Knowing that close-port was called on a port is not sufficient to tell if the port is “closed” or not. Apart from what it means for a port to be “closed”, there are ports that don’t close permanently when close-port is called on them. See the example below of a pipe used for the communication between two threads. It allows using close-port to send an “end-of-file” to the other thread multiple times.
For “device” ports however, there is a state in the port object at the C level. The fields read_stage and write_stage will be different from ___STAGE_OPEN when the device port no longer accepts reading or writing. Perhaps that is the information you want. Note that not all ports are device ports.
Marc
(define in #f) (define out #f)
(receive (i o) (open-string-pipe (list permanent-close: #f)) (set! in i) (set! out o))
(define (send x) (write x out) (newline out) (force-output out) (thread-sleep! 0.5))
(define (close) (close-output-port out) (thread-sleep! 0.5))
(thread-start! (make-thread (lambda () (let loop () (let ((x (read in))) (pp x) (loop))))))
(send '(11)) (send '(22))
(close)
(send '(33)) (send '(44))
(close) (close)
(send '(55))
;; output: ;; (11) ;; (22) ;; #!eof ;; (33) ;; (44) ;; #!eof ;; #!eof ;; (55)
On Mar 24, 2018, at 5:51 AM, Dimitris Vyzovitis vyzo@hackzen.org wrote:
You can't tell if a file descriptor is closed in general, that's not what I am after. I just want to know if close-port was applied to the port.
-- vyzo
On Sat, Mar 24, 2018 at 11:43 AM, Adam adam.mlmb@gmail.com wrote: The BSD/unix API does not allow this for TCP sockets, as in tapping into the OS' knowledge of whether a connection was closed, the only way to learn that is by trying to write to it.
However with respect to Gambit knowing whether |close-port| was applied on a port, of course you should be able to retrieve that.
2018-03-24 16:29 GMT+08:00 Dimitris Vyzovitis vyzo@hackzen.org: Is there a reasonable way to detect whether a port has been closed? I want to implement input-port-open? and output-port-open? for r7rs coverage...
-- vyzo
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