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Cygwin: FIFO: designate one reader as owner

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Among all the open readers of a FIFO, one is declared to be the owner.
This is the only reader that listens for client connections, and it is
the only one that has an accurate fc_handler list.

Add shared data and methods for getting and setting the owner, as well
as a lock to prevent more than one reader from accessing these data
simultaneously.

Modify the fifo_reader_thread so that it checks the owner at the
beginning of its loop.  If there is no owner, it takes ownership.  If
there is an owner but it is a different reader, the thread just waits
to be canceled.  Otherwise, it listens for client connections as
before.

Remove the 'first' argument from create_pipe_instance.  It is not
needed, and it may be confusing in the future since only the owner
knows whether a pipe instance is the first.

When opening a reader, don't return until the fifo_reader_thread has
time to set an owner.

If the owner closes, indicate that there is no longer an owner.

Clear the child's fc_handler list in dup, and don't bother duplicating
the handles.  The child never starts out as owner, so it can't use
those handles.

Do the same thing in fixup_after_fork in the close-on-exec case.  In
the non-close-on-exec case, the child inherits an fc_handler list that
it can't use, but we can just leave it alone; the handles will be
closed when the child is closed.
This commit is contained in:
Ken Brown 2020-03-26 14:32:10 -04:00
parent 16e7c10578
commit 606baf5566
2 changed files with 143 additions and 111 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
winsup/cygwin/fhandler.h
View File

@ -1324,10 +1324,17 @@ struct fifo_reader_id_t
class fifo_shmem_t
{
LONG _nreaders;
fifo_reader_id_t _owner;
af_unix_spinlock_t _owner_lock;
public:
int inc_nreaders () { return (int) InterlockedIncrement (&_nreaders); }
int dec_nreaders () { return (int) InterlockedDecrement (&_nreaders); }
fifo_reader_id_t get_owner () const { return _owner; }
void set_owner (fifo_reader_id_t fr_id) { _owner = fr_id; }
void owner_lock () { _owner_lock.lock (); }
void owner_unlock () { _owner_lock.unlock (); }
};
class fhandler_fifo: public fhandler_base
@ -1356,7 +1363,7 @@ class fhandler_fifo: public fhandler_base
bool __reg2 wait (HANDLE);
static NTSTATUS npfs_handle (HANDLE &);
HANDLE create_pipe_instance (bool);
HANDLE create_pipe_instance ();
NTSTATUS open_pipe (HANDLE&);
NTSTATUS wait_open_pipe (HANDLE&);
int add_client_handler ();
@ -1384,6 +1391,10 @@ public:
void fifo_client_unlock () { _fifo_client_lock.unlock (); }
fifo_reader_id_t get_me () const { return me; }
fifo_reader_id_t get_owner () const { return shmem->get_owner (); }
void set_owner (fifo_reader_id_t fr_id) { shmem->set_owner (fr_id); }
void owner_lock () { shmem->owner_lock (); }
void owner_unlock () { shmem->owner_unlock (); }
int open (int, mode_t);
off_t lseek (off_t offset, int whence);

