From: Lennart Poettering <lennart@poettering.net>
Date: Wed, 20 Jan 2010 01:12:51 +0000 (+0100)
Subject: implement transaction engine
X-Git-Tag: 0.git+20100605+dfd8ee-1~445
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e5b5ae50f02d7814f37b15329da2adce0fb30825;p=systemd

implement transaction engine
---

diff --git a/job.c b/job.c
index 2f7912d2..3e8cca1e 100644
--- a/job.c
+++ b/job.c
@@ -20,7 +20,7 @@ Job* job_new(Manager *m, JobType type, Name *name) {
         j->type = type;
         j->name = name;
 
-        /* We don't link it here, that's what job_link() is for */
+        /* We don't link it here, that's what job_dependency() is for */
 
         return j;
 }
@@ -37,13 +37,96 @@ void job_free(Job *j) {
                 hashmap_remove(j->manager->jobs, UINT32_TO_PTR(j->id));
         }
 
-        hashmap_remove(j->manager->jobs_to_add, j->name);
-        set_remove(j->manager->jobs_to_remove, j);
+        manager_transaction_delete_job(j->manager, j);
 
-        /* Free data and next 'smaller' objects */
         free(j);
 }
 
+JobDependency* job_dependency_new(Job *subject, Job *object, bool matters) {
+        JobDependency *l;
+
+        assert(object);
+
+        /* Adds a new job link, which encodes that the 'subject' job
+         * needs the 'object' job in some way. If 'subject' is NULL
+         * this means the 'anchor' job (i.e. the one the user
+         * explcitily asked for) is the requester. */
+
+        if (!(l = new(JobDependency, 1)))
+                return NULL;
+
+        l->subject = subject;
+        l->object = object;
+        l->matters = matters;
+
+        if (subject) {
+                l->subject_next = subject->subject_list;
+                subject->subject_list = l;
+        } else {
+                l->subject_next = object->manager->transaction_anchor;
+                object->manager->transaction_anchor = l;
+        }
+
+        if (l->subject_next)
+                l->subject_next->subject_prev = l;
+        l->subject_prev = NULL;
+
+        if ((l->object_next = object->object_list))
+                l->object_next->object_prev = l;
+        l->object_prev = NULL;
+        object->object_list = l;
+
+        return l;
+}
+
+void job_dependency_free(JobDependency *l) {
+        assert(l);
+
+        if (l->subject_prev)
+                l->subject_prev->subject_next = l->subject_next;
+        else if (l->subject)
+                l->subject->subject_list = l->subject_next;
+        else
+                l->object->manager->transaction_anchor = l->subject_next;
+
+        if (l->subject_next)
+                l->subject_next->subject_prev = l->subject_prev;
+
+        if (l->object_prev)
+                l->object_prev->object_next = l->object_next;
+        else
+                l->object->object_list = l->object_next;
+
+        if (l->object_next)
+                l->object_next->object_prev = l->object_prev;
+
+        free(l);
+}
+
+void job_dependency_delete(Job *subject, Job *object, bool *matters) {
+        JobDependency *l;
+
+        assert(object);
+
+        for (l = object->object_list; l; l = l->object_next) {
+                assert(l->object == object);
+
+                if (l->subject == subject)
+                        break;
+        }
+
+        if (!l) {
+                if (matters)
+                        *matters = false;
+                return;
+        }
+
+        if (matters)
+                *matters = l->matters;
+
+        job_dependency_free(l);
+}
+
 void job_dump(Job *j, FILE*f) {
 
         static const char* const job_type_table[_JOB_TYPE_MAX] = {
@@ -51,9 +134,9 @@ void job_dump(Job *j, FILE*f) {
                 [JOB_STOP] = "stop",
                 [JOB_VERIFY_STARTED] = "verify-started",
                 [JOB_RELOAD] = "reload",
+                [JOB_RELOAD_OR_START] = "reload-or-start",
                 [JOB_RESTART] = "restart",
                 [JOB_TRY_RESTART] = "try-restart",
-                [JOB_RESTART_FINISH] = "restart-finish"
         };
 
         static const char* const job_state_table[_JOB_STATE_MAX] = {
@@ -71,3 +154,15 @@ void job_dump(Job *j, FILE*f) {
                 job_type_table[j->type],
                 job_state_table[j->state]);
 }
+
+bool job_is_anchor(Job *j) {
+        JobDependency *l;
+
+        assert(j);
+
+        for (l = j->object_list; l; l = l->object_next)
+                if (!l->subject)
+                        return true;
+
+        return false;
+}
diff --git a/job.h b/job.h
index 0cb0a6e8..f337307f 100644
--- a/job.h
+++ b/job.h
@@ -7,8 +7,10 @@
 #include <inttypes.h>
 
 typedef struct Job Job;
+typedef struct JobDependency JobDependency;
 typedef enum JobType JobType;
 typedef enum JobMode JobMode;
+typedef enum JobState JobState;
 
