From 9ec5c0000e9a45441417a6ee4138cdcbf1b1f2b2 Mon Sep 17 00:00:00 2001 From: Carlo Zancanaro Date: Thu, 9 Aug 2018 22:30:38 +1000 Subject: [PATCH] service: Add a replacement slot for delayed service replacement. * modules/shepherd/service.scm (): Add replacement slot (replace-service): New procedure. (stop): Call replace-service after stopping a service. (register-services): Replace existing services where possible, setting the new replacement slot if they are currently running. * tests/replacement.sh: Add a test for it. * Makefile.am (TESTS): Add the new test. * doc/shepherd.texi (Slots of services): Document it. --- Makefile.am | 1 + doc/shepherd.texi | 9 +++ modules/shepherd/service.scm | 68 ++++++++++++++++++----- tests/replacement.sh | 105 +++++++++++++++++++++++++++++++++++ 4 files changed, 168 insertions(+), 15 deletions(-) create mode 100644 tests/replacement.sh diff --git a/Makefile.am b/Makefile.am index 8dad006..4322d7f 100644 --- a/Makefile.am +++ b/Makefile.am @@ -184,6 +184,7 @@ SUFFIXES = .go TESTS = \ tests/basic.sh \ + tests/replacement.sh \ tests/respawn.sh \ tests/respawn-throttling.sh \ tests/misbehaved-client.sh \ diff --git a/doc/shepherd.texi b/doc/shepherd.texi index 7946f8b..1de6d80 100644 --- a/doc/shepherd.texi +++ b/doc/shepherd.texi @@ -708,6 +708,15 @@ handler will not start it again. otherwise @code{#f}. +@item +@vindex replacement (slot of ) +@code{replacement} specifies a service to be used to replace this one +when it is stopped. This service will continue to function normally +until the @code{stop} action is invoked. After the service has been +successfully stopped, its definition will be replaced by the value of +this slot, which must itself be a service. This slot is ignored if +its value is @code{#f}. + @end itemize @c @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ diff --git a/modules/shepherd/service.scm b/modules/shepherd/service.scm index 5653388..006309c 100644 --- a/modules/shepherd/service.scm +++ b/modules/shepherd/service.scm @@ -205,7 +205,10 @@ respawned, shows that it has been respawned more than TIMES in SECONDS." (stop-delay? #:init-keyword #:stop-delay? #:init-value #f) ;; The times of the last respawns, most recent first. - (last-respawns #:init-form '())) + (last-respawns #:init-form '()) + ;; A replacement for when this service is stopped. + (replacement #:init-keyword #:replacement + #:init-value #f)) (define (service? obj) "Return true if OBJ is a service." @@ -341,6 +344,20 @@ wire." (canonical-name obj))))) (slot-ref obj 'running)) +(define (replace-service old-service new-service) + "Replace OLD-SERVICE with NEW-SERVICE in the services registry. This +completely removes all references to OLD-SERVICE before registering +NEW-SERVICE." + (define (remove-service name) + (let* ((old (hashq-ref %services name)) + (new (delete old-service old))) + (if (null? new) + (hashq-remove! %services name) + (hashq-set! %services name new)))) + (when new-service + (for-each remove-service (provided-by old-service)) + (register-services new-service))) + ;; Stop the service, including services that depend on it. If the ;; latter fails, continue anyway. Return `#f' if it could be stopped. (define-method (stop (obj ) . args) @@ -385,6 +402,11 @@ wire." ;; Reset the list of respawns. (slot-set! obj 'last-respawns '()) + ;; Replace the service with its replacement, if it has one + (let ((replacement (slot-ref obj 'replacement))) + (when replacement + (replace-service obj replacement))) + ;; Status message. (let ((name (canonical-name obj))) (if (running? obj) @@ -1038,25 +1060,41 @@ then disable it." ;; Add NEW-SERVICES to the list of known services. (define (register-services . new-services) + "Add NEW-SERVICES to the list of known services. If a service has already +been registered, arrange to have it replaced when it is next stopped. If it +is currently stopped, replace it immediately." (define (register-single-service new) ;; Sanity-checks first. (assert (list-of-symbols? (provided-by new))) (assert (list-of-symbols? (required-by