Changes between Version 1 and Version 2 of Python_SIP/Basic_Concept

Timestamp:

Jul 22, 2008 10:11:14 PM (16 years ago)

Author:

bennylp

Comment:

--

Python_SIP/Basic_Concept

@@ -40 +40 @@
 It's with the callback classes.
 
-Callback classes also provide the mean to ''connect'' pjsua objects with your application's objects. The idea is like this. All the pjsua main classes above (''Lib'', ''Account'', ''Call'', and ''Buddy'') are final classes, meaning they are not intended to be subclasses or derived. Each of these classes (except ''Lib'') have their corresponding callback class ([http://www.pjsip.org/python/pjsua.htm#AccountCallback AccountCallback], [[http://www.pjsip.org/python/pjsua.htm#CallCallback CallCallback], and [[http://www.pjsip.org/python/pjsua.htm#BuddyCallback BuddyCallback]), and events emitted by these classes will be sent to the callback class. These callback classes are subclass-able, and in fact you must derive a class from these callback class in order to customize the processing of the events.
+Callback classes also provide the mean to ''connect'' pjsua objects with your application's objects. The idea is like this. All the pjsua main classes above (''Lib'', ''Account'', ''Call'', and ''Buddy'') are final classes, meaning they are not intended to be subclasses or derived. Each of these classes (except ''Lib'') have their corresponding callback class ([http://www.pjsip.org/python/pjsua.htm#AccountCallback AccountCallback], [http://www.pjsip.org/python/pjsua.htm#CallCallback CallCallback], and [http://www.pjsip.org/python/pjsua.htm#BuddyCallback BuddyCallback]), and events emitted by these classes will be sent to the callback class. These callback classes are subclass-able, and in fact you must derive a class from these callback class in order to customize the processing of the events.
 
 It's probably much easier to explain with an example.
@@ -59 +59 @@
     def on_state(self):
         text_ctrl.set_text("Call state is " + self.call.info().state_text)
+  }}}
 
+As you can see above, the primary objective of deriving a class from the callback class is to customize the processing of an event. And in your callback class, you can put your own object attributes there to connect the call object with your application objects.
+
+Then you ''install'' your callback to the Call object like this:
+
+  {{{
+#!python
 
 def make_call(dst_uri):
@@ -70 +77 @@
     return call
   }}}
+
+or using {{{set_callback()}}} method like this:
+
+  {{{
+#!python
+
+def make_call(dst_uri):
+    my_cb = MyCallCallback(none)
+    try:
+        call = acc.make_call(dst_uri)
+        call.set_callback(my_cb)
+    except pjsua.Error, err:
+        print 'Error making call', err
+        return None
+    return call
+  }}}
+
+This later method is not preferred since it is possible to loose events with this method, e.g. due to the use of multi-threading, events may be emitted by the call object while the callback is not installed. It is possible to avoid loosing events this way by using library lock though, as will be explained later.
 
 I hope the snippet above will give you a bit of info on the basic pattern used by the library. More will be explained in later sections.
@@ -93 +118 @@
 
 
-==== Threading ====
+==== Threading and Concurrency ====
 
 For platforms that require polling, the pjsua module provides it's own worker thread to poll pjsip, so it is not necessary to instantiate own your polling thread. Having said that the application should be prepared to have the callbacks called by different thread than the main thread.
 
 The pjsua module should be thread safe.
+
+Internally, the pjsua module actually is not re-entrant, since we found there is a deadlock somewhere when more than one threads are used. The library uses one single lock object to prevent the main thread and pjsua module worker thread from deadlocking. 
+
+The {{{lib.auto_lock()}}} returns an object that automatically acquires the library lock and it will automatically release the lock when the object is destroyed. So to protect a function, the code will be like this:
+
+{{{
+#!python
+
+def my_function():
+    # this will acquire library lock:
+    lck = pjsua.Lib.instance().auto_lock()
+    # and when lck is destroyed, the lock will be released
+}}}
+
+