mirror of
https://github.com/systemd/systemd.git
synced 2024-12-23 21:35:11 +03:00
The systemd System and Service Manager
62a769136d
Previously, we'd maintain two hashmaps keyed by PIDs, pointing to Unit interested in SIGCHLD events for them. This scheme allowed a specific PID to be watched by exactly 0, 1 or 2 units. With this rework this is replaced by a single hashmap which is primarily keyed by the PID and points to a Unit interested in it. However, it optionally also keyed by the negated PID, in which case it points to a NULL terminated array of additional Unit objects also interested. This scheme means arbitrary numbers of Units may now watch the same PID. Runtime and memory behaviour should not be impact by this change, as for the common case (i.e. each PID only watched by a single unit) behaviour stays the same, but for the uncommon case (a PID watched by more than one unit) we only pay with a single additional memory allocation for the array. Why this all? Primarily, because allowing exactly two units to watch a specific PID is not sufficient for some niche cases, as processes can belong to more than one unit these days: 1. sd_notify() with MAINPID= can be used to attach a process from a different cgroup to multiple units. 2. Similar, the PIDFile= setting in unit files can be used for similar setups, 3. By creating a scope unit a main process of a service may join a different unit, too. 4. On cgroupsv1 we frequently end up watching all processes remaining in a scope, and if a process opens lots of scopes one after the other it might thus end up being watch by many of them. This patch hence removes the 2-unit-per-PID limit. It also makes a couple of other changes, some of them quite relevant: - manager_get_unit_by_pid() (and the bus call wrapping it) when there's ambiguity will prefer returning the Unit the process belongs to based on cgroup membership, and only check the watch-pids hashmap if that fails. This change in logic is probably more in line with what people expect and makes things more stable as each process can belong to exactly one cgroup only. - Every SIGCHLD event is now dispatched to all units interested in its PID. Previously, there was some magic conditionalization: the SIGCHLD would only be dispatched to the unit if it was only interested in a single PID only, or the PID belonged to the control or main PID or we didn't dispatch a signle SIGCHLD to the unit in the current event loop iteration yet. These rules were quite arbitrary and also redundant as the the per-unit handlers would filter the PIDs anyway a second time. With this change we'll hence relax the rules: all we do now is dispatch every SIGCHLD event exactly once to each unit interested in it, and it's up to the unit to then use or ignore this. We use a generation counter in the unit to ensure that we only invoke the unit handler once for each event, protecting us from confusion if a unit is both associated with a specific PID through cgroup membership and through the "watch_pids" logic. It also protects us from being confused if the "watch_pids" hashmap is altered while we are dispatching to it (which is a very likely case). - sd_notify() message dispatching has been reworked to be very similar to SIGCHLD handling now. A generation counter is used for dispatching as well. This also adds a new test that validates that "watch_pid" registration and unregstration works correctly. |
||
|---|---|---|
| .github | ||
| .mkosi | ||
| catalog | ||
| coccinelle | ||
| docs | ||
| factory/etc | ||
| hwdb | ||
| man | ||
| modprobe.d | ||
| network | ||
| po | ||
| presets | ||
| rules | ||
| scripts | ||
| shell-completion | ||
| src | ||
| sysctl.d | ||
| sysusers.d | ||
| test | ||
| tmpfiles.d | ||
| tools | ||
| travis-ci | ||
| units | ||
| xorg | ||
| .dir-locals.el | ||
| .editorconfig | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .travis.yml | ||
| .vimrc | ||
| .ycm_extra_conf.py | ||
| CODING_STYLE | ||
| configure | ||
| DISTRO_PORTING | ||
| ENVIRONMENT.md | ||
| HACKING | ||
| LICENSE.GPL2 | ||
| LICENSE.LGPL2.1 | ||
| Makefile | ||
| meson_options.txt | ||
| meson.build | ||
| mkosi.build | ||
| mkosi.default | ||
| NEWS | ||
| README | ||
| README.md | ||
| TODO | ||
| TRANSIENT-SETTINGS.md | ||
| UIDS-GIDS.md | ||
systemd - System and Service Manager
Details
General information about systemd can be found in the systemd Wiki.
Information about build requirements are provided in the README file.
Consult our NEWS file for information about what's new in the most recent systemd versions.
Please see the HACKING file for information how to hack on systemd and test your modifications.
Please see our Contribution Guidelines for more information about filing GitHub Issues and posting GitHub Pull Requests.
When preparing patches for systemd, please follow our Coding Style Guidelines.
If you are looking for support, please contact our mailing list or join our IRC channel.