* vm_trace.c (rb_tracepoint_new): Add documentation for

  rb_tracepoint_new C level API [ci skip]
  Provided by @emilsoman. [fix GH-869]



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50321 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 30 insertions, 0 deletions

diff --git a/vm_trace.c b/vm_trace.c
index e50ea992f2..a186e0d364 100644
--- a/vm_trace.c
+++ b/vm_trace.c
@@ -1171,6 +1171,36 @@ tracepoint_new(VALUE klass, rb_thread_t *target_th, rb_event_flag_t events, void
     return tpval;
 }
 
+/*
+ * Creates a tracepoint by registering a callback function for one or more
+ * tracepoint events. Once the tracepoint is created, you can use
+ * rb_tracepoint_enable to enable the tracepoint.
+ *
+ * Parameters:
+ *   1. VALUE target_thval - Meant for picking the thread in which the tracepoint
+ *      is to be created. However, current implementation ignore this parameter,
+ *      tracepoint is created for all threads. Simply specify Qnil.
+ *   2. rb_event_flag_t events - Event(s) to listen to.
+ *   3. void (*func)(VALUE, void *) - A callback function.
+ *   4. void *data - Void pointer that will be passed to the callback function.
+ *
+ * When the callback function is called, it will be passed 2 parameters:
+ *   1)VALUE tpval - the TracePoint object from which trace args can be extracted.
+ *   2)void *data - A void pointer which helps to share scope with the callback function.
+ *
+ * It is important to note that you cannot register callbacks for normal events and internal events
+ * simultaneously because they are different purpose.
+ * You can use any Ruby APIs (calling methods and so on) on normal event hooks.
+ * However, you can not use any Ruby APIs (even object creations).
+ * This is why we can't specify internal events by TracePoint directly.
+ * Limitations are MRI version specific.
+ *
+ * Example:
+ *   rb_tracepoint_new(Qnil, RUBY_INTERNAL_EVENT_NEWOBJ | RUBY_INTERNAL_EVENT_FREEOBJ, obj_event_i, data);
+ *
+ *   In this example, a callback function obj_event_i will be registered for
+ *   internal events RUBY_INTERNAL_EVENT_NEWOBJ and RUBY_INTERNAL_EVENT_FREEOBJ.
+ */
 VALUE
 rb_tracepoint_new(VALUE target_thval, rb_event_flag_t events, void (*func)(VALUE, void *), void *data)
 {