Add deferrable callbacks

Deferrable callbacks delay callback invocation until a
pre configured length of time has elapsed.  One example
scenario where deferrable callbacks help is to avoid
oscillation when testing a condition and making callbacks
frequently.

Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
Change-Id: I180c99b57ec1c9bde4da76d947a026f809341c8a

1 files changed, 24 insertions, 3 deletions

diff --git a/src/example/example.yaml b/src/example/example.yaml
index d76e3ad..899c4c8 100644
--- a/src/example/example.yaml
+++ b/src/example/example.yaml
@@ -103,14 +103,13 @@
     For example for a given event, one may wish to trace multiple
     messages to the systemd journal.  The journal callback does not
     support tracing multiple messages.  To do that, define a callback
-    group composed of multiple journal callbacks.
+    group composed of multiple journal callbacks.'
 
-    This example callback group only has one member.  To add more, add
-    additional callbacks to the members element.'
   class: callback
   callback: group
   members:
     - example journal callback
+    - example deferred condition
 
 - name: example count condition
   description: >
@@ -138,3 +137,25 @@
   countbound: 3
   op: '>='
   bound: 115
+
+- name: example deferred condition
+  description: >
+    'Deferred conditions operate in the same fashion as conditional callbacks
+    with the added behavior that when the condition is tested and is met,
+    invocation of the callback is deferred by the interval specified.
+
+    When the configured time has elapsed, if the condition has not been reevaluated
+    the callback is invoked.
+
+    Any condition type can be deferred in this way by setting the defer attribute.'
+
+  class: condition
+  condition: count
+  paths: example path group
+  properties: example property group
+  defer: 1000us
+  callback: example callback group
+  countop: '>='
+  countbound: 3
+  op: '>='
+  bound: 115