread sync event during fork, %E");
inc_nreaders ();
new cygthread (fifo_reader_thread, this, "fifo_reader", thr_sync_evt);
}
}
@ -1180,6 +1183,9 @@ fhandler_fifo::fixup_after_exec ()
api_fatal ("Can't create reader thread cancel event during exec, %E");
if (!(thr_sync_evt = create_event ()))
api_fatal ("Can't create reader thread sync event during exec, %E");
/* At this moment we're a new reader. The count will be
decremented when the parent closes. */
inc_nreaders ();
new cygthread (fifo_reader_thread, this, "fifo_reader", thr_sync_evt);
}
}