292 lines
10 KiB
Scheme
292 lines
10 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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(%status #f) ; The cached exit status of the process;
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; #f if we haven't wait(2)'d the process yet.
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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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;;; Indexing this table by pid requires a linear scan.
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;;; Probably not an important op, tho.
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(define process-table (make-population))
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(define (maybe-pid->proc pid)
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(call/cc (lambda (quit)
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;; Search the table.
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(walk-population (lambda (p)
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(if (= (proc:pid p) pid) (quit p)))
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process-table)
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#f)))
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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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(add-to-population! p process-table)
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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.
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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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;;;
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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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;;;
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;;; - Reaping can be encouraged by calling (REAP-ZOMBIES).
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;;; (autoreap-policy [new-policy])
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(define *autoreap-policy* 'early) ; 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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old-policy))
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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 wait/poll)
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(if pid
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(begin (add-reaped-proc! pid status)
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(lp))
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status))))
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;;; This list contains procs that haven't exited yet. FORK adds new
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;;; procs to the list. When a proc exits, it is removed from the list.
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;;; Being on this list keeps live children's proc objects from being gc'd.
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(define unexited-procs '())
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(define (new-child-proc pid)
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(let ((proc (make-proc pid)))
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(add-to-population! proc process-table)
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(set! unexited-procs (cons proc unexited-procs))
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proc))
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(define (mark-proc-exited proc)
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(set! unexited-procs (del proc unexited-procs)))
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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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;;; WAIT waits for a specific process. Currently, if the autoreap policy is
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;;; 'early, it also does a (reap-zombies) Before performing a waitpid(2)
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;;; systcall, wait first consults the proc object to see if a/the process has
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;;; been reaped already. If so, its saved status is returned immediately.
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;;;
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;;; (wait-any [flags]) => [proc status]
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;;; [#f #f] => non-blocking, none ready.
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;;; [#f #t] => no more.
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;;; (wait-process-group [pid/proc flags]) => [proc status]
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;;; [#f #f] => non-blocking, none ready.
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;;; [#f #t] => no more.
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(define (wait pid/proc . maybe-flags)
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(if (not *autoreap-policy*) (reap-zombies))
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(let ((flags (:optional maybe-flags 0))
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(proc (->proc pid/proc)))
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(cond ((proc:%status proc) => ; Already reaped.
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(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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(else ; Really wait.
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(cache-wait-status proc (%wait-pid (proc:pid proc)
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flags))))))
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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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(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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(define (wait-any . maybe-flags)
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(if (not *autoreap-policy*) (reap-zombies))
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(cond ((get-reaped-proc!) => ; Check internal table.
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(lambda (proc) (values proc (proc:%status proc)))) ; Hit.
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(else
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(receive (pid status) (%wait-any (:optional maybe-flags 0)) ; Wait.
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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-process-group [proc-group flags])
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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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(define (wait-process-group . args)
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(let-optionals args ((proc-group 0) (flags 0))
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(if (not *autoreap-policy*) (reap-zombies))
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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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;;; Whenever WAIT, WAIT-ANY, WAIT-PROCESS-GROUP waits on a process to exit,
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;;; it removes the process from this table if it's in it.
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;;; This code is bogus -- we use weak pointers. We need populations that
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;;; support deletion or filtering.
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(define reaped-procs '()) ; Reaped, but not yet waited.
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(define (filter-weak-ptr-list pred lis)
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(reverse (reduce (lambda (wptr result)
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(let ((val (weak-pointer-ref wptr)))
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(if (and val (pred val))
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(cons wptr result)
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result)))
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'()
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lis)))
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;;; Add a newly-reaped proc to the list.
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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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(set-proc:%status proc status)
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(set! reaped-procs (cons (make-weak-pointer proc)
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reaped-procs))))
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(else (error "Child pid mysteriously missing proc object." pid))))
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;;; Pop one off the list.
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(define (get-reaped-proc!)
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(and (pair? reaped-procs)
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(let ((proc (weak-pointer-ref (car reaped-procs))))
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(set! reaped-procs (cdr reaped-procs))
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(or proc (get-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! reaped-procs (filter-weak-ptr-list (lambda (elt) (not (eq? proc elt)))
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reaped-procs)))
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;;; The mark-proc-waited! machinery above is a crock. It is inefficient --
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;;; we should have a flag in the proc saying if it's eligible for a WAIT-ANY.
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;;; Starts off #t, changes to #f after a wait. On a #t->#f transition, we
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;;; delete it from the WAIT-ANY population. Right now, every time the user
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;;; waits on the proc, we re-delete it from the population -- which is
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;;; a no-op after the first time.
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