 #include "manager.h"
 #include "name.h"
@@ -19,19 +21,20 @@ enum JobType {
         JOB_START,
         JOB_STOP,
         JOB_VERIFY_STARTED,
-        JOB_RELOAD,
-        JOB_RESTART,
-        JOB_TRY_RESTART, /* restart if running */
-        JOB_RESTART_FINISH, /* 2nd part of a restart, i.e. the actual starting */
-        _JOB_TYPE_MAX
+        JOB_RELOAD,          /* reload if running */
+        JOB_RELOAD_OR_START, /* reload if running, start if not running */
+        JOB_RESTART,         /* stop if running, then start unconditionally */
+        JOB_TRY_RESTART,     /* stop and start if running */
+        _JOB_TYPE_MAX,
+        _JOB_TYPE_INVALID = -1
 };
 
-typedef enum JobState {
+enum JobState {
         JOB_WAITING,
         JOB_RUNNING,
         JOB_DONE,
         _JOB_STATE_MAX
-} JobState;
+};
 
 enum JobMode {
         JOB_FAIL,
@@ -39,19 +42,52 @@ enum JobMode {
         _JOB_MODE_MAX
 };
 
+struct JobDependency {
+        /* Encodes that the 'subject' job needs the 'object' job in
+         * some way. This structure is used only while building a transaction. */
+        Job *subject;
+        Job *object;
+
+        bool matters;
+
+        /* Linked list for the subjects, resp objects */
+        JobDependency *subject_prev, *subject_next;
+        JobDependency *object_prev, *object_next;
+};
+
 struct Job {
         Manager *manager;
         uint32_t id;
 
+        Name *name;
+
         JobType type;
         JobState state;
-        Name *name;
 
         bool linked:1;
+        bool matters_to_anchor:1;
+
+        /* These fields are used only while building a transaction */
+        Job *transaction_next, *transaction_prev;
+
+        JobDependency *subject_list;
+        JobDependency *object_list;
+
+        /* used for graph algs as a "I have been here" marker */
+        Job* marker;
+        unsigned generation;
 };
 
 Job* job_new(Manager *m, JobType type, Name *name);
 void job_free(Job *job);
 void job_dump(Job *j, FILE*f);
 
+JobDependency* job_dependency_new(Job *subject, Job *object, bool matters);
+void job_dependency_free(JobDependency *l);
+void job_dependency_delete(Job *subject, Job *object, bool *matters);
+
+bool job_is_anchor(Job *j);
+
+int job_merge(Job *j, Job *other);
+
 #endif
diff --git a/main.c b/main.c
index a5c16945..de7572ef 100644
--- a/main.c
+++ b/main.c
@@ -24,7 +24,7 @@ int main(int argc, char *argv[]) {
         }
 
 
-        if ((r = manager_add_job(m, JOB_START, milestone, JOB_REPLACE, &job)) < 0) {
+        if ((r = manager_add_job(m, JOB_START, milestone, JOB_REPLACE, false, &job)) < 0) {
                 fprintf(stderr, "Failed to start default milestone: %s\n", strerror(-r));
                 goto finish;
         }
diff --git a/manager.c b/manager.c
index d2708aac..a870db6c 100644
--- a/manager.c
+++ b/manager.c
@@ -22,10 +22,7 @@ Manager* manager_new(void) {
         if (!(m->jobs = hashmap_new(trivial_hash_func, trivial_compare_func)))
                 goto fail;
 
-        if (!(m->jobs_to_add = hashmap_new(trivial_hash_func, trivial_compare_func)))
-                goto fail;
-
-        if (!(m->jobs_to_remove = set_new(trivial_hash_func, trivial_compare_func)))
+        if (!(m->transaction_jobs = hashmap_new(trivial_hash_func, trivial_compare_func)))
                 goto fail;
 
         return m;
@@ -37,19 +34,19 @@ fail:
 
 void manager_free(Manager *m) {
         Name *n;
+        Job *j;
 
         assert(m);
 
         while ((n = hashmap_first(m->names)))
                 name_free(n);
 
