356 lines
13 KiB
Scheme
356 lines
13 KiB
Scheme
;;; Unix wait & process objects for scsh
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;;; Copyright (c) 1993, 1994, 1995 by Olin Shivers.
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;;; This is a GC'd abstraction for Unix process id's.
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;;; The problem with Unix pids is (a) they clutter up the kernel
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;;; process table until you wait(2) them, and (b) you can only
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;;; wait(2) them once. Scsh's process objects are similar, but
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;;; allow the storage to be allocated in the scsh address space,
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;;; and out of the kernel process table, and they can be waited on
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;;; multiple times.
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;;; Process objects
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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(define-record proc ; A process object
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pid ; Proc's pid.
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(finished? #f) ; Running, stopped, done
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(status (make-placeholder)) ; The cached exit status of the process
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(zombie #t) ; Misnomer. Whether or not the process has
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; (not) been waited on.
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;; Make proc objects print like #{proc 2318}.
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((disclose p) (list "proc" (proc:pid p))))
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;; Weak pointer tables. Much more efficient than populations.
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;; Maps pids to processes. Unexited processes are strong pointers, exited
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;; procs are weak pointers (to allow gc'ing).
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(define process-table (make-integer-table))
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(define (weak-table-ref t n)
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(let ((r (table-ref t n)))
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(if (weak-pointer? r)
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(weak-pointer-ref r)
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r)))
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(define (weak-table-set! t n s)
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(table-set! t n (make-weak-pointer s)))
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(define (weaken-table-ref! t n)
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(weak-table-set! t n (weak-table-ref t n)))
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(define (maybe-pid->proc pid)
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(weak-table-ref process-table pid))
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(define (pid->proc pid . maybe-probe?)
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(let ((probe? (:optional maybe-probe? #f)))
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(or (maybe-pid->proc pid)
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(case probe?
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((#f) (error "Pid has no corresponding process object" pid))
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((create) (let ((p (make-proc pid))) ; Install a new one.
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;; Weak because we don't know what's up with this thing.
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(weak-table-set! process-table pid p)
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p))
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(else #f)))))
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;;; Coerce pids and procs to procs.
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(define (->proc proc/pid)
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(cond ((proc? proc/pid) proc/pid)
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((and (integer? proc/pid) (>= proc/pid 0))
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(pid->proc proc/pid))
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(else (error "Illegal parameter" ->proc proc/pid))))
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;;; Is X a pid or a proc?
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(define (pid/proc? x) (or (proc? x) (and (integer? x) (>= pid 0))))
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;;; Process reaping
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; "Reaping" a process means using wait(2) to move its exit status from the
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;;; kernel's process table into scsh, thus cleaning up the kernel's process
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;;; table and saving the value in a gc'd data structure, where it can be
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;;; referenced multiple times.
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;;;
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;;; - Stopped processes are never reaped, only dead ones. (May change -df)
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;;;
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;;; - Stopped process status codes are never cached in proc objects,
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;;; only status codes for dead processes. So you can wait for a
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;;; dead process multiple times, but only once per process-stop.
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;;; (May change -df)
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;;;
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;;; - Unfortunately, reaping a process loses the information specifying its
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;;; process group, so if a process is reaped into scsh, it cannot be
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;;; waited for by WAIT-PROCESS-GROUP. Notice that only dead processes are
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;;; reaped, not suspended ones. Programs almost never use WAIT-PROCESS-GROUP
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;;; to wait for dead processes, so this is not likely to be a problem. If
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;;; it is, turn autoreaping off with (autoreap-policy #f).
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;;; (This never worked right, and it might be wiped out completely -fd)
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;;;
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;;; - Reaping can be encouraged by calling (REAP-ZOMBIES).
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;;; (autoreap-policy [new-policy])
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;;; Watch this area
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(define *autoreap-policy* #f) ; Not exported from this module.
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(define (autoreap-policy . maybe-policy)
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(let ((old-policy *autoreap-policy*))
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(if (pair? maybe-policy)
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(let ((new-policy (car maybe-policy)))
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(cond ((pair? (cdr maybe-policy))
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(error "Too many args to autoreap-policy" maybe-policy))
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((not (memq new-policy '(early #f)))
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(error "Illegal autoreap policy." new-policy))
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(else (set! *autoreap-policy* new-policy)
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(if (eq? new-policy 'early)
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(set-interrupt-handler interrupt/chld
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(lambda (enabled-ints) (reap-zombies))))))))
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old-policy))
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;;; New (scsh 0.6)
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(define (install-autoreaping)
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(set-interrupt-handler interrupt/chld
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(lambda (enabled-ints)
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(reap-zombies))))
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;;; (reap-zombies) => bool
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;;; Move any zombies from the kernel process table into scsh.