241
winsup/cygwin/fhandler_fifo.cc
View File

@ -164,7 +164,7 @@ fhandler_fifo::npfs_handle (HANDLE &nph)
blocking mode so that we can easily wait for a connection. After
it is connected, it is put in nonblocking mode. */
HANDLE
fhandler_fifo::create_pipe_instance (bool first)
fhandler_fifo::create_pipe_instance ()
{
NTSTATUS status;
HANDLE npfsh;
@ -187,14 +187,12 @@ fhandler_fifo::create_pipe_instance (bool first)
access = GENERIC_READ | FILE_READ_ATTRIBUTES | FILE_WRITE_ATTRIBUTES
| SYNCHRONIZE;
sharing = FILE_SHARE_READ | FILE_SHARE_WRITE;
hattr = openflags & O_CLOEXEC ? 0 : OBJ_INHERIT;
if (first)
hattr |= OBJ_CASE_INSENSITIVE;
hattr = (openflags & O_CLOEXEC ? 0 : OBJ_INHERIT) | OBJ_CASE_INSENSITIVE;
InitializeObjectAttributes (&attr, get_pipe_name (),
hattr, npfsh, NULL);
timeout.QuadPart = -500000;
status = NtCreateNamedPipeFile (&ph, access, &attr, &io, sharing,
first ? FILE_CREATE : FILE_OPEN, 0,
FILE_OPEN_IF, 0,
FILE_PIPE_MESSAGE_TYPE
| FILE_PIPE_REJECT_REMOTE_CLIENTS,
FILE_PIPE_MESSAGE_MODE,
@ -292,14 +290,13 @@ fhandler_fifo::add_client_handler ()
int ret = -1;
fifo_client_handler fc;
HANDLE ph = NULL;
bool first = (nhandlers == 0);
if (nhandlers == MAX_CLIENTS)
{
set_errno (EMFILE);
goto out;
}
ph = create_pipe_instance (first);
ph = create_pipe_instance ();
if (!ph)
goto out;
else
@ -349,92 +346,120 @@ fhandler_fifo::fifo_reader_thread_func ()
while (1)
{
/* Cleanup the fc_handler list. */
fifo_client_lock ();
int i = 0;
while (i < nhandlers)
fifo_reader_id_t cur_owner;
owner_lock ();
cur_owner = get_owner ();
if (!cur_owner)
{
if (fc_handler[i].state < fc_connected)
delete_client_handler (i);
else
i++;
set_owner (me);
owner_unlock ();
continue;
}
/* Create a new client handler. */
if (add_client_handler () < 0)
api_fatal ("Can't add a client handler, %E");
/* Listen for a writer to connect to the new client handler. */
fifo_client_handler& fc = fc_handler[nhandlers - 1];
fifo_client_unlock ();
NTSTATUS status;
IO_STATUS_BLOCK io;
bool cancel = false;
status = NtFsControlFile (fc.h, conn_evt, NULL, NULL, &io,
FSCTL_PIPE_LISTEN, NULL, 0, NULL, 0);
if (status == STATUS_PENDING)
else if (cur_owner != me)
{
HANDLE w[2] = { conn_evt, cancel_evt };
switch (WaitForMultipleObjects (2, w, false, INFINITE))
owner_unlock ();
WaitForSingleObject (cancel_evt, INFINITE);
goto canceled;
}
else
{
/* I'm the owner */
fifo_client_lock ();
/* Cleanup the fc_handler list. */
fifo_client_lock ();
int i = 0;
while (i < nhandlers)
{
case WAIT_OBJECT_0:
status = io.Status;
if (fc_handler[i].state < fc_connected)
delete_client_handler (i);
else
i++;
}
/* Create a new client handler. */
if (add_client_handler () < 0)
api_fatal ("Can't add a client handler, %E");
/* Listen for a writer to connect to the new client handler. */
fifo_client_handler& fc = fc_handler[nhandlers - 1];
fifo_client_unlock ();
owner_unlock ();
NTSTATUS status;
IO_STATUS_BLOCK io;
bool cancel = false;
status = NtFsControlFile (fc.h, conn_evt, NULL, NULL, &io,
FSCTL_PIPE_LISTEN, NULL, 0, NULL, 0);
if (status == STATUS_PENDING)
{
HANDLE w[2] = { conn_evt, cancel_evt };
switch (WaitForMultipleObjects (2, w, false, INFINITE))
{
case WAIT_OBJECT_0:
status = io.Status;
debug_printf ("NtFsControlFile STATUS_PENDING, then %y",
status);
break;
case WAIT_OBJECT_0 + 1:
status = STATUS_THREAD_IS_TERMINATING;
cancel = true;
break;
default:
api_fatal ("WFMO failed, %E");
}
}
else
debug_printf ("NtFsControlFile status %y, no STATUS_PENDING",
status);
HANDLE ph = NULL;
NTSTATUS status1;
fifo_client_lock ();
switch (status)
{
case STATUS_SUCCESS:
case STATUS_PIPE_CONNECTED:
record_connection (fc);
break;
case WAIT_OBJECT_0 + 1:
status = STATUS_THREAD_IS_TERMINATING;
cancel = true;
case STATUS_PIPE_CLOSING:
record_connection (fc, fc_closing);
break;
case STATUS_THREAD_IS_TERMINATING:
/* Try to connect a bogus client. Otherwise fc is still
listening, and the next connection might not get recorded. */
status1 = open_pipe (ph);
WaitForSingleObject (conn_evt, INFINITE);
if (NT_SUCCESS (status1))
/* Bogus cilent connected. */
delete_client_handler (nhandlers - 1);
else
/* Did a real client connect? */
switch (io.Status)
{
case STATUS_SUCCESS:
case STATUS_PIPE_CONNECTED:
record_connection (fc);