+        while ((j = hashmap_steal_first(m->transaction_jobs)))
+                job_free(j);
+
         hashmap_free(m->names);
         hashmap_free(m->jobs);
-
-        /* FIXME: This is incomplete */
-
-        hashmap_free(m->jobs_to_add);
-        set_free(m->jobs_to_remove);
+        hashmap_free(m->transaction_jobs);
 
         free(m);
 }
@@ -58,140 +55,521 @@ static void transaction_abort(Manager *m) {
         Job *j;
 
         assert(m);
-        assert(m->n_dependency_depth == 0);
 
-        while ((j = hashmap_steal_first(m->jobs_to_add)))
-                job_free(j);
+        while ((j = hashmap_first(m->transaction_jobs)))
+                if (j->linked)
+                        manager_transaction_delete_job(m, j);
+                else
+                        job_free(j);
+
+        assert(hashmap_isempty(m->transaction_jobs));
+        assert(!m->transaction_anchor);
+}
+
+static void transaction_find_jobs_that_matter_to_anchor(Manager *m, Job *j, unsigned generation) {
+        JobDependency *l;
+
+        assert(m);
+
+        for (l = j ? j->subject_list : m->transaction_anchor; l; l = l->subject_next) {
+
+                /* This link does not matter */
+                if (!l->matters)
+                        continue;
+
+                /* This name has already been marked */
+                if (l->object->generation == generation)
+                        continue;
+
+                l->object->matters_to_anchor = true;
+                l->object->generation = generation;
+
+                transaction_find_jobs_that_matter_to_anchor(m, l->object, generation);
+        }
+}
+
+static bool types_match(JobType a, JobType b, JobType c, JobType d) {
+        return
+                (a == c && b == d) ||
+                (a == d && b == c);
+}
+
+static int types_merge(JobType *a, JobType b) {
+        if (*a == b)
+                return 0;
 
-        set_clear(m->jobs_to_remove);
+        if (types_match(*a, b, JOB_START, JOB_VERIFY_STARTED))
+                *a = JOB_START;
+        else if (types_match(*a, b, JOB_START, JOB_RELOAD) ||
+                 types_match(*a, b, JOB_START, JOB_RELOAD_OR_START) ||
+                 types_match(*a, b, JOB_VERIFY_STARTED, JOB_RELOAD_OR_START) ||
+                 types_match(*a, b, JOB_RELOAD, JOB_RELOAD_OR_START))
+                *a = JOB_RELOAD_OR_START;
+        else if (types_match(*a, b, JOB_START, JOB_RESTART) ||
+                 types_match(*a, b, JOB_START, JOB_TRY_RESTART) ||
+                 types_match(*a, b, JOB_VERIFY_STARTED, JOB_RESTART) ||
+                 types_match(*a, b, JOB_RELOAD, JOB_RESTART) ||
+                 types_match(*a, b, JOB_RELOAD_OR_START, JOB_RESTART) ||
+                 types_match(*a, b, JOB_RELOAD_OR_START, JOB_TRY_RESTART) ||
+                 types_match(*a, b, JOB_RESTART, JOB_TRY_RESTART))
+                *a = JOB_RESTART;
+        else if (types_match(*a, b, JOB_VERIFY_STARTED, JOB_RELOAD))
+                *a = JOB_RELOAD;
+        else if (types_match(*a, b, JOB_VERIFY_STARTED, JOB_TRY_RESTART) ||
+                 types_match(*a, b, JOB_RELOAD, JOB_TRY_RESTART))
+                *a = JOB_TRY_RESTART;
+
+        return -EEXIST;
 }
 