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;;; Return true if no more outstanding children; #f if some still live.
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(define (reap-zombies)
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(let lp ()
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(receive (pid status) (%wait-any (bitwise-ior wait/poll wait/stopped-children))
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(if pid
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(begin (add-reaped-proc! pid status)
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; (format (current-error-port)
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; "Reaping ~d[~d]~%" pid status)
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(lp))
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status))))
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(define (new-child-proc pid)
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(let ((proc (make-proc pid)))
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(table-set! process-table pid proc)
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proc))
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(define (mark-proc-exited proc)
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(weaken-table-ref! process-table (proc:pid proc)))
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;;; (WAIT proc/pid [flags])
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; (wait proc/pid [flags]) => status or #f
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;;;
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;;; FLAGS (default 0) is the exclusive or of the following:
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;;; wait/poll
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;;; Return #f immediately if there are no
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;;; unwaited children available.
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;;; wait/stopped-children
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;;; Report on suspended children as well.
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;;;
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;;; If the process hasn't terminated (or suspended, if wait/stopped
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;;; is set) and wait/poll is set, return #f.
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;;; (I'm working on the flags -df)
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(define (wait pid/proc . maybe-flags)
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(let* ((flags (:optional maybe-flags 0))
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(proc (->proc pid/proc))
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(win (lambda (status)
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(mark-proc-waited! proc) ; Not eligible for a WAIT-ANY
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status)))
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(if (or (zero? (bitwise-and flags wait/poll))
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(proc:finished? proc))
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(win (placeholder-value (proc:status proc)))
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(proc:finished? proc))))
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;;; Another way to do it:
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;;; Every time we reap a process, we pop out of our SIGCHLD
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;;; block so that we can service an interrupt if the system
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;;; so wishes.
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;(define (wait/pid pid)
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; ((let lp ()
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; (blocking signal/chld
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; (or (waited pid) ; Previously waited or reaped
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; (receive (next-dead status) (reap-a-pid)
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; (if (= pid next-dead) (lambda () status)
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; lp)))))))
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;The above seems to use Olin's event model. Even so, I'm not
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;sure that's the best way to do that.
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;Generally correct idea, tho
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(define (cache-wait-status proc status)
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(cond ((and (integer? status)
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(not (status:stop-sig status))) ; He's dead, Jim.
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(placeholder-set! (proc:status proc) status) ; Cache exit status.
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(mark-proc-exited proc))) ; We're now gc'able.
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status)
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;;; (wait-any [flags]) => [proc status]
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; [#f #f] => non-blocking, none ready.
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;;; [#f #t] => no more.
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(define (wait-any . maybe-flags)
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(let ((flags (:optional maybe-flags 0)))
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(if (zero? (bitwise-and flags wait/poll))
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(let ((win (get-reaped-proc!)))
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(values win (placeholder-value (proc:status win))))
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;The rest of this is quite crude and can be safely ignored. -df
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(if (maybe-obtain-lock reaped-proc-pop-lock)
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(if (eq? reaped-proc-head reaped-proc-tail)
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(begin
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(release-lock reaped-proc-pop-lock)
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(values #f #f))
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(let* ((retnode (placeholder-value reaped-proc-head))
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(retval (weak-pointer-ref (reaped-proc:proc retnode))))
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(set! reaped-proc-head (reaped-proc:next retnode))
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(release-lock reaped-proc-pop-lock)
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(if retval
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(values retval (placeholder-value (proc:status retval)))
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(values #f #f))
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(values #f #f)))))))
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;;; (wait-process-group [proc-group flags]) => [proc status]
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; [#f #f] => non-blocking, none ready.
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;;; [#f #t] => no more.
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;;;
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;;;
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;;; If you are doing process-group waits, you do *not* want to use
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;;; early autoreaping, since the reaper loses process-group information.
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;;; (I'm working on it -df)
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(define (wait-process-group . args)
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(let-optionals args ((proc-group 0) (flags 0))
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(let ((proc-group (cond ((integer? proc-group) proc-group)
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((proc? proc-group) (proc:pid proc-group))
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(else (error "Illegal argument" wait-process-group
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proc-group)))))
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(receive (pid status) (%wait-process-group proc-group flags)
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(if pid
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(let ((proc (pid->proc pid)))
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(cache-wait-status proc status)
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(values proc status))
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(values pid status)))))) ; pid = #f -- Empty poll.
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;;; (%wait-any flags) (%wait-pid pid flags) (%wait-process-group pgrp flags)
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; Direct interfaces to waitpid(2) call.