new))) (assert (boolean? (respawn? new))) - ;; Canonical name actually must be canonical. (FIXME: This test - ;; is incomplete, since we may add a service later that makes it - ;; non-cannonical.) - (assert (null? (lookup-services (canonical-name new)))) - ;; FIXME: Verify consistency: Check that there are no circular - ;; dependencies, check for bogus conflicts/dependencies, whatever - ;; else makes sense. - - ;; Insert into the hash table. - (for-each (lambda (name) - (let ((old (lookup-services name))) - ;; Actually add the new service now. - (hashq-set! %services name (cons new old)))) - (provided-by new))) + + ;; FIXME: Just because we have a unique canonical name now doesn't mean it + ;; will remain unique as other services are added. Whenever a service is + ;; added it should check that it's not conflicting with any already + ;; registered canonical names. + (match (lookup-services (canonical-name new)) + (() ;; empty, so we can safely add ourselves + (for-each (lambda (name) + (let ((old (lookup-services name))) + (hashq-set! %services name (cons new old)))) + (provided-by new))) + ((old) ;; one service registered, so it may be an old version of us + (cond + ((not (eq? (canonical-name new) (canonical-name old))) + (local-output + "Cannot register service ~a: canonical name is not unique." + (canonical-name new)) + (throw 'non-canonical-name)) + ((running? old) + (slot-set! old 'replacement new)) + (#:else + (replace-service old new)))) + (_ ;; in any other case, there are too many services to register + (local-output + "Cannot register service ~a: canonical name is not unique." + (canonical-name new)) + (throw 'non-canonical-name)))) (for-each register-single-service new-services)) diff --git a/tests/replacement.sh b/tests/replacement.sh new file mode 100644 index 0000000..e06cb93 --- /dev/null +++ b/tests/replacement.sh @@ -0,0 +1,105 @@ +# GNU Shepherd --- Ensure replacing services works properly +# Copyright © 2014, 2016 Ludovic Courtès +# Copyright © 2018 Carlo Zancanaro +# +# This file is part of the GNU Shepherd. +# +# The GNU Shepherd is free software; you can redistribute it and/or modify it +# under the terms of the GNU General Public License as published by +# the Free Software Foundation; either version 3 of the License, or (at +# your option) any later version. +# +# The GNU Shepherd is distributed in the hope that it will be useful, but +# WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with the GNU Shepherd. If not, see . + +shepherd --version +herd --version + +socket="t-socket-$$" +conf="t-conf-$$" +rconf="t-rconf-$$" +log="t-log-$$" +stamp="t-stamp-$$" +pid="t-pid-$$" + +herd="herd -s $socket" + +trap "rm -f $socket $conf $rconf $stamp $log; + test -f $pid && kill \`cat $pid\` || true; rm -f $pid" EXIT + +cat > "$conf"< + #:provides '(test) + #:start (const #t) + #:actions (make-actions + (say-hello (lambda _ + (call-with-output-file "$stamp" + (lambda (port) + (display "Hello" port)))))) + #:respawn? #f)) +EOF + +rm -f "$pid" "$stamp" "$socket" +shepherd -I -s "$socket" -c "$conf" --pid="$pid" --log="$log" & + +while ! test -f "$pid"; do sleep 0.5 ; done + +$herd start test + +if ! $herd say-hello test; then + echo "say-hello failed" + exit 1 +fi + +cat > "$rconf"< + #:provides '(test) + #:start (const #t) + #:actions (make-actions + (say-goodbye (lambda _ + (call-with-output-file "$stamp" + (lambda (port) + (display "Goodbye" port)))))) + #:respawn? #f)) +EOF + +$herd load root "$rconf" + +if ! $herd say-hello test; then + echo "say-hello failed after setting replacement" + exit 1 +fi + +if test "`cat $stamp`" != "Hello"; then + echo "Output file had the wrong contents! Was:" + cat $stamp + exit 1 +fi + +$herd stop test + +$herd start test + +if $herd say-hello test; then + echo "say-hello should have failed after stop/start" + exit 1 +fi + +if ! $herd say-goodbye test; then + echo "say-goodbye failed after replacement" + exit 1 +fi + +if test "`cat $stamp`" != "Goodbye"; then + echo "Output file had the wrong contents! Was:" + cat $stamp + exit 1 +fi -- 2.18.0