From: Lennart Poettering Date: Wed, 30 May 2018 14:33:12 +0000 (+0200) Subject: man: document the new sd_bus_slot_set_floating() call X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?a=commitdiff_plain;h=b26856f052f63443124a779c0cafa5a222c762f1;p=elogind.git man: document the new sd_bus_slot_set_floating() call Also extend the memory management description of sd-bus highlighting the effect of "floating" slot objects a bit. --- diff --git a/man/rules/meson.build b/man/rules/meson.build index 8239834c4..77be71d42 100644 --- a/man/rules/meson.build +++ b/man/rules/meson.build @@ -231,6 +231,7 @@ manpages = [ ['sd_bus_set_connected_signal', '3', ['sd_bus_get_connected_signal'], ''], ['sd_bus_set_sender', '3', ['sd_bus_get_sender'], ''], ['sd_bus_set_watch_bind', '3', ['sd_bus_get_watch_bind'], ''], + ['sd_bus_slot_set_floating', '3', ['sd_bus_slot_get_floating'], ''], ['sd_bus_track_add_name', '3', ['sd_bus_track_add_sender', diff --git a/man/sd_bus_add_match.xml b/man/sd_bus_add_match.xml index e8ee2b02b..1ca9b4392 100644 --- a/man/sd_bus_add_match.xml +++ b/man/sd_bus_add_match.xml @@ -132,7 +132,9 @@ at a later time with sd_bus_slot_unref3. If specified as NULL the lifetime of the match is bound to the lifetime of the bus object itself, and the - match cannot be removed independently. + match is generally not removed independently. See + sd_bus_slot_set_floating3 for + details. The message m passed to the callback is only borrowed, that is, the callback should not call sd_bus_message_unref3 @@ -175,7 +177,8 @@ sd-bus3, sd_bus_slot_unref3, sd_bus_message_ref3, - sd_bus_set_bus_client3 + sd_bus_set_bus_client3, + sd_bus_slot_set_floating3 diff --git a/man/sd_bus_default.xml b/man/sd_bus_default.xml index 2605edf4f..693fa37b1 100644 --- a/man/sd_bus_default.xml +++ b/man/sd_bus_default.xml @@ -206,21 +206,26 @@ sd_bus_unref3 to drop the reference. - Queued but unwritten/unread messages also keep a reference - to their bus connection object. For this reason, even if an - application dropped all references to a bus connection, it might - not get destroyed right away. Until all incoming queued - messages are read, and until all outgoing unwritten messages are - written, the bus object will stay - alive. sd_bus_flush() may be used to write - all outgoing queued messages so they drop their references. To - flush the unread incoming messages, use - sd_bus_close(), which will also close the bus - connection. When using the default bus logic, it is a good idea to - first invoke sd_bus_flush() followed by - sd_bus_close() when a thread or process - terminates, and thus its bus connection object should be - freed. + Queued but unwritten/unread messages keep a reference to their bus connection object. For this reason, even + if an application dropped all references to a bus connection, it might not get destroyed right away. Until all + incoming queued messages are read, and until all outgoing unwritten messages are written, the bus object will stay + alive. sd_bus_flush() may be used to write all outgoing queued messages so they drop their + references. To flush the unread incoming messages, use sd_bus_close(), which will also close + the bus connection. When using the default bus logic, it is a good idea to first invoke + sd_bus_flush() followed by sd_bus_close() when a thread or process + terminates, and thus its bus connection object should be freed. + + Normally, slot objects (as created by + sd_bus_add_match3 and similar + calls) keep a reference to their bus connection object, too. Thus, as long as a bus slot object remains referenced + its bus object will remain allocated too. Optionally, bus slot objects may be placed in "floating" mode. When in + floating mode the life cycle of the bus slot object is bound to the bus object, i.e. when the bus object is freed + the bus slot object is automatically unreferenced too. The floating state of a slot object may be controlled + explicitly with + sd_bus_slot_set_floating3, + though usually floating bus slot objects are created by passing NULL as the + slot parameter of sd_bus_add_match() and related calls, thus indicating + that the caller is not directly interested in referencing and managing the bus slot object. The life cycle of the default bus connection should be the responsibility of the code that creates/owns the thread the diff --git a/man/sd_bus_slot_set_floating.xml b/man/sd_bus_slot_set_floating.xml new file mode 100644 index 000000000..afae8629f --- /dev/null +++ b/man/sd_bus_slot_set_floating.xml @@ -0,0 +1,118 @@ + + + + + + + + + sd_bus_slot_set_floating + elogind + + + + sd_bus_slot_set_floating + 3 + + + + sd_bus_slot_set_floating + sd_bus_slot_get_floating + + Control whether a bus slot object is "floating". + + + + + #include <elogind/sd-bus.h> + + + int sd_bus_slot_set_floating + sd_bus_slot *bus + int b + + + + int sd_bus_slot_get_floating + sd_bus_slot *slot + + + + + + + Description + + sd_bus_slot_set_floating() controls whether the specified bus slot object + slot shall be "floating" or not. A floating bus slot object's lifetime is bound to the + lifetime of the bus object it is associated with, meaning that it remains allocated as long as the bus object + itself and is freed automatically when the bus object is freed. Regular (i.e. non-floating) bus slot objects keep + the bus referenced, hence the bus object remains allocated at least as long as there remains at least one + referenced bus slot object around. The floating state hence controls the direction of referencing between the bus + object and the bus slot objects: if floating the bus pins the the bus slot, and otherwise the bus slot pins the bus + objects. Use sd_bus_slot_set_floating() to switch between both modes: if the + b parameter is zero, the slot object is considered floating, otherwise it is made a regular + (non-floating) slot object. + + Bus slot objects may be allocated with calls such as + sd_bus_add_match3. If the + slot of these functions is non-NULL the slot object will be of the + regular kind (i.e. non-floating), otherwise it will be created floating. With + sd_bus_slot_set_floating() a bus slot object allocated as regular can be converted into a + floating object and back. This is particularly useful for creating a bus slot object, then changing parameters of + it, and then turning it into a floating object, whose lifecycle is managed by the bus object. + + sd_bus_slot_get_floating() returns the current floating state of the specified bus slot + object. It returns negative on error, zero if the bus slot object is a regular (non-floating) object and positive + otherwise. + + + + Return Value + + On success, these functions return 0 or a positive integer. On failure, they return a negative errno-style + error code. + + + + Errors + + Returned errors may indicate the following problems: + + + + -ECHILD + + The bus connection has been created in a different process. + + + + -ESTALE + + The bus object the specified bus slot object is associated with has already been freed, and + hence no change in the floating state can be made anymore. + + + + + + Notes + + sd_bus_slot_set_floating() and sd_bus_slot_get_floating() are + available as a shared library, which can be compiled and linked to with the + libelogind pkg-config1 file. + + + + See Also + + + elogind1, + sd-bus3, + sd_bus_add_match3 + + + +