-static int transaction_activate(Manager *m) {
+static void manager_merge_and_delete_prospective_job(Manager *m, Job *j, Job *other, JobType t) {
+        JobDependency *l, *last;
+
+        assert(j);
+        assert(other);
+        assert(j->name == other->name);
+        assert(!j->linked);
+
+        j->type = t;
+        j->state = JOB_WAITING;
+
+        j->matters_to_anchor = j->matters_to_anchor || other->matters_to_anchor;
+
+        /* Patch us in as new owner of the JobDependency objects */
+        last = NULL;
+        for (l = other->subject_list; l; l = l->subject_next) {
+                assert(l->subject == other);
+                l->subject = j;
+                last = l;
+        }
+
+        /* Merge both lists */
+        if (last) {
+                last->subject_next = j->subject_list;
+                if (j->subject_list)
+                        j->subject_list->subject_prev = last;
+                j->subject_list = other->subject_list;
+        }
+
+        /* Patch us in as new owner of the JobDependency objects */
+        last = NULL;
+        for (l = other->object_list; l; l = l->object_next) {
+                assert(l->object == other);
+                l->object = j;
+                last = l;
+        }
+
+        /* Merge both lists */
+        if (last) {
+                last->object_next = j->object_list;
+                if (j->object_list)
+                        j->object_list->object_prev = last;
+                j->object_list = other->object_list;
+        }
+
+
+        /* Kill the other job */
+        other->subject_list = NULL;
+        other->object_list = NULL;
+        manager_transaction_delete_job(m, other);
+}
+
+static int transaction_merge_jobs(Manager *m) {
         Job *j;
+        void *state;
+        int r;
+
+        assert(m);
+
+        HASHMAP_FOREACH(j, m->transaction_jobs, state) {
+                JobType t = j->type;
+                Job *k;
+
+                for (k = j->transaction_next; k; k = k->transaction_next)
+                        if ((r = types_merge(&t, k->type)) < 0)
+                                return r;
+
+                while ((k = j->transaction_next)) {
+                        if (j->linked) {
+                                manager_merge_and_delete_prospective_job(m, k, j, t);
+                                j = k;
+                        } else
+                                manager_merge_and_delete_prospective_job(m, j, k, t);
+                }
+
+                assert(!j->transaction_next);
+                assert(!j->transaction_prev);
+        }
+
+        return r;
+}
+
+static int transaction_verify_order_one(Manager *m, Job *j, Job *from, unsigned generation) {
+        void *state;
+        Name *n;
         int r;
+
+        assert(m);
+        assert(j);
+
+        /* Did we find a loop? */
+        if (j->marker && j->generation == generation) {
+                Job *k;
+
+                /* So, we already have been here. We have a
+                 * loop. Let's try to break it. We go backwards in our
+                 * path and try to find a suitable job to remove. */
+
+                for (k = from; k; k = (k->generation == generation ? k->marker : NULL)) {
+                        if (!k->matters_to_anchor) {
+                                manager_transaction_delete_job(m, k);
+                                return -EAGAIN;
+                        }
+
+                        /* Check if this in fact was the beginning of
+                         * the loop */
+                        if (k == j)
+                                break;
+                }
+
+                return -ELOOP;
+        }
+
+        j->marker = from;
+        j->generation = generation;
+
+        /* We assume that the the dependencies are both-ways, and
+         * hence can ignore NAME_AFTER */
+
+        SET_FOREACH(n, j->name->meta.dependencies[NAME_BEFORE], state) {
+                Job *o;
+
+                if (!(o = hashmap_get(m->transaction_jobs, n)))
+                        if (!(o = n->meta.job))
+                                continue;
+
+                if ((r = transaction_verify_order_one(m, o, j, generation)) < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+static int transaction_verify_order(Manager *m, unsigned *generation) {
+        bool again;
+        assert(m);
+        assert(generation);
+
+        do {
+                Job *j;
+                int r;
+                void *state;
+
+                again = false;
+
+                HASHMAP_FOREACH(j, m->transaction_jobs, state) {
+
+                        /* Assume merged */
+                        assert(!j->transaction_next);
+                        assert(!j->transaction_prev);
+
+                        if ((r = transaction_verify_order_one(m, j, NULL, (*generation)++)) < 0)  {
+
+                                /* There was a loop, but it was fixed,
+                                 * we need to restart our algorithm */
+                                if (r == -EAGAIN) {
+                                        again = true;
+                                        break;
+                                }
+
+                                return r;
+                        }
+                }
+        } while (again);
+
+        return 0;
+}
+
+static void transaction_collect_garbage(Manager *m) {
+        bool again;
+
+        assert(m);
+
+        do {
+                void *state;
+                Job *j;
+
+                again = false;
+
+                HASHMAP_FOREACH(j, m->transaction_jobs, state) {
+                        if (j->object_list)
+                                continue;
+
+                        manager_transaction_delete_job(m, j);
+                        again = true;
+                        break;
+                }
+
+        } while (again);
+}
+
+static int transaction_is_destructive(Manager *m, JobMode mode) {
         void *state;
+        Job *j;
 
         assert(m);
-        assert(m->n_dependency_depth == 0);
 
-        /* This applies the changes recorded in jobs_to_add and
-         * jobs_to_remove to the actual list of jobs */
+        /* Checks whether applying this transaction means that
+         * existing jobs would be replaced */
 
-        HASHMAP_FOREACH(j, m->jobs_to_add, state) {
-                assert(!j->linked);
+        HASHMAP_FOREACH(j, m->transaction_jobs, state)
+                if (j->name->meta.job && j->name->meta.job != j)
+                        return -EEXIST;
 
-                if ((r = hashmap_put(j->manager->jobs, UINT32_TO_PTR(j->id), j)) < 0)
+        return 0;
+}
+
+static int transaction_apply(Manager *m, JobMode mode) {
+        void *state;
+        Job *j;
+        int r;
+
+        HASHMAP_FOREACH(j, m->transaction_jobs, state) {
+                if (j->linked)
+                        continue;
+
+                if ((r = hashmap_put(m->jobs, UINT32_TO_PTR(j->id), j)) < 0)
                         goto rollback;
         }
 