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;;; [#f #f] means no processes ready on a non-blocking wait.
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;;; [#f #t] means no waitable process on wait-any.
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(define (%wait-pid pid flags)
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(let lp ()
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(receive (err pid status) (%wait-pid/errno pid flags)
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(cond ((not err) (and (not (zero? pid)) status)) ; pid=0 => none ready.
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((= err errno/intr) (lp))
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(else (errno-error err %wait-pid pid flags))))))
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(define (%wait-any flags)
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(let lp ()
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(receive (err pid status) (%wait-pid/errno -1 flags)
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(cond (err (cond ((= err errno/child) (values #f #t)) ; No more.
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((= err errno/intr) (lp))
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(else (errno-error err %wait-any flags))))
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((zero? pid) (values #f #f)) ; None ready.
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(else (values pid status))))))
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(define (%wait-process-group pgrp flags)
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(let lp ()
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(receive (err pid status) (%wait-pid/errno (- pgrp) flags)
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(cond (err (cond ((= err errno/child) (values #f #t)) ; No more.
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((= err errno/intr) (lp))
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(else (errno-error err %wait-process-group pgrp flags))))
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((zero? pid) (values #f #f)) ; None ready.
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(else (values pid status))))))
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;;; Reaped process table
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; We keep track of procs that have been reaped but not yet waited on by
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;;; the user's code. These proces are eligible for return by WAIT-ANY.
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;;; We keep track of these so that WAIT-ANY will hand them out exactly once.
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;;; What this code needs is traditional condition variables.
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;;; This is (so far) reliable in the following ways:
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;;; 1. No process will be returned twice by wait-any, ever. Even two different
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;;; wait-anys.
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;;; 2. Being un-reaped will not prevent garbage collection.
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;;; (actually, there seems to be a problem with this -df)
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;;; 3. If a process is waited on, or is gc'ed, wait-any will do the Right
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;;; Thing.
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;;; And UNreliable in the following ways:
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;;; 1. If a wait and a wait-any are blocking simultaneously, the wait will
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;;; always return the object. However, whether the wait-any will or not
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;;; is based on racing semaphores.
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;;; 2. While processes can still be garbage collected, the nodes on the
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;;; wait-any list will not, and if the program never wait-any's, the queue
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;;; will snake around, eating up memory like pac-man with the munchies.
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;;; 3. The process may be garbage collected before wait-any gets to it, and
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;;; that's just tough.
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;;; -df
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(define-record reaped-proc
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proc
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(next (make-placeholder))
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prev)
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(define reaped-proc-tail (make-placeholder))
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(define reaped-proc-head reaped-proc-tail)
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(define reaped-proc-push-lock (make-lock))
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(define reaped-proc-pop-lock (make-lock)) ;;; Zippy sez: pop lock!
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(define (push-reaped-proc proc)
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(obtain-lock reaped-proc-push-lock)
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(let ((push-me (make-reaped-proc (make-weak-pointer proc) reaped-proc-tail)))
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(placeholder-set! reaped-proc-tail push-me)
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; (add-finalizer! proc (lambda ignore (remove-reaped-proc push-me)))
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(set! reaped-proc-tail (reaped-proc:next push-me)))
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(release-lock reaped-proc-push-lock))
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(define (remove-reaped-proc reaped-proc)
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(spawn (lambda () ;This is blocking, so should run by itself
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(placeholder-set! (reaped-proc:prev reaped-proc)
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(placeholder-value
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(reaped-proc:next reaped-proc))))
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"reaped-proc-removing-thread"))
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(define (pop-reaped-proc)
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(obtain-lock reaped-proc-pop-lock) ;;; pop lock pop lock pop lock!
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(let ((pop-me (placeholder-value reaped-proc-head)))
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(set! reaped-proc-head (reaped-proc:next pop-me))
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(release-lock reaped-proc-pop-lock)
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(weak-pointer-ref (reaped-proc:proc pop-me))))
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(define (add-reaped-proc! pid status)
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(cond ((maybe-pid->proc pid) =>
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(lambda (proc)
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(placeholder-set! (proc:status proc) status)
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(set-proc:finished? proc #t)
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(push-reaped-proc proc)
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(mark-proc-exited proc))
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(else (warn "Exiting child pid has no proc object." pid status)))))
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;;; Pop one off the list.
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(define (get-reaped-proc!)
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(let loop ((try (pop-reaped-proc)))
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(if (and try (proc:zombie try))
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try
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(loop (pop-reaped-proc)))))
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;;; PROC no longer eligible to be in the list. Delete it.
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(define (mark-proc-waited! proc)
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(set-proc:zombie proc #f))
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