xpc_events(3) BSD Library Functions Manual xpc_events(3)NAMExpc_events — launch-on-demand for high-level events
SYNOPSIS
#include <xpc/xpc.h>
void
xpc_set_event_stream_handler(const char *name, dispatch_queue_t targetq,
xpc_handler_t handler);
DESCRIPTION
XPC provides a mechanism by which launchd jobs may launch on-demand for
certain higher-level events, such as IOKit events or BSD Notifications.
These events are delivered to the job through a handler that is set early
in its execution. The period between when the event is delivered to the
job and when a handler is set is race-free, and any pending events will
be queued up for consumption by the job. An event is consumed when it is
delivered to the handler.
EVENT STREAMS
Providers of events are known as streams. Two example event streams are
the IOKit stream and the BSD Notifications stream. Streams are denoted by
a reverse-DNS naming scheme. For the aforementioned examples, the stream
names are "com.apple.iokit.matching" and "com.apple.notifyd.matching",
respectively. These are currently the only two supported event streams.
EVENT NAMES
A launchd job may be interested in multiple events from different event
streams. Each of these events has a name provided by the job in the
launchd.plist(5).
The occurrence of any of these events will launch the job on-demand if it
is not already running.
PLIST SCHEMA
Events are specified through the launchd.plist(5) with the LaunchEvents
key. The value for this key is a dictionary. Each value of this dictio‐
nary is itself a dictionary corresponding to an event stream. The values
of this inner dictionary are events that may cause the job to be launched
on-demand.
<key>LaunchEvents</key>
<dict>
<key>com.apple.iokit.matching</key>
<dict>
<key>com.apple.device-attach</key>
<dict>
<key>idProduct</key>
<integer>2794</integer>
<key>idVendor</key>
<integer>725</integer>
<key>IOProviderClass</key>
<string>IOUSBDevice</string>
<key>IOMatchLaunchStream</key>
<true/>
</dict>
</dict>
<key>com.apple.notifyd.matching</key>
<dict>
<key>com.apple.interesting-notification</key>
<dict>
<key>Notification</key>
<string>com.apple.interesting-notification</string>
</dict>
</dict>
</dict>
The above specifies that the job will be launched when a node matching
the given matching dictionary appears in the IORegistry or when a notifi‐
cation named "com.apple.interesting-notification" is posted using
notify_post(3).
NOTE: The IOMatchLaunchStream key is required to be present and be a
Boolean set to true for use with XPC Events. It will be filtered out of
the rest of the dictionary when given to IOKit to match. The reasons for
this are historical and not applicable to other event streams.
Each event stream has a different plist schema.
EVENT CONSUMPTION
Events are consumed with the xpc_set_event_stream_handler() API. The
stream argument specifies from which event stream the given handler will
receive events. The targetq parameter specifies on which queue the han‐
dler will be synchronized. The handler will only ever receive dictionar‐
ies. Each dictionary is guaranteed to have the XPC_EVENT_KEY_NAME key
set. The value for this key is the string that was given as the name for
the event in the launchd.plist(5). So if the IOKit event in the above
example was received, the value of this key would be "com.apple.device-
attach".
In addition to the standard payload, events from the IOKit stream also
have the "IOMatchLaunchServiceID" key set to a uint64_t which specifies
the unique IORegistry ID of the node which matched the given dictionary
as obtained by IORegistryEntryGetRegistryEntryID(). This value may be
given to IORegistryEntryIDMatching() to obtain the registry entry which
caused the event to fire.
BSD Notfication events have no additional payload.
xpc_set_event_stream_handler("com.apple.iokit.matching", q, ^(xpc_object_t event) {
const char *name = xpc_dictionary_get_string(event, XPC_EVENT_KEY_NAME);
uint64_t id = xpc_dictionary_get_uint64(event, "IOMatchLaunchServiceID");
CFMutableDictionaryRef matching = IORegistryEntryIDMatching(id);
// Pass to IOServiceGetMatchingServices() or IOServiceAddNotification().
});
IMPORTANT: xpc_set_event_stream_handler() is NOT shareable. Two different
subsystems in a process cannot safely both register for events from the
same event stream. Therefore, libraries and frameworks should NEVER call
this API.
SEE ALSOxpc_object(3), xpc_dictionary_create(3), xpc_array_create(3), notify(3)Darwin 1 July, 2011 Darwin