-        /* all entries are now registered, now make sure the names
-         * know about that. */
+        while ((j = hashmap_steal_first(m->transaction_jobs))) {
+                if (j->linked)
+                        continue;
+
+                if (j->name->meta.job)
+                        job_free(j->name->meta.job);
 
-        while ((j = hashmap_steal_first(m->jobs_to_add))) {
                 j->name->meta.job = j;
                 j->linked = true;
-        }
 
-        while ((j = set_steal_first(m->jobs_to_remove)))
-                job_free(j);
+                /* We're fully installed. Now let's free data we don't
+                 * need anymore. */
+
+                assert(!j->transaction_next);
+                assert(!j->transaction_prev);
+
+                while (j->subject_list)
+                        job_dependency_free(j->subject_list);
+                while (j->object_list)
+                        job_dependency_free(j->object_list);
+        }
 
         return 0;
 
 rollback:
 
-        HASHMAP_FOREACH(j, m->jobs_to_add, state)
-                hashmap_remove(j->manager->jobs, UINT32_TO_PTR(j->id));
+        HASHMAP_FOREACH(j, m->transaction_jobs, state) {
+                if (j->linked)
+                        continue;
+
+                hashmap_remove(m->jobs, UINT32_TO_PTR(j->id));
+        }
+
+        return r;
+}
+
+
+static int transaction_activate(Manager *m, JobMode mode) {
+        int r;
+        unsigned generation = 1;
+
+        assert(m);
+
+        /* This applies the changes recorded in transaction_jobs to
+         * the actual list of jobs, if possible. */
+
+        /* First step: figure out which jobs matter */
+        transaction_find_jobs_that_matter_to_anchor(m, NULL, generation++);
+
+        /* Second step: let's merge entries we can merge */
+        if ((r = transaction_merge_jobs(m)) < 0)
+                goto rollback;
+
+        /* Third step: verify order makes sense */
+        if ((r = transaction_verify_order(m, &generation)) < 0)
+                goto rollback;
+
+        /* Third step: do garbage colletion */
+        transaction_collect_garbage(m);
+
+        /* Fourth step: check whether we can actually apply this */
+        if (mode == JOB_FAIL)
+                if ((r = transaction_is_destructive(m, mode)) < 0)
+                        goto rollback;
+
+        /* Fifth step: apply changes */
+        if ((r = transaction_apply(m, mode)) < 0)
+                goto rollback;
+
+        assert(hashmap_isempty(m->transaction_jobs));
+        assert(!m->transaction_anchor);
+
+        return 0;
 
+rollback:
         transaction_abort(m);
         return r;
 }
 
-int manager_add_job(Manager *m, JobType type, Name *name, JobMode mode, Job **_ret) {
-        Job *ret, *other;
-        void *state;
-        Name *dep;
+static Job* transaction_add_job(Manager *m, JobType type, Name *name, bool *is_new) {
+        Job *j, *f;
         int r;
 
         assert(m);
-        assert(type < _JOB_TYPE_MAX);
         assert(name);
-        assert(mode < _JOB_MODE_MAX);
 
-        /* Check for conflicts, first against the jobs we shall
-         * create */
-        if ((other = hashmap_get(m->jobs_to_add, name))) {
+        /* Looks for an axisting prospective job and returns that. If
+         * it doesn't exist it is created and added to the prospective
+         * jobs list. */
 
-                if (other->type != type)
-                        return -EEXIST;
+        f = hashmap_get(m->transaction_jobs, name);
 
-        } else if (name->meta.job) {
+        for (j = f; j; j = j->transaction_next) {
+                assert(j->name == name);
 
-                if (name->meta.job->type != type) {
+                if (j->type == type) {
+                        if (is_new)
+                                *is_new = false;
+                        return j;
+                }
+        }
 
-                        if (mode == JOB_FAIL)
-                                return -EEXIST;
+        if (name->meta.job && name->meta.job->type == type)
+                j = name->meta.job;
+        else if (!(j = job_new(m, type, name)))
+                return NULL;
 
-                        if ((r = set_put(m->jobs_to_remove, name->meta.job)) < 0)
-                                return r;
-                }
+        if ((r = hashmap_replace(m->transaction_jobs, name, j)) < 0) {
+                job_free(j);
+                return NULL;
         }
 
-        if (!(ret = job_new(m, type, name)))
-                return -ENOMEM;
+        j->transaction_next = f;
 