break;
case STATUS_PIPE_CLOSING:
record_connection (fc, fc_closing);
break;
default:
debug_printf ("NtFsControlFile status %y after failing to connect bogus client or real client", io.Status);
fc.state = fc_unknown;
break;
}
break;
default:
api_fatal ("WFMO failed, %E");
break;
}
fifo_client_unlock ();
if (ph)
NtClose (ph);
if (cancel)
goto canceled;
}
HANDLE ph = NULL;
NTSTATUS status1;
fifo_client_lock ();
switch (status)
{
case STATUS_SUCCESS:
case STATUS_PIPE_CONNECTED:
record_connection (fc);
break;
case STATUS_PIPE_CLOSING:
record_connection (fc, fc_closing);
break;
case STATUS_THREAD_IS_TERMINATING:
/* Try to connect a bogus client. Otherwise fc is still
listening, and the next connection might not get recorded. */
status1 = open_pipe (ph);
WaitForSingleObject (conn_evt, INFINITE);
if (NT_SUCCESS (status1))
/* Bogus cilent connected. */
delete_client_handler (nhandlers - 1);
else
/* Did a real client connect? */
switch (io.Status)
{
case STATUS_SUCCESS:
case STATUS_PIPE_CONNECTED:
record_connection (fc);
break;
case STATUS_PIPE_CLOSING:
record_connection (fc, fc_closing);
break;
default:
debug_printf ("NtFsControlFile status %y after failing to connect bogus client or real client", io.Status);
fc.state = fc_unknown;
break;
}
break;
default:
break;
}
fifo_client_unlock ();
if (ph)
NtClose (ph);
if (cancel)
goto canceled;
}
canceled:
if (conn_evt)
@ -580,6 +605,15 @@ fhandler_fifo::open (int flags, mode_t)
me.winpid = GetCurrentProcessId ();
me.fh = this;
new cygthread (fifo_reader_thread, this, "fifo_reader", thr_sync_evt);
/* Wait until there's an owner. */
owner_lock ();
while (!get_owner ())
{
owner_unlock ();
yield ();
owner_lock ();
}
owner_unlock ();
/* If we're a duplexer, we need a handle for writing. */
if (duplexer)
@ -1014,6 +1048,10 @@ fhandler_fifo::close ()
if (dec_nreaders () == 0)
ResetEvent (read_ready);
cancel_reader_thread ();
owner_lock ();
if (get_owner () == me)
set_owner (null_fr_id);
owner_unlock ();
if (cancel_evt)
NtClose (cancel_evt);
if (thr_sync_evt)
@ -1056,7 +1094,6 @@ fhandler_fifo::fcntl (int cmd, intptr_t arg)
int
fhandler_fifo::dup (fhandler_base *child, int flags)
{
int i = 0;
fhandler_fifo *fhf = NULL;
if (get_flags () & O_PATH)
@ -1092,6 +1129,9 @@ fhandler_fifo::dup (fhandler_base *child, int flags)
/* Make sure the child starts unlocked. */
fhf->fifo_client_unlock ();
/* Clear fc_handler list; the child never starts as owner. */
fhf->nhandlers = 0;
if (!DuplicateHandle (GetCurrentProcess (), shmem_handle,
GetCurrentProcess (), &fhf->shmem_handle,
0, !(flags & O_CLOEXEC), DUPLICATE_SAME_ACCESS))
@ -1101,25 +1141,8 @@ fhandler_fifo::dup (fhandler_base *child, int flags)
}
if (fhf->reopen_shmem () < 0)
goto err_close_shmem_handle;
fifo_client_lock ();
for (i = 0; i < nhandlers; i++)
{
if (!DuplicateHandle (GetCurrentProcess (), fc_handler[i].h,
GetCurrentProcess (), &fhf->fc_handler[i].h,
0, !(flags & O_CLOEXEC), DUPLICATE_SAME_ACCESS))
{
__seterrno ();
break;
}
}
if (i < nhandlers)
{
fifo_client_unlock ();
goto err_close_handlers;
}
fifo_client_unlock ();
if (!(fhf->cancel_evt = create_event ()))
goto err_close_handlers;
goto err_close_shmem;
if (!(fhf->thr_sync_evt = create_event ()))
goto err_close_cancel_evt;
inc_nreaders ();
@ -1129,9 +1152,7 @@ fhandler_fifo::dup (fhandler_base *child, int flags)
return 0;
err_close_cancel_evt:
NtClose (fhf->cancel_evt);
err_close_handlers:
for (int j = 0; j < i; j++)
fhf->fc_handler[j].close ();
err_close_shmem:
NtUnmapViewOfSection (GetCurrentProcess (), fhf->shmem);
err_close_shmem_handle:
NtClose (fhf->shmem_handle);
@ -1160,10 +1181,10 @@ fhandler_fifo::fixup_after_fork (HANDLE parent)
fork_fixup (parent, shmem_handle, "shmem_handle");
if (reopen_shmem () < 0)
api_fatal ("Can't reopen shared memory during fork, %E");
fifo_client_lock ();
for (int i = 0; i < nhandlers; i++)
fork_fixup (parent, fc_handler[i].h, "fc_handler[].h");
fifo_client_unlock ();
if (close_on_exec ())
/* Prevent a later attempt to close the non-inherited
pipe-instance handles copied from the parent. */
nhandlers = 0;
if (!(cancel_evt = create_event ()))
api_fatal ("Can't create reader thread cancel event during fork, %E");
if (!(thr_sync_evt = create_event ()))