ape: fix thread race with close() and select()

in ape close(), do the real filedescriptor _CLOSE() *after* we cleared
the _fdinfo[] slot because once closed, we dont own the slot anymore and
another process doing open() can trash the slot. make sure open() retuns
fd < OPEN_MAX.

double check in _startbuf() holding mux->lock if the fd is already buffered
preveting running double copyprocs on a fd.

dont zero the mux->rwant/ewant bitmaps at the end of select() as we do not
hold the mix->lock.

in _closebuf() kill copyproc while holding the mux->lock to make sure the
copyproc isnt holding it at the time it is killed. run kill() multiple times
to make sure the proc is gone.

1 files changed, 3 insertions, 3 deletions

diff --git a/sys/src/ape/lib/ap/plan9/close.c b/sys/src/ape/lib/ap/plan9/close.c
index 258788a39..0b86d2009 100644
--- a/sys/src/ape/lib/ap/plan9/close.c
+++ b/sys/src/ape/lib/ap/plan9/close.c
@@ -20,15 +20,15 @@ close(int d)
 				_closebuf(d);
 			f->flags &= ~FD_BUFFERED;
 		}
-		n = _CLOSE(d);
-		if(n < 0)
-			_syserrno();
 		_fdinfo[d].flags = 0;
 		_fdinfo[d].oflags = 0;
 		if(_fdinfo[d].name){
 			free(_fdinfo[d].name);
 			_fdinfo[d].name = 0;
 		}
+		n = _CLOSE(d);
+		if(n < 0)
+			_syserrno();
 	}
 	return n;
 }