-        m->n_dependency_depth ++;
+        if (f)
+                f->transaction_prev = j;
 
-        if ((r = hashmap_put(m->jobs_to_add, name, ret)) < 0)
-                goto fail;
+        j->generation = 0;
+        j->marker = NULL;
+        j->matters_to_anchor = false;
 
-        if (type == JOB_START || type == JOB_VERIFY_STARTED || type == JOB_RESTART_FINISH) {
-                SET_FOREACH(dep, ret->name->meta.dependencies[NAME_REQUIRES], state)
-                        if ((r = manager_add_job(m, type, dep, mode, NULL)) < 0)
-                                goto fail;
-                SET_FOREACH(dep, ret->name->meta.dependencies[NAME_SOFT_REQUIRES], state)
-                        if ((r = manager_add_job(m, type, dep, JOB_FAIL, NULL)) < 0)
-                                goto fail;
-                SET_FOREACH(dep, ret->name->meta.dependencies[NAME_WANTS], state)
-                        if ((r = manager_add_job(m, type, dep, JOB_FAIL, NULL)) < 0)
-                                goto fail;
-                SET_FOREACH(dep, ret->name->meta.dependencies[NAME_REQUISITE], state)
-                        if ((r = manager_add_job(m, JOB_VERIFY_STARTED, dep, mode, NULL)) < 0)
-                                goto fail;
-                SET_FOREACH(dep, ret->name->meta.dependencies[NAME_SOFT_REQUISITE], state)
-                        if ((r = manager_add_job(m, JOB_VERIFY_STARTED, dep, JOB_FAIL, NULL)) < 0)
-                                goto fail;
-                SET_FOREACH(dep, ret->name->meta.dependencies[NAME_CONFLICTS], state)
-                        if ((r = manager_add_job(m, type, dep, mode, NULL)) < 0)
-                                goto fail;
-
-        } else if (type == JOB_STOP || type == JOB_RESTART || type == JOB_TRY_RESTART) {
-
-                SET_FOREACH(dep, ret->name->meta.dependencies[NAME_REQUIRED_BY], state)
-                        if ((r = manager_add_job(m, type, dep, mode, NULL)) < 0)
-                                goto fail;
-        }
+        if (is_new)
+                *is_new = true;
 
-        if (--m->n_dependency_depth <= 0)
-                if ((r = transaction_activate(m)) < 0) {
-                        transaction_abort(m);
-                        return r;
-                }
+        return j;
+}
 
+void manager_transaction_delete_job(Manager *m, Job *j) {
+        assert(m);
+        assert(j);
 
-        if (_ret)
-                *_ret = ret;
+        if (j->transaction_prev)
+                j->transaction_prev->transaction_next = j->transaction_next;
+        else if (j->transaction_next)
+                hashmap_replace(m->transaction_jobs, j->name, j->transaction_next);
+        else
+                hashmap_remove_value(m->transaction_jobs, j->name, j);
+
+        if (j->transaction_next)
+                j->transaction_next->transaction_prev = j->transaction_prev;
+
+        j->transaction_prev = j->transaction_next = NULL;
+
+        while (j->subject_list)
+                job_dependency_free(j->subject_list);
+        while (j->object_list)
+                job_dependency_free(j->object_list);
+}
+
+static int real_add_job(Manager *m, JobType type, Name *name, Job *by, bool matters, bool force, Job **_ret) {
+        Job *ret;
+        void *state;
+        Name *dep;
+        int r;
+        bool is_new;
+
+        assert(m);
+        assert(type < _JOB_TYPE_MAX);
+        assert(name);
+
+        /* First add the job. */
+        if (!(ret = transaction_add_job(m, type, name, &is_new)))
+                return -ENOMEM;
+
+        /* Then, add a link to the job. */
+        if (!job_dependency_new(by, ret, matters))
+                return -ENOMEM;
+
+        if (is_new) {
+                /* Finally, recursively add in all dependencies. */
+                if (type == JOB_START || type == JOB_RELOAD_OR_START) {
+                        SET_FOREACH(dep, ret->name->meta.dependencies[NAME_REQUIRES], state)
+                                if ((r = real_add_job(m, JOB_START, dep, ret, true, force, NULL)) < 0)
+                                        goto fail;
+                        SET_FOREACH(dep, ret->name->meta.dependencies[NAME_SOFT_REQUIRES], state)
+                                if ((r = real_add_job(m, JOB_START, dep, ret, !force, force, NULL)) < 0)
+                                        goto fail;
+                        SET_FOREACH(dep, ret->name->meta.dependencies[NAME_WANTS], state)
+                                if ((r = real_add_job(m, JOB_START, dep, ret, false, force, NULL)) < 0)
+                                        goto fail;
+                        SET_FOREACH(dep, ret->name->meta.dependencies[NAME_REQUISITE], state)
+                                if ((r = real_add_job(m, JOB_VERIFY_STARTED, dep, ret, true, force, NULL)) < 0)
+                                        goto fail;
+                        SET_FOREACH(dep, ret->name->meta.dependencies[NAME_SOFT_REQUISITE], state)
+                                if ((r = real_add_job(m, JOB_VERIFY_STARTED, dep, ret, !force, force, NULL)) < 0)
+                                        goto fail;
+                        SET_FOREACH(dep, ret->name->meta.dependencies[NAME_CONFLICTS], state)
+                                if ((r = real_add_job(m, JOB_STOP, dep, ret, true, force, NULL)) < 0)
+                                        goto fail;
+
+                } else if (type == JOB_STOP || type == JOB_RESTART || type == JOB_TRY_RESTART) {
+
+                        SET_FOREACH(dep, ret->name->meta.dependencies[NAME_REQUIRED_BY], state)
+                                if ((r = real_add_job(m, type, dep, ret, true, force, NULL)) < 0)
+                                        goto fail;
+                }
+
+                /* JOB_VERIFY_STARTED, JOB_RELOAD require no dependency handling */
+        }
 
         return 0;
 
 fail:
-        job_free(ret);
+        return r;
+}
+
+int manager_add_job(Manager *m, JobType type, Name *name, JobMode mode, bool force, Job **_ret) {
+        int r;
+        Job *ret;
+
+        assert(m);
+        assert(type < _JOB_TYPE_MAX);
+        assert(name);
+        assert(mode < _JOB_MODE_MAX);
 
-        if (--m->n_dependency_depth <= 0)
+        if ((r = real_add_job(m, type, name, NULL, true, force, &ret))) {
                 transaction_abort(m);
+                return r;
+        }
 
-        return r;
-}
+        if ((r = transaction_activate(m, mode)) < 0)
+                return r;
+
+        if (_ret)
+                *_ret = ret;
 
+        return 0;
+}
 
 Job *manager_get_job(Manager *m, uint32_t id) {
         assert(m);
@@ -314,7 +692,7 @@ finish:
         if ((r = name_load_dropin(name)) < 0)
                 return r;
 
-        if ((r = name_link_names(name)) < 0)
+        if ((r = name_link_names(name, true)) < 0)
                 return r;
 
         name->meta.state = NAME_LOADED;
diff --git a/manager.h b/manager.h
index 3ee3b0ac..ad62b74a 100644
--- a/manager.h
+++ b/manager.h
@@ -29,13 +29,11 @@ struct Manager {
         /* Names that need to be loaded */
         LIST_HEAD(Meta, load_queue); /* this is actually more a stack than a queue, but uh. */
 
-        /* Jobs to be added resp. removed. */
-        Hashmap *jobs_to_add;  /* Name object => Job object 1:1 */
-        Set *jobs_to_remove;
+        /* Jobs to be added */
+        Hashmap *transaction_jobs;      /* Name object => Job object list 1:1 */
+        JobDependency *transaction_anchor;
 
         bool dispatching_load_queue:1;
-
-        unsigned n_dependency_depth;
 };
 
 Manager* manager_new(void);
@@ -45,9 +43,11 @@ Job *manager_get_job(Manager *m, uint32_t id);
 Name *manager_get_name(Manager *m, const char *name);
 
 int manager_load_name(Manager *m, const char *name, Name **_ret);
-int manager_add_job(Manager *m, JobType job, Name *name, JobMode mode, Job **_ret);
+int manager_add_job(Manager *m, JobType type, Name *name, JobMode mode, bool force, Job **_ret);
 
 void manager_dump_names(Manager *s, FILE *f);
 void manager_dump_jobs(Manager *s, FILE *f);
 
+void manager_transaction_delete_job(Manager *m, Job *j);
+
 #endif
diff --git a/name.c b/name.c
index 0ef7a77f..f4ad1768 100644
--- a/name.c
+++ b/name.c
@@ -80,7 +80,8 @@ Name *name_new(Manager *m) {
         return n;
 }
 
-int name_link_names(Name *n) {
+/* FIXME: Does not rollback on failure! */
+int name_link_names(Name *n, bool replace) {
         char *t;
         void *state;
         int r;
@@ -90,15 +91,15 @@ int name_link_names(Name *n) {
         if (!n->meta.linked)
                 return 0;
 
-        /* Link all names that aren't linked yet */
+        /* Link all names that aren't linked yet. */
 
         SET_FOREACH(t, n->meta.names, state)
-                if ((r = hashmap_put(n->meta.manager->names, t, n)) < 0) {
-
-                        if (r == -EEXIST && hashmap_get(n->meta.manager->names, t) == n)
-                                continue;
-
-                        return r;
+                if (replace) {
+                        if ((r = hashmap_replace(n->meta.manager->names, t, n)) < 0)
+                                return r;
+                } else {
+                        if ((r = hashmap_put(n->meta.manager->names, t, n)) < 0)
+                                return r;
                 }
 
         return 0;
@@ -113,13 +114,13 @@ int name_link(Name *n) {
 
         n->meta.linked = true;
 
-        if ((r = name_link_names(n) < 0)) {
+        if ((r = name_link_names(n, false) < 0)) {
                 char *t;
                 void *state;
 
                 /* Rollback the registered names */
                 SET_FOREACH(t, n->meta.names, state)
-                        hashmap_remove(n->meta.manager->names, t);
+                        hashmap_remove_value(n->meta.manager->names, t, n);
 
                 n->meta.linked = false;
                 return r;
@@ -162,7 +163,7 @@ void name_free(Name *name) {
                 void *state;
 
                 SET_FOREACH(t, name->meta.names, state)
-                        assert_se(hashmap_remove(name->meta.manager->names, t) == name);
+                        hashmap_remove_value(name->meta.manager->names, t, name);
 
                 if (name->meta.state == NAME_STUB)
                         LIST_REMOVE(Meta, name->meta.manager->load_queue, &name->meta);
@@ -303,6 +304,7 @@ static int ensure_in_set(Set **s, void *data) {
         return 0;
 }
 
+/* FIXME: Does not rollback on failure! */
 int name_augment(Name *n) {
         int r;
         void* state;
@@ -310,7 +312,8 @@ int name_augment(Name *n) {
 
         assert(n);
 
-        /* Adds in the missing links to make all dependencies bidirectional */
+        /* Adds in the missing links to make all dependencies
+         * bidirectional. */
 
         SET_FOREACH(other, n->meta.dependencies[NAME_BEFORE], state)
                 if ((r = ensure_in_set(&other->meta.dependencies[NAME_AFTER], n) < 0))
@@ -357,15 +360,18 @@ static int ensure_merge(Set **s, Set *other) {
         return 0;
 }
 
+/* FIXME: Does not rollback on failure! */
 int name_merge(Name *name, Name *other) {
         int r;
         NameDependency d;
 
         assert(name);
         assert(other);
-
         assert(name->meta.manager == other->meta.manager);
 
+        /* This merges 'other' into 'name'. FIXME: This does not
+         * rollback on failure. */
+
         if (name->meta.type != other->meta.type)
                 return -EINVAL;
 
@@ -381,10 +387,15 @@ int name_merge(Name *name, Name *other) {
                 if ((r = ensure_merge(&name->meta.dependencies[d], other->meta.dependencies[d])) < 0)
                         return r;
 
-        if (name->meta.linked)
-                if ((r = name_link_names(name)) < 0)
+        /* Hookup new deps and names */
+        if (name->meta.linked) {
+                if ((r = name_augment(name)) < 0)
                         return r;
 
+                if ((r = name_link_names(name, true)) < 0)
+                        return r;
+        }
+
         return 0;
 }
 
@@ -424,7 +435,7 @@ void name_dump(Name *n, FILE *f) {
         fprintf(f,
                 "Name %s\n"
                 "\tDescription: %s\n"
-                "\tState: %s\n",
+                "\tName State: %s\n",
                 name_id(n),
                 n->meta.description ? n->meta.description : name_id(n),
                 state_table[n->meta.state]);
@@ -445,7 +456,12 @@ void name_dump(Name *n, FILE *f) {
                         else
                                 t = s;
 
-                        fprintf(f, "\t%s in state %s\n", t, socket_state_table[n->socket.state]);
+                        fprintf(f,
+                                "\tAddress: %s\n"
+                                "\tSocket State: %s\n",
+                                t,
+                                socket_state_table[n->socket.state]);
+
                         free(s);
                         break;
                 }
diff --git a/name.h b/name.h
index 67ca6f10..c67e839d 100644
--- a/name.h
+++ b/name.h
@@ -279,7 +279,7 @@ bool name_is_valid(const char *n);
 Name *name_new(Manager *m);
 void name_free(Name *name);
 int name_link(Name *name);
-int name_link_names(Name *name);
+int name_link_names(Name *name, bool replace);
 int name_merge(Name *name, Name *other);
 int name_augment(Name *n);
 const char* name_id(Name